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    • CommentAuthormarsaday
    • CommentTimeJun 4th 2017
    I am doing a standard brick and block single story extension.

    I am planning on using 100mm solid insulation in the cavity. Someone has said the soft insulation is best and seeing as my cavity is 150mm wide it would be filled up with the soft stuff. We are not in an exposed location, so driving rain is not an issue.

    Any ideas on best way forward for me here ? How does 100mm solid compare to 150mm soft insulation in the wall.

    I will be doing the work myself so not bothered from a labour point of view regarding expense. I would like to do the best job possible with what i am using.
    • CommentAuthortony
    • CommentTimeJun 4th 2017
    What does best mean? Best insulation is aerogel, phenomoly expensive.

    Best bang for your buck is r32 fibreglass batts, sheet insulation is better in theory but in practice performs pootly due to thermal bypass (unless installed by Mike George).

    Fully filled for me send seamlessly joined to roof insulation.
    • CommentAuthormarsaday
    • CommentTimeJun 4th 2017
    I mean which is the best stuff to use out of my two options (not aerogel).

    So the batts are cheaper, and give better performance. Will look into them.
    • CommentAuthorcjard
    • CommentTimeJun 5th 2017
    Still need to define "best" - e.g. Do you mean "the cheapest way of getting through building regs/best for my wallet", do you mean "best performance at a price point", "best for the future wellbeing of the planet" etc
    • CommentTimeJun 5th 2017
    Posted By: tonyaerogel, phenomoly expensive
    phenolic comes next!
    • CommentAuthorgravelld
    • CommentTimeJun 5th 2017 edited
    I think you need to work backwards a bit, because you've stated the depth of the insulation layer already... obviously depending on the insulant and installation quality you're going to get different performance levels.

    What sort of house do you want to build?

    You may want more than 150mm if you're using mineral wool.
    It might also be worth considering who will be installing the insulation and which method you believe they will be best able to achieve a good result with.
    • CommentAuthormarsaday
    • CommentTimeJun 5th 2017
    I will be doing all work.

    So labour cost is not relevant.

    I want the best job for the least money. I am not interested in saving the planet. Because i am doing it myself i can be confident the rigid board will be installed tightly. I did my own attic conversion and used exp foam to fill any missed gaps.

    I am doing a block and brick wall and the internal insulation has to be 50mm minimum for new extensions (i think). I was thinking of using 100mm initially, but someone has told be full fill 150mm would be better (cheaper and easier to install), plus tony has recommended this option as well.

    So basically i am looking to do a better job than standard building regs, but would like the best solution in terms of ease of fitting and cost. I thought solid insulation was miles better than fulfil, hence the replies are interesting.
    • CommentAuthorHollyBush
    • CommentTimeJun 5th 2017
    I considered the implications of wool v board and ended up with wool. The reasons;
    - if a gap is left between boards, then when in a cavity the thermal bypass is higher than a fulfil option with a small gap
    - price - 150mm wool came out cheaper with labour and materials
    - easier to butt up and install correctly, especially where cuts and corners are
    - suitable for environment - rainfall on external v need for empty cavity
    - long term performance - some people say boards shrink, but wool doesn't - though I don't have a source for this

    You need to establish what price you can get the materials at. Wool needs to be OK for fulfil installation - and that is more expensive than stuff you put in the loft space. Also get Building control to agree before you buy.

    Good luck
    • CommentTimeJun 5th 2017
    Posted By: marsadaythe internal insulation has to be 50mm minimum for new extensions (i think)
    How d'ya mean? Who says? Surely you can do CWI instead?
    Unless you are stuck with planning / aesthetic issues I would go for solid block wall with EWI, quicker and easier to put up and easier to get a decent 'u' value on the wall.

    If you must have a cavity wall then I would agree with Tony - glass wool bats
    • CommentAuthormarsaday
    • CommentTimeJun 5th 2017
    EWI ??? This is a 100 y/o brick semi. Brick all the way for me.

    The general concensus seems to be full fill with bats. This sounds fine for me.

    What is the minimum fill for bat insulation then ? From reading just now i think 100mm is around the amount needed. Happy with 150mm though.
    100mm gives a 'u' of about 0,3 and 150mm gives a 'u' of about 0,22 Both values dependent on the type of bricks/blocks
    Pick your 'u' target which defines your insulation thickness, wall tie length, foundation width...........
    Full fill with bats? Are you only allowed to use that at certain times of the year?
    • CommentAuthorDarylP
    • CommentTimeJun 6th 2017
    @marsaday, you are subject to the AD L1B minimum elemental performance standards?
    If so, who told you that you need 50mm internal insulation? have your plans/specs been approved by your Building Control Body?
    Good luck:smile:
    • CommentAuthormarsaday
    • CommentTimeJun 6th 2017
    What is the minimum then please ? I thought it was around 50mm solid insulation.

    I have used the kingpan calculator
    • CommentAuthorCWatters
    • CommentTimeJun 6th 2017
    Check with Building Control if you plan to fully fill the cavity. Not all BCO are happy with that even if you are in a sheltered location.
    • CommentAuthorDarylP
    • CommentTimeJun 7th 2017
    marsaday, see
    • CommentTimeJun 7th 2017
    marsaday - some confusion? - nothing says the insulation has to be internal, external or in the cavity. Can be all in one of those places, or a bit in each.
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