This week we started on the framing for the roof. The stucture is pretty straight forward with LVL (Laminated veneer lumber) beams spanning the ICF walls. When the roof was being engineered we did as much as we could to reduce the amount of steel, to reduce thermal bridges. The results was that some of the beams needed to be doubled up. Their crossection is 300x58 and typically 9m long, so lifting the into position was fun!
Towards the end of the first week. The roof over the master bedroom was complete and all but one of the double rafters was in place.
While the carpenters continued with the roof frame, the first membrane Mento plus was installed over the rafters. Initially, the roll, which is 1.5m wide, was rolled onto the roof and secured one width at a time but working at heights added complexity and it was decided to roll out the membrane on the slab, cut to length and tape togethe before moving to the roof. This proved much easier and ended up with a better result. Below shows the first two lengths that were taped together on top of the roof. The membrane is stapled to the fascia temporarily but will be fed over the flashing into the gutter when installed.
The skillion roof and the pic below shows the "high" side of the roof. As we will not be insulating under the eaves, the membrane is used as barrier for the insulation which will be installed between the rafters. 35x45mm betters were nailed between the rafters above the wall aligned to the outside edge of the ICF insulation, so the bulk insulation would be able to overlap the top of the wall.
The membrane was then cut around and taped to the rafters. The end result is a wind tight area where the bulk insulation can be installed with good overlap with the wall insulation.
Finally, a 35x45mm batten was then nailed over the membrane parallel to and on top of each rafter. While the membrane, acts as vapour permeable, but water tight layer and can be used as a sarking, the design of the roof has a further foil based sarking installed over the top of the first battens, to provide a reflective barrier. On top of the foil sarking, the roof battens will be fixed and then the roofing. As there is an air gap between the membrane and the foil of 35mm and then a further 40mm to the roofing iron, we are confident that the foil will operate as designed and the membrane will also be able to "breathe". Photos of the completed roof in later posts.
