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Insulation - Cost vs. Benefit - Walls or flat roof

Discussion in 'Building' started by _DCG_, 20 Oct 2020.

  1. _DCG_

    _DCG_

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    Hi,

    We live in a semi detached house built in 1949 which has a double storey side extension that was built in 1996 to add a garage and additional reception room on the ground floor, and a bedroom and bathroom upstairs. The bedroom and bathroom are above the garage, however the reception room is single storey and has a flat roof.

    We've since found out that the extension is built from single layer 9 inch Thermalite blocks, i.e. no cavity wall. The extended part of the house has always felt much colder than the main house - in particular the reception room is very very cold and needs a lot of heating.

    We have the chance to add some insulation with the Green Homes Grant scheme and have had two quotes:
    1. External wall insulation to the side gable wall - this would cover walls to the garage, bedroom and bathroom and the reception room. Cost: £2,000 after grant
    2. Insulate the flat roof which covers the reception room, part of the kitchen and part of the main living room. Cost: £6,000 after grant
    The question I am trying to answer here, and would appreciate some help with is: Which option would give the most benefit?

    I know these Thermalite blocks are meant to be insulating, however that whole section of the house does feel cold. Will we feel a lot of benefit by adding EWI?

    It feels like by doing the wall we will add benefit to more rooms and obviously 2k is a lot cheaper than 6k! We also plan to partition the garage to create a utility room in time, that would also get some benefit from the EWI.

    While the kitchen and main living room do feel a bit cold sometimes, they're never as cold as that extension part of the house. However, that second reception room (covered by the same flat roof) is freezing cold a lot of the time!

    Any thoughts or advice would be gratefully received.

    Thank you, DCG
     
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  3. IT Minion

    IT Minion

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    £6k for the roof, after 5k means they think it'll cost £11k all in? That's a lot to insulate a single story roof. Are they stripping the entire lot off and then redoing it afterwards? I'd get another quote on the roof.

    With EWI the bedroom would lose heat slower, meaning anyone in it won't get as cold overnight if that's an issue.

    To make the rooms warmer, install bigger radiators. They're dirt cheap and not that hard to DIY, or quick for a plumber to swap out.

    I'd be tempted to do the EWI and wait for the next batch to show up or to find another way of doing the roof.
     
  4. MeldrewsMate

    MeldrewsMate

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    Apart from being shocked at the 'before discount' prices, I'm also shocked that the extension, built in 1996, isn't better insulated. Perhaps a word with your local Building Control Dept. to establish if it conformed in 1996. I'm assuming it was signed off by LABC when it was built.
    IMHO you cannot waste money on insulation, but you can pay more for it than you should. Have you asked for quotes from companies that aren't part of this scheme?
    Whilst larger rads will give out more heat, you'll pay for that heat over and over again in higher bills, plus it is my belief that a poorly insulated room does not give the same 'comfort quality' as a well insulated one - it will cool rapidly once the heating switches off, and will have hot spots and cold spots around the room.
     
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  5. _DCG_

    _DCG_

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    Thanks so much IT Minion, really appreciate your thoughts. Yes, the 11k is to fit a Bauderflex warm roof system and its £11,220 so even more! The roof area is 9.3m width x 4m depth so roughly 37 metres squared. We're just inside the M25 so should probably factor in location. Does that still sound very expensive?

    I know very little about building or bricks but the EWI does seem like a good idea. My only concern is that since the extension is built with these Thermalite blocks that are meant to be insulating themselves, I'm worried that the additional EWI might not make much difference and could therefore be a waste of £2k.

    If anyone has a view on Thermalite blocks and whether they are any good I would be very grateful. (I have read quite a few threads saying never bother with single skin and cavity walls are a must :( we bought the house like this :()

    With respect to the radiators, yes fully agree and the second reception room definitely needs a double panel radiator / something better, as does the kitchen.

    We just wanted to try to insulate the house better to reduce heating bills over the long term, and the Green Homes Grant scheme is our only chance of affording to get something done.
     
  6. _DCG_

    _DCG_

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    Thank you MeldrewsMate, it is indeed a huge shock and also a huge lesson learned that we didn't pay close attention to the walls etc. before buying the house! I assumed that since it was built in 1996 it would automatically be well insulated, apparently not.

    I did get a reply from the Building Control Dept last week - they advised there is no completion certificate as "they werent always produced back then" but the works were "signed off and recorded as complete". Not particularly helpful :(

    Haven't asked for any quotes from companies that are not part of the GHG scheme, I suspected they may increase prices somewhat but was hoping it would not be extortionate and that we'd still be better off given the £5k voucher.

    The quote for EWI is £6k so we'd pay £2k with the voucher as you get two thirds off.

    As mentioned, we do want to try to insulate the house better and lower our bills long term.
     
