Building Regulations Checklist for Garage Conversions in Brighton & Hove

Everything inspectors look for—structure, insulation, fire safety and more.

Why Building Control Matters

Planning consent (or a lawful-development certificate) says “yes, you may do it.”
Building Regulations approval proves you’ve done it safely — protecting future buyers, mortgage lenders and, most importantly, the people using your new space. Brighton & Hove Building Control officers (or an approved inspector) visit at key stages to sign off the items below.

Structural Stability

Goal-post frame
- Steel or glulam uprights plus top beam sized by a structural engineer
- Padstones or spreader plates distribute load over the slab or new pads
- Galvanised bolts with torque certificates (marine grade for coastal sites)
Floor loading
- Existing slab depth checked (many 1980s garages have only 75 mm concrete)
- EPS / XPS insulation laid beneath a new screed ties slab to dwarf walls
- Bungaroosh walls may need resin anchors or mini-piles for heavier rooms

Moisture Protection & Damp Proofing

Damp-proof membrane (DPM)
- 1200-gauge polythene lapped up walls 100 mm and taped to the new cavity wall
- Joints sealed with double-sided butyl tape
Existing walls
- Cement render removed from bungaroosh; hot-lime render reinstated so the wall can breathe
- Tanking slurry or cavity-drain membrane applied to earth-retaining side walls where required

Insulation & Thermal Performance (Part L 2025 Targets)

Walls
- Aim for U-value ≤ 0.18 W/m²K
- Common build-up: 50 mm PIR between studs plus 37 mm insulated plasterboard
Floor
- Aim for U-value ≤ 0.15 W/m²K
- Typical build-up: 100 mm PIR over slab topped with 65 mm screed
Flat roof
- Aim for U-value ≤ 0.13 W/m²K
- Typical build-up: 120 mm PIR over deck beneath single-ply membrane and OSB
Windows & doors
- Whole-unit U-value ≤ 1.2 W/m²K
- Best practice on the coast: argon-filled low-E glazing in marine-grade aluminium frames

Airtightness & Ventilation (Part F)

Continuous vapour-control layer taped to beams, lintels and wall plates
Target air-permeability ≤ 8 m³/h·m² @ 50 Pa
Background ventilation via 5 000 mm² trickle vents or a continuous-running MVHR unit
Bathrooms need 15 L · s⁻¹ intermittent extract or 8 L · s⁻¹ continuous

Heating, Electrics & Plumbing (Parts P & G)

Electrics
- New ring or radial circuit on RCBO
- Interlinked, mains-powered smoke alarms
- At least one twin socket per 2 m of wall space plus CAT-6 for home offices
Heating
- Oversized radiators on the existing system, electric under-floor mats, or air-to-air heat pump
Plumbing
- Soil pipe to existing stack within 6 m; use a macerator if gravity falls short
- Insulate hot-water pipes with 25 mm lagging

Fire Safety (Part B)

New room must open onto a hallway leading to an external door or include an egress-size window (clear opening ≥ 0.33 m², min 450 mm height)
Ceilings below habitable rooms: 30-minute fire-resistant build-up (double 12.5 mm board or one 15 mm Type F)
Doors to integral kitchens: FD30 self-closer or smoke-sealed if the inspector approves open-plan layout

Acoustic Performance (Part E)

Party walls adjoining neighbours: 50 mm acoustic mineral wool plus resilient bars under 12.5 mm plasterboard
Floating floor detail: 5 mm acoustic mat beneath engineered-wood or laminate

Accessibility (Part M)

Thresholds level or ramped < 15 mm to garden or driveway
Door clear opening ≥ 775 mm
Light switches positioned 900–1200 mm above finished-floor level

Inspection Stages

Commencement: slab survey and DPM placement
Structural: goal-post frame, padstones, wall ties
Insulation: floor PIR before screed; wall cavities before plasterboard
First fix: electrics, plumbing, ventilation ducting
Pre-plaster: fire collars, cavity closures, service penetrations sealed
Final: decoration complete, certificates handed over, Building Control sign-off

Certificates & Documents You’ll Need at Final Sign-Off

Structural engineer calculations and beam sign-off
Electrical installation certificate (Part P)
Gas-Safe or G3 unvented hot-water cert where applicable
U-value and condensation-risk calculations
Ventilation commissioning sheet (if MVHR fitted)
Smoke-alarm test certificate

Keep digital copies; solicitors request them on sale or remortgage.

Cost of Compliance (2025 Guide Prices)

Building Control plan check & inspections £495–£575
Structural engineer goal-post design £400–£850
SAP calculation & BRUKL printout £220–£300
Air-pressure test (optional but wise) £180–£250

Budget an extra £1,100–£1,500 on top of your build cost to cover professional and approval fees.

Tips for Stress-Free Approval

Email drawings to the inspector before work starts—questions answered early avoid delays.
Photograph hidden layers (slab, insulation, membranes) so evidence exists if an inspection is postponed.
Upload all completion certificates to the Council portal the same day the final visit occurs.