3. Design and construction standards

Date published: 26 August, 2015

Technical guidance for the Crofting Agricultural Grant Scheme, Small Farmers Grant Scheme and New Entrants Capital Grant Scheme.

3.1.1
The purpose of this section is to give guidance on design and constructional standards to be used by professional officers.

3.1.2
Standards for design and construction are considered under two separate categories:
a) General requirements which are applicable to all works and facilities.
b) Specific requirements applying to the following works:
- buildings of framed construction
- buildings of traditional construction
- prefabricated buildings and structures of proprietary manufacture
- sites, loadings, floors, walls, insulation and ventilation, internal partitions, door openings, drainage, storage containers for foul matter, water supply and painting
- materials used in building construction
- land drainage
- roads, bridges, culverts and grids for livestock
- croft/farm fences, walls and gates

3.1.3
In the case of all other works and facilities for which a standard is not specified, officers should apply what they regard as the nationally accepted standard or practice appropriate in the particular circumstances.

However, it may be permissible to depart from a too rigid adherence to the guidance and standards laid down where this is justified but such a change must be regarded as exceptional and must be capable of being supported on technical grounds.

3.2.1
Certain buildings erected on agricultural land for the purpose of agriculture are exempt from the Building Standards (Scotland) Regulations 1990 (see section 1.2). In those cases where claimants are relieved of the responsibility of complying with the Regulations, officers should make sure that the standards applied under the schemes are not below the standards of the Regulations particularly with regard to the fire resistance requirements. The Town and Country Planning (General Permitted Development) Order 1992 now requires that Prior Notification Procedures be adopted on certain developments on agricultural land.

3.2.2
All designs, materials and constructions are expected to comply with the appropriate British Standards and/or Codes of Practice summarised at Appendices II and III. When interpreting these, officers must use their professional and technical judgement bearing in mind the desired life of the structure, human safety and animal welfare. Surveyors are supplied with all relevant British Standards and Codes of Practice.

3.2.3
The responsibility for insuring against all risks of injury, damage or loss arising while work is being carried out as well as for the design, erection and completion of any works and their subsequent performance, durability and safety, rests with the claimant and this should be made clear to him, when appropriate. Insurance costs are usually included in a contractor's estimate and are eligible costs.

Where the army are carrying out work in lieu of contractors they will insist on insurance being taken out by the applicant. This is an eligible cost under the scheme.

3.2.4
When dealing with applications for approval of more complex farm buildings, no authority to proceed with work should be issued until such plans, calculations and specifications as are considered necessary have been provided and checked or alternatively where the surveyor and/or engineer have considered it necessary, a design certificate from a professionally qualified civil or structural engineer has been provided. In these cases the caution at paragraph (3.2.3 above should be included in the approval letter.)

3.2.5
In relation to livestock buildings, the recommendations contained in the Codes of Recommendations for the Welfare of Livestock should be taken into account.

3.2.6
Although the fire resistance requirements under the Building Standards (Scotland) Regulations 1990 with subsequent amendments do not apply to exempted buildings, officers must nevertheless assess the fire hazards both to humans and livestock. In addition it cannot be safely assumed that buildings which have been approved by the local building authority under the Buildings Standards (Scotland) Regulations will necessarily have sufficient fire resistance to comply with the Welfare of Livestock Codes.

Such matters as the arrangements for emergency procedures and the distance from other buildings, boundaries or potential fire hazards should therefore be considered when applying the technical soundness test.

3.3.1
A new EU directive means that from 1 July, 2014 all new farm buildings manufactured using a steel frame to be CE marked.

The CE mark is an industry standard that proves that buildings comply with all relevant EU legislation and therefore "fit for purpose".

British Standard BS 5502 Part 22, (the Standard in question), has changed so that there are now only two main classifications of farm buildings (previously four classes):

  • Class 2 are agricultural buildings occupied for less than six hours per day at a maximum occupancy of one person/100m² with up to a maximum of 10 people in the building.
  • Class 2 buildings must be single-storey other than small mezzanine floors. They must also be located no higher than 200 metres above sea level. Finally they must have no loads applied to them other than normal environmental loads, i.e. wind and snow.
  • a Class 2 building will be built to last 20 years and is designed to a lower design standard to withstand less loading
  • Class 1 is any permanent agricultural building which falls outside of the above parameters is a Class 1 building. A Class 1 building will be built to last 50 years and is designed to a higher standard to withstand more loading

Some examples:

  • Class 1 – small 18.30 x 9.15 x 3.66 metres (60' x 30' x 12') sheep building located at 300 metres above sea level
  • Class 1 – grain store / silage store – m any size, any location
  • Class 1 – farm workshop with solar panels on the roof
  • Class 2 – cattle shed on level ground, lowland position
  • BS 5502 classification – the buyer needs to make sure they specify what loads will be on the building when talking to the supplier so that they can correctly design and build it. Think about possible future uses as these may change the demands on the building. Importantly these changes being made should make sure that you are buying a properly designed and engineered building, safe and fit for purpose

All building should wherever possible be designed in accordance with Class 1, 2 or 3 of BS 5202 being the Code of Practice for the Design of the Buildings and Structures for Agriculture.

Buildings designed to Class 4 are classed as temporary buildings and are ineligible. Building work which does not meet with these specifications e.g. certain alteration works, may nevertheless be acceptable for grant provided they incorporate good building practice and satisfy the scheme conditions.

It should be noted that all building work is required to pass the Capital Nature Test.

3.3.2
Buildings of framed construction – a building of framed construction is one in which the roof is supported independently of the walls on stanchions, pillars or posts and the frame is designed as a total entity.

3.3.2.1
The framework may be of steel, reinforced concrete, timber or aluminium alloy or a combination of any of these materials and should be designed for the uses intended for the particular site and for an adequate life.

