Is cavity wall insultion worth it

2010
2010 Posts: 5,323
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Is CWI worth getting.
I have been informed that I require an extractor fan for both kitchen and bathroom.
Also trickle vents on windows plus bits cutting off the bottom of some doors.
All this on top of the fact that CWI can cause damp and mould problems.

From what i can gather they drill holes all aorund your outside walls and inject beads to fill the cavity but if an area is somehow missed this can then cause a cold spot which can result in damp and mould and even make your house colder.
Is all the hassle worth it?
Opinions would be appreciated.

Comments

  • FreeBear
    FreeBear Posts: 14,262
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    2010 said:
    Is CWI worth getting.
    I have been informed that I require an extractor fan for both kitchen and bathroom.
    Also trickle vents on windows plus bits cutting off the bottom of some doors.
    All this on top of the fact that CWI can cause damp and mould problems.

    A lot of houses with suspended timber floors do not have ducts through the cavity - Any insulation pumped in to the wall will block these vents leading to problems further down the line.

    As for trickle vents - There is a requirement in the Building Regulations to improve background ventilation when doing certain "improvements". This is not a mandate to fit trickle vents despite what some will tell you. In fact, the documents that are touted as "Building Regulations" clearly state on the first page that they are "for guidance". If you want background ventilation, there are other ways of meeting the requirement without resorting to trickle vents. PIV and MHRV are just two methods..

    Extractors in kitchens & bathrooms are always a good idea, and if you can get them fitted neatly and for free, worth having. As for chopping bits off the internal doors, up to you to say yay or nay. There is no mandatory requirement to have your doors butchered.

    In answer to your first question "is CWI worth having", for some properties it can make a difference. In others, particularly if you are in an exposed area subject to driving rain, not a good idea. I had CWI some 25 years ago, and it made no noticeable difference.
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  • Scot_39
    Scot_39 Posts: 1,684
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    edited 17 January at 12:24PM
    CWI if home and location suitable is good thermally, good for heating bills, but is not without potential problems.

    Many may have been mis-sold during green grant rush - by less reputable firms.  Some have had to have it removed.

    Due to dampness concerns, newer building regs are much more fussy about ventillation levels - anyone looking for more sealed homes etc needs alternative ventillation - e.g. pumped heat exchange air exchangers common in many passivhaus designs to recover heating costs.  

    But have to wonder how much is to cope with buildings themselves drying out - remember brother advised only to paint not paper walls in new build for 1-2 years.

    Big vote for kitchen bathroom fans, to minimise retained dampness after cooking, bathing etc.

    My home - iirc c25 years old now - and parents double glazing - over 10 yrs old now has trickle vents - both with sealing flaps.

    Door bottoms seems extreme. People often resort to draught excluders to avoid that heat loss - even on internal doors - in winter.

    Back to CWI.

    Would always want any supplier to properly investigate particular property.

    As for instance it can increase risk of dampness transfer across the cavity.

    And there are different ways - filling material - for doing so retrospectively over the years - wool, foam, bonded beads etc. 


    My parents have the latter.  It did seem to lower their heating bills - but they had much thicker roof insulation at same time too - under a council grant scheme as disabled OAP.

    As well as benefits, it may impose costs, for instance it arguably makes external maintenance more critical - render, mortar, window seals etc. Let dampness into cavity, depending on filling type, it can more easily transfer across or be held in there (potentially impacting wall ties) - and no longer "breath away" as it were.

    As an introduction - try reading - some of it is a bit old now

    https://www.which.co.uk/reviews/insulation/article/cavity-wall-insulation/cavity-wall-insulation-installation-arnH44k0K4gA

    Some even find it has to be removed due to problems.  Google is full of companies offering the service.

    So my advice - get more than one quote with good cavity inspection / survey  - if in any doubt raised by one or more survey / install firm  - simply for location or on basis of survey -  probably best to avoid.

    And it may not be your only option - thermal cladding external, thermal insulation internal etc.

    My parents semi has CWI the adjoining neighbour went external thermal cladding when did their roof - rather than cost of re-rendering and to avoid regular repainting costs long term.

    The council estate nearby have also gone external cladding route. 

    That's in a damp cold windy location cf many parts of UK - West Central belt of Scotland.
  • 2010
    2010 Posts: 5,323
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    Thank you both for your very useful, informative and helpful comments.
  • wrf12345
    wrf12345 Posts: 354
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    Complete waste of money in two of my houses (one was free and the other already done), most of the heat escapes through the windows so radically downsizing all but south facing ones is the way to go.
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