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    • CommentAuthorThorvaia
    • CommentTimeSep 8th 2020
     
    Hello all, first post! I have bought a 1950's house, and it has been basically untouched since the 1970's (in terms of wiring, insulation, décor and heating). we are in the process of improving things, especially before winter kicks in (the house is freezing). The house has cavity walls, which to my knowledge are unfilled (seems no evidence of drilling). We are considering external wall insulation to improve things, but I cant seem to get a clear answer on whether or not you can apply EWI to an unfilled cavity. In my mind, the heat would be lost through the cavity before it even hits the external wall. The company who have quoted us, believe it is fine to apply without the cavity being filled. again in my mind, the cavity should be filled before EWI is applied. The other thing we are considering is just increasing the room insulation to 100mm (from nothing).

    what are peoples thoughts?

    thanks :D
    •  
      CommentAuthordjh
    • CommentTimeSep 8th 2020
     
    Welcome to the forum. If you apply EWI without filling the cavity first, then you will need to be very sure that the cavity is not vented to the outside anywhere, in which case the whole wall will warm up to interior temperatures. If there is any way for exterior air to flow into the cavity then it will be very cold as you say.

    What do you mean by room insulation? If it's a typo for roof insulation, then 100 mm is nowhere near enough. Think 300 mm or even 400 mm.

    I'm sure there are many other things to look at, but if the wiring has not been touched since the 1970s then I would inspect it where possible and get it safety-tested by an electrician as soon as possible. It may need a complete rewiring.
  1.  
    I would fill the cavities, otherwise there will be air currents in them (convection) and through them (draughts) which will carry heat from where it should be. It would be extremely difficult to make the cavity airtight, and even harder to keep it so! Cavity insulation is also a cheap and well-proven way to add insulation value of the wall.

    (Edit: you might get it done free, under Energy Company Obligation or subsidised under Green Homes Grant Scheme)

    Also think about how you can connect up the wall insulation to the roof insulation so you don't get a cold area if they don't meet.

    Good also to think about controlled ventilation.

    Good luck, it will make a big improvement to your house!
    • CommentAuthorRobL
    • CommentTimeSep 9th 2020
     
    +1 for cavity filling first! It’s relatively cheap and quick, the uk is set up to do it.
    Our 1963 house had various bits of pvc cladding on it - and these didn’t get filled years ago. Now I’m Ewi - Ing , I’ve removed those and I’ve filled all of those myself (poly beads + a bit of dilute pva).
    We had glass wool type CWI, which is ok, but our house had no cavity closers at the top, so was a bit iffy there. I’ve done my best to fix all around the house at the top of the wall while we have scaffolding for Ewi. At front and back of house I used Celotex as a cavity closer, and at the top of the gable ends I augmented the glass fibre fill with expanding foam to make it more airtight. I think if I was getting it done again I’d consider foam filling the cavity, as it should be more convection proof.
    Good luck with your project!
    • CommentAuthorrevor
    • CommentTimeSep 9th 2020
     
    If you decide one CWI only do it if you are not in an exposed situation. Our 1st house built in the 1930's we did cavity fill that was in about 1973 and it worked very well but we were in a sheltered position. Where I live now close to west coast it is exposed and would not entertain filling a cavity and there have been many horror stories of houses having severe trouble with damp. There are cowboys about in this industry so would choose carefully.

    If you have very large rooms you could consider internal insulation you get the best of 2 worlds very efficient insulation with the benefit of a cavity to keep the house dry. It would of course be very disruptive to do.The benefits of a cavity is often overlooked.
    • CommentAuthorphiledge
    • CommentTimeSep 9th 2020
     
    Posted By: Thorvaia The company who have quoted us, believe it is fine to apply without the cavity being filled.


    Unless the company have shown an appreciation of the need to seal the cavity, Id be looking to use a different company as they dont appear to understand what they are doing!
    •  
      CommentAuthordjh
    • CommentTimeSep 9th 2020
     
    Posted By: revorWhere I live now close to west coast it is exposed and would not entertain filling a cavity and there have been many horror stories of houses having severe trouble with damp.

    Is there still a risk of damp in a cavity if EWI is put on outside the walls? If so, then a rainscreen on the outside of the EWI ought to remove any risk at all.
    • CommentAuthorbxman
    • CommentTimeSep 9th 2020 edited
     
    `How thick a layer of EWI do you propose using ?

