Utherm Wall LE in cavity walls: checking insulation around a window

Use the face of the structural leaf as the datum. Measure to the intended inside face of the outer leaf and deduct the insulation thickness. Compare the result with the clear space specified in the design. Repeat at both jambs, where masonry tolerances may differ.

Utherm Wall LE is a PIR board with a multilayer laminate on both faces. Unilin lists a declared thermal conductivity of 0.022 W/(m·K). The declared resistance is 3.60 m²K/W at 80 mm and 4.50 m²K/W at 100 mm. Use the data sheet entry for the thickness to be ordered.

On the lintel drawing, trace the outer face of the insulation up to the window frame. If the line breaks or the insulation thins at a masonry support, flag the junction for thermal bridge analysis. Give the designer the total length of these junctions across the elevation.

Prepare the substrate by removing projecting mortar as specified. Check the fit around the tie and the contact between neighbouring board edges. If a board stands proud of the masonry, measuring only at its midpoint may miss a narrowed cavity at the corner.

Take tie spacing from the masonry design, including any additional ties specified beside the opening. The board has a declared compressive stress of at least 150 kPa at 10% deformation. Determine the tie capacity and anchorage for the particular masonry substrate.

Follow the water path from the back of the outer leaf to the discharge above the window. Check the specified cavity tray and that the outlets are open. Mortar droppings here can block an outlet that will be difficult to clear once the masonry is complete.

Protect the open top of the wall against rain during breaks in masonry work. Inspect the masonry and insulation before closing the bay. If the wall has been wetted, consider the available drying path and the vapour resistance of the facing when assessing whether work can proceed.

Wall LE has reaction to fire class E. Where the design calls for a cavity barrier at a floor edge, refer to the detail and documentation for the specified barrier. Check its position relative to the insulation and outer leaf while both sides of the junction are visible.

For rooms with sound insulation requirements, assess both masonry leaves, the floor junction and the window specification. A gap between the frame and reveal can affect the performance of the whole façade. Include this seal in the window inspection.

In the take-off, list the area of uninterrupted wall, the length of reveals and the number of lintels. Check the effective coverage of the tongue-and-groove board before converting these figures to packs. Allow separately for cuts and components above windows.

Specify laminate-faced Wall LE for the cavity. If a separate item calls for insulation bonded to plasterboard, identify its installation location and both component thicknesses. Separate order lines help the masonry and finishing crews receive the right materials.

At the first window, photograph the lintel junction, a wall tie with the board retainer and the drain outlet. Record the grid reference and measured cavity width with the photographs. On the next storey, check that the detail still fits the window dimensions and masonry support position.