How to Assemble a Garden Shed (Stratco / Absco)
By Cal — outdoor and structures, Perth.
I’ve put up a lot of Stratco and Absco sheds over the years — for myself, for mates, for clients. The thing nobody tells you when you buy the shed kit is that the slab matters more than the shed. A $1,200 Absco Eco shed sitting on a bad slab will warp, leak, and rust at the base inside 5 years. The same shed on a properly prepped base will last 20+ years and look new on year 10.
The good news: you don’t need a concreter. There’s a quick-pour DIY option for under $400, and there’s a “no concrete at all” option using compacted road base and a treated-pine perimeter that costs under $150 and works just as well for a 3×3 m shed in a typical suburban backyard. I’ll cover both.
The Aussie-specific bit that catches people: most Australian councils require sheds over 10 m² to have a building permit, and they need to sit at least 900 mm from any boundary. The 10 m² threshold is calculated on the building footprint (the eaves overhang), not the floor area inside — so a 3.0 × 3.4 m shed with 200 mm eaves all round comes out at 11.56 m² and needs a permit, even though the floor inside is only 10.2 m². Check your council’s planning page before you order.
What you’ll need
- Your Stratco or Absco shed kit (instructions in the box)
- A second adult — non-negotiable for the wall and roof stages
- Either: 60 × 20 kg bags of concrete + reinforcing mesh + form timber (slab option); or 1 m³ of road base + 4 lengths of 100×100 H4 treated pine + 16 GalvBugle screws (compacted-base option)
- A power drill with Phillips and Tek-screw bits
- Tin snips (for ridge cap trims)
- A 1.2 m spirit level
- A measuring tape and string line
- A rubber mallet
- Plate compactor (Kennards $80/day) — for compacted-base option
- Silicone sealant (Selleys Roof and Gutter, neutral cure)
- Dynabolts (M10 × 75 mm) — to anchor frame to slab/timber base
Step 1: Check your council planning rules first
Five minutes on the council website saves a $2,000 demolition order later. Search “[council name] outbuildings exempt development” — most councils publish a one-page guide. Key thresholds:
- Footprint typically 10 m² or 20 m² depending on council
- Boundary setback usually 900 mm (some councils 1,500 mm)
- Maximum height usually 2.4 m (eaves) or 3.0 m (ridge)
- Not in front of the building line (front yard)
- Bushfire zones have additional cladding rules
If your shed exceeds any threshold, you need a planning permit. Don’t be the bloke whose neighbour dobs and faces a Stop Work order.
Step 2: Mark out the shed footprint with string lines
Use star pickets and builder’s twine to mark the 4 corners of the shed base. Add 100 mm extra each side beyond the shed footprint — that’s your slab or compacted-base perimeter. Check the diagonals are equal (3-4-5 triangle method or just measure both diagonals — if equal, the rectangle is square).
Re-check the 900 mm setback from boundaries with the tape. Doors should face an open direction, not a fence — strong winds plus an open shed door equals a bent door track.
Step 3a: SLAB option — quick-pour your own concrete
Skip this step if going with the compacted-base option (Step 3b).
Excavate 100 mm deep across the slab footprint. Form up with H3 treated pine 100×50 set on edge as your form. Lay reinforcing mesh (SL62 from Bunnings, $40 a sheet) on bar chairs to suspend it 50 mm above the ground.
Hire a concrete mixer ($60/day Kennards) and mix 60 × 20 kg bags of N20 concrete. That’s enough for a 3.0 × 3.0 × 0.10 m slab. Pour, screed flat with a straightedge, float with a wooden float once water has risen and disappeared, broom finish for grip. Cover with plastic sheeting and water-cure for 7 days before standing the shed up.
Step 3b: COMPACTED-BASE option — road base + treated-pine perimeter
Excavate 100 mm deep. Lay 4 lengths of 100×100 H4 treated pine around the perimeter, screwed at each corner with 150 mm GalvBugle screws — this is your edge restraint. Check level with the spirit level and shim under the timber as needed.