    Far better to spend your money on the outside jacket if you must make sure the rendering is very well sealed to the apertures and avoid any cold bridges in that jacket both are essential .

    The rendering if correctly done should stop all air flow into the property .

    If you can take the EWI down below ground level all the better.

    I would personally recommend 'foamglas' for the bottom course if at all possible .

    Also consider having the the soffit boards removed so the insulation can join up with insulation in the roof.

    How about the windows and doors ? they are best improved first and consider having the window reveals bevelled, as you will find with the thicker covering to the property the views and light levels are substantially reduced something you may only appreciate after the job is done .

    Watch the contractor like a hawk his operatives will probably not care about anything apart from getting the job finished .

    As ever attention to detail.

    The existing brick work will come up to internal temp of the dwelling and should act as a heat store at all times of year making life far more pleasant .


    Good luck with the project
    • CommentAuthorgyrogear
    • CommentTimeSep 9th 2020
     
    Posted By: Thorvaia(the house is freezing).


    Does it have a basement and/or a crawlspace ?

    gg
  2.  
    >>>>"The rendering if correctly done should stop all air flow into the property .”

    Not sure this is the whole story though... Cavities are often open at the top into the roof void, and at the bottom round the ends of the ground floor joists (if present), and through gaps in the pointing of the inner leaf of the gables into the loft, and gaps round cables and pipes and under window sills etc etc.

    You could try to seal all these, but it would take a lot of labour (£££) and be difficult to get 100% airtight, and gaps may open up again a few years.

    Even then, there would be convection in the cavities, carrying the heat away from the warm places to cold (loft gables again)

    I would get a specialist cavity wall company to fill them for free under ECO, then get the EWI people back afterwards, since they don't seem interested in doing the cavity fill.
  3.  
    Posted By: WillInAberdeen>>>>"The rendering if correctly done should stop all air flow into the property .”

    Not sure this is the whole story though... Cavities are often open at the top into the roof void, and at the bottom round the ends of the ground floor joists (if present), and through gaps in the pointing of the inner leaf of the gables into the loft, and gaps round cables and pipes and under window sills etc etc.

    +1
    Any cavity I have had dealings with has had a gale blowing through it! (which is why I prefer solid wall with EWI). The EPS EWI with thin coat render should stop any chance of rain ingress through the outer skin.

    Thorvaia - before you shell out the (considerable) money on EWI make sure all the draughts are fixed. If the windows are sound then frames can be improved with better sealing and often double glazed units can be fitted to replace single glazing which is usually cheaper than new windows.
    You haven't mentioned the loft - that is often a quick cheap fix. If the place hasn't been touched since the 70s then there is probably only 100mm of sagged out insulation up there. Target between 200mm - 300mm.
    • CommentAuthortony
    • CommentTimeSep 12th 2020
     
    Or more, last one I did on a grant was 400mm for 36 Almshouse flats

    Probably the inner skin is brick and with a ventilated cavity, and I have never seen one that isn’t, infilled they are always draughty and even when filled they can still be. So you are effectively living in a half brick uninsulated building, twice as cold as a solid wall home.

    I would fill the cavities with eps beads, preferably platinum eps.

    Then do your EWI

    Like they say do the air sealing first

    Decide what is going to happen at the top of the cavity, often it is closed with a brick that causes a thermal bridge and gets in the way of insulation, they flick off easily and then cavity and loft insulation can be joined.
    • CommentAuthorJeff B
    • CommentTimeSep 12th 2020
     
    Tony - would it be effective just to stuff some fibreglass quilt material tightly into the top of the filled cavity (i.e. filled with EPS beads or blown fibres) to prevent air moving up through it?
    • CommentAuthorjms452
    • CommentTimeSep 13th 2020 edited
     
    Posted By: Jeff BTony - would it be effective just to stuff some fibreglass quilt material tightly into the top of the filled cavity (i.e. filled with EPS beads or blown fibres) to prevent air moving up through it?


    You want to fill the top of the cavity with some thing to stop airflow and enable full fill without the beads pouring out the top. RobL's approach sounds good at stopping airflow, but the quilt would probably be ok, providing it stays put, if access is hard.

    The beads stop convection in the cavity, reduce the effects of any air leakage (nothings 100% air tight) and give you some very cost effective extra insulation) as they are fairly cheap to have installed.
    You can also get PU injected which is airtight in itself and sticks the leaves together but is not breathable and more expensive.

