Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)

Categories



Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

Buy individually or both books together. Delivery is free!


powered by Surfing Waves




Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.




    • CommentAuthorHadyn98
    • CommentTimeSep 22nd 2020
     
    Hello,

    Some year back I tried to take advantage of the green deals by getting CWI. The guy came round and quickly said it wasn't feasible, due to excessive mortar in the joint, on the inside of the cavity (did he call it mortar snot?). It's a mid 1950's build semi-detached.

    He checked all the walls to make sure and while checking the party wall in the loft space, I saw on his camera up draughts causing spider webs to be blown around. !

    Does that explain why the party wall feels colder than external walls? When I measure the walls internally using infrared thermometer in winter, it's around 0.5-1.5 deg colder on the party wall. Built in cupboards against the party wall get damp and mould during winter as well.

    My questions are:
    1/ Surely air draughts in cavity walls are a problem. It's supposed to be a semi-sealed void to limit heat loss, surely?
    2/ If that's correct, how could I seal up the cavity to prevent air flow? Even just preventing airflow without sealing the cavity should be an improvement?
    3/ Is there any internal cavity insulation solution for walls with uneven mortar? As far as I can tell the cavity is standard 50mm.

    The front wall has some local stone around the bay window (another problem he highlighted), the kitchen has been extended out the back wall, and there is a garage on the other side wall (which we will eventually be including in the living space).

    We're in SW London if anyone is able to make recommendations.

    Many thanks,
    Hadyn
    • CommentAuthorrevor
    • CommentTimeSep 22nd 2020
     
    Sounds like you had an honest installer. A cavity wall is meant to have air flowing through it, it is there to dry out the wall if it suffers from driving rain or other source of damp. It is a problem with CWI that it blocks off the air flow so that bridging caused by mortar snots does not dry out and you get damp patches from the wall ties.
    I am not sure what you mean by the party wall having a draught normally semis have a single brick party wall so if you are having damp on this wall it could be condensation particularly if your neighbour does not heat their house. Do you have a shared chimney stack that could also be a source of damp. So many thousands of house have had CWI installed when it was not suitable costing millions nationwide to remove you fill a cavity at your peril although in a sheltered spot it works well. We once had a 1930's house we cavity filled in the 70's and it worked well.
    • CommentAuthorphiledge
    • CommentTimeSep 22nd 2020 edited
     
    Posted By: revorSounds like you had an honest installer. A cavity wall is meant to have air flowing through it, it is there to dry out the wall if it suffers from driving rain or other source of damp.


    Im fairly sure that a CW doesnt need to have air flow to keep the inner leaf dry. Any penetrating moisture runs down the inside of the outer leaf and drains away. This keeps the inner leaf dry whether theres air flow or not. Problems arise with sloppy bricklayers dropping mortar into the cavity that accumulates on ties to bridge the cavity
    • CommentAuthorjms452
    • CommentTimeSep 22nd 2020
     
    Poly bead is the most tolerant of irregular cavity.

    If your cavity is dry, not bridged and you're in a sheltered area worth digging deeper.
    • CommentAuthorphiledge
    • CommentTimeSep 22nd 2020 edited
     
    Posted By: Hadyn98

    He checked all the walls to make sure and while checking the party wall in the loft space, I saw on his camera up draughts causing spider webs to be blown around. !

    Does that explain why the party wall feels colder than external walls?


    With ambient air blowing through the cavity that wall will be no better than a single leaf wall, so will be cold in the winter which has likely caused your internal damp problems. As its an internal wall to both adjoining houses theres no risk of penetrating damp, unless the neighbours are doing something odd!! Theres no reason why you cant fill this cavity but youll need to stop whatever gets poured/blown in from travelling into the external wall cavities. A column of squirty foam either end of the internal cavity injected from holes drilled in the external wall junction??

    For the external walls, Im not sure how much success youd have with a 2 storey building but Ive cleaned up a single storey cavity by stripping the roof covering and knocking motar snots off the ties with a roofing batten. Had to take a few bricks out at DPC level to clean all the rubbish out

    As a party wall, you probably need to get the neighbours to agree to any work you do!
    • CommentAuthortony
    • CommentTimeSep 22nd 2020
     
    DraughtBusters needed!

    It is well known that party walls cool buildings, for many many years these were not allowed to be insulated. Thankfully they are now

    They are on my list of in-house winter cooling systems

    I would get cavities filled with platinum EPS including party wall.

    BUT that is a woefully inadequate quantity of insulation. See thread on EWI to cavity wall.
    • CommentAuthorHadyn98
    • CommentTimeOct 1st 2020
     
    Hi

    Thanks all for your comments, and thanks for confirming my suspicions regarding air draughts in cavity walls. I would be quite happy to fill all the cavities, if I could get it done correctly.

