Build Guide
Step-by-Step Build Guide
From trailer selection to move-in day — a 12-stage build process with checklists, costs, and expert tips for every stage of your tiny house.
1
Trailer / Foundation Selection
1–2 weeks £2,000–£6,000
Your foundation choice determines everything — from legal classification to structural approach. For a tiny house on wheels (THOW), a purpose-built galvanised steel trailer is essential. For a permanent build, consider screw piles, concrete pad, or strip foundations.
What you need to know
- Purpose-built tiny house trailers (e.g. from Tiny House Trailer Co, Brian James) are designed with a flat deck and outrigger supports, unlike standard car trailers.
- Standard UK trailer widths: 2.55m (road-legal without escort) or up to 3.5m (requires wide-load escort). Max towing length: 7m without articulated registration.
- For permanent foundations, screw piles are popular — no concrete needed, reversible, and often preferred by planners in sensitive areas.
- Ensure your trailer is rated for the total weight of your build (typically 3,500kg for a single-axle, up to 5,000kg for twin-axle).
Stage 1 Checklist
- Decide: wheels or permanent foundation
- Calculate target total weight (structure + contents)
- Source trailer or commission foundation design
- Check trailer is galvanised and rated for load
- Verify road-legal dimensions if THOW
- Level and brace the trailer/foundation on site
Pro Tips
- →Don't buy a secondhand car trailer — they're not designed for static loads and will flex.
- →If going permanent, get a structural engineer to sign off your foundation design.
2
Design & Planning
2–4 weeks £0–£2,000
Finalise your floor plan, elevation drawings, and material schedule before you pick up a single tool. This is where you decide on layout, window positions, door placement, and roof pitch.
What you need to know
- Use free tools like SketchUp or paid software like Chief Architect to model your design in 3D.
- Consider the 'work triangle' for kitchen layout — sink, cooker, and fridge within easy reach.
- Plan your electrical layout at this stage: socket positions, lighting runs, consumer unit location.
- If you need planning permission, your drawings will need to be to scale with a site plan, floor plans, and elevations.
Stage 2 Checklist
- Choose floor plan layout (open-plan, loft bedroom, ground-floor bedroom)
- Decide on roof style (shed, gable, gambrel)
- Mark window and door positions
- Plan electrical socket and switch locations
- Plan plumbing runs (kitchen sink, bathroom, shower)
- Create material take-off list and budget
- Submit planning application if required
Pro Tips
- →Build a cardboard mock-up at full scale to test the layout before committing.
- →Standard UK door width is 762mm — go narrower at your peril.
3
Subfloor & Floor Framing
3–5 days £500–£1,500
The subfloor sits on top of your trailer deck or foundation and provides the structural base for walls. Insulate it well — cold floors are the number one complaint in poorly built tiny houses.
What you need to know
- For THOW: bolt pressure-treated timber joists to the trailer chassis using carriage bolts or welded brackets.
- Insulate between joists with rigid PIR board (e.g. Celotex/Kingspan) — 50mm minimum, 100mm recommended for UK climate.
- Seal all joints with foil tape to create a continuous vapour barrier.
- Top with 18mm structural plywood or OSB as your subfloor deck.
Stage 3 Checklist
- Bolt or weld joist brackets to trailer/foundation
- Install pressure-treated floor joists at 400mm centres
- Cut and fit rigid insulation between joists
- Tape all insulation joints with foil tape
- Lay and screw subfloor plywood/OSB
- Check level across entire floor (max 3mm deviation per metre)
Pro Tips
- →Use stainless steel or hot-dip galvanised fixings throughout the subfloor — moisture will find its way in.
- →Leave access points if you're running underfloor plumbing.
4
Wall Framing
3–5 days £800–£2,500
Frame your walls using 50×100mm (2×4) or 50×150mm (2×6) CLS timber. The thicker option gives more insulation depth, crucial for UK winters. Build each wall as a flat panel on the floor, then raise it into position.
What you need to know
- Space studs at 600mm centres to match standard insulation batt widths.
- Double up studs at corners and either side of window/door openings. Add cripple studs and headers above openings.
- Use a sole plate (bottom) and double top plate for structural continuity. Bolt sole plates to the subfloor/trailer.
- Brace walls temporarily with diagonal battens until sheathing is applied.
Stage 4 Checklist
- Cut all studs, headers, and plates to length
- Assemble each wall panel on the deck
- Raise walls and brace temporarily
- Check plumb and square with a spirit level
- Bolt sole plates to subfloor
- Install double top plate, lapping joints at corners
- Frame window and door openings with headers
Pro Tips
- →Pre-drill and screw rather than nail — it's easier to correct mistakes and results in a stronger joint.
- →Mark stud positions on the floor before raising so you know exactly where they'll land.
5
Roof Framing
2–4 days £600–£2,000
Your roof structure can be rafters (for gable/gambrel) or a simple mono-pitch (shed roof). A shed roof is easiest for beginners and works well for loft bedrooms. Ensure adequate pitch for water runoff — minimum 15° for most coverings.
