Hallo all,
I would be grateful for some advice on upgrading the insulation in my house. I will be doing it myself and as such won't need to involve BC. The goal is to make a significant reduction in my fuel bills/increase in comfort whilst not taking too much space out of the upstairs rooms. I need to avoid spending more than I have to, as well.
It's a chalet bungalow & for various reasons probably easier to insulate the roof rather than the ceilings. The rafters are 100 x 50mm and the underfelt is non-breathable, which means I can only put max. 50mm of PIR board between the rafters. I really don't want to lose more space than I have to from the underside of the sloping bit of the ceilings as the rooms are small enough as it is. I'm thinking to put another 50mm of PIR board under the rafters, which appears to give a U value of around 0.25. It looks like this would be roughly twice as good as what is currently there, 100mm of fibreglass blanket between the underside of the roofing felt and the top of the plasterboard below (I'm not sure how the lack of an air gap will have affected the levels of condensation but from what I can see it all looks ok).
It looks like an alternative to the PIR board might be to use a multifoil under the rafters (which looks like it would take up a similar amount of space to the PIR board for a similar U value) and leave the fibreglass in place. Looking around the internet there seem to be a variety of different opinions on multifoil ranging from snake oil to wonder material and I wonder which material I am better off using? I'm leaning towards PIR board, which seems to be more of a guaranteed result.
I will also need some guidance on the finer details of installing whatever I end up with (for example how to apply the insulation around the purlins, what tape to use, etc) and would be grateful for a pointer towards where I could find this info.
Thanks very much in advance,
Chris