    If it was my house I'd take out a brick have a look at the wall ties and cavity too:
    o The cavity should be dry inside - if it's not you need to work out why and rectify it.
    o Wall ties can corrode where they join the outside leaf and you want most of the metal to still be there.

    If there were problems in either of these areas they are much easier to diagnose/fix before the EWI goes up.
    • CommentAuthorJeff B
    • CommentTimeSep 13th 2020
     
    jms452 - so stuffing quilt tightly into the top of the cavity would do the job do you think? I only ask because this would be a very simple thing for me to do with my cavity walls which are filled with Rockwool blown-in fibres.
    • CommentAuthortony
    • CommentTimeSep 14th 2020
     
    It is nice if the insulation in the cavity can be joined seamlessly to the loft/roof insulation
    • CommentAuthorphiledge
    • CommentTimeSep 14th 2020 edited
     
    Posted By: Jeff Bjms452 - so stuffing quilt tightly into the top of the cavity would do the job do you think? I only ask because this would be a very simple thing for me to do with my cavity walls which are filled with Rockwool blown-in fibres.


    I dont think stuffing compressed quilt would such a good idea as even squashed its not air tight and squashing it tight would remove much of its insulation properties and give a degree of cold bridging. If the cavity is pretty well sealed aside from the top I personally dont think theres likely to be much air movement through blown cavity insulation. If you want to be sure then its probably best to use a squirty foam bead to close the top of the cavity and then extend the loft insulation to sit on top of the foam.

    Weve got blown CWI in part of the original house and all weve done is levelled the blown fibres with the top of the outer brick leaf then cut pieces of loft roll to fill from the top of the blown fibres to level with the top of the wall plate cutting to fill under and around the rafter ends without leaving gaps and avoiding squashing the insulation too much. Then weve run a short length of 75mm roll over the top of the wall plate to join with the loft insulation. Cant get any more than 75mm without block the ventilation gaps. That level of detail has made a big difference to one of the bedrooms below where there had been black mould on some of the edges of the ceiling/top of the wall due to cold spots. Same usage of the room and theres been no recurrence of the mould since😊
    • CommentAuthorjms452
    • CommentTimeSep 14th 2020
     
    Posted By: philedgeI dont think stuffing compressed quilt would such a good idea as even squashed its not air tight and squashing it tight would remove much of its insulation properties and give a degree of cold bridging


    Posted By: philedgePosted By: Jeff Bjms452 - so stuffing quilt tightly into the top of the cavity would do the job do you think? I only ask because this would be a very simple thing for me to do with my cavity walls which are filled with Rockwool blown-in fibres.


    Given your spending quite a lot on EWI I'd spend a few days on sealing it as well as you could.

    Squirty foam (buy a reusable foam gun) is fairly easy to work with. If you have to fill up with fibre glass quilt in the odd area I would take the (very small) risk as it is behind EWI anyway.

    Posted By: tonyIt is nice if the insulation in the cavity can be joined seamlessly to the loft/roof insulation


    +1 this helps in every way.
    • CommentAuthorThorvaia
    • CommentTime7 days ago
     
    Hi everyone, thank you all for the comments, its nice to get some more info on EWI. After discussing with another company, they matched what has been said here, that the cavity should be filled (and the loft insulated to "seal" the cavity) before EWI is applied. We are now planning on installing internal insulation, after discovering all i have in the walls is 10mm of polystyrene.... I would rather stop the heat (or limit the heat) entering the cavity. We are looking at between 100-150mm of kinspan now, funds dependent. The loft has 300mm of mineral wool, but planning on boosting that to 400mm. We have rooms in the loft, and there is little insulation in the walls or on the roof itself, so another area to look at.

    I have also been discussing getting the cavity filled, and it seems to be a no-no up here in Orkney, due to the driving rain (the council no longer recommends CWI when renovating their properties). I will see what the estimated cost of internal insulation will be
  4.  
    IMO filling the CWI will not be an issue if EWI is put on as part of the works as the EPS will not allow driving rain to get to the outer skin of brickwork let alone the cavity. (assumes good attention to detail around windows etc.).

    And IMO EWI is much better than IWI
    • CommentAuthorJeff B
    • CommentTime7 days ago
     
    philedge and jms452 - thanks for your further comments. I have tried to ensure that the loft insulation extends over the wall plate and cavity and taking care to leave a gap above for air to circulate. Maybe that's sufficient then?

