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.

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