Planning swissporPIR Alu installation on a large pitched roof

Show the rafters, PIR, underlay, counter-battens, battens and covering on one drawing. At the window frame, mark where each layer terminates. Check the window instructions for the permitted flashing position relative to the new roof surface.

The PIR layer provides continuous insulation across the rafters. The manufacturer declares a thermal conductivity of 0.022 W/(m·K) for swissporPIR Alu. At the wall head, trace the wall insulation all the way to its junction with the roof board.

At the eaves, mark the edge of the covering and the termination of the underlay separately. Check both against the eaves flashing and gutter. A trial fit shows whether the fascia and gutter brackets suit the revised height.

Check timber condition and alignment before laying boards. Measure the actual rafter spacing and mark their centrelines where they will remain visible after covering. This matters especially in an existing roof where spacing can change on either side of a window.

The screw transfers forces from the counter-batten through the insulation into the rafter. Take length, angle and spacing from the roof design and the fastener documentation. Recheck embedment in the timber if the PIR thickness changes.

Above the window, trace the water path along the underlay. Form laps, drainage above the frame and seals around penetrations in accordance with the window and membrane instructions. Photograph the upper corner before fitting the flashing.

On the loft side, locate the airtight layer in section and identify where it joins the frame. Leave the lower corners accessible for inspection. The gas-tight board facing alone cannot seal the perimeter of the opening.

At the chimney, obtain clearances and material requirements from the documentation for the installed flue system. The swissporPIR Alu board has reaction-to-fire class E. Establish the insulation termination and chimney flashing detail before cutting the first board.

When assessing summer temperatures, include window orientation and area, shading and air exchange. Two rooms beneath identically insulated slopes can reach different temperatures if one has a large unshaded west-facing window.

Measure eaves, ridges and valleys by length, and count windows and chimneys individually. Raising the roof affects each detail differently. Record the flashing type at windows and the width and support for valley flashings.

Mark which flashings can be made from a repeatable template and which require measurement after the counter-battens are in place. This lets you order bent pieces to the installed dimensions and include fabrication time in the roofing schedule.

If the crew can lay insulation around three windows in a shift but weatherproof only two, finish the section at the second. Agree the position of the protected edge with the incoming crew. When work resumes, inspect that edge and the previous day’s windows first.