The frame may comprise stanchions and trusses which may be triangulated, curved, mono-pitch or of the portal type in which the principal rafters and stanchions are constructed to form a rigid arch without any tie beam in the roof space. Where stanchions are to be subjected to lateral pressure, e.g. in "on the floor" grain stores and silage barns they should be designed accordingly or otherwise strengthened.

3.3.2.2
Roof and wall coverings may be of galvanised steel, fibre cement, aluminium alloy, rigid plastics sheeting, timber or other acceptable material, fixed in accordance with the manufacturer's instructions or in the absence of these with accepted practice. The roof or wall covering may be insulated against heat transmission or coloured for amenity reasons.

3.3.2.3
Bay spaces between the stanchions may be open or in-filled with either solid walling, prefabricated wall units, cladding, or space boarding, or a combination of these. Cladding should be fixed to sheeting rails secured to the frame. It is most important to make sure that walls acting as retaining walls, e.g. in silage barns and "on the floor" grain stores, and their supports, are designed and constructed to resist the pressure involved.

3.3.2.4
Bracing – roof, gable, side or knee bracing should be provided as necessary. Rafter and gable end bracing will restrain against any tendency of the roof to rack; side bracing will restrain stanchion movement and knee bracing will give rigidity across the spans. Bracing may be provided in the form of additional struts fixed at an angle or as an integral part of the frame, e.g. the gussets on portal frames and stiffeners cast on as haunches in reinforced concrete stanchions.

3.3.2.5
Purlins – roof purlins should be of steel, reinforced concrete, or timber of section and dimensions suitable for the span between the supporting members. The spacing between individual purlins will depend on the type of sheeting to be used and the roof loading.

3.3.2.6
Sheeting rails – sheeting rails or studding to support vertical cladding should be of steel, reinforced concrete, timber, or other acceptable material securely fixed to the stanchion or gable frame. The section, dimension and spacing of the rails should be adequate to safely support side cladding and resist the wind loads without deflection or buckling.

3.3.2.7
Stanchion foundations – all foundations should be designed with due regard to the nature of the ground; they should safely sustain and transmit to the ground the combined dead and imposed load, and any dynamic loads, so as not to allow any settlement or other movement which might impair the stability of the building. Stanchions with fixed bases in normal ground should rest upon a concrete pad of not less than 150 millimetres thick. The overall dimensions of the concrete base including the pad should be not less than 600 x 600 x 750 millimetres deep. Reinforced concrete pads of increased area and not less than 300 millimetres thick may be required when soft ground is encountered. To drain water away from the stanchion, the top of the foundation can be projected 150 millimetres above ground level and be sloped away from the stanchion, where the wall construction permits.

3.3.2.8
Steel framed buildings the members of steel framed buildings should be arc welded or bolted together with high tensile bolts. Stanchions should have fixed, or have pin base foundations. Where stanchions are secured by holding down bolts embedded in a concrete base the bolt heads or nuts should be concreted over.

3.3.2.9
Concrete framed buildings – concrete stanchions have fixed bases which are usually cast in site with a socket into which the stanchion is inserted and grouted. Because of the weight of the frame it is essential that the bases are sufficiently large to prevent spread particularly on sloping sites. All fixing bolts should be galvanised and straps and other metal work galvanised or painted to resist corrosion. All spalled concrete members should be repaired in an approved manner particularly if the reinforcement is exposed. Shattered or cracked members should not be used.

3.3.2.10
Timber framed buildings – all structural timber exposed to the weather or embedded in the ground should be preserved in an approved manner. Wooden stanchions for the timber structures when embedded in the ground should be not less than 1300 millimetres deep and the stanchion should rest on a 150 millimetres thick pad of concrete. Excavated material should be replaced in layers and well rammed. Members should be bolted together with timber connectors, or glued and nailed or fixed by other approved methods.

3.3.3
Buildings of traditional construction – a building of traditional construction is one in which the roof is supported on load bearing walls constructed of brick, concrete block, stone, timber, studding, or other material and where necessary incorporating a damp proof course or membrane. Load bearing walls should be at least 150 millimetres thick (200 millimetres if in brick) constructed with piers of not less than 200 x 325 millimetres sectional area, exclusive of the wall, at suitable intervals, e.g. under each roof truss. As a general rule the ratio of height to thickness for a load bearing wall should not exceed 18 to one between piers.

The roof trusses and members spanning between the walls should be constructed of steel, concrete or timber properly secured into supporting piers. In all other respects the constructional standards for traditional buildings are similar to those specified for buildings of framed construction.

3.3.4
Prefabricated buildings and structures of proprietary manufacture – cases involving applications for new or proprietary forms of design of buildings and components not previously grant-aided must be referred, via the Principal Agricultural Officer, to the scheme technical officer.

3.3.4.1
Buildings – the construction standards for proprietary prefabricated buildings for livestock, silage, grain storage and other agricultural purposes should be in all respects similar to the standards applied to their counterparts in framed buildings as described previously. In the case of lighter types of prefabricated buildings the superstructure must be seen to have been anchored satisfactorily to site concrete, brick or concrete block dwarf walls by means of steel fixing plates or brackets, or holding down bolts.

3.3.4.2
Crop storage containers – containers constructed of flexible materials must be on a permanent base and adequately supported. The container must be fire retardant but butyl lining is acceptable, being capable of resisting chemical attack from the stored product. The design of rigid containers or bins and the supporting foundation must be such that they are capable of resisting safely the vertical and lateral loads and overturning movements induced by the stored material and weather conditions (see paragraph 3.13.4.10).

