How to choose a PIR render carrier board for an aerated concrete wall

Before bonding, check surface strength, dust, flatness and absorbency. Loose cutting dust reduces adhesion. Follow the system instructions for preparation and primer. Include patched areas, infill and reinforced concrete in the substrate assessment.

In an external thermal insulation composite system (ETICS), the board must work with both the adhesive and the reinforced base coat. Suitable facings include glass fleece approved for the particular system. Their thermal conductivity may differ from that of a board faced with aluminium on both sides. A common core material does not make boards interchangeable.

Check which side faces the substrate and which components the system permits. Changing adhesive, mesh or render affects the assessment of the assembly. Check the fire requirements for the building as well. Neither facing colour nor the board’s appearance in a shop identifies a system reliably.

Suppose the wall, finishes and surface resistances together give R = 1.80 m²K/W. An 80 mm render carrier board with conductivity 0.026 W/(mK) adds about 3.08 m²K/W. The simplified U-value for the uninterrupted wall area is about 0.205 W/(m²K). At 100 mm the same board gives about 0.177 W/(m²K).

If the design target is 0.20 W/(m²K), the first option needs revision. This calculation uses the assumed masonry and conductivity, without fixing corrections. It is not a thickness table for every aerated concrete wall. Recalculate and reassess the junctions if the block, board or assembly changes.

Use fixings intended for aerated concrete. Check the fixing type, installation method, embedment and load capacity in the actual substrate class. The fixing pattern depends on the design, wind load and façade zone. Corners and edges may need a different arrangement from the middle of the wall.

For refurbishment or an uncertain substrate, allow for on-site fixing tests. Smooth-looking old render is not necessarily load-bearing. The fixing length must accommodate all intermediate layers and the required anchorage. Do not determine it by adding an arbitrary allowance to the PIR thickness.

Design the roof, balcony, sill and plinth junctions before insulating. Water should drain clear of the finished façade face. Check falls on horizontal surfaces and the ends of flashings. Design the geometry to keep water out rather than relying solely on a final bead of sealant.

Follow the system layout and reinforcement details around openings. Cracks at window corners can let water in. Prepare fixing points for lights, canopies and downpipes in advance. Detail each attachment so tightening a screw does not crush the insulation.

Specify the system type, thickness, facing, edge profile and area of each façade zone in the enquiry. Check boards per pack and how much material the order actually buys. Estimate cutting waste on a façade drawing. Small reveals often take more labour than their area suggests.

Include system adhesives and compounds, mesh, profiles, fixings, substrate preparation and scaffolding. Specify documentation and how substitutes will be accepted. On delivery, inspect labels and edges. A different facing needs confirmation of compatibility even if colour and thickness look similar.

If the quote includes several thicknesses, check that profiles and fixings suit each. Switching from 80 to 100 mm may mean different accessories. Update the complete order list when the board changes.