Why do I need render carrier boards on timber frame?

Timber frame construction moves with moisture and temperature changes, which causes traditional sand:cement render to crack. Render carrier boards (such as Knauf Aquapanel, Cembrit, or Masterboard) provide a rigid, dimensionally stable substrate that doesn't move with the frame. The render is applied to the board rather than directly to the sheathing, preventing cracking.

What fixing pattern should I use?

Render carrier boards should be fixed to timber studs at 300mm centres maximum with appropriate corrosion-resistant screws. Use 200mm centres around board edges and perimeters. Screws must penetrate a minimum of 25mm into the timber stud. For Aquapanel, use Knauf Aquapanel screws (38mm for 12.5mm board). Leave a 3-5mm gap between boards for movement joints.

Do I need mesh over the boards?

Yes — all render carrier board systems require a layer of alkali-resistant fibreglass mesh embedded in the basecoat. The mesh reinforces the render, bridges board joints, and prevents cracking. Standard mesh is 160 g/m² with a minimum 100mm overlap at joints. Some systems use a double mesh layer at ground floor level for impact resistance.

What is the maximum board size available?

Standard Knauf Aquapanel Outdoor boards are 900mm × 2500mm (2.25 m²). Cement particle boards and fibre cement boards typically come in 1200mm × 2400mm (2.88 m²). Larger formats (1200mm × 3000mm) are available for some products but less common. Choose the largest practical size to minimise joints, as each joint is a potential weakness.

Can I use render carrier boards below DPC level?

Most render carrier boards are suitable for use below DPC (damp proof course) level, but check the specific product data sheet. Knauf Aquapanel is fully waterproof and can be used below grade. Cement particle boards are also suitable. However, fibre cement boards vary — some absorb moisture and are not recommended below DPC. Always provide drainage and a starter track at the base.

TradeCalculator

Render Carrier Board Calculator — Timber Frame Sheathing

Calculate render carrier boards, fixings, basecoat, and mesh for external render on timber frame and SIP construction.

Wall Area

Total external wall area to be boarded

Wall Height

Used to calculate number of joints

Board Type

Aquapanel is most common for timber frame

Price Per Board (optional)

Per sheet of render carrier board

How We Calculate This

This calculator estimates the number of render carrier boards, fixings, and render system materials needed for external rendering on timber frame or SIP construction. It accounts for different board sizes and fixing patterns.

The formula

Boards = (Wall area × Wastage factor) ÷ Board area

Fixings are calculated per board: perimeter screws at 200mm centres plus intermediate stud fixings at your chosen centres (default 300mm). For a standard 1.2m × 2.4m board at 300mm stud centres, this gives approximately 60-70 screws per board.

Basecoat, mesh, and primer quantities are calculated from the total wall area using manufacturer consumption rates. Joint tape is estimated from the number and length of vertical and horizontal board joints.

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.