Build a Garage or Workshop
Slab, walls, roof, electrics and fit-out — one small building planned as one sequence, not five separate jobs.
A garage is a small building, and small buildings punish work done out of order. The slab sets the wall line, the walls carry the roof, and every cable and light fitting runs through both — so the concrete, blockwork, roofing and electrical numbers all depend on decisions made at the very start. Planning it as one sequence is the whole game.
This hub orders the takeoffs the way the build goes up: slab volume from footprint and thickness, block counts from wall area minus openings, roof materials from the rafter area, then lighting levels and circuit loads for the fit-out. A workshop gets the same sequence with different numbers — more light, more sockets, and machinery that changes what the slab and the electrics have to carry.
The scope here is deliberately honest: this hub plans quantities so you can brief trades, order materials and sanity-check quotes — the structure itself and all fixed electrics belong to qualified, registered people. The safety section below says exactly where the line sits.
The Plan
- Size it and site it. Fix the footprint, door position and access before anything else — and check boundary distances and height limits early, because outbuilding rules vary by area and can dictate the design.
- Pour the slab. Thickness by use: 100–150 mm (4–6 in) is typical for domestic garages, with edge thickening common. Volume is footprint area times thickness — the concrete calculator totals bags or truck-loads.
- Build the walls. Block or brick count comes from wall area minus door and window openings — single or double skin, with a 5% waste allowance typical. Timber frame follows the same wall-area logic with different units.
- Put the roof on. Roofing materials come from the rafter area — plan footprint times the pitch factor — and the rain has to leave: the gutter and downpipe calculator sizes the eaves run for the catchment.
- Plan the electrics. Lighting circuits, sockets, the door opener and any machinery add up into a load calculation that tells you what supply the building needs. This is design work for a qualified electrician — the calculator is for briefing them, not replacing them.
- Light it properly. Typical lighting-industry guidance is around 300 lux for general workshop tasks and 500 lux for fine detail — a room-size and target level turns into a lumen total and a fitting count.
- Fit out. Benches, shelving and racking — floor-standing loads the slab handles, but anything fixed to walls needs fixings into the structure, not the lining.
Calculators for This Project
- Concrete Slab & Footing Calculator Slab volume by footprint and thickness — cubic metres, yards or bag counts.
- Brick & Block Calculator Unit counts per m² for any wall area, with mortar volume and opening deductions.
- Roofing Materials Calculator Covering area from plan size and pitch — squares, bundles and underlayment.
- Lighting Calculator Lumens and fitting counts from room size and task level — general to precision work.
- Electrical Service Load Calculator Standard and optional method load totals — what the building's supply has to carry.
Guides Worth Reading
- Concrete Slab Thickness Choosing thickness by use — cars, workshops and heavier loads — with the reasoning.
- Brick Wall Quantity Guide Counts per m², openings, single versus double skin — garage walls worked through.
- Workshop Lighting Guide Lux targets by task, fitting placement and why garages end up under-lit.
- Electrical Service Load, Explained How service size is calculated and when 100 amps is enough — the method behind the tool.
What This Hub Doesn't Cover
Garage electrics and structure need qualified, registered trades. In most countries, fixed wiring in a new outbuilding must be installed or certified by a registered electrician, and outbuildings themselves commonly need permits. Use this hub to plan quantities and brief the people doing that work — not as a wiring or structural design guide.
This hub doesn't design the building. Foundations for masonry structures, lintels over doors, roof framing and every part of the electrical installation are jobs for qualified people, and a workshop slab carrying a vehicle lift or heavy machinery needs engineering beyond typical garage practice. Drainage, fire separation from the house and boundary rules all vary by country and region — settle them with your local authority before the first bucket of soil moves.
Frequently Asked Questions
How thick should a garage slab be?
100–150 mm (4–6 in) is typical for domestic garages and workshops, with thicker edges and reinforcement common. Heavier vehicles, machinery or a lift change the answer — the slab thickness guide covers the bands.
How many blocks for a single garage?
Work from wall area minus openings. A 6 × 6 m garage at 2.5 m eaves has about 54 m² of wall after a door and window — roughly 540 standard 440 × 215 mm blocks at about 10 per m², plus 5% waste. The brick and block calculator does the count for any size.
How bright should a workshop be?
Typical lighting-industry guidance is around 300 lux for general workshop tasks and 500 lux for fine detail, with 150 lux for basic circulation. The lighting calculator converts room size and target level into a lumen total and fitting count.