The 2VP Knowledge Base

Max pitch 42°, rise 150–220mm, going 220–300mm. Min 2m headroom, reduced to 1.9m at the centre and 1.8m at the side of a loft stair. Handrail 900–1000mm above pitch line.

900mm min to stairs and internal guarding; 1100mm to balconies, landings and external edges. Gaps must not allow a 100mm sphere to pass (Part K).

A protected escape stair enclosure, FD30 (30-minute) fire doors to habitable rooms off the stair, and mains-powered interlinked smoke alarms on every storey. New third-storey usually needs a protected route to final exit (Part B).

Habitable rooms in loft and first-floor conversions need an openable escape window: clear openable area ≥ 0.33m², at least 450mm high and 450mm wide, with the bottom of the opening ≤ 1100mm above floor.

Grade D, mains-powered with battery backup, interlinked. Smoke alarms on every storey in circulation space; heat alarm in the kitchen (Part B / BS 5839-6).

Typical targets: walls 0.18, floors 0.18, pitched roof (insulation at rafter) 0.16, flat roof 0.15, windows/doors 1.4 W/m²K. Confirm the trade-off route via SAP where glazing is high.

Openings limited to about 25% of the extension's floor area (plus the area of any windows/doors covered by the new build), unless compensated by better U-values through a SAP calculation (Part L).

Provide background ventilation (trickle vents) and purge (openable window). Intermittent extract: kitchen 30l/s at the hob or 60l/s elsewhere, utility 30l/s, bathroom 15l/s, WC 6l/s (Part F).

A cold roof needs ventilation — 25mm continuous at eaves and 5mm at ridge — or use a breathable membrane. A warm roof (insulation at rafter with VCL) avoids the need for a ventilated void. Prevents condensation and rot.

Damp-proof course at least 150mm above finished external ground level, linked to the floor DPM, with cavity trays and weep holes over openings (Part C).

Typical strip foundation ~1m deep, but governed by ground and trees — near trees on shrinkable clay, foundations often 1.5–2.5m+ with clayboard. Building control inspects the trench before concrete.

Steel needs adequate end bearing (commonly 150mm min) onto a padstone/spreader sized by the structural engineer, on dense concrete block or concrete. Beam size and connections per SE design (Part A).

Notches only in the top, between 0.07 and 0.25 of span, max depth 0.125 of joist depth. Holes on the neutral axis, between 0.25 and 0.4 of span, max diameter 0.25 of depth. Keep notches and holes apart.

The breast above must be supported — typically a gallows bracket (with neighbour/party-wall agreement) or a steel beam. Requires building control approval and often an SE calculation.

Every opening needs a correctly sized lintel with min 150mm end bearing, plus a cavity tray and weep holes above external openings to shed water.

Separating walls and floors between dwellings must meet Part E and be sound-tested (or use Robust Details). Typical solutions: independent ceilings, resilient bars, acoustic quilt and floating floors.

New circuits, consumer-unit replacement and work in bathrooms/kitchens are notifiable. Use a registered competent-person electrician (self-certifies) or notify building control before work.

New dwellings and many extensions require an accessible WC at entrance level and level/accessible thresholds. Check Part M category for the project.

Serve notice for work on a shared wall (2 months' notice) or excavating within 3m/6m of a neighbour's structure (1 month). Not a building reg, but essential — get a schedule of condition and, if needed, a surveyor's award.

Single-storey rear: 3m (terraced/semi) or 4m (detached), up to 4m high; larger schemes to 6m/8m under Prior Approval. PD rights are removed in conservation areas, on flats and listed buildings — check before relying on PD.

Building over/near a public sewer needs a build-over agreement with the water authority; keep foundations clear or bridge the sewer with a lintel and provide access.

100mm foul drains typically laid at 1:40, 150mm at 1:150. Rodding/inspection access at changes of direction. Confirm connection and levels with building control.

In radon-affected areas, provide a radon barrier and/or sump per BR 211. Check the postcode against the radon map at design stage.

Removing a load-bearing wall needs an SE-designed beam with correct bearing and, where it supports masonry above, propping during the works and building-control inspection before closing up.

Survey and CCTV the run, then agree a build-over with the water authority — either divert the drain or bridge it with a reinforced lintel and keep access. Never simply build over blind.

Install trench sheeting/props, dewater with a pump, and stage the dig. In rain, cover with a temporary roof so you can keep working without flooding the trench.

Check for DPC bridging (raised external ground, render over the DPC, debris in the cavity). Clear the bridge, reinstate or inject a new DPC, and re-plaster with a salt-resistant system.

Verify the SE design and end bearings, add noggins, sister the joists or reduce the span with a beam. Steel should bear on a correctly sized padstone.

Old and new move differently — use a movement/bell-cast bead, scrim and mesh the junction, and allow the new structure to settle before final decoration.

Maintain continuous insulation across the junction, insulate reveals and the floor perimeter, and add a thermal break so you avoid cold spots and surface condensation.

Improve ventilation (eaves and ridge) on a cold roof, or convert to a warm roof with insulation at rafter level and a vapour-control layer on the warm side.

Work in short (≈1m) hit-and-miss bays, never adjacent bays at once, to an engineer-approved sequence — the wrong sequence can collapse the wall.

