Improving loft insulation, and heat loss in general

Discussion in 'Eco Talk' started by MFD, Jan 30, 2020.

  1. MFD

    MFD New Member

    Hello all,

    We recently moved into a 1950s bungalow with a dormer conversion bedroom and all-electric heating (no gas to village). The power bill back in the summer was fine, but has nearly tripled over the past few months, so we've had to start turning some of the heaters off and just dealing with the cold.

    There are quite a few drafts and questionable exterior walls I can work on that will probably improve things, but I'd like to upgrade the loft insulation if that makes sense too.

    The loft floor is insulated with wool of varying thicknesses which I think was put down at different times, while the dormer walls (to the loft) are insulated with wool between the studs retained with strips of wood along the back (3 inches thick if memory serves), and there is insulation board between the dormer ceiling and flat roof that is perhaps 1.5 inches thick (can't get to it).

    I can find plenty of literature on loft floor insulation and the effectiveness of various thicknesses, but not so much on the thickness of WALL insulation - how thick should the wool around the room's walls be, and is there a possibility of introducing damp/rot problems in the structure if I add more over it?

    We are also intending to convert the remaining loft space into an additional room sometime in the next few years. Will Building Control want the entire roof space brought up to current standards (including the inaccessible dormer ceiling), or only the areas being touched by the conversion work?

  2. Hans_25

    Hans_25 Well-Known Member

    The dormer walls are providing much the same barrier to heat as the floor so I'd think the requirements are much the same. Knauf Earthwool is nice to use and regs state 270mm of the "rockwool" type insulation I believe. PIR type insulation is about twice as good (need to look at the figures), a recent build quote I had contained in it 100mm PIR. Exactly what is required might be influenced by your situation. PIR is easier to fit into walls.

    I would think, again not 100% sure, BC would want to see the whole roof properly insulated if adding a room up there.
  3. Jimbo

    Jimbo Well-Known Member

    You might consider overboarding with a foam backed plasterboard if you can afford 50mm.

    Increasing the loft insulation will help. The first 100mm is perhaps the most important.

    Re heating itself - look at getting a heat pump system. This will cost a fair bit but you will get 2/3rds or more of the cost back through the MCS scheme over seven years. Plus your electricity bill will be reduced by 2/3rds.
  4. rogerk101

    rogerk101 Well-Known Member

    ... assuming you were heating with traditional electrical radiators!
  5. MFD

    MFD New Member

    We haven't really looked at anything like that - no money for it right now. Is getting such a system installed practical when the front/side of the building is all concrete driveway and there's no access for plant machinery (diggers etc) to the back?

    Yup. Quite a few of them!
  6. Jimbo

    Jimbo Well-Known Member

    Air source heat pump I mean. Basically you have a box like an air conditioner has outside, and a hot water storage tank inside instead of a boiler. The heat pump heats the water, which is then transferred directly or indirectly to ordinary radiators.

    really you need the property to be 30 to 40W/m2 so as to avoid having disproportionate radiators.

    there might be funding available depending on your personal situation. With the MCS grant, the payback from electric heating will be pretty quick. There are some issues around planning but the latest systems are so quiet that they are exempt. Any MCS installer will be able to advise anyway.
  7. Jimbo

    Jimbo Well-Known Member

    greenback78 likes this.
  8. MFD

    MFD New Member

    Well, this is getting more urgent... despite using the heating a bit less, the bill came in at even more than estimated a fortnight ago!

    I've been trying to get a thermal survey done to see where we're losing heat the worst, but naturally noone I've contacted has come back to me, so I've resorted to the highly scientific method of seeing which walls are coldest to the touch. Obviously the timber framed sections of the exterior walls are the worst, but some of the internal stud walls (mainly those attached to an external wall) are also cold to the touch. I'm going to poke around in the loft and see if I can find any openings into them left from the building's sordid history.

    The external walls in a few rooms are good candidates for lining with celotex boards or similar as we can spare a few inches of the room length, but will this have a significant impact? It seems like the heat will continue conducting through the plasterboard walls running through it and into the original wall on either side to me.
  9. Jimbo

    Jimbo Well-Known Member

    You can estimate the U value using the formula

    U = (inside air temperature - inside wall surface temperature) * 10 / (inside air temperature - outside wall surface temperature)

    Measure the walls with a non-contact infrared thermometer (eBay, about £15).

    This is very approximate but will give an idea.
  10. MFD

    MFD New Member

    That's good to know, will definitely get a thermometer and give it a go.

    I went draught hunting yesterday and found a bit of cold air leaking in around the edges of one of our kitchen walls, seeping in between the inner cavity wall and a doorframe I suspect. The wall in question is an insulated cavity wall, with some plasterboard fixed directly to it, and then a layer of hardboard panels held on by a mixture of panel pins and the wallpaper covering. Also toilet paper has been used to plug up the gaps to the loft etc, 'cause I guess he ran out of silicone after using it to fix all the electrical cables in place...

    A nearby section of (good) plaster is approx 25mm proud of the brickwork, it looks like a skim of plaster over a thick base of some kind of mortar or other cement mixture to me, but I'm not a builder, so happy to learn if its something else/common.

    To improve the thermal properties a bit further, should I put a thin (i.e. 12-20mm) layer of insulation board directly on the inside cavity wall, then a thin layer of plaster up to the adjacent wall, or is that going to risk causing problems, should I just build up a ~25mm thick plasterboard layer from the brickwork, or a thinner plasterboard one on some battens on the bricks?


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