Recticel Powerroof for roof refurbishment. Working from above

Open up a representative section at the eaves. Record rafter size and spacing, timber condition and the termination of the room-side layer. Check whether it can be connected to the wall without stripping the entire ceiling.

Mark the rafter centrelines on the working plan. Once the boards cover the timber, these lines locate the counterbatten fixings.

Screws transfer forces from the counterbattens into the timber. Their length, spacing and installation angle depend on insulation thickness, roof geometry, substrate and loads. Adding the board thickness to an old screw length does not establish the fixing design.

Powerroof declares CS(10/Y)150 in compression and a D-s2,d0 reaction-to-fire class. These figures describe the board. Fixing capacity and any required fire resistance of the roof assembly need their own evidence.

The manufacturer gives λ as 0.022 W/(m·K). Declared resistance is 4.50 m²·K/W at 100 mm and 6.35 m²·K/W at 140 mm. When comparing these versions, show the additional 40 mm perpendicular to the slope on the section.

Before ordering flashings, check the position of the gutter relative to the new covering edge. At rooflights, also measure the installation height and select flashing to suit the revised geometry.

Gross board dimensions are 2400 × 1200 mm. Use cover dimensions of 2380 × 1180 mm, approximately 2.81 m² per full board, in the layout. The difference accumulates along a row as the edges engage.

Draw valley cuts and rooflight strips separately. Count a triangular offcut towards the next bay only after checking its tongue-and-groove orientation and the support it will need.

Trace the drainage path on the roof underlay from the top corner of the rooflight to the eaves. Mark laps and the drainage provision above the window before battens conceal them.

At the chimney, obtain combustible-material clearances from the flue documentation. Detail this zone separately from rain flashing and coordinate both with the finished covering height.

Before opening the next strip, check that the preceding area is protected against rain throughout and has a secure eaves termination. Photograph rafter and opening details before concealment.

Price continuous insulation areas separately from work at windows, chimney, gutters and valley. State opening quantities and flashing lengths. Timber repairs identified only after stripping can then be recorded as a separate item.