Serve the correct notice, agree a schedule of condition, and appoint a party-wall surveyor to produce an award if the neighbour dissents. Document everything with photos.

Map the levels first; correct with self-levelling compound or packing, or rebuild if severe. Agree tolerances with the client and note them before finishes go down.

Ensure the upstand is ≥150mm, dress the membrane (EPDM/GRP) fully up and over, and cap/flash the top. Most flat-roof leaks are upstand and detailing failures, not the field.

Reposition the flue to meet Gas Safe clearances, or fit a plume-management kit. Confirm distances before first fix so you don't move it later.

Plan the SVP early; where an external stack isn't wanted, an air-admittance valve may be allowed internally, provided at least one open vent stack serves the system.

Reconfigure the stair, add or extend a dormer over the stair, or drop the ceiling in the room below. Resolve at design stage — it is the classic loft-conversion trap.

Provide a protected stair enclosure with FD30 doors and interlinked alarms, or a compliant escape window — agree the strategy with building control before framing.

Specify solar-control glass, add shading/brise-soleil or a roof overhang, and provide cross- and purge ventilation. Model it before ordering the glazing.

Where you can't project past the boundary, use an eccentric or reinforced foundation designed by the SE so the load stays within your land.

Scribe and pack the new work, or rebuild the leaf if severe. Agree visible tolerances with the client up front so it isn't a snag later.

Repoint defective mortar, use a breathable render or internal insulated plasterboard with a managed cavity, and avoid trapping moisture with impermeable finishes.

Where sound, stabilise; where blown, hack off and re-plaster (lime on period walls), scrim the joints, and isolate dissimilar backgrounds to control cracking.

Form a dry-pack screed to the correct fall toward the drain over a waterproofed, reinforced pan, then tank before tiling. Re-lay if the falls are wrong.

Space cables evenly (5–15cm), never cross them, match the output to the floor finish, and insulate below the system so heat goes up, not down.

Add dedicated circuits and, if needed, upgrade the consumer unit; all notifiable under Part P and certified by a registered electrician.

Fit trickle vents and correctly rated extract fans (humidity-sensing where useful), and provide purge ventilation — moisture has to have a way out.

Retie with mechanical/helical remedial ties at the correct spacing after a survey; failing ties cause horizontal cracking and bulging.

Cut out and replace affected timber, treat the remainder, lay a DPM, and restore sub-floor ventilation with clear air bricks.

Form the valley in lead or GRP with correct laps and upstands; most valley leaks are undersized or short-lapped detailing.

Stop and regularise — apply for a variation, retrospective permission or a Lawful Development Certificate. Don't cover it up; it surfaces at sale.

Rectify to the Approved Document, request a re-inspection, and keep dated photos of everything before it's covered so sign-off isn't held up.

Stop work in that area and get a licensed survey and removal before continuing — never disturb suspected ACMs.

Get an SE assessment; stitch with helical bars in the bed joints, address the cause (movement, drains, trees), and monitor before making good.

Erect a temporary roof/scaffold cover and keep a dewatering pump running so wet weather doesn't cost the programme or risk a trench collapse.

Photograph every delivery on arrival, log shortages immediately, store goods securely, and claim quickly so it never becomes the client's delay.

Survey the room accurately before ordering, allow scribe fillers, and set out from a datum — never assume the drawing dimensions on an old building.

Almost always an out-of-level or out-of-square structural opening — form the opening precisely and level the cill. Making our own glazing lets us match opening and unit exactly.

Use a Type C cavity-drain membrane with a sump and pump (plus battery backup), and keep the drainage maintainable — belt-and-braces beats a single tanking layer.

Detail airtightness deliberately — tape membrane laps, seal service penetrations and junctions — or insulation underperforms and you get cold draughts and condensation.

Build the separating element to Part E (or Robust Details) with resilient bars, isolation and acoustic quilt, and sound-test before completion.

Install a radon barrier and/or sump to BR 211, detailed and sealed at the design stage — retrofitting is far harder.

Deepen the foundation and use compressible clayboard to the face on the heave side, to an engineer's design based on the tree species and distance.

Step or bench the foundation, or underpin the existing, so you never undermine the neighbouring/existing footing.

Price every variation and get it signed before the work is done, against an agreed schedule of rates. Open-book pricing keeps it visible — no silent creep.

Run to a Gantt chart with dated stages and daily updates, so slippage shows immediately and a catch-up plan is agreed early, not at the end.

Lock a decisions schedule with 'needed-by' dates before work starts, so late choices don't stall the trades or trigger costly changes.

Sign off stage by stage, issue a clear snagging list at handover, and hold a fair retention — disputes come from surprises, not from process.

Re-lay to the correct gradient (≈1:40 for 100mm) with proper access; too shallow silts up, too steep leaves solids behind.

Position the vapour-control layer on the warm side and keep the outer layers breathable; run a condensation-risk analysis on any retrofit build-up.

Needle and prop, then install a correctly sized lintel with full bearing and a cavity tray — a sagging opening is often a hidden lintel failure.

Hold batts with retaining clips and fit full-fill correctly; slumped or gapped insulation causes cold spots and mould. Inspect before boarding over.

Agree access early (or use the Access to Neighbouring Land Act if refused), with a schedule of condition and dates, so the programme doesn't stall at the boundary.