Which Building Regs Apply to My Job? The Quick Lookup

‍‌​​‌‌‌​​​‌‌​​​‌​‌‌‌‌​‌‌​​​​‌​​​‍Reference for working builders (England)

Last reviewed: March 2026

If you're changing structure, services, fire, access or drains, assume Building Regs are in play. This is the fast way to see which Parts you're actually dealing with on the jobs you do all the time.

Loft conversion (two-storey house to three storeys)

• Part A - Structure - new floor joists, trimming for stairs and rooflights, dormers, and often removing/altering load-bearing walls.
• Part B - Fire safety - you've just added a storey: protected stair, fire doors to rooms off the stair, upgraded ceilings, alarms, maybe mist/sprinklers.
• Part C - Site prep & damp - less of an issue, but any new external walls/roofs and junctions must not create damp paths.
• Part E - Sound - new loft floor over party wall, and sometimes upgrades to existing party walls/floors to meet separating-element standards.
• Part F - Ventilation - new habitable rooms and bathrooms need compliant extract, background and purge ventilation.
• Part G - Sanitation & hot water - new bathrooms/ensuites must have proper hot/cold, safe hot water (TMVs), and count into water-efficiency calcs on new dwellings.
• Part H - Drainage - new WCs/showers need proper foul connections and venting.
• Part J - Combustion - any changes near existing flues/chimneys, or if you're adding a stove in the loft room.
• Part K - Stairs & guarding - new stair to loft must meet rise/going/headroom/guarding rules; guarding at stairwells/open edges.
• Part L - Energy - upgrade roof insulation, often improve existing thermal elements; airtightness details at dormers/rooflights.
• Part M - Access - higher-risk if you mess with entrance storey WC/rooms while doing the loft - whole dwelling must still be reasonably accessible.
• Part O - Overheating - if it's a new dwelling or part of one, overheated top storey rooms can trigger Part O on new-build shells.
• Part P - Electrics - new circuits, downlighters, fans, heaters in a new habitable storey.

Single-storey rear extension

• Part A - foundations, walls, beams/lintels where you knock through, roof structure.
• Part B - don't wreck the escape route with open-plan layouts; inner rooms, doors, alarm coverage all matter.
• Part C - slabs, DPM, DPCs, external levels; don't build in damp or bridge the DPC with patios.
• Part E - if you touch party walls or create new separating elements (e.g. semi-detached, extension on boundary).
• Part F - new kitchen/dining/living space needs adequate extract, background and purge ventilation.
• Part G - if there's a new WC/shower room, sanitation and hot water safety apply.
• Part H - foul and surface drainage from new WCs/sinks/roof; soakaways, connections and manholes.
• Part J - any new or altered appliances/flues in the extension; also CO alarm if fitting new fixed combustion appliances.
• Part K - doors, steps, ramps, thresholds, guarding at level changes and any new glazing in critical locations.
• Part L - new walls/roof/floor must meet U-values; extra glazing and airtightness affect SAP for bigger works.
• Part M - thresholds, access into and through the new space; don't create steps or tight access that break basic visitability.
• Part O - for new dwellings, big south/west glazing and bifolds can trigger overheating checks.
• Part P - new circuits for kitchen/bifolds/lighting/sockets.

Two-storey extension

Everything in the single-storey list, plus:

• Part A - more load, more structure: second-storey floors, extra bracing, often more serious foundation design.
• Part B - escape routes from new rooms, extra alarms, and protected stairs if you've effectively created a three-storey arrangement.
• Part E - extra floors/walls affecting party elements; more chance of sound tests on bigger jobs.

Kitchen refurb (moving stuff, not just swapping doors)

• Part A - if you knock out walls, widen openings or move structural nibs to "open it up".
• Part B - open-plan to the stair can wreck the protected escape route; alarms and sometimes extra protection needed.
• Part C - any floor/wall work at ground level must not compromise DPM/DPC or create cold bridges.
• Part E - if you're moving walls adjoining other rooms/units, internal sound separation can be hit.
• Part F - upgraded kitchen extract and background ventilation (especially with new windows/doors).
• Part G - sinks, dishwashers and hot water safety (especially if the cylinder/boiler is touched).
• Part H - new or altered waste runs and gully locations.
• Part J - if you touch the boiler, flue or add/remove a gas/hob or solid fuel appliance.
• Part K - new glazing/doors, steps to outside, floor level changes.
• Part L - replacement windows/doors and major fabric changes must meet current energy performance.
• Part P - new circuits, RCD protection, alterations to kitchen wiring.

