I have started installing the insulation in the extension. There is 130mm of insulation being installed in the roof (100mm between the rafters and 30mm on the back of the plasterboard). There is 75mm of insulation going underneath the floor. The underfloor heating is clipped to this and then 75mm of screed goes on top. This insulation is in addition to the 100mm of insulation that has gone into the wall cavities. Current building regulations require 50mm, so we are well above the current specification.
The insulation comes in large sheets (1.2m 2.4m) of foil backed high density polystrene. Kingspan is the most well known make, but there are others that are just as good and half the price. The sheets are cut to length with a hand saw. It isn’t a difficult job, but it is messy and the bits of polystrene get everywhere.
The complication with the extension is that the rooms have high ceilings and you have to use tower scaffold to reach the ceiling. You can’t do this off a set of ladders.
By my reckoning, it will take about 41 sheets to do the floors and 48 for the ceilings. We have order 30 sheets of each (75mm for the floor and 100mm for the ceiling). Once these are installed, we will order a top up. It only takes a couple of days to arrive. The sheets are around £30 each, so this part order is £1,800. Insulation isn’t cheap.
We are putting 100mm insulated boards between the rafters in the new extension. This is then covered with insulated plasterboard. This will leave the oak trusses exposed. Because the ceiling is so high, this has to be completed using tower scaffold inside the building as ladders will not reach.
It starts to get dark at this time of the year by about 4pm. We are using lights indoors from about 3:30pm and here you can see the inside of the kitchen ceiling.