3.3.4.3
Storage tanks – storage tanks for solids or liquids should be lined or constructed of a material which is not liable to attack by the material to be stored. Vessels for the storage of liquefied petroleum gas must comply with the Gas Safety Regulations (see BS 5502).3.3.5 Standards applicable to all buildings

3.3.5.1
Sites – all sites for buildings should be adequately drained. Existing drains which are to be disused or any cavities, e.g. old cesspits, which are likely to become harbours for vermin should be grubbed up or filled in with either well consolidated hardcore or concrete.

3.3.5.2
Loadings – the foundations, structural frame, floors, walls and roofs of the buildings should be designed in such a way as to withstand any climatic loads that may be applied, all self-loads of the building, loads either dead or dynamic due to the intended use of the building and lateral loads due to storage against the sides, or earth and water pressure below ground level.

3.3.5.3
Floors – upper or suspended floors should be constructed in one of these ways:

  • of timber boarding of not less than 19 millimetres finished thickness or the equivalent in plywood or reconstituted timber with wooden joists strutted as necessary; intermediate supporting beams, if required, should be of wood, steel or concrete
  • of reinforced concrete cast in site, or of hollow or solid concrete slabs, or of hollow blocks supported on steel or reinforced concrete beams
  • in accordance with other accepted design

Piers, columns or stanchions supporting the floor should be of brick, concrete, steel, wood or other acceptable material. New suspended floors and improvements to existing ones should be constructed to carry the intended loading with an adequate margin of safety. The minimum loading
for which this type of floor should be designed is 5 kN/m2. Slatted floors of concrete or other materials should be designed in accordance with BS 5502 Part 51.

Concrete floors intended for storage should include a damp-proof membrane of polythene or other suitable material laid over the hardcore or incorporated in the concrete to form a sandwich floor. The membrane should be lapped into the DPC of the walls.

The floors of bedded areas in livestock buildings may be insulated against heat loss. The insulation may be hollow clay blocks, no-fines lightweight concrete, expanded polystyrene, resin bonded glass fibre or other suitable material laid on a waterproof membrane where necessary and covered with concrete or a protective screed of cement and sand.

3.3.5.4
Walls – the external walls of a building should be constructed so as to have adequate weather resistance. Bricks, blocks or like components should be properly bonded and solidly laid with a suitable mortar and built off a concrete foundation reinforced as necessary. A horizontal damp-proof course should be provided, whenever necessary.

Where hollow blocks are used below ground level the cores should be filled with weak concrete as the work proceeds and, where a high degree of moisture resistance is required or where the bricks or blocks are of a porous nature, the walls should be rendered externally or alternatively continuous cavity walls should be used.

Mass concrete walls should be not less than 150 millimetres thick constructed of concrete of suitable mix and thoroughly tamped. The wall may be supported by stanchions or other suitable means and should be reinforced as necessary.

Precast wall panels may be fixed either at the top and bottom or at either end. The panels should be reinforced and not less than 40 millimetres thick for non-thrust resistant walls.

Walls subject to lateral pressure resulting from stored grain, potatoes, silage, liquid or earth can be built between supporting piers or stanchions and should be reinforced against tensional stress by steel bars or mesh reinforcement.

Where the retaining walls transfer their loading to the structural frame the frame should be designed to accommodate all the loadings applied to it.

3.3.5.5
Ventilation – buildings should be adequately ventilated without draught to the standard required for the well-being of the stock to be housed, or for the crops to be stored, or for such other use as the building is intended.

The ventilation system may be either mechanical or natural or a combination of both. Ventilating ducts to which humans have access should be of sufficient strength and dimension so as not to present a hazard (see paragraph 3.22.3 ventilation fans).

3.3.5.6
Insulation – buildings should be adequately insulated to the necessary degree and penetration of moisture into the insulation prevented by the provision of a suitable vapour barrier normally on the side next to the warm air.

3.3.5.7
Walls, internal partitions, etc in livestock buildings – internal wall surfaces, gates, partitions, fittings etc constructed of materials liable to be damaged or deteriorated due to contact with livestock or manure should be properly protected with galvanised steel or other suitable sheeting to an effective height and along with floor surfaces, should be constructed so that they can be cleaned easily and will not cause injury to livestock.

3.3.5.8
Lighting – natural lighting is a desirable feature in most farm buildings and the number and positioning of windows and roof lights should be considered in relation to the intended use of the building. The levels of illumination both from natural and artificial sources should be sufficient for effective and safe execution of work being done and for proper welfare of stock.

3.3.5.9
Door openings – door openings in farm buildings should be large enough to permit the safe and unimpeded movement of vehicles servicing the building.

3.3.5.10
Drainage – adequate means of drainage should be provided to convey any foul liquid and rainwater to a suitable place of storage or disposal. Drains should be constructed of materials of sufficient durability having regard to the liquid passing through them and the nature of the ground in which they are laid.

Drains should be bedded or supported for the loads and forces to which they may be subjected and laid at a gradient and in such direction as to make sure that they will be self-cleansing and capable of discharging the full volume of drainage for which they are designed.

Gullies, manholes, inspection chambers and rodding eyes should be provided where necessary with heavy duty covers where subject to animal or vehicular traffic.

3.3.5.11
Containers for the storage of foul matter – any tanks, slurry pit, lagoon or holding area intended for the storage or settlement of foul matter from the farm-stead should be sited where it will not pollute any stream, spring, well or other source of water or become a source of nuisance or danger to human and animal health.

There should be no overflow or discharge from the container unless the effluent discharged is satisfactorily treated before disposal. Where containers present a hazard they should be covered or fenced in (see paragraph 2.19 Pollution Regulations.)

3.3.5.12
Water supplies in buildings – livestock buildings should be connected to an adequate water supply and due allowance should be made for adequate storage particularly where the supply is intermittent.

Watering points in buildings may be troughs, water bowls, drinkers or other approved fittings. The supply, the fittings and the installation must comply with the relevant current local water byelaws.