Bathroom / ensuite refurb

• Part A - if you're cutting big holes in joists or moving structural walls for layouts.
• Part B - doors/ceilings on escape routes if you mess with the stair/hall.
• Part C - wet areas, tanking, junctions that can drive damp into structure.
• Part E - sound separation around WCs and bedrooms.
• Part F - fan spec and background ventilation must meet current Part F.
• Part G - hot water safety (TMVs, 48°C max at bath), new WCs/basins, water-efficiency on new dwellings.
• Part H - soil/waste pipework, fall, venting and traps.
• Part J - if there's a flue in that wall/room and you start cutting/boxing.
• Part K - any new low-level glazing, steps, slip/guarding issues.
• Part P - electrics in zones, fans, showers, bonding where required.

Window / external door replacement

• Part B - escape windows; don't downgrade egress from bedrooms and escape routes.
• Part F - trickle vents/background ventilation; can't make ventilation worse.
• Part K - safety glazing in critical locations, guarding where needed.
• Part L - replacement windows/doors must meet limiting U-values.
• Part Q - on new dwellings or certain conversions, windows/doors must be security-rated.
• Reg 7 - materials and workmanship; use properly tested doorsets/windows, especially for fire and security.

HMO / flat conversion (house → flats/rooms)

• Part A - new floors, walls, openings, stair alterations; structure often heavily reworked.
• Part B - full fire strategy: escape routes, fire doors, alarms (Grade A/C LD2 etc.), compartmentation.
• Part C - damp proofing and site conditions where you're adding bathrooms/kitchens and basements.
• Part D - if you're injecting insulation into cavities using foam systems.
• Part E - separating walls/floors between flats/rooms; sound tests or Robust Details.
• Part F - more kitchens/bathrooms = more extract and background ventilation.
• Part G - more WCs/bathrooms; hot water safety, water-efficiency on "material change of use to dwellings".
• Part H - extra foul connections, manholes, possible capacity issues.
• Part J - flues, new boilers, stoves, and CO alarms.
• Part K - stairs, guarding, safety glazing.
• Part L - changed use triggers insulation upgrades/energy targets in many cases.
• Part M - access in and around flats, level thresholds, WCs on entrance storey; sometimes higher standards in planning.
• Part O - if it's a new-build envelope or major conversion with overheating risk (small, highly glazed flats).
• Part P - new/altered circuits, boards, RCDs.
• Part Q - security for new flats' doors/windows.
• Part R - comms infrastructure on larger schemes.
• Reg 7 - materials and workmanship, plus external wall fire rules on taller blocks.

New-build house

Pretty much everything:

A, B, C, D (if foam), E, F, G, H, J, K, L, M, O, P, Q, R, S, Reg 7 - all apply in some way on a new dwelling.

You're into full SAP, airtightness, sound, fire, access, energy, overheating, EV charging, broadband, security and material standards from the start.

New-build block of flats

Same as a house, but more intense:

A-H, J, K, L, M, O, P, Q, R, S, Reg 7 - plus tougher expectations on B (fire), E (sound), M (common parts), O (overheating), and Reg 7/7(2) (external wall materials on taller blocks).

Garage conversion (attached or integral)

• Part A - new openings, floor upgrades, any nibs/walls cut out.
• Part B - fire separation between former garage and house; escape route and alarm coverage.
• Part C - garage floors/walls are often cold/damp - need DPM, insulation, DPC continuity.
• Part E - sound between new habitable room and other spaces/party walls.
• Part F - ventilation for a new habitable room or bathroom.
• Part G - if adding WC/shower.
• Part H - new foul drainage to WCs/sinks.
• Part J - sealing redundant flues/appliance vents; any new boiler.
• Part K - steps, thresholds, glazing, guarding.
• Part L - new thermal elements, upgraded walls/roof/floor.
• Part M - access into the new room and through the entrance storey.
• Part P - wiring the new habitable space.

Barn / office-to-residential conversion

• Part A - often major structural strengthening, new floors/roofs, new openings.
• Part B - full fire strategy for new dwellings; lofted/complex layouts need careful design.
• Part C - damp, ground conditions, DPM/DPC on what started life as "non-habitable".
• Part D - if foam cavity insulation is involved.
• Part E - sound between units and internally.
• Part F - ventilation in airtight, highly insulated conversions.
• Part G - full sanitation and hot water set-up, water efficiency.
• Part H - foul and rainwater drainage from scratch.
• Part J - all combustion appliances, flues, and CO alarms.
• Part K - stairs, guarding, glazing.
• Part L - treated as new dwellings or "change of use" with specific energy targets.
• Part M - access, thresholds, entrance-storey WCs.
• Part O - overheating risk in highly glazed/metal roofs.
• Part P, Q, R, S, Reg 7 - electrics, security, broadband, EV, materials.

Chimney breast / chimney removal

• Part A - supporting remaining chimney/stack; beams, gallows brackets, load paths.
• Part B - fire separation and compartmentation where chimneys form part of walls; sealing off flues.
• Part C - making good external walls/roofs to avoid damp.
• Part J - decommissioning flues and appliances properly; notice plates where required.
• Reg 7 - using suitable structural materials/supports.

