Hedgehog Self Build - Specification


These houses are designed using the “Segal Method” of timber construction. This method of construction was originally developed 30 years ago by the architect Walter Segal. Since its original conception it has been used in the design and construction of a large variety of buildings including housing. Architype have developed and updated the method and have given particular emphasis to its ecological development.


The design for this scheme is based on ecological principles which aim to limit the energy use and pollution which can result from both the building process and the subsequent use. The aim is for energy efficient houses which are cheap to run and which are healthy to build and live in. Materials are chosen for their low energy and pollution in manufacture as well as for their life cycle and technical performance. Structural frames are softwood, a renewable low energy resource, with toxic timber treatments only used for columns in contact with the ground. Wall, roof and floor constructions are have high levels of insulation. Finishes are safe and non-toxic including organic paints and stains and natural linoleum. Heating systems are energy efficient with intelligent control systems.


Foundations will be isolated concrete pad foundations with 600 x 600 x 50 pre-cast concrete paving slabs bedded on top of foundation pads.


Topsoil stripped to depth of 100mm, 75mm layer of shingle on black perforated 1000 gauge polythene over entire area under building.


Post and beam timber frames with bolted connections. Joists at 400 centres at ground floor and Masonite composite timber joists at 400 centres at roof levels. All in accordance with calculations to BS 5268. Timber to be either home grown Douglas Fir / Larch or imported European Redwood / Whitewood / Canadian Hem-Fir. XOX steel bolts and washers. All structural timber stress graded as GS or SS to BS 4978:1973. Sizes to BS 4471 and permitted defects to BS 4978. The structure is braced in both directions with bolted steel rods below ground floor and Panelvent sarking board, in combination with diagonal timber braces at ground floor level.

All timber columns are to be treated with CCA preservative in factory. A code 4 lead DPC & bituthene layer separates the posts from the precast concrete paving slab.


Ground floor joists will sit on top of the timber beams and will be nailed in place. Double joists are fixed at perimeters and below partitions. The Masonite rafters will likewise sit on top of the timber beams and will be clipped in place.

7. ROOF :

The roof finish will be a suitable drought tolerant grass specification, on a 75mm soil growing medium, on a geotextile filter membrane on a butyl single ply roof membrane, laid on a 15 deg / 17.5 deg slope.

The 18mm thick t&g Sterling Board deck is laid directly onto 75 x 50 ventilation / spacer battens which cantilever to support the deck at eaves and verge. These are fixed down to the tops of the Masonite rafters with a scrim layer between to hold down the insulation.


22mm fin x Ex 150mm T&G s/w floorboards nailed to joists, either face fixed, or secret nailed. All edges are to be supported. Warmcel insulation will be dry blown between joists, over 6mm Gyproc multi-board fixed to the underside of beams and joists.

Scrim stapled to underside of joists. Warmcel insulation will be dry blown between joists to full depth.

12.5mm foil backed plasterboard (Gyproc Duplex wallboard) nailed or screwed to underside of rafters with 40mm galvanised plasterboard nails at 150mm c/c or 38mm drywall screws at 230mm c/c. Note: fix boards along the rafters (with long edge centered over the rafter, ensure ends are located over a support.

Ex 19 x 100 s/w battens screwed to underside of joist using 21/2” no.8 pozidrive screws (or 65mm lost heads) at 300mm c/c.

Alternatively use taper edge board and tape joints.


ex 25 x 125 feather edged douglas fir / larch boarding fixed horizontally with 25mm overlap. All external cladding treated with Dricon fire treatment to Class 1.

25mm ventilation space formed by 25 x 100 vertical battens.

9.2mm Panelvent sheathing fixed to:
50x50 vertical studs at 600c/c fixed externally directly to beam/joists, with pre-cut hardboard stiffener panels at 1200 c/s.

150 mm Warmcel wet blown between studs against Panelvent

12.5mm foil backed plasterboard (butt edge or tapered), with ex 19 x 100mm s/w cover battens or taped joints.

Ex 25 x 25mm internal head piece and ex 25 x 100mm skirting.


12.5 mm plasterboard fixed to one side of 50 x 75mm studs with 40mm galvanised plasterboard nails at 150mm c/c or 38mm drywall screws at 300mm c/c. Note: fix boards vertically and center over studs.

75mm Warmcel insulation wet blown into wall.

12.5mm plasterboard fixed to other side of studs (as above). Note use Gyproc moisture resistant board on walls and ceilings of bath and shower rooms fixed as above.