3.3.5.13
Painting – in the case of woodwork which is normally painted, e.g. doors, windows, etc, three coats of non-toxic paint should be applied - priming, undercoat and finishing coat. As an alternative suitable preservative treatment is acceptable.

All structural and other steelwork, unless galvanised should be painted with two coats of bituminous or other acceptable non-toxic paint. The first coat of paint should be applied before erection and the second during or after erection but before any sheeting is fixed.

Alternatively, both coats may be applied at the works before delivery. Damaged paintwork should be touched up on site.

3.3.6
Standards for materials used in building construction

3.3.6.1
General – materials and components used as structural members must have a life at least equal to the constructional materials or components being supported, having due regard to any loads which may be applied. Materials used for finishing surfaces must not contain substances which are toxic or have deleterious effect on humans or animals. Reference should be made to BS 5502: Part 21, paragraph 3.2.2.

3.3.6.2
Galvanised steel – the minimum gauge of profiled galvanised mild steel sheeting should normally be 0.5 millimetres overall but galvanised and coated high tensile sheeting of 0.4 millimetres thickness may be accepted.

Attention should be paid to the need to seal laps at low pitches and on exposed sites. Steel sheeting galvanised or otherwise protected and fixed with the troughings running longitudinally may be accepted and should be laid to a fall of 1 in 40 and have end laps of at least 300 millimetres sealed with mastic.

Sheeting over highly corrosive internal atmospheres (e.g. stock housing) requires a higher standard of protection. Protection should be provided between steel supporting members or timber-treated with metallic preservatives and the metal roof sheeting. See BS 5502: Part 21, Paragraph 7.3.

3.3.6.3
Fibre cement sheeting – roof and wall covering of fibre cement sheeting with 75 millimetres and 150 millimetres corrugations should be at least 5.5 millimetres thick.

For low pitches, heavier types of troughing or decking specially designed for such pitches should normally be used unless there are special circumstances appropriate to the use of the building.

Attention should be paid to the need for sealing laps at low pitches and on exposed sites. See BS 5502: Part 21, paragraph 8.

3.3.6.4
Aluminium sheeting – all aluminium profiled sheeting should have a minimum thickness of 0.5 millimetres. Attention should be paid to the need for sealing laps and to prevent corrosion due to electrolytic action resulting from contact with other materials.

3.3.6.5
Plywood and hardboard – external grade plywood at least eight millimetres thick or WBP grade may be accepted in suitable circumstances as cladding materials for walls. Tempered hardboard may be used for internal linings. Plywood as above may be used as a cladding material for roofs providing that it is covered with acceptable felt.

3.3.6.6
Roofing felt – roofing felt should be at least one layer of mineral surfaced bitumen felt complying with the requirements of BS 747 and weighing not less than four kilogrammes per square metre properly laid on adequately supported timber bearing or other approved base.

High performance roofing should be either two layer fully bonded or three layer partially bonded with either polyester or glass fibre base laid in accordance with the manufacturer's recommendations. Flat roofing should generally follow the published recommendations of the British Flat Roofing Council.

3.3.6.7
Translucent plastic sheeting – translucent plastic sheeting should match the profile of the roof or wall cladding and have a fire resisting performance equal to that of the roof cladding or equal to that which is necessary for the cladding into which it is fixed.

3.3.6.8
Other cladding materials – all other cladding materials should be of a suitable quality in relation to the purpose for which they are used and the degree of exposure to which they will be exposed and should have a fire resistance appropriate to the needs of the building.

Cladding should be fixed in accordance with the relevant British Standards or, where these are not appropriate, in accordance with the manufacturers recommendations.

3.3.6.9
Timber – all timber used should be of good quality, straight in grain, free from large knots and waney edges.

Except for the heartwood or oak, larch, sweet chestnut, yew or Western red cedar, all timber and plywood (except that comprised wholly of a durable species) which is in contact with the ground or manure, or enclosed in brickwork, masonry or concrete, or inadequately ventilated, or liable to remain damp for long periods, should be preserved by creosote or an approved waterborne preservative.

The application of the preservative should be by impregnation under pressure or by hot and cold treatment in an open tank. Where timber is exposed to the weather but is not in contact with the ground or manure and is not liable to remain damp for long periods then it may be protected by painting with three coats of non-toxic paint.

If the timber is of a pine species then in these circumstances only it may be treated with creosote or an approved organic solvent preservative applied by steeping for not less than thirty minutes. Paint or preservatives toxic to humans, animals or living plants or deleterious to stored crops should not be accepted.

3.3.6.10
Drainage pipes – salt glazed fireclay, concrete, or rigid plastic pipes may be used for farm drainage systems. Cast iron pipes may be necessary where there is a risk of damage, e.g. shallow drains under roads or pavings.

Pipes should be encased in concrete where necessary. Unjointed or perforated pipes may be used for certain systems of surface water drainage at shallow levels or in conjunction with the disposal of treated effluent.

3.3.6.11
Water pipes – galvanised steel, copper, polyethylene, PVC, plastics, asbestos cement or other suitable pipes and fittings may be used for water supplies within the accepted limitations of the materials and only where acceptable to the local water authority and in accordance with the local water byelaws.

Pipes should be laid and fixed in accordance with the requirements of the water authority where applicable.

3.3.6.11
Fire hose reels – the fire hose reel assembly should be permanently connected to a water supply and fixed to the structure of the building. Where not of the automatic type a 19 millimetre stop valve should be fitted to the supply pipe at the reel connection.

The rubber hose should be not less than 19 millimetre bore and should comply with BS 3169 and should be fitted with a shut-off nozzle which may be either the plain jet or spray type. Where two or more hose reels are installed the supply piping should normally be not less than 50 millimetre bore. Piping to individual reels should be not less than 25 millimetres bore.

Supply piping should be connected directly to a public or private mains supply. As a minimum, the pressure of water should be such that when two hoses are used simultaneously each will provide a jet of approximately six metres in length and will deliver not less than 23 litres per minute.