Fill the inside with road base (CBR 80 from a quarry or Bunnings bulk bags). Compact in 2 layers of 50 mm with a hired plate compactor — wet the road base lightly between layers. The finished surface should be hard enough that a boot heel barely dents it.
This base is dimensionally stable, drains well, and accepts the shed frame Dynabolts directly into the timber edge.
Step 4: Build the floor frame on the base
Most modern Absco and Stratco kits include a steel floor channel that bolts into a closed rectangle. Lay it on your slab/base. Square it up by measuring the diagonals — must be equal within 5 mm.
Mark Dynabolt positions through the floor channel holes onto the slab (or timber edge for compacted-base). Drill 10 mm holes 70 mm deep with a hammer drill. Don’t drill all 8 holes before installing — drill, install, move to next; if the channel shifts you’ll mis-align.
Step 5: Assemble the wall panels — flat first, then stand
Wall panels go together flat on the ground. Most Absco wall panels are pre-assembled — you slot the corner posts in and screw together. Stratco wall panels are flat-pack — sheet, frame channel, then sheet over.
Build all 4 walls flat before standing any of them. Two people can stand and join one wall at a time; trying to do it solo guarantees a bent panel.
Step 6: Stand walls in opposing-pair order
Rear wall first, then front wall (with door cutout), then sides. Hold each wall in place with temporary bracing — a 90×35 length of pine screwed to the wall and to the slab edge holds it vertical until adjacent walls are joined.
Tek-screw the corner joins from the inside. Snug only — don’t fully tighten until all 4 walls are connected and squared. Final squaring happens after the roof goes on.
Step 7: Fit roof beams and sheeting
Roof structure varies by kit. Absco uses pre-formed gable trusses; Stratco uses Z-purlins. Fit them per kit instructions.
Sheet the roof from one end to the other, lapping each sheet over the previous by one corrugation. Tek-screw at every second corrugation along each purlin. Run a bead of Selleys Roof and Gutter sealant along each lap before screwing — sounds excessive, but it’s the difference between a 5-year and a 20-year shed in WA’s heat-and-rain cycle.
Step 8: Fit ridge cap and barge boards
Ridge cap covers the apex. Tin-snip to length, sit it over the ridge with butyl tape underneath, screw at every corrugation. Barge boards (gable end trims) cover the cut sheet edges — same idea, butyl tape behind.
Don’t skip the butyl tape. Aussie storms drive water uphill under the cap during high-wind events — without sealing, the shed leaks at the apex every time.
Step 9: Hang the doors last
Sliding or swing doors are the last thing on. Track-mounted sliders need the track perfectly horizontal — check with the spirit level and shim if needed. Swing doors hang on heavy-duty galvanised hinges; the kit usually supplies butt hinges that are adequate but not flash. If you want better, swap to T-hinges from Bunnings ($25 a pair).
Door alignment is the make-or-break user experience. A door that drags or won’t latch is the thing you’ll curse every weekend for the next 15 years. Take 20 minutes here, get it right.
Step 10: Sealant pass and tidy-up
Walk around the inside with the silicone gun and seal every panel-to-panel join, every corner, the door track lower edge. From outside, seal the bottom edge of the wall panels to the slab/base — stops driving rain entering at the base.
Sweep the slab clean and you’re done. Total time: 1 weekend for a 3×3 m shed with two people, including the slab cure if you go with the compacted-base option.
The Cal rule
Slab matters more than the shed. A great kit on a bad base lasts 5 years; an average kit on a great base lasts 20. Compacted road base with a treated-pine perimeter is genuinely as good as a slab for a typical garden shed and saves you $400. And check the 10 m² threshold against the eaves footprint, not the floor — that’s the catch that bites every second DIY shed builder I’ve worked with.
Built something the right way and got 20 years out of it? Send us a write-up.