Installing a log burner / solid fuel stove

• Part J - the main one: flue size/height/route, hearths, clearances to combustibles, ventilation and CO alarm.
• Part A - if you cut structure for chimney/twin-wall or alter load-bearing walls.
• Part B - openings through floors/roofs; fire-stopping and compartmentation.
• Part C - weather-tight penetrations and damp around new flues.
• Part K - safety glazing and guarding near the stove.
• Part P - any electrical connection (fans, controls).

External wall insulation (EWI) / cladding

• Part A - fixings, wind load, weight on existing structure.
• Part B & Reg 7(2) - external wall fire performance, especially on taller/more complex buildings.
• Part C - moisture, breathability, DPC/DPM links; don't create trapped damp.
• Part L - improved U-values; details round openings and junctions affect thermal bridging.
• Part M - thresholds and access if you build up around doorways.
• Part K - window sill heights and guarding changes.

Replacing a boiler

• Part J - flue route and terminal clearances; combustion air; CO alarm now required with new/replacement fixed gas/oil appliances (except cookers).
• Part L - boiler efficiency, controls, and sometimes system upgrades if it's part of a bigger energy package.
• Part G - hot water systems and scald protection where cylinders/TMVs are touched.
• Part P - electrical work for boiler controls/power.

Adding a garden office / outbuilding

• Part A - structure and foundations to suit size and ground; especially close to boundaries.
• Part B - escape and fire spread become an issue as size/use moves from shed to habitable; also distances to boundaries.
• Part C - DPM, DPC and damp detailing on "posh sheds".
• Part E - sound only if it becomes a separate dwelling/flat.
• Part F - ventilation if used as a proper office/habitable space.
• Part G/H - if you add WCs/showers and drainage.
• Part K - steps, ramps, glazing and guarding.
• Part L - insulated "garden rooms" used as habitable space must meet thermal standards.
• Part P - power supply and circuits to the outbuilding.

Porch under 3 m²

• Part A - structure still has to be safe, even if exempt from full regs.
• Part B - don't block or compromise the main escape route or door width.
• Part C - don't bridge DPC or trap damp.
• Part K - steps, thresholds, glazing and guarding.
• Part L/F - kick in if the porch is heated or you mess with existing doors/windows/vents.
• Part M - thresholds and access can still be an issue if you create steps or tight doorways.

Re-roofing

• Part A - structural adequacy of rafters/trusses if you change loads (heavier tiles, solar).
• Part B - fire spread over roof, separation distances, and any work on party parapets.
• Part C - underlay, ventilation, condensation risk.
• Part L - upgrading roof insulation to current standards when re-roofing is often required.
• Part O - in new builds, rooflights and dark/light finishes feed into overheating.
• Part S - if you're adding PV as part of the job.

Knocking through internal walls (open-plan)

• Part A - is the wall load-bearing? If yes, beam/lintel and calcs.
• Part B - opening to the stair/escape route can kill your protected route; you may need extra measures.
• Part E - internal sound separation between rooms and possibly between dwellings.
• Part K - guarding at split levels, stairs, and any low-level glazing you create.
• Part L - bigger open-plan volumes can change heating and energy performance; sometimes SAP tweaks needed.

New driveway over or near a sewer

• Part H - building over/near public sewers, load on covers/pipes, access for maintenance; water company build-over rules.
• Part A - loadings on manholes/structures and ground conditions.
• Part C - surface water run-off, falls away from house, no ponding against walls.

Print this and stick it on the office wall. Add notes for your own jobs. If a job isn't on here but you're touching structure, fire, access, services or drains, assume at least A, B, L, P and H are somewhere in the mix and check.

This page is a general guide for small builders and main contractors working on dwellings in England. It doesn't cover every edge case or non-domestic job. Always check the latest Approved Documents, your drawings/spec, planning conditions and Building Control before you start cutting or pouring. SiteKiln does not provide legal, financial or tax advice. All content is for general information purposes only. Always seek professional advice for your specific situation.

Common questions

Do I need building regs for a garden room?

Usually no, if it's under 30m² floor area, single-storey, more than 1m from any boundary, with no sleeping use. If anyone will sleep in it, or it sits closer than 1m to a boundary without fire-resistant walls, full Building Regulations approval is required. Electrical work must comply with Part P regardless.

Building Regs Checker tool.

What is a Lawful Development Certificate?

A formal document from your council confirming a building or use is lawful and doesn't need planning permission. It costs around £120 for proposed work, takes 8 weeks, and protects you from future enforcement. Buyers' solicitors regularly demand one when the property is sold.

Planning Permission Checker tool.

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