3.3.6.12
Second-hand materials – second-hand building materials for any purpose may be accepted for grant under actual costs provided that they meet the capital nature and other requirements of the Scheme and are suitable for their intended purpose.

However, for work intended to be claimed for under standard costs, only new or previously unused materials may be used. The only exceptions are items which involve stone or hardcore (e.g. soakaways or dry stone walling) for which previously used brick stone or other suitable material may be used.

3.3.7. Tables of concrete mixes for farm use

3.3.7.3
The surface finish of floors and pavings should be appropriate to their use and should not be such as to create animal welfare problems.

3.3.7.4
Steel reinforcement should comply with BS 4449, 4466, 4482, 4483 or 6744 as appropriate and should be free of rust scale and other deleterious matter.

3.4.1
Roads – roads should be designed to allow for the anticipated traffic, the climatic conditions and the natural ground conditions. For a main access, the width should normally be at least 900 millimetres greater than the track dimension of the largest vehicles liable to use the road.

All the usual materials, including materials of local origin, may be allowed, such as broken stone, quarry waste, binding gravel or mine waste.

Care must be taken in the use of mine or quarry waste to make sure that no metallic or other organic matter is involved which may be harmful to stock etc. The foundation of a road should be excavated and in-filled in layers with compacted hard material, well drained and soft patches should be filled in with hard material.

Geo-textile matting may be used where necessary. Provision should be made for surface drainage and on sloping sites cross grips may be provided.

3.4.1.1
Hardcore roads – the hardcore should be spread in layers to a minimum consolidated total thickness of 150 millimetres of new roads on rolled and blinded with quarry scalpings and dust or gravel/sand mixture.

3.4.1.2
Concrete roads – the thickness should be not less than 100 millimetres but will be determined by the quality of the road foundation and the likely traffic weight and frequency. If standard costs are claimed 125 millimetres is the acceptable minimum.

The mix of concrete should be not weaker than GEN4 or ST5 equivalent. A hardcore sub-base is normally necessary but can be omitted where the sub-strata is firm and of a sand and gravel mixture.

Reinforcement should not normally be required but may be necessary where the foundation of the road is soft or where heavy loads are to be carried. Damage to concrete from de-icing salts can be minimised by using 'air-entrained' concrete.

This should be used for at least the first 50 metres of the farm access road.

3.4.1.3
Surface dressings – surface dressings of uncoated material should be laid to a minimum compacted thickness of 75 millimetres. Coated macadam suitably surface sealed, should be laid to a depth appropriate to the grade of the macadam and strength of base.

3.4.2
Bridges and culverts – bridges and culverts should be designed and constructed to suit the needs of the agricultural business, in accordance with good civil engineering practice and, if appropriate, any local authority requirements of any loading notices restricting the passage of vehicles where the bridge has been designed with a limited capacity.

It is however strongly advised that irrespective of a local authority requirement, bridges designed for a specific maximum loading should have loading notices displayed.

Bridges should be constructed of steel, concrete, reinforced concrete or impregnated timber with abutments, wing walls and aprons soundly built to prevent any movement or subsidence from loading or erosion.

Wheel kerbs and guard rails should be provided where necessary. Pipe culverts should be of concrete or suitable preformed steel sections, not less than 225 millimetres in diameter adequately protected and having suitable head walls, wing walls and aprons.

3.4.3
Livestock grids – grids should be designed to suit vehicle loadings and may be constructed of steel tubes or sections supported on longitudinal walls of concrete, impregnated timber, brick or metal.

The supporting walls should be as narrow as possible consistent with safety and rounded off where they meet the cross members.

Where a pit is incorporated, this should be suitably drained, the guard fencing (along the grid) should be erected immediately over the internal faces of the pit walls. Small ramps should be incorporated in the pit walls to allow the escape of small animals.

Livestock grids should be constructed in accordance with BS 4008 or with any other additional requirement requested by the local authority.

3.5.1
General – for all types of fences and gates it is a general requirement for construction to be of a design and to a durable standard that permits satisfactory use for the intended agricultural purpose. Fences should be erected in accordance with BS 1722 as appropriate.

New materials must be used for works to be claimed on the basis of Standard Costs. Where it is intended to claim grant on the basis of actual costs, the straining posts and gate posts may be of good quality, adequately protected, second-hand materials, but all other components must be new. See also paragraph 3.17.6.

Claims based on actual costs for materials and the "labour only" standard cost rate are acceptable.

3.5.2 Fence and gate posts

3.5.2.1
Straining posts should be at least 2.1 metres long. If round timber they should have a minimum diameter of 125 millimetres for three wire fences increasing to a minimum diameter of 175 millimetres for heavy duty fences of six or more wires.

On the same basis the minimum cross-sectional dimensions for sawn timber straining posts should be 125 x 125 millimetres increasing to 150 x 150 millimetres or to other cross sections giving equivalent strength.

They should be set at centres not exceeding 150 metres for normal, strained-line fences (mild steel wires) or 200 metres for high tensile fences. In addition there should be a straining post set at each change of direction and at each significant change of gradient.

Post holes for strainers must be at least 450 millimetres deep and excavated as narrow as practicable with vertical sides. When the post is in position the soil should be rammed back in 150 millimetre layers.

Gate posts should be of similar dimensions and securely set in the ground as described for strainer posts. Posts made from other materials, like reinforced concrete, should be of dimensions that provide an equivalent strength and set in the ground according to any specific instructions supplied by the manufacturers. All gate posts must be to BS 3470.

3.5.2.2
Struts to support strainer posts should be at least 1.8 metres long. Round timber struts should not be less than 100 millimetres in diameter and sawn timber struts should have cross-sectional dimensions not less than 100 x 100 millimetres.

