Slab Thickness by Use Case
| Application | Min Thickness | Recommended | Reinforcement |
|---|---|---|---|
| Sidewalk / Walkway | 3.5" | 4" | Optional fiber |
| Patio | 4" | 4" | Mesh recommended |
| Residential Driveway | 4" | 5" | Mesh or rebar grid |
| Garage Floor | 4" | 5–6" | Rebar grid required |
| RV/Truck Pad | 6" | 6–8" | Heavy rebar grid |
| Shed Foundation (small) | 4" | 4" | Mesh |
| Pool Deck | 4" | 4–5" | Mesh + control joints |
| Hot Tub Pad | 4" | 6" | Rebar grid |
For freeze-thaw climates (Northeast, Midwest, Mountain West), add 1 inch to the recommended thickness. Always check your local building code — some jurisdictions require 6" minimum for driveways regardless of use.
Slab Pour Checklist
- Excavate to depth. Slab thickness + base depth + 2" for forms = total dig depth. For a 4" slab on 4" base, dig 10" below final grade.
- Compact subgrade. Native soil should be compacted to 95% before adding base. Don't skip this on clay or recently disturbed soil.
- Lay 4" of crushed stone or roadbase. Compact in 2" lifts. 95% compaction is the target.
- Set forms. 2x4 lumber for 3.5" slabs, 2x6 for 5" slabs. Stake every 4 feet. Check for level and proper slope (¼" per foot away from buildings).
- Place vapor barrier and reinforcement. 6 mil poly under interior slabs. Wire mesh or rebar grid raised 1.5–2" off the base on chairs.
- Pour and screed. Pour from far end working back. Screed level with the forms using a 2x4. Don't over-work the surface.
- Float, edge, and joint. Bull float once water sheen disappears. Edge the perimeter with an edging tool. Cut control joints every 8–10 feet.
- Final finish and cure. Broom finish for traction or trowel for smooth. Cover with plastic for 7 days minimum, lightly mist daily.
- Wait before loading. Foot traffic 24–48 hours. Vehicles 7 days. Heavy equipment 28 days.
Standard Stair Dimensions — Code Requirements
| Dimension | IRC Code (Residential) | Ideal Comfort Range | Notes |
|---|---|---|---|
| Rise (riser height) | 4" min, 7¾" max | 6" – 7½" | Must be consistent ±⅜" across all risers |
| Run (tread depth) | 10" min | 11" – 12" | Measured nose to nose |
| Width (clear) | 36" min | 48" – 60" for exterior | More comfortable for moving furniture |
| Landing depth | 36" min | 36" – 48" | At top and bottom of any stair run |
| Headroom | 80" min | 84"+ | Measured vertically from tread nosing |
| Nosing projection | ¾" – 1¼" | 1" | Broom finish nosing for traction |
Concrete Needed by Number of Steps
| Steps | Total Rise | Cu Ft | Cubic Yards | 80lb Bags | Material Cost |
|---|---|---|---|---|---|
| 2 steps | 14" | 4.8 | 0.18 | 9 bags | $45–$70 |
| 3 steps | 21" | 10.1 | 0.37 | 17 bags | $85–$135 |
| 4 steps | 28" | 18.2 | 0.67 | 31 bags | $155–$245 |
| 5 steps | 35" | 28.2 | 1.05 | 48 bags | $240–$380 |
| 6 steps | 42" | 40.3 | 1.49 | 68 bags | $340–$540 |
| 8 steps | 56" | 71.5 | 2.65 | ready-mix | $600–$950 |
Values use 7" rise, 11" run, 4ft width, 36in landing. Includes 10% waste. Material cost based on $5.00/bag or $130-$200/yard ready-mix.
Concrete Stair Forms — How to Build Them Right
Use 3/4-inch plywood for the side forms that show the stair profile. Mark out your rise and run dimensions carefully — a framing square works well for this. The stringer must be perfectly plumb and braced securely because wet concrete exerts enormous pressure on the forms.
Use 2×8 or 2×10 lumber for the riser boards — the vertical face of each step. Bevel the bottom edge back 1 inch so you can finish the tread fully to the riser face. Stake and brace each riser so it won't bow or move during the pour.
This is where most DIY stair pours fail. Concrete weighs 150 lbs per cubic foot. Four steps with a 4-foot landing is 8+ cubic feet — over 1,200 lbs pushing against your forms. Brace every 12 inches with stakes driven deep. Test your forms by pushing hard on them before you mix a single bag.
Pour from the bottom step up. Consolidate concrete by rodding or using a vibrator to eliminate voids. Fill each riser section completely before moving up. Work quickly — stairs have a lot of surface area and cure faster than a flat slab.