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Housing - Renovation: Next steps for insulation- internal or external?

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  1.  
    • CommentAuthorDougmlancs
    • CommentTimeApr 16th 2023 edited
     
    We bought a 1960’s semi last year and we’re in the process of trying to minimise heat loss so that we can switch to an ASHP. The loft has 270mm rockwool and the floor downstairs is concrete slab (insulation status unknown but it replaced a suspended timber floor in the noughties) so I’m looking to the walls to add further internal/external insulation. They are brick cavity construction and have been filled with mineral wool (circa 2011). Most of the info I can find on IWI/EWI is around solid wall construction.

    We’re planning on redecorating most of the house at some point so the disruption of insulating internally doesn’t matter and I could do the work myself but there are some areas like the kitchen and bathrooms which are all on external walls which would be very difficult to do internally. I’m hoping the answers to a few questions might help clarify things.

    I understand EWI will only be fully effective on a cavity wall if the cavity is sealed/not full of holes so that there’s no great big cold draughts whistling through the cavity around the mineral wool. Now I assume they sealed the cavity when they did the CWI otherwise the loft would’ve been full of wool but is there a way I can check this? I would imagine there’s no way of telling if there are holes elsewhere though.

    How would it work transitioning from your wall to your neighbour’s once you’ve fitted EWI given the differing depth of material? Can you taper it down?
    How do you manage the condensation risk- I’m trying to get my head around dew point calculations!

    We aren’t planning on replacing the DG in the near future- will that change anything apart from having deeper reveals and extending the sills?
    Many thanks in advance
      631158AB-5698-41DC-A90C-1156FAD1F3B5.jpeg
    • CommentAuthorMike1
    • CommentTimeApr 17th 2023
     
    Posted By: DougmlancsI assume they sealed the cavity when they did the CWI otherwise the loft would’ve been full of wool but is there a way I can check this?
    If the cavity has been filled, then I wouldn't worry too much about the cavity sealing as you're not likely to get a through-draft, but you'd need to take off some tiles and underflelt if you wanted to check - get a scaffold tower up to that left-hand front corner.

    Posted By: DougmlancsHow would it work transitioning from your wall to your neighbour’s once you’ve fitted EWI given the differing depth of material?
    Ideally get them to have theirs done at the same time. Otherwise you'd ideally want IWI for 1m or so from the junction (as well as the EWI) - though the visual impact in the rooms concerned may mean you just need to forget that.

    Posted By: DougmlancsCan you taper it down?
    You could, but it would look and perform better without.

    Posted By: DougmlancsHow do you manage the condensation risk
    With EWI, don't worry about it - the risk is significantly decreased or eliminated compared to now.

    Posted By: DougmlancsWe aren’t planning on replacing the DG in the near future- will that change anything apart from having deeper reveals and extending the sills?
    No, but if you're thinking of replacing them in the not-near-future, you may want to bring that forward.
  3.  
    We have a similar dilemma. The problem with EWI is that heat leaks around the edges of the insulation layer (cold bridge) where the EWI ends at the neighbours' wall, and where it meets the roof line (especially on the head of the gable wall), and where it meets the foundations, the window reveals, and items like the porch. For our house, when all these cold bridges are added up they significantly reduce the potential value of EWI.

    These are easier to resolve if you are rebuilding the whole building (both semis together) with new windows, roof lines, porch etc, but harder to fix otherwise.

    Set against that, IWI can be done one-room-at-a-time but is disruptive, reduces internal area, and also has cold bridging if not turned back along solid internal or party walls. Condensation concerns were raised about IWI on historic solid walls but less so on cavity walls.

    So overall, neither option is right for every house, a lot does come down to circumstances!

    What kind of wall linings do you have? If it's plasterboard on dot-and-dab or on studs, you might have cold air circulating behind the plasterboard, worth replacing with solid plaster and IWIing while you are at it. Your age of house might already have solid plaster onto the walls which is better.
    •  
      CommentAuthordjh
    • CommentTimeApr 17th 2023
     
    Posted By: DougmlancsHow do you manage the condensation risk- I’m trying to get my head around dew point calculations!
    EWI generally reduces condensation risks, so you don't need to worry about that too much. Though if you make the building more airtight, then you will need to think about ventilation.

    Will points out some of the areas where care is needed and details need to be properly designed, but that can generally be done.

    Your house looks like a good candidate for EWI. I suspect that finding a good local contractor is important, and that taking your time over the whole planning and research stage is time well invested.