The top end should fit into a notch in the strainer post and the lower end should be at least 300 millimetres below ground level resting against a suitable base plate.

3.5.2.3
Fence posts (intermediate posts) to carry the wires should be at least 1.6 metres long.

Round posts should have a diameter not less than 63 millimetres for a three-wire fence and not less than 75 millimetres for a heavy duty fence. Similarly, if they are sawn posts the cross-sectional dimensions should range from 63 x 63 millimetres to 75 x 75 millimetres, minimum, depending on the type of stock to be controlled.

Timber posts should be pointed and firmly driven into the ground to form a straight line between strainers. They need to be set at centres not exceeding 3.5 metres for three-wire strained-line fences and not exceeding 2.1 metres for heavy duty fences while, for all high tensile fences, post spacing should not exceed 50 metres.

Other types of posts should be secured as recommended by the manufacturers.

3.5.2.4
Fence wires must be to BS 4102, galvanised and equivalent in strength and durability to:

  • four millimetre mild steel wire, or
  • 2.50 millimetre (12 g) and 2.64 millimetre (12.5 g) high tensile steel wire, or
  • 2.5 millimetre mild steel two-ply twisted barbed wire, or
  • oval section 13 gauge barbed wire

NB: 3.15 millimetres high tensile wire can be used where atmospheric pollution is a serious problem or where salt laden sea winds could be severe, and must be used in all standard cost cases.

The wires should be sufficiently strained and fastened to posts with galvanised staples which should be driven in obliquely but not fully home to leave the wires free to move. The top wire must be fixed at not less than 1.05 metres above the general ground level. Wires should be tied off at straining posts.

3.5.2.5
Woven wire must be galvanised and comply with BS 4102. If the woven wire selected is less than 1.05 metres in width, the required fence height must be achieved by fixing additional wires above or below the woven wire.

If the woven wire selected is 1.15 metres in width, the fence posts must not be less than 1.8 metres long. Heavy gauge woven wire is recommended for areas subject to rapid corrosion due to atmospheric pollution.

3.5.2.6
Proofing against rabbits and hares requires galvanised wire netting to BS 1485. The netting should be not less than 1.05 metres wide, BS designation 18, and have a mesh no larger than 31 millimetres.

The top edge of the netting must be at least 090 centimetres above ground level. The netting should be fastened to the fence and the bottom edge of the netting should be buried in the ground to a suitable depth or turned outwards and anchored.

All gates in proofed fences must also be proofed.

3.5.2.7
Droppers for high tensile fences with widely spaced posts must be of galvanised steel or timber and spaced so that the distance between droppers or between a dropper and a post is not more than 3.5 metres.

All droppers must be kept clear of the ground.

3.5.2.8
Wooden post and rail fencing should not be less than 1.05 metres high from the general ground level to the top of the top rail. The posts may be rectangular or half round and at least 8800 square millimetres in cross-sectional area.

For rectangular posts no side shall be less than 63 millimetres and for half round posts the flat face must be at least 150 millimetres wide when barked and peeled.

The posts should be at least 1.8 metres long and set at centres not exceeding 1.8 metres. The rails should be 75 x 38 millimetres sawn timber or half round timber not less than 100 millimetres across the flat face when barked and peeled.

The rails should be skew nailed to posts with galvanised nails.

3.5.2.9
A concrete foundation may be required to secure posts in unstable ground. In conditions where it must be used the posts should be set in concrete not less than 400 x 400 x 500 millimetres deep.

3.5.2.10
Electric fencing – permanently sited electric fencing, supplied either from the mains or batteries is eligible for grant provided the controller complies with the appropriate BS.

Mains controller/energisers must comply with BS 2632, battery controller/energisers with BS 6167 while dual mains/battery units must comply with BS 6369.

The batteries are not eligible. Where permanent electric fencing is supplied from the mains the claimant must provide a certificate stating that the work complies with the requirements of the Institution of Electrical Engineers Regulations.

Certain wind generators are eligible for grant. The following points should be noted:

  • barbed wires must not be used in electric fencing. Where electrified stand-off wires are used on a fence incorporating barbed wires, the offset brackets must not be attached to barbed wires and the stand-off wire must not be less than 150 millimetres from the vertical plane through the strained wires of the fence
  • where it is proposed to erect a permanent electric fence alongside a public road or footpath, the fence must always be separated from it by a verge, ditch, bank or hedge. Claimants must have consulted the local Authority before starting work and taken account of any comments or advice during construction before grant can be paid
  • electric fencing powered by mains, mains/battery or battery operated controller/energisers can cause interference on nearby telephone circuits, particularly those that are underground. Care is needed to make sure that such interference with telephone circuitry does not occur. Proposals to erect electric fences in the vicinity of telephone lines cannot be accepted unless the applicant can show that he has consulted British Telecom who have no objections to the work. British Telecom will require to see an accurate map to 1:2500 or 1:10000 scale showing the lines of proposed fences and grid reference of the croft or holding and the location of the fence energiser.

3.5.3
Gates – gates should be soundly framed, soundly constructed and of suitable materials to comply with BS 3470. They may be constructed of timber or of steel as follows:

  • steel tubes to BS 6323
  • rectangular hollow section steel to BS 4848 part 2
  • circular hollow section steel to BS 4848 part 2, and
  • steel sections to BS 4 part 1 or BS 4848 part 4

The dimensions of components used for the construction of gates should be adequate for the design, size and intended use for each kind of material.

Steel gates must be hot dipped galvanised after manufacture or painted with two coats of suitable non-toxic paint. Cold galvanising is classed as a painted finish.

All gates must have a minimum height of 1.1 metres from the bottom of the bottom rail to the top of the top rail. The width should be adequate for the intended agricultural purpose and not less than three metres where access is required for fire fighting purposes.