What you need to know
- For a shed roof: run rafters from a raised wall (front) to a lower wall (rear) at the desired pitch. Use joist hangers or birdsmouth cuts.
- For a gable roof: build triangular trusses on the ground and lift into position. Brace with purlins.
- Overhang rafters by 300–450mm to protect walls from rain (critical in the UK).
- Consider a loft hatch vs. permanent loft ladder for bedroom access.
Stage 5 Checklist
- Decide roof style and pitch angle
- Cut rafters with birdsmouth notches
- Install rafters at 600mm centres
- Add ridge board (gable) or fix to wall plates (shed)
- Install purlins for mid-span support if needed
- Add fascia boards and soffit
- Check roof is square and level
Pro Tips
- →A shed roof with a 20° pitch is the sweet spot for UK rain runoff and loft headroom.
- →If using a loft bedroom, ensure at least 900mm sitting height at the mattress position.
6
Sheathing & Weatherproofing
3–5 days £800–£2,500
Before insulation goes in, the outside of your frame needs structural sheathing (OSB or plywood) and a breathable membrane. This creates the weather-tight shell — known as getting to 'dry envelope'.
What you need to know
- Apply 9mm or 12mm OSB3 or plywood sheathing to the exterior of wall and roof framing.
- Wrap the entire structure in a breathable membrane (e.g. Tyvek Housewrap) — this allows moisture vapour out but keeps wind and rain out.
- Tape all membrane overlaps with approved tape (minimum 150mm overlap).
- Install the roofing membrane or felt underlay, working from eaves to ridge.
Stage 6 Checklist
- Fix sheathing boards to wall studs and roof rafters
- Stagger joints between sheets (avoid continuous vertical lines)
- Wrap breathable membrane around walls, bottom to top
- Tape all membrane joints and around openings
- Install roof underlay from eaves to ridge
- Fit drip edges and any lead flashing
- Check for any gaps or tears in the membrane
Pro Tips
- →Get to dry envelope as fast as possible — UK weather won't wait for you.
- →Don't use non-breathable membranes (polythene) on the outside — moisture will be trapped in your walls.
7
Roofing & Cladding
3–5 days £1,000–£4,000
Now your shell is weatherproof, add the final roof covering and exterior cladding. Popular UK choices: corrugated metal roofing (lightweight, durable) and timber cladding (larch, cedar, or Siberian larch).
What you need to know
- Corrugated metal (steel or aluminium) is the go-to for THOW — lightweight, long-lasting, and easy to install with tek screws.
- For timber cladding, larch is the best UK-native option — it silvers beautifully and needs no treatment. Cedar is excellent but pricier.
- Always install cladding on battens (25mm minimum) to create a ventilated rain screen — this is critical for preventing rot.
- Consider Cedral fibre-cement boards for a maintenance-free alternative.
Stage 7 Checklist
- Install roof covering (metal sheets, tiles, or EPDM rubber)
- Fit ridge caps and verge trims
- Install vertical battens for ventilated rain screen
- Fix cladding boards from bottom to top
- Seal around window and door openings with flashing tape
- Apply treatment/oil to cladding if required (not needed for larch)
- Install guttering and downpipes
Pro Tips
- →Larch from a local sawmill is often half the price of merchant timber — and you're supporting UK forestry.
- →EPDM rubber membrane is excellent for flat or low-pitch roofs — a single sheet, no joints, 50-year lifespan.
8
Insulation & Vapour Barrier
2–4 days £800–£2,500
Insulation is arguably the most important stage for UK comfort. Your tiny house has a high surface-area-to-volume ratio, so it loses heat fast. Insulate walls, roof, and floor to the highest standard you can afford.
What you need to know
- PIR rigid board (Celotex/Kingspan): Best thermal performance per mm. U-value of 0.022 W/mK. Cut to friction-fit between studs, seal edges with expanding foam.
- Sheep's wool: Natural, breathable, handles moisture brilliantly. Slightly lower R-value but excellent for UK damp climate. Treats itself for moths.
- Wood fibre board: Excellent thermal mass (keeps cool in summer too). Breathable. More expensive but outstanding performance.
- Apply a vapour control layer (VCL) on the warm side (interior) of insulation. Use a smart membrane like Intello Plus that adapts to humidity.
Stage 8 Checklist
- Insulate walls between studs (full depth, no gaps)
- Insulate roof between and/or over rafters
- Verify floor insulation is complete and sealed
- Fill all gaps around pipes and wires with expanding foam
- Install VCL on interior side of all insulated surfaces
- Tape all VCL joints and seal around penetrations
- Check for thermal bridges at corners and junctions
Pro Tips
- →The cheapest insulation is the insulation you install properly — gaps and compression destroy performance.
- →Don't skimp on the roof — heat rises, and an under-insulated roof is your biggest energy loss.
9
Electrical First Fix
2–3 days £500–£2,000
Run all cables, install back boxes, and position your consumer unit before the walls are closed up. In the UK, electrical work in a dwelling must comply with Part P of the Building Regulations.