    PS whereabouts are you? I'm guessing Lancs, but that's quite a big area.
    • CommentAuthorRobL
    • CommentTimeApr 17th 2023
     
    We have a similar age 1963 detatched 4 bed house, with rockwool filled cavities. I diy EWI'd it with 150mm platinum EPS, and also XPS below DPC down to the top of the foundation footings - I couldn't persuade Mrs RobL we should dig up and insulate the solid concrete floor!
    The cavities were open at the top, fixed while the scaffolding was up. I went on a course by EWI-shop, there are plenty of other to pick from, but it will help you understand the process.
    I'd do it the same again still - all the insulation makes the house very comfortable.
    • CommentAuthorDougmlancs
    • CommentTimeApr 17th 2023 edited
     
    Thanks for all your replies everyone, it’s reassuring that the condensation risk doesn’t seem to be a major factor. I’ve tried to answer questions below.
    Posted By: WillInAberdeenWhat kind of wall linings do you have? If it's plasterboard on dot-and-dab or on studs, you might have cold air circulating behind the plasterboard, worth replacing with solid plaster and IWIing while you are at it. Your age of house might already have solid plaster onto the walls which is better.

    We’ve got solid plaster on the external walls and dotn’dab p/b on the internals.

    Posted By: djh
    Your house looks like a good candidate for EWI. I suspect that finding a good local contractor is important, and that taking your time over the whole planning and research stage is time well invested. PS whereabouts are you? I'm guessing Lancs, but that's quite a big area.

    Yes this is another concern I have- any recommendations are welcome! We’re in Lancaster by the way.
    Posted By: RobL We have a similar age 1963 detatched 4 bed house, with rockwool filled cavities. I diy EWI'd it with 150mm platinum EPS, and also XPS below DPC down to the top of the foundation footings - I couldn't persuade Mrs RobL we should dig up and insulate the solid concrete floor!
    The cavities were open at the top, fixed while the scaffolding was up. I went on a course by EWI-shop, there are plenty of other to pick from, but it will help you understand the process.
    I'd do it the same again still - all the insulation makes the house very comfortable.


    That’s very impressive! I’d love to do a course like that and DIY it but I don’t think work/family commitments are going to give me a clear window to do it all at once! And good point about XPS for the footing. Handily I’ve already carved a trench out of the driveway and rear patio as they’d both been bridging the dpc so that’d be one less job to do!

    So assuming our neighbour doesn’t want to shell out on external insulation then you would just have our wall sticking out compared to theirs?
    •  
      CommentAuthordjh
    • CommentTimeApr 17th 2023 edited
     
    Posted By: DougmlancsYes this is another concern I have- any recommendations are welcome! We’re in Lancaster by the way.
    My brother lives in Lancaster. :) I've asked him if he happens to know of any.

    good point about XPS for the footing
    You can use either XPS or EPS; there're various opinions as to which is best. But either will do a good job.

    you would just have our wall sticking out compared to theirs?
    It doesn't look as bad as you might think, just a neat line, and might encourage them to follow suit once they see it.

    edit: Just to note that you can edit your post to correct the quoting if you wish :)
    • CommentAuthorDougmlancs
    • CommentTimeApr 17th 2023 edited
     
    Posted By: djh
    Posted By: DougmlancsYes this is another concern I have- any recommendations are welcome! We’re in Lancaster by the way.
    My brother lives in Lancaster. :) I've asked him if he happens to know of any.

    good point about XPS for the footing
    You can use either XPS or EPS; there're various opinions as to which is best. But either will do a good job.

    you would just have our wall sticking out compared to theirs?
    It doesn't look as bad as you might think, just a neat line, and might encourage them to follow suit once they see it.

    edit: Just to note that you can edit your post to correct the quoting if you wish :)


    Thanks! I did try to correct it but I couldn’t find the difference between the first quote that formatted it ok and the other quotes- viewing on my phone doesn’t help

    EDIT: worked it out! :)
    •  
      CommentAuthordjh
    • CommentTimeApr 18th 2023
     
    My brother looked at EWI a little while ago. He's going to send me the list he compiled, which will at least give you a starting point. He says there are a couple of firms in Blackburn and one in Blackpool but other than that they seem to be concentrated around Manchester. There is one firm in Lancaster/Morecambe but don't know much about them https://globalbuildingukltd.com/
    • CommentAuthorDougmlancs
    • CommentTimeApr 18th 2023
     
    That would be such a help! Thanks @djh!

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