Openings greater than 4.5 metres must have two gates. All gates must be complete with all the fittings needed for their efficient operation. They should be securely hung on hinges, affixed to the gate post, so that they can swing freely to the fully open position without coming in contact with the ground and easily closed with a securing latch or bolt.

3.5.4
Protection of materials used in fences and gates – all timber should be treated as specified in Appendix E of BS 1722. Fence wires and woven wire netting must be galvanised to BS 729.

Steelwork may be either galvanised to the appropriate BS or painted with one coat appropriate primer and one coat finishing paint. All paintwork damaged during construction should be repaired before the work is completed.

3.6.1
General – land drainage can be a complex investment requiring a range of designs to solve a number of distinct drainage problems and is unlike most other investments under capital grant schemes in that the completed work is buried in the ground and out of sight.

For these reasons it is essential that the efficiency of the design, the standards of workmanship and quality of materials used are all of a sufficiently high standard at the time of installation.

It is not intended that this section is a complete specification but the minimum standards indicated will provide the basis of sound land drainage work.

It should be borne in mind that poorly designed or poorly executed projects or the use of poor quality materials may cause an investment to fail to meet the capital nature test.

3.6.2 Workmanship standards for ditch Improvements

3.6.2.1
All woody growth which would obstruct the work should be trimmed or grubbed out before the excavations begin. Where branches of trees require to be lopped this should be done with care to avoid damaging the trees. All branches and trimmings should be burnt or carted away so that they do not become mixed with spoil from the ditch.

The removal of bankside vegetation should be the very minimum necessary for the efficient functioning of the ditch.

3.6.2.2
Ditches should be cut to the design dimensions as determined by the depth needed to provide outfall for drains, the gradient and the amount of water to be carried.

The ditch bottom must have an even gradient and the sides need to be sufficiently stable to avoid bank slips in the type of soil forming the banks.

Care is needed to avoid undermining dykes, roads or buildings. Excavated material must be placed at least 600 millimetres from the edge of the ditch and spread in such a way that it does not cause ponding of surface water.

Bank slips must be cleared and rectified and any silt accumulated during excavation should be cleared before the scheme is completed.

3.6.2.3
Ditch banks should be examined for old drains. If functional they should be cleared and provided with satisfactory outlets as described in paragraph 4.6.3.8.

3.6.2.4
Where ditch crossings are required the necessary bridges or culverts should be constructed with adequate dimensions and to a standard which allows them to withstand the weight of vehicles crossing.

The culvert pipes should be suitable for the situation and have positive joints to preserve alignment. The pipe diameters should be sufficient to carry the anticipated flows and in any case not less than 225 millimetres.

Pipes should be set on a firm bed in a recessed trench bottom and aligned to provide an unimpeded continuation of the adjoining ditch. Protective measures may be needed to prevent erosion of the ditch channel at the outflow end of the culvert. Headwalls may be required at both ends of the culvert.

3.6.2.5
Protective fences alongside ditches should be erected at least 450 millimetres back from the edge. The fences should be soundly constructed using good quality adequately protected materials as described in section 4.5.2.

3.6.2.6 In the absence of a piped water supply stock watering points should be constructed in such a way that the animals cannot block the main channel or cause bank collapse.

3.6.2.7
Hill ditching should have a top width of not less than 550 millimetres and the bottom width not less than 150 millimetres with the sides sloped to a stable angle. Hill drains shall be opened with a tracked excavator with "V", or standard, bucket. The provision of a new system of hill drains is no longer eligible.

Excavated material must be placed at least 600 millimetres from the edge of the ditch and spread in such a way that it does not cause ponding of surface water. Bank slips must be cleared and rectified and any silt accumulated during excavation should be cleared before the scheme is completed.

3.6.3 Workmanship standards for under-drainage

3.6.3.1
Attempting land drainage operations with modern heavy tackle when the soil is wet can leave the land in a poorer condition than before, especially on heavy land. If at all possible drainage should be carried out during the summer months when land is in grass, or after early harvest, or through a standing crop early in the growing season.

3.6.3.2
Drain trenches should be cut to design depth, true to line and gradient and the trench bottom should provide a secure seating for the pipes. The minimum depth of cover over any lateral drain should be 600 millimetres and over leader drains 675 millimetres.
When drains are laid in peat the minimum cover should be 900 millimetres to allow for shrinkage. Gradients normally should not be less than one in 400 and sealed pipes are necessary in leader drains at gradients greater than 1 in 60.

3.6.3.3
Pipes should be laid in a true line and gradient on a firm bed free from loose soil and must never be laid on soil backfill or when the trench is in a slurried condition. Clay tiles should be evenly aligned and well butted together to avoid large gaps.

When plastic pipes are used the bottom of the trench should be shaped to support the side walls of the pipes and where the plastic is PVC the pipes should not be laid or backfilled when the temperature is less than five degrees Celsius.

All drain junctions should be made with purpose-made tile or plastic branch pieces. Where possible pipes should be blinded by stone-free earth to avoid damage or displacement during backfilling.

3.6.3.4
With the exceptions of very deep drains on level sites and shallow systems that can be completely disrupted by subsoiling, all old drains encountered during the drain-laying operation must be positively connected to the new drains by means of purpose-made junctions or by using sufficient amounts of permeable infill to connect the two systems.

When the old drains are deeper than the new system on a sloping site a number of deeper drains are needed to cut and bleed the old system.

3.6.3.5
When draining in peat, running sand, old ditch lines or other unstable conditions, special precautions are needed to maintain drain alignment. A preliminary de-watering system of open channels is of great value in waterlogged peaty soils and the laying of tiles on boards may be essential in deep peats.

Where drains pass through unstable land such as backfilled pipeline trenches or deep ditches, the pipes should be supported on a bridging device of wood, reinforced concrete or steel.