What you need to know
- For a permanent dwelling: all electrical work must be designed, installed, or certified by a registered electrician (e.g. NICEIC, NAPIT, ELECSA).
- For a caravan-classified THOW: wiring should follow BS 7671 (IET Wiring Regulations) and ideally be signed off by a qualified electrician.
- Use 2.5mm² twin & earth for ring mains (sockets), 1.5mm² for lighting circuits, and 6mm² or 10mm² for high-draw appliances (oven, shower).
- Install an RCD-protected consumer unit. Consider a dual-supply setup: mains hook-up + solar inverter.
Stage 9 Checklist
- Plan and mark all socket, switch, and light positions
- Install consumer unit in accessible location
- Run cable routes through studs (drill centre of stud, never notch)
- Install back boxes for sockets and switches
- Run cables for dedicated circuits (cooker, shower, hot water)
- Install smoke and CO alarm wiring
- Photograph all cable routes before closing walls
Pro Tips
- →Always photograph your cable routes before plasterboarding — future-you will thank present-you.
- →Consider USB sockets throughout — they're cheap and incredibly convenient in a small space.
10
Plumbing & Gas
2–4 days £500–£2,000
Install all water supply pipes, waste pipes, and any gas lines before closing up walls. In a tiny house, short pipe runs and a compact layout mean plumbing is simpler than in a conventional house.
What you need to know
- Use 15mm push-fit (e.g. JG Speedfit) for hot and cold water supply — easy to install, no soldering, and leak-free if done properly.
- Run 40mm waste pipes for sink/shower, 110mm for toilet (if using a conventional flush).
- Consider a combi boiler (Rinnai, Paloma) for instant hot water — no tank needed. Or an electric point-of-use heater.
- If using gas (LPG): all gas work must be done by a Gas Safe registered engineer. No exceptions.
Stage 10 Checklist
- Install hot and cold supply pipes to kitchen and bathroom
- Install waste pipes with correct falls (1:40 minimum)
- Fit isolation valves at each appliance
- Install water heater (combi boiler, electric, or heat pump)
- Run overflow and pressure relief pipes to exterior
- Pressure test all supply pipes before closing walls
- Install any gas supply lines (Gas Safe engineer only)
Pro Tips
- →A composting toilet eliminates the need for a 110mm soil pipe and sewage connection — massively simplifying your build.
- →Insulate all hot water pipes to reduce heat loss in such a small space.
11
Interior Fit-Out
2–4 weeks £2,000–£8,000
The fun part! Close up walls with plasterboard or tongue-and-groove timber, install your kitchen, bathroom, flooring, and all fixtures. This is where your tiny house starts to feel like home.
What you need to know
- Plasterboard (12.5mm) gives a smooth, paintable finish but adds weight. Tongue-and-groove timber (pine, spruce) is lighter and adds warmth.
- For kitchens, IKEA METOD units are popular — compact, affordable, and well-designed for small spaces. Or go bespoke with birch plywood.
- Engineered wood or vinyl click flooring is ideal — it's thin, durable, and handles the movement of a THOW.
- Install a folding/Murphy bed or loft bed to maximise floor space.
Stage 11 Checklist
- Install wall lining (plasterboard or T&G timber)
- Skim plasterboard and let dry (if applicable)
- Install flooring throughout
- Fit kitchen units, worktop, and splashback
- Install bathroom (shower tray, basin, toilet)
- Hang interior doors
- Complete electrical second fix (sockets, switches, lights)
- Complete plumbing second fix (taps, shower, connections)
- Paint / treat all interior surfaces
Pro Tips
- →Build in as much storage as possible — under stairs, under beds, above doors. You'll need every cubic centimetre.
- →Use light colours and mirrors to make the space feel bigger. A single accent wall adds character without closing the space in.
12
Final Fix & Move-In
1–2 weeks £500–£2,000
Snagging, certification, final connections, and making it yours. This stage is about getting everything inspected, fixing any issues, and preparing for occupancy.
What you need to know
- Walk through every system: test every socket, check every tap, flush the toilet, run the shower, test all lighting circuits.
- Get your electrical installation tested and certificated (Electrical Installation Certificate or Minor Works Certificate).
- If gas has been installed, get a Gas Safe certificate.
- If on permanent foundations, arrange your Building Control completion inspection.
- Set up utilities: water supply connection, electricity meter, broadband.
Stage 12 Checklist
- Complete a full snagging list (walk every surface, check every fitting)
- Get electrical certification
- Get gas certification (if applicable)
- Get Building Control sign-off (if applicable)
- Install smoke alarms and CO detector (hard-wired or sealed battery)
- Set up broadband / mobile signal booster
- Install exterior lighting and house number
- Connect to water and drainage (or set up off-grid systems)
- Move in and celebrate 🎉
Pro Tips
- →Create a snagging spreadsheet — go room by room and be ruthless. Fix everything before you move in.
- →Take photos of your completed build from every angle — you'll want them for insurance purposes.