My house was built in 2002 with a raised ground floor, air bricks every two meters and dot and dab dry lining throughout. The loft was "ready convert ed" with two rooms upstairs and a full second staircase. Sold as a 6 bed p lace but really 4 bed plus 2 loft rooms. Since moving in 3 years ago and h aving had time to poke around and get to know the place, it is now clear it was built in a hurry and to a tight budget, despite the fairly good reputa tion of the (local) house builder (company since dissolved).
My main gripe with the place is that our energy usage seems high for a new build. The crappy original gas boiler kicked the bucket last year and I re placed it with a decent one. With two of the bedrooms and one loft room le ft completely unheated a year round, and only the small office room in the loft heated occasionally, *and* being tight with the thermostat (two jumper s for everyone!) we went through 30,000 kWh of gas last year. The place ge ts cold *really* fast once the heating goes off. I think I may have found the reason...
Recently I was routing some network cables from one of the loft rooms down the behind the drywall all the way to the living room downstairs. When I c ut a hole in the plasterboard to fit a faceplate for the network point I wa s struck by a howling cold draught from the hole, which appeared to just ai r blowing from under the raised floor (at outdoor temperature) and up behin d the drywall. I lifted a floorboard in the living room near the wall unde r the network socket, pushed the mineral wool insulation to one side, and I could easily get my fingers between the plasterboard and blockwork. Its l ike the floorboards were installed a good inch away from the blocks, which seems wrong to me. Having lifted some boards immediately above this area o n the 1st floor, the draft is blowing all the way up the wall and chilling the air in the ceiling void too. I think they call this a "plasterboard te nt".
So my questions are:
1) What remedial action is recommended for preventing thermal bypass behind poorly installed D&D drywalls without ripping it all off and plastering th e blockwork ? I thought maybe drilling holes and injecting expanding foam all the way around the top of the skirting / around windows. Any better id eas ?
2) Do we risk any moisture/mould problems having taken such remedial action ? I'd have thought it would make things better if anything, as the plaste rboard wouldn't be so cold and less prone to condensation, but any thoughts on this ?
3) The survey says there's sheet insulation in the cavity and there's certa inly some visible in the roof (eaves of the loft rooms allow access). Any ideas how to establish the quality of the cavity wall insulation, in case t his is causing loss of heat ?
4) It's a big house. perhaps 30,000 kWh a year is normal even when being t ight with the heating ?