  7. _DCG_

    _DCG_

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    To add, what I am trying to work out is where we will get most bang for our buck if you like.

    If adding EWI to walls built out of Thermalite blocks will only make it a little bit warmer then that £2k would be better off saved and put towards the roof. :confused:

    However given that upstairs feels cold, something tells me that these Thermalite blocks are not very good (despite being sufficient for BC) and that we should try to add more insulation while there is help / a grant scheme on offer.
     
  8. Mr Chibs

    Mr Chibs

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    Don't get worked up about the bricks. I lived in an old house with 9" solid brickwork (1900 construction), it was freezing.
    Once it was insultated... it was warm as toast.

    The insulation was done on the inside (IWI) external is meant to be slightly more efficient (EWI) but at the end of the day, it doesn't really matter, being warm matters.
    As for costs, depends how long you are staying put, as to wether it's worth it or not.

    Any insulation will be better...
     
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  9. wgt52

    wgt52

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    Definitely obtain a couple of quotes outside of the scheme.

    The wall insulation - a neighbour has just had an extension completed; walls thermalite blocks, 2inches of PIR on outside with composite cladding. As a suggestion I'd go for that.
    As for the roof, are you intending to have a 'fall' on it (if it doesn't have one already)? What is the flat roof construction? If you can insulate right up to the roof then insulation on top (with necessary ventilation) is probably the way to go.

    If you decide on internal insulation then insulate the roof on the inside also.

    Do have to think the insulation scheme has all the hallmarks of not being good value for the home owner, even if you can find a company to do the work. And has it has to be completed by the end of March '21 completed in the worst of the weather and likely to be rushed.
     
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  11. _DCG_

    _DCG_

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    Mr Chibs - Thank you glad your house is warmer. Planning to hopefully stay put for the long term so should be worth it to do something.
    My concern regarding the bricks is that the bricks are not what is causing that section of the house to be cold, and that the true cause is instead the fact that there is a draughty garage underneath with rubbish doors that let loads of cold air in, and then the reception room next to the garage is cold because of the roof. This would then mean that adding EWI would be a waste of money :(

    I have been trying to find the U value of these 9 inch Thermalite blocks so we can do some heat loss calculations but cant seem to find it. Any pointers would be really appreciated.
     
  12. _DCG_

    _DCG_

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    WGT52 - Thank you for the reply, sorry I don't know much about building so not sure what a fall is on a roof. Do you mean a slight slope? If so then yes it is not totally flat there is a bit of a slope to it. We don't know what the roof construction is and the builder who put in our loft insulation told us he couldn't tell whether the flat roof was insulated without damaging the ceiling indoors... however given it was built in 1996 we assume it's not insulated or barely insulated.

    We'd like to avoid internal insulation so as not to lose ceiling height.

    Re the GHG scheme... totally agree and the middle of winter really isn't the best time, I'm also concerned the works will be rushed. I haven't got any quotes yet from installers not part of the scheme but had so far assumed that without the government voucher there's no way we could afford to get anything done at all.
     
  13. wgt52

    wgt52

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    Fall - yes it is the name for the slope on a flat roof (or for that matter any surface that has a slope on it to cause water to run off).

    Probably help the DIYnot community to help you if you can post some photo's of where you have concerns or want advice on.
     
  14. Mr Chibs

    Mr Chibs

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    Does this help?

    https://www.cba-blocks.org.uk/u-value-calculator/

    No insulation will be a waste of money, but you'll need to address the heat loss from doors, windows and roof etc.
     
  15. JP_

    JP_

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    If you don't mind losing 6cm or so from the room, you could have internal insulation and DIY. If the room needs decorating anyway, maybe an opportunity to give it a fresh look. But £2k for EWI might be a good option.
     
  16. phatboy

    phatboy

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    A neighbour is currently building an extension with Thermalite, 9" laid on flat so no cavity, and then adding 70mm EWI. Our house was built in the 50's and is solid 9" block on flat. 90mm EWI changed our lives, and the house became liveable, cosy, and generally very comfortable.

    5 years ago our EWI cost about £100 / square metre, no subsidy here.

    The price you have for the roof seems very high.
     
  17. _DCG_

    _DCG_

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    Hi phatboy, thank you for your thoughts. Interesting that your neighbour is choosing to use 9" Thermalite and then add EWI, rather than building a cavity wall and insulating that. I thought the better option was always to do a cavity wall if possible.

    Do you remember the make of the EWI you had installed on your house please? Both our quotes are for InstaClad, and my step dad is now terrifying us by saying that we could have problems with it not being adhered to the existing render properly and then later falling off, or the render not being able to take the weight of the products applied.

    I would hope that if it is installed by a TrustMark registered installer then they would do a good job, my greater concern is that it is combustible.
     
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