3.6.3.6
Solid pipes or pipes with sealed joints are required near trees and hedges so that roots cannot enter and block the drains.

3.6.3.7
Where the design specifies permeable infill, care should be taken to prevent mixing with earth and the pipes should be covered to design depth. The depth of infill should be sufficient to provide a suitable connection, as appropriate, between the new drains and any old drains, channels created by moling or subsoiling or the plough layer where the subsoil is slowly permeable.

3.6.3.8
A properly constructed outfall is essential where leader drains discharge into an open channel. The last length of the buried pipe and any projecting part of the pipe must be solid and frost-proof and the outfall should be at least 150 millimetres above normal ditch water level wherever possible.

The last two metres of buried pipe must be sealed with well-rammed soil to avoid water flow outside the pipe. Headwalls of cemented stones or bricks or purpose built installations are needed to stabilise the bank and to keep the pipe in position. Drip stones or concrete aprons may be needed to prevent erosion of the channel.

3.6.3.9
At major pipe junctions or at reductions of gradient in leader drains it is advisable to construct inspection chambers with silt traps of satisfactory design.

3.6.3.10
All inlets for the entry of water from an open channel must be provided with a silt trap and grating of satisfactory design.

3.6.3.11
Piping open ditches is an operation requiring careful planning and assessment of likely flow rates. In particular the pipe must be large enough to carry peak flow rates and where open channels discharge into the pipe it must be capable of carrying storm water flows.

All existing drains discharging into the ditch must be located and connected to the new pipe. Special precautions are needed where circumstances demand that water should not leak from the pipe. In the interest of conservation of the countryside, the piping and filling of ditches should be restricted to the minimum amount required for efficient land drainage.

3.6.3.12 Trenches must never be backfilled when the soil is in a slurried condition. Large stones should be removed and the trenches carefully backfilled with excavated material in such a way that the pipes are not damaged or displaced and the fill should be firm but not compacted.

3.6.3.13
Trenchless drainage techniques present difficulties. It is particularly important to make sure that where required a sufficient amount of permeable backfill is installed to provide adequate permeability in the "trench" and the necessary connections between old drains and the new system.

3.6.4
Workmanship standards for soil treatments

3.6.4.1
Mole draining should only be carried out on suitable subsoils, over an efficient under-drainage system and in the right soil moisture conditions. The subsoil requires to be plastic at mole depth to form a stable channel but dry enough above to promote soil fissuring.

These conditions are most likely to occur when the soil is drying out in late spring and early summer.

The equipment used must be capable of drawing a mole channel of circular shape (not less than 75 millimetres diameter) evenly and continuously at the design depth parallel to the general ground surface. The channels should be deep enough to avoid damage by subsequent cultivations and close enough to make sure good drainage usually 1.5 to 2.5 metres apart.

Gradients may range from one in 300, to one in 15. Steeper gradients which may cause erosion of the channel can be avoided by moling diagonally across slopes. All mole channels should be connected to the drains by permeable infill in the drain trenches.

The top level of the permeable backfill should be at least 150 millimetres above base of the mole channel which should be drawn across the line of the collector drains.

3.6.4.2
Subsoiling should be carried out only when the subsoil is dry enough to obtain adequate shattering and fissuring of the soil and over an efficient under-drainage system. Suitable conditions for subsoiling occur in a dry summer or autumn after plant growth has removed a substantial amount of moisture from the subsoil.

The subsoiling should be carried out at the depth needed to burst the compact layer in the subsoil and at intervals of not more than 1.2 metres. When soil conditions are right for maximum effect a high power capability is essential.

3.6.5 Workmanship standards for hill drains

3.6.5.1
Before starting the work serious consideration should be given to the effect the drainage may have on the grazings, the general environment and local waterways. Where necessary consultations should be arranged with interested parties.

3.6.5.2
The channel should have a tapered section with a bottom width of 150 millimetres to 300 millimetres, a top width not less than 550 millimetres, a depth of not less than 350 millimetres and continuously graded to one or both ends of its length. The excavated material should be deposited on the downslope side at least 550 millimetres from the near edge.

The laterals should be connected to the leaders with a clean and undiminished cross-section, hand labour being used where necessary.

The channels should be cut in such a direction that the gradient is sufficient to allow self-cleansing flow velocities in average conditions but in no case so steep that scouring can occur. Lateral drains should be cut across slopes to intercept surface water.

Special care is needed to make sure that main outlet channels are not seriously scoured and eroded.

3.6.6
Quality of materials used

3.6.6.1
All pipes must be suitable for their required drainage function and conform to the appropriate British Standard – BS 1196 for clayware tiles and BS 4962 for plastic piping. Pipes not covered by a British Standard should be of a type approved by the Department.

All pipes under roads and bridges and pipes over 750 millimetres (30") diameter require special consideration, see paragraphs 4.6.2.4 and 4.4.2.

3.6.6.2
Some soils cause the rapid deterioration of concrete pipes and restrictions on their use are necessary. In general, pipes made of high alumina cement are not suitable for field drainage. Pipes made from Portland or sulphate resistant cement may be used as follows:

a) porous pipes can be used only in soils where the pH is more than 6.5 and the sulphate content is less than 0.06 per cent
b) dense concrete pipes can be used in similar conditions or where local experience has shown that they last for a reasonable period

3.6.6.3
Reject asbestos cement pipes may be suitable for use as culverts or for the larger carrier drains. Pipes of this type sometimes fail the stringent tests required for pressure pipes in water and sewerage works. They can be used as field drains only in situations where sealed joints or precise alignments are not essential.

3.6.6.4
Permeable backfill must be clean gravel, stone chips or other approved durable material with no dimensions greater than 50 millimetres or less than six millimetres. Other materials used for land drainage works, usually building materials or fencing materials should be of a standard specified in the appropriate sections above.