🏗️ Cavity Wall Materials Calculator
🧱 Cavity Wall Construction Materials Explained
- Bricks or Blocks: Outer skin typically uses facing bricks; inner skin uses concrete blocks for strength and speed.
- Mortar: Mix of cement, sand, and optionally lime or plasticiser for workability. Standard ratio: 4:1 or 5:1 sand to cement.
- Wall Ties: 2.5–3 per m². Common types include stainless steel butterfly or fishtail ties for cavity bonding.
- Cavity Insulation: Options include PIR rigid board, mineral wool batts (partial fill), or injected foam (full fill).
- Damp Proof Course (DPC): Horizontal waterproof roll installed above footing level to prevent rising damp.
- Fixings: Use insulation retaining clips or tie clips to secure insulation in cavity walls.
- Optional Features:
- Cavity trays over windows/doors to redirect moisture
- Weep vents for moisture escape and ventilation
- Movement joints every ~6 metres for thermal movement
Cavity Wall Materials Calculator
Planning a cavity wall? This calculator helps estimate the number of bricks or blocks for both inner and outer leaves, mortar volume, insulation materials, and essential extras like wall ties and DPC. Perfect for UK and USA construction standards.
Technical Guidance
- Standard cavity: 50–100mm (UK), 2"–4" (USA)
- Two walls (leaves): calculate both skins separately and double your materials
- Wall ties required every 900mm horizontally and 450mm vertically
- Use a 1:4 cement:sand mortar mix, allow 10% for wastage
Cavity Wall Material Estimates
| Wall Area | Unit Type | Total Units | Mortar Volume | Insulation Volume | Cement Bags |
|---|---|---|---|---|---|
| 20 m² | UK Brick (both skins) | ~1000 | ~0.40 m³ | ~1.6 m³ | ~16 |
| 150 ft² | US CMU Block (2 walls) | ~280 | ~11 ft³ | ~60 ft³ | ~12 |
What You’ll Need for a Cavity Wall
- Bricks or blocks: Outer and inner skins
- Mortar: Cement, sand, and optional plasticiser or lime
- Wall ties: 2.5–3 per m² (e.g. stainless steel butterfly or fishtail types)
- Cavity insulation: Rigid board (e.g. PIR), mineral wool batts, or foam fill
- Damp proof course (DPC): Horizontal roll to sit above footing level
- Fixings: Insulation retaining clips or tie clips for partial-fill systems
- Optional: Cavity trays, weep vents, movement joints
Pro Tips
- Buy full packs of bricks or blocks to avoid batch colour differences
- Keep wall ties level and staggered — never reuse bent ones
- For insulation, leave no air gaps — thermal bridging reduces wall efficiency
Common Mistakes
- Only calculating for one skin of the wall — always double!
- Forgetting to order wall ties and DPC
- Installing insulation with unsealed joints or no retaining clips
FAQs
- How many wall ties per m²? → 2.5–3 ties per square metre, plus extras around openings
- What insulation fits a 75mm cavity? → Use 70mm PIR or 65mm semi-rigid mineral wool
- Do I need DPC on both leaves? → Yes — DPC should continue across the cavity with laps
