Improving loft insulation, and heat loss in general

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

  1. MFD

    MFD 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 Screwfix Select

    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 Screwfix Select

    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 Screwfix Select

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

    MFD 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 Screwfix Select

    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 Screwfix Select

    greenback78 likes this.
  8. MFD

    MFD 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 Screwfix Select

    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 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?

  11. MFD

    MFD Member

    Had a bit more of a poke around today. I've confirmed the original brick cavity gable wall has been insulated all along the side of the house, but from a few holes I looked through I think the timber front and rear walls are empty.

    The sections I could see into used 4" studs, with plasterboard on the inside edge and from the looks of it, tongue and groove cladding nailed directly to the outside. From my research, I was expecting at least a layer of sheet material (e.g. OSB) and some kind of moisture/vapour control layers, is what I've described normal for a 50s/60s timber frame wall?

    Who should I contact to get the outer wall stripped back and brought up to date? The company who injected the cavity wall insulation don't do this sort of work. Would most builders be able to advise on the insulation aspect? Does Building Control need to be involved?

  12. Jimbo

    Jimbo Screwfix Select

    Try posting in builders talk
  13. DannyDoLittle

    DannyDoLittle Active Member

    This is my 1962 dormer... This was during the total renovation process when the new windows were going in.. You'll see the colour change in the brick work on the gable end because of the cladding that was initially there. It was basically 4 long windows along the front with just brick stanchions to support the joists and the frame above, I took the cladding off and replaced with full brick work & changed the entire face of the house, but the mistake I made was I never did where you see the cladding above, I just insulated from the inside as previously there was absolutely nothing behind it apart from a water proof plastic sheet, then plasterboard which was knackered then straight into the bedroom... I wish I'd of ripped the entire front end off, top to bottom and bricked the lot... the upstairs bedroom is really cold in the winter, but roasting in the summer... It's like a poorly constructed conservatory. Whilst fully stripping out the house I realized that I'd most likely spent the best part of 250k on a house that was built on the cheap and the previous owners hadn't done a single thing to it since it was constructed.

    The roof is coming off in the summer & i'll have the cladding replaced and fully insulated because the house on the whole is cold, when people stay at ours they always say it's cold.

    Attached Files:

  14. MFD

    MFD Member

    So its still a timber frame behind the bricks on the ground floor, you didn't rebuild it as a cavity wall? Did you add any insulation or other layers in addition to the bricks?
    DannyDoLittle likes this.
  15. DannyDoLittle

    DannyDoLittle Active Member

    No pal, not any more but it was initially.
    It’s now a double skin brick all the way round the ground floor, but timber framing all round upstairs. I added 100mm of sheet rock wool where I could between the timber framing upstairs because I literally took all the previous internal boarding off where I could. I’d dread to think just how cold it would be if I didn’t add that insulation, but it’s still cold when the air temp is cold outside.

    I’ve been in the loft, that’s insulated but it’s old stuff & the roof is in need of replacing as the Stonewold tiles are past their life expectancy and I can see gabs & cracks in the bitumen sheeting that was used during the initial construction of the roof back in the 1960’s.

    When I get the roof done I’ll have the cladding removed off the front and back and have a double skin brick with cavity insulation with added insulating internal boarding.

    It’ll cost around £6000 to have it all done, but it really needs doing and I want to do it properly.

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