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Solid wall insulation

Hi everyone,

We are about to move in to a 1930s detached house requiring full renovation. Given the walls are going to be stripped and skimmed etc, I am minded to insulate the walls internally at the same time. There is obviously a cost element to that and our budget is already tight, but wondering if anyone has any experience of this to say whether it is definitely worth it? For context, we are also having brand new central heating system, rewire, new windows and insulation in the roof - so will the gains from internal wall insulation be worthy of the extra cost?

The main rooms that would benefit would be a large living room and bedrooms. Having not lived in the house I have no idea if they get particularly cold in the winter, but presume they would do. 

Thanks all,
Tom
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Comments

  • FreeBear
    FreeBear Posts: 17,351 Forumite
    Ninth Anniversary 10,000 Posts Name Dropper Photogenic
    Got a 1920s semi here with cavity walls on the lower half and solid brick on the upper half. Having insulated the two walls of a box room, I'm of the mind that it was well worth doing. Prior to doing the work, the room had always been cold and condensation/damp an ongoing problem even with an oversized radiator under the window.
    Fitted a new window, added ~50mm of Celotex to the walls (25mm around the window reveals), plasterboarded all four walls plus ceiling, and mounted a small type 21 radiator to one of the internal walls. No more damp walls, and so much easier to keep warm.

    A few words of advice - Knocking old lime plaster off the walls and ceilings is very, very messy work. You also need to be meticulous in removing nails that hold the old laths (wood strips) in place. Don't underestimate the amount of spoil you generate (I had approx 1t from stripping a 4x4m ceiling).
    Get a foam gun & canisters - Much easier to lay down a thin bead of expanding foam with a gun - Go round the edge of each room and seal the gap between floor & wall, and when the foam has gone off, reattach skirting boards. This will kill most of the draughts.
    In a well insulated and draught free house, there is no need to mount radiators under the windows - Position them on an internal wall and keep the pipe runs to a minimum.
    Wiring - Fit 35mm back boxes for light switches, and run a neutral wire to each one. If you ever decide to fit smart switches, you'll need the deeper boxes & neutral.
    Her courage will change the world.

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  • Bendy_House
    Bendy_House Posts: 4,756 Forumite
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    edited 20 September 2021 pm30 9:53PM
    As FB says - do it, do it, do it.
    If space is at a premium, fit the thinnest - it's only ~35mm total thickness. This will still transform the insulation value of your room.
    Only on the outside walls, of course! And carry it around the reveals as FB says.
    Also - sigh, as FB says - kill the draught. Seal between the floorboards - use sealant, or perhaps just a sheet (paper?) put down before the underlay - and absolutely seal between the walls and the floor before the skirtings go on.
    Do it. x 3
  • We did this to the original 9 inch solid brick walls of our last house and it made a huge difference.  
  • FreeBear
    FreeBear Posts: 17,351 Forumite
    Ninth Anniversary 10,000 Posts Name Dropper Photogenic
    edited 21 September 2021 pm30 1:29PM
    Bendy_House said: Also - sigh, as FB says - kill the draught. Seal between the floorboards - use sealant, or perhaps just a sheet (paper?) put down before the underlay
    That will be FreeBear to you B_H if you don't mind :p

    In a 1930s house, the floorboards on the ground floor should be tongue & groove, but if they have been butchered in lifting for a rewire, then there will be gaps - I put a layer of aluminium foil down (the extra wide Bacofoil stuff) followed by a layer of 5mm woodfibre boards (laminate underlay). Both wall to wall. With a decent thick foam underlay topped off with carpet, that room is now nice & toasty in the winter.
    Her courage will change the world.

    Treasure the moments that you have. Savour them for as long as you can for they will never come back again.
  • Thanks all! At one end of the living room is a bay window, can this still be insulated with plasterboard?

    I presume every (external) wall would need to have the same level of insulation or else it would be fairly pointless...
  • The area under the bay, obviously 'yes', and also the ceiling will likely be worth doing; unless it's been renovated at some point, there will be next-to-no insulation up there.
    Any thickness of high-quality insulation will make a significant difference, and it doesn't have to be the same throughout - the reveals, for example, might only be able to cope with the thinnest, whereas you might be happy to go 2" on the walls.
    A north-facing wall, again, would benefit more from 2" than others.
    Even 1" of high-quality insulation will transform your walls.
  • 1920s house here, I had the external render stripped back to brick before adding 75mm insulation and new render. The total thickness to the brickwork is 100mm and it is so much warmer than the icebox that it was.
    No man is worth crawling on this earth.

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  • FreeBear
    FreeBear Posts: 17,351 Forumite
    Ninth Anniversary 10,000 Posts Name Dropper Photogenic
    takay9 said: I presume every (external) wall would need to have the same level of insulation or else it would be fairly pointless...
    All external walls should be done where access permits. Stairwells are often the problematic areas, as to insulate the walls internally requires moving the stairs. That is a major, and very expensive undertaking, so really not worth the hassle. Make up for it by fitting better windows/doors & plugging the draughts.
    Her courage will change the world.

    Treasure the moments that you have. Savour them for as long as you can for they will never come back again.
  • 1920s house here, I had the external render stripped back to brick before adding 75mm insulation and new render. The total thickness to the brickwork is 100mm and it is so much warmer than the icebox that it was.

    Is this a solid wall, Rosa, or cavity?
  • 1920s house here, I had the external render stripped back to brick before adding 75mm insulation and new render. The total thickness to the brickwork is 100mm and it is so much warmer than the icebox that it was.
    Ditto.
    Transformed our cold 1930's semi. Looks great on the outside, warm and cosy inside. Saved on bills.
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