    I appreciate that filling the cavities might not be sufficient insulation to significantly lower energy consumption, but given the fact we have a "wind tunnel" in our cavities currently, blocking that up and some insulation will be a massive improvement!

    I've thought about this quite a bit and written and rewritten replies : the reality is I'm not sure how to proceed. I think accessing the top of the cavities to seal them up would be quite difficult for me - I did have the wacky idea of a line of expandable foam at the top of the wall to at least prevent updraught - but no idea how I would get access to that, nor whether that is a good idea or not.

    Can anyone offer any guidance in terms of roughly what's required to seal the cavities?

    I have to be realistic though and say I'm not going to be able to get the knowledge and experience required to implement this myself.
    But having looked at comments on this forum and others, plus reports in the press about CWI problems after a few years, it seems the knowledge or experience to carry out good quality installations and remedial work, is not that common.

    Is that a fair comment?

    Is there a list of recommended builders somewhere who know how to implement insulation properly (air seal with tape, etc) rather than just doing the building work that looks good?

    Lastly, I was wondering why solid insulation isn't retrofitted in existing cavities? I see aerogel sheeting in a variety of thicknesses. Is it not possible to push those down from above? Is blown fibre or bead insulation _really_ the best solution for all the existing properties out there? external or internal insulation is possible, but surely there is a technical solution to use the cavity to maximum benefit?

    Many thanks,
    Hadyn
    • CommentAuthortony
    • CommentTimeOct 1st 2020
     
    I would try again for CWI preferring eps beads and get them do the lot at your risk.
    • CommentAuthorphiledge
    • CommentTimeOct 1st 2020
     
    Posted By: Hadyn98

    Can anyone offer any guidance in terms of roughly what's required to seal the cavities?

    Lastly, I was wondering why solid insulation isn't retrofitted in existing cavities?
    Hadyn


    Your cavities are likely to be connected to the adjoining house so sealing just along the top is no guarantee to stop draughts. If you seal along the top of the party wall theres nothing to stop airflow from the front of your neighbours house, along the party wall, then out of the back of your neighbours house.

    Solid insulation cant be dropped down the cavity as theres wall ties bridging the cavity to hold the inner and outer leaves together. Even if you could get solid insulation into the cavity its likely to be next to useless as it needs to sit tight against the inner leaf without gaps. If theres gaps there will be draughts that will just blow out most if not all of the warmth that the insulation is trying to trap.
    • CommentAuthorRobL
    • CommentTimeOct 1st 2020
     
    I have heard on and off about aerogel granules being considered for cavity walls. They're just ridiculously expensive, at £50/litre(link). I accept that there's probably a volume discount, but it seems likely the meagre 50mm cavity in our 4bed house would then cost >£100k. While aerogel might be a brilliant insulant, it can do nothing to improve the thermal bridges that are all too common in any unfilled cavity walled house, for which as Tony says, you ideally need EWI (after CWI, otherwise warm air leaks up the cavity). We had thermal bridges (non CWI) around doors, windows, chimney, wood/upvc slats, below dpc, cavity closer (mostly missing). All told they probably amounted to as much loss as through the CWI.

    Pic of house? Single roofline, or any chance of water leakage from roof between houses, down the party wall cavity?

    We had CWI years ago. We went with glass wool, as EPS beads can make PVC elec cables brittle, and ours are routed in the cavity ('63 build). No issues with CWI, and I think unless you're in a rainy area, it's generally trouble free. Now we're doing EWI :-)

    Some regions of the country have too much "wind driven rain" for full fill CWI to be recommended in a brick cavity. There's a map in the link, London is ok according to:
    http://nhbccampaigns.co.uk/landingpages/techzone/previous_versions/2010/Part6/section1/appendix.htm

    aerogel expensive link:
    http://www.buyaerogel.com/product/enova-aerogel-ic3100/
  1.  
    IMO wind driven rain won't be a problem if EWI is put on after the CWI. The EPS, adhesive and thin film render just won't allow rain anywhere near the brickwork
    •  
      CommentAuthordjh
    • CommentTimeOct 1st 2020
     
    Posted By: Peter_in_HungaryIMO wind driven rain won't be a problem if EWI is put on after the CWI. The EPS, adhesive and thin film render just won't allow rain anywhere near the brickwork

    +1 IMHO too.
    • CommentAuthorbxman
    • CommentTime3 days ago
     
    Wacky idea may be !

    If you can fit EWI, how about filling the cavities with grout you will then be achieving some mass and would stop air movement within the walls .
    • CommentAuthortony
    • CommentTime3 days ago
     
    Eps beads for me, grout a bit too wet, likely to seep out under g/f and into f/f void, foam is an alternative.
Add your comments

    Username Password
  • Format comments as
 
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press