Our new passive house has a flat roof. How do you drain off the rainwater? You build a pitched deck and a parapet around the perimeter.
Read Brothers of Norwich designed a set of firrings - tapered pieces of timber that create the required 1 in 60 falls across the roof, draining into gulleys and 2 outlets in the parapet.
We had some expert help from Ed Masters and his mate Paul to install the firrings on top of the Beattie battens:
The deck is made of 18 mm OSB boards, screwed down on to the firrings - we did this part ourselves:
The parapet provides an upstand for the felt roof covering, concealed on the outside by our cladding and capped with an aluminium trim.
We chose a multi-layer, torched-on felt system for our roof covering. With the arrival of some fine weather in the first week of July, it was expertly installed by Mal Pritchard of Beta Roofing.
He constructed 2 lead-lined outlets on the house and this one on the garage roof.
The base layer of felt was nailed to the deck.
The next layer was torched on, with strips running down the gulleys towards the outlets. After enduring weeks of heavy rain, the weather promptly turned too hot for Mal to apply the bituminous felt without sinking into it. This layer is also laid on the upstand and laps over the top of the parapet.
Our top layer will be a black capsheet, which is fire-resistant (timber-frame and proximity to neighbours).
It's a great feeling to finally have a water-tight roof :)