Fix ex 25 x 100mm skirtings and ex19 x 100mm cover battens using 65mm lost heads or 21/2” no. 8 pozidrive screws.


Windows and doors will be of high performance double glazed softwood. Aluminium or European Oak cill extensions to windows. European Oak cills to door frames.


Internal door and window linings made up on site. Glazed doors Boulton and Paul or similar softwood fully glazed internal doors. Doors and windows glazed with single leaf of 4 or 6mm (depending on size of opening) toughened glass. Solid doors Boulton and Paul or similar pine faced flush doors.

Other doors as required by self builders, to approval. All room doors to be 838mm wide. All external doors to be 905mm clear opening width.


Ex 32 x 150mm oak decking fixed using 21/2” no.8 pozidrive screws (2 per board per joist). Treated and finished as specified under section 23 below. Posts fixed using M12 Galvanised bolts plus washers. Rails and handrails fixed using 3” no.10 pozidrive screws. Hangers fixed using 21/2” no.8 pozidrive screws. See drawing 680/D/32.


A whole house passive stack ventilation system will be provided, using a humidistat controlled system ‘Passivent PSV’ to be specified in detail by WILLAN in accordance with their BBA Certificate.

All rooms have windows with a greater openable area than 1/20th of the floor, and all windows are provided with trickle ventilators in accordance with the passive ventialtion BBA certificate..


Pipes, fittings and accessories: UPVC to BS 4514 / BS 4576:Part1; manufactured by Key Terrain or similar. Black coloured round downpipes from 2100 range, 82mm dia.

All to be installed in accordance with BS8000: Part 13, section 3 to ensure the complete discharge of rainwater from the building without leaking. Obtain all components from the same manufacturer. Fix securely at specified centres providing additional supports as necessary to support pipe collars, particularly at changes in direction. All in accordance with manufacturer's instructions.


Stacks and WC branches pipes, fittings and accessories: UPVC to BS 4514, Kitemark certified, by Key Terrain or similar. Branch pipes, fittings and accessories to BS5255 Kitemark certified, by Key Terrain. Include for all necessary traps etc, pipe work to sizes indicated on drawings.

All to be installed in accordance with BS8000: Part 13, section 3 and BS 5572. Obtain all components from the same manufacturer. Form junctions using fittings intended for the purpose. Fix securely at centres not greater than those specified in BS 8000 providing additional supports as necessary at junctions and changes in directions. Access points at all changes in direction and at base of soil stack. All in accordance with manufacturer's instructions. Comply with restrictions on the cutting of holes, notches etc as detailed in Electrical and Pipework Specifications.

Pipework test: use Hep20 joint test kit in accordance with manufacturers recommendations.

Rainwater from roof will be stored in butts at ground level. Butts to be fitted with high level overflow leading to 100 diameter pipe to soakaways.


The heating and hot water system will be a condensing gas fired combination boiler (Worcester 350). All cold water to be mains fed with no cold water storage.

Radiators are by Barlo, sized to suit each room. Heating System control is by means of a plug in programmer and thermostatic radiator valves. All hot and cold pipework is in plastic (except the last 600mm of all connections to the boiler which are in copper), using the Hep2O push fit system and fittings by Hepworth. Gas supply pipework to be in copper and fitted by a registered CORGI installer. Test certificates will be required before completion of the buildings.


All fittings to be MK Electric or similar to approval. Test certificates will be required before completion of the buildings. A mains supplied smoke detector with battery backup will be provided in both the kitchen & hallway (one to sound, all to sound).


Standard range of pre-assembled kitchen fittings will be installed on site, to layouts chosen by the self builders.


Standard sanitaryware, with steel baths. Showers will have thermostatic mixers.


All timber to be decorated with natural based stains and waxes, made by OS Colour.

All exposed external timber 1 coat of One Coat Only Timber Stain (apply 2 coats to all joinery timber, windows, fascias etc and any exposed end grain) / or OS Country Colour (2 coats)

Internal timber 1 coat Wood Wax Finish

All plasterboard to be decorated with emulsion paint (1 mist and 2 top coats).


All T&G floors to have 2 coats of OS Color Wood Wax Oil.

Kitchens and bathrooms to have 2mm natural linoleum made by Farbo Nairn. Shower rooms to have 2mm natural linoleum made by Farbo Nairn with welded joints and upstands at edges.

[nb. see also ‘nailing schedule’ for fixing details not specified here.]

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