    Thorvaia - what do you mean by "all I have in the walls is 10mm of polystyrene"?
  5.  
    Thorvaia, make sure you get a condensation risk analysis done if you are using 100 - 150mm PIR. It'll make the external wall a lot colder. Is frost an issue there?
    • CommentAuthorjms452
    • CommentTime7 days ago
     
    Posted By: ThorvaiaI have also been discussing getting the cavity filled, and it seems to be a no-no up here in Orkney, due to the driving rain (the council no longer recommends CWI when renovating their properties).



    Orkney - see p34 here - unsurprisingly it looks like you are rather exposed:
    https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/431943/BR_PDF_AD_C_2013.pdf

    This is well worth a read (there may be a more recent version?) as the answers to many of your questions are location dependent.

    We did CWI and EWI (separately on different bits of the house) but are about as sheltered as you get.
    • CommentAuthorgravelld
    • CommentTime7 days ago
     
    As djh said above you could make your own cavity on the outside of the EWI and still fill the masonry cavity. EWI is generally preferable to IWI, all things equal (granted, they aren't often!).

    There are loads of old threads on EWI on cavities btw.
    •  
      CommentAuthordjh
    • CommentTime7 days ago
     
    Posted By: jms452Orkney - see p34 here - unsurprisingly it looks like you are rather exposed:
    https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/431943/BR_PDF_AD_C_2013.pdf

    This is well worth a read (there may be a more recent version?) as the answers to many of your questions are location dependent.

    I think that is the latest version, and it is definitely helpful, but note that it says on the front cover "For use in England". I think that https://www.gov.scot/publications/building-standards-2017-domestic/3-environment/310-precipitation/ may be more relevant for Orkney.

    The Scottish document doesn't discuss EWI on cavity construction, but I think that may be because it is focussed on new construction. I expect there are good documents on retrofitting that our Scottish members can point to. The document does mention cladding the outside of EWI as an alternatvie to render, and I would argue that if EWI over a solid wall is safe, then EWI over a cavity-filled wall must be a fortiori. But I can see why comments like "This construction is only recommended for sheltered conditions" with regard to insulated cavities might be putting people off if they don't consider the whole context.
    • CommentAuthorgravelld
    • CommentTime6 days ago
     
    I suppose there are going to be a lot of "it depends" - there are good and bad ways of installing EWI. Checkout the Preston debacle. E.g. I wouldn't want plastic caps on the top of the EWI! You'd have to extend the roof line.
    • CommentAuthorThorvaia
    • CommentTime5 days ago edited
     
    <blockquote><cite>Posted By: Jeff B</cite>philedge and jms452 - thanks for your further comments. I have tried to ensure that the loft insulation extends over the wall plate and cavity and taking care to leave a gap above for air to circulate. Maybe that's sufficient then?

    Thorvaia - what do you mean by "all I have in the walls is 10mm of polystyrene"?</blockquote>

    Hi, my internal walls (well the internal walls on the external walls if that makes sense), consists of a 1inch stud, with 10mm of polystyrene sheet then the plaster board...thats it.....
    • CommentAuthorThorvaia
    • CommentTime5 days ago edited
     
    <blockquote><cite>Posted By: Nick Parsons</cite>Thorvaia, make sure you get a condensation risk analysis done if you are using 100 - 150mm PIR. It'll make the external wall a lot colder. Is frost an issue there?</blockquote>

    Not really, because we are so close to the sea, we only occasionally get frost. Bigger issue is the wind and rain :cry:
    • CommentAuthorbxman
    • CommentTime4 days ago edited
     
    If you have the time to read and understand the information from

    http://www.sensiblehouse.org/nrg_heatloss.htm
    which I have not yet done and as I do not have the knowledge to know how correct it is .

    It may help on your decision

    What I do know is that If you have the ability to have the roof adequately cover the EWI and can minimise and successfully seal all intrusions through the EWI there should be no penetration of air or water in any of it's forms through the EWI.

    All movements of air and moisture within the envelope should then be entirely under your control.



    I believe you will be surprised as to how little energy you will need to input

    My entire energy import for the year in a 3 bed semi is less than 1000 kWh with the aid of 7.5 kW of PV panels and a 20kW battery.
  6.  
    Posted By: bxmanWhat I do know is that If you have the ability to have the roof adequately cover the EWI and can minimise and successfully seal all intrusions through the EWI there should be no penetration of air or water in any of it's forms through the EWI.

    +1
   
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