a pressure and infrared assessment revealed significant convection loops and heat loss due to air movement in our dormer house.
We have decided to implement an isover vario air tightness solution. Which means constructing a warm roof. The insulation under the rafters is 150mm rockwool flexi which was in place but there were gaps. It is important to keep a 50 mm gap between the rockwool flexi and the roofing felt as its non breathable. The key to air tightness is attention to detail which means that it a slow job. So far I would calculate that 2 sqm is taking me 1 hour to complete.
A big issue I have is restricting air flow from the soffit to the floor joists as its open. I am using a swiss roll insulation approach to prevent this air flow and allow the air to pass up the roof behind the rocckwool flexi.
I would recommend a powered respirator as shown in the picture above. I purchased a trend air ace which weighs nearly 1 kg and has an 8 hour lithium ion battery. It means I have filtered air passing over my face and the filters take out all the insulation dust that is floating in the area. The hard hat aspect helps when you are crawling around a dormer crawlspace. If the respirator was half the weight it would be perfect but I am happy enough with it. I am also using a 60 Watt LED light wand which lasts 4 hours on a charge and a staple gun with 10mm staples.
An airtightness system has a variety of tapes and I use double sided protape, KB1 and multitape SL1. These take getting used to and I would recommend attaching the protape to the membrane before you bring it into the attic area as it sticks to everything !!
This job will take several weeks as warm weather usually restricts me to 1 – 2 hours in the morning before things get to warm. As I stated earlier it is slow and steady work and I will get there eventually. There is no pointing doing a half assed job as it is a waste of time and money.