Our house has been designed with the “cold roof” – that is, the loft space is intended to not be heated and be used as a storage space rather than a heated area that could be a room.
Since it’s a “cold roof”, the part we need to insulate is its floor (or the first floor ceiling) so we can keep the heat inside the main house and out of the loft. In many existing houses, this would be done using rolls of mineral wool or maybe blown insulation.
However, since we have a new build in quite an exposed area, we need to go one step further to ensure we have an energy efficient house that also has a usable loft space – that means installting rigid insulation panels (also known as PIR). These panels are roughly twice as efficient as mineral wool, and so you only need half the thickness for the same effect.
In our case, our ceiling joists are 100mm thick, so we started off with 100mm thick insulation panels, cut to fit between the joists. The carpenter had already installed ceiling battens to fit the plasterboard on to, which keep the insulation in place, but also make it a lot harder to get it in place to start with (especially when combined with timbers running across the top of the joists which act to “sandwich” the insulation in between)!
At this point, we’ve stopped to allow the plumbers to install our MVHR system (which will be running partially in the loft). After this, we will overlay 100mm of mineral wool on top. This will allow the insulation to run over and around the MVHR ducts as well as in all the intricate gaps between and around the roof trusses. Once this is then boarded over to provide a stable platform, we’ll have our finished loft space.