Choosing render-compatible PIR insulation for aerated concrete walls

Aerated concrete comes in different variants with different properties and applications. To determine wall resistance, identify the exact product, thickness and masonry method. Do not transfer a lightweight block’s properties to another variant.

Check delivery records in a new house; an older building may need an opening-up inspection. Assess dampness and surface condition. Insulation must not conceal damaged plaster or active leakage. Thermal selection and substrate assessment are separate tasks, both needed before ordering.

Glass-fleece-faced PIR intended for a particular insulation system is one option beneath render. A grey facing alone does not prove suitability. Check the board type and installation side; printing is not always meant to face the same direction. Follow that product’s instructions.

Lambda can vary with thickness. An illustrative comparison may use 0.026 W/(m·K) for 100 mm and 0.025 for 120 mm, but orders need the chosen variant’s data. Gas-tight aluminium facings have a different surface; do not substitute them into a glass-fleece system. The same discipline applies to adhesive, mesh and render.

Assume an example masonry-and-plaster resistance of 1.30 m²·K/W. This is a calculation assumption, not a property of all aerated concrete. Add surface resistances of 0.17. With 100 mm insulation at lambda = 0.026, the insulation resistance is about 3.85.

The resulting U-value is about 0.188 W/(m²·K), before corrections. Different actual masonry properties change the answer. Here we sum layer and surface resistances; the target of 0.20 W/(m²·K) is for comparison only. Establish the project’s actual requirement in the design, not from the masonry material’s name.

Adhesion depends on the masonry surface, not just the adhesive name. The substrate should be level, load-bearing, dry and dust-free. Choose priming according to the system documents, avoiding an arbitrary product that changes adhesion between layers.

ETICS instructions describe wall preparation and work sequence. Adhesive cannot correct major geometric errors. Select fixings intended for that substrate, with documented embedment length, drilling method and capacity. A generic “façade anchor” label is insufficient.

Water must not run behind the insulation. Plan window-sill flashings, roof termination and the base connection before installation. Check material suitability in moisture-exposed zones; a board used in the main façade area may not suit the ground-level zone.

Provide correct reinforcement at window corners and place joints and fixings according to the system. Do not defer these choices until adhesive is mixed. Keep execution drawings on site and discuss them with installers, including sill, reveal and top-edge details.

Specify the full board name, thickness, format, edge type and finishing system. Compare packaging labels with the order at delivery. Assess damaged surfaces and edges before installation. Similar packaging colour is not enough to identify the correct product.

Keep labels and photographs of the first rows to document orientation, fixing positions and materials. Acceptance should not focus only on the finished render, when most important layers are hidden. Schedule inspections throughout the work.

Compare the same thermal result and scope in both quotations. Include adhesive, fixings, mesh, trims, render and flashings alongside boards, plus scaffolding and wall preparation. Only then does the price difference mean something useful.

Ordering requires the project’s actual requirement and assessment of the whole system. Confirm board type, facing, fixing and finish rather than relying on a claim that one thickness suits every aerated concrete house. If the material changes, revisit the calculations and other layers.

No. It must be intended for the specific façade system.

It may be enough in a particular assembly. The masonry and insulation properties and the design requirement are needed to decide.