Our timber frame completed a few days ago, and since then, we’ve been planning and getting materials ready for installing the first few layers of the roof. This will make it ready for the metal roofing company to arrive and install the final finish.
There are essentially four things that need to be done at this stage.
First is to install a breather membrane, which can be seen in blue in the photo above. This is similar to the familiar roofing felt which is installed under tile or slate roofs. While in that case it provides waterproofing, the breather membrane here simply provides a means of covering the roof and allowing any condensation to bead off.
The membrane comes in long rolls that we pre-cut so that each length was half of the overall length of the roof. This allowed us to install it more easily on site, which we did by stapling it to each roof truss using a heavy duty staple gun.
It’s important to layer each row of membrane on top of the row under it so that any water drips onto the next row on its way down rather than dripping underneath and into the loft space.
Next are the battens. These are long lengths of wood, 50mm × 50mm square and 4.7m long, that are attached parallel to the roof trusses running from top to bottom. This is as opposed to battens used for tiles or slates that run perpendicular to the roof trusses, from one end of the house to the other.
These battens do two jobs – they completely pin down the breather membrane and they provide a gap of 50mm between the membrane and the next layer. This gap allows air to pass and ensure any water or condensation is cleared away.
We installed these with 90mm corrosion-resistant wood screws. We chose screws that are self-drilling so that we didn’t need to pre-drill any pilot holes, and ones with Torx (star-shaped) heads to help them slip less when using a drill. 90mm ensures they go through the 50mm batten and 40mm into the roof truss for a secure attachment.
Thirdly, we have the plywood. These come in large 2.4m × 1.2m sheets that are 18mm thick and weigh about 36kg each! The plywood provides a flat deck on which the final metal roof will be installed. Since we’re using the plywood for roofing, we went with WPD structural plywood. This is a waterproof plywood that is designed for structural loading.
The detail from the roofing company specified that the first 150mm at the bottom of the roof should be 12mm plywood instead of 18mm, so we cut these strips and installed them first. Then we cut the main ply sheets so that they always start and end on a batten (this is important to make sure they’re fully supported). It’s also important to make sure each row is staggered so all the joins don’t line up – this ensures maximum structural integrity.
We installed these with a first fix nail gun. This is an invaluable tool that we hired from Jewson along with a set of 90mm nails. This made the installation much faster.
Fasicas and barge boards
Finally, we need to install the fascias and barge boards. These are narrow strips of 18mm plywood that run across the front and back of the roof as well as up and down the gable ends at each side. Guttering is attached to these boards. These will also be nailed using the nail gun.
Once all of these jobs are complete, the metal roofing company will install the aluminium standing seam roof and one job will be complete!