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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.

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    • CommentAuthorOsprey
    • CommentTimeDec 13th 2024
     
    As part of upgrading my 1920s property, I have planned an extension. Over a year ago, I fixed on using EPS beads for a full (150mm) cavity fill on the extension. This after reading of the variable standard installation of batts/solid insulation, dirty cavities, rain etc, and posts favorable to EPS beads by several contributors. (my architect was originally going with 100mm cavities (half filled PIR) and 50mm Insulated plasterboard)

    As I am now planning the building schedule in detail, is this approach still appropriate? The exterior walls will be rendered.
    • CommentAuthorrevor
    • CommentTimeDec 14th 2024
     
    I would consider 150 mm cavities with 100mm PIR. It will be a pain to fix things to the wall going through 50mm insulation. Foundations will be 50 mm wider so that is an extra cost but get back as rooms will be that bit bigger than would have been otherwise. Running power cables will be a hindrance and extra care needed. Choice of render important avoid monocouche they dirty very easily Sto and Alumasc are much better as have self cleaning properties. I personally would not fil the cavity. I asked my BCO about doing this and was warned off as whilst an approved system he had seen many failures. Good luck.
  1.  
    I would do solid block, porotherm or alike (250mm if single floor 300mm if you ever want + 1st floor) then EWI to what ever U value you want.
    • CommentAuthorOsprey
    • CommentTimeDec 15th 2024
     
    Thanks both.
    revor - yes the problem of fixings with IWI is part of the reason I rejected it. But it was 100mm partfill cavity with 50mm IWI, or 150mm cavity - so no gain in room area. Had BCO seen failures of full-fill cavity, or EPS beads? I have not managed to find any real problems with EPS bonded beads: I have the 50mm cavities filled in the old part of the house last year. I am told that in Germany (son lives there) that they are recommending that 1980's built houses with partial filled cavities have the 'gap' filled with EPS beads to upgrade the insulation levels.

    Your comment on render is interesting - that's exactly one of my concerns. I have seen so many 'dirty' looking buildings. Any ideas on finding a good installer for the products in the South UK?

    Peter_in_Hungary - thanks, but I think prefer having a cavity even if filled!
    •  
      CommentAuthordjh
    • CommentTimeDec 15th 2024
     
    Posted By: OspreyPeter_in_Hungary - thanks, but I think prefer having a cavity even if filled!
    Is there a specific reason for that that you can express, or just a general feeling? (says the man living in a lime-straw-lime house who isn't concerned about the lack of a cavity :cool: )
    • CommentAuthorbxman
    • CommentTimeDec 16th 2024
     
    PiH has the answer you will get the benefit of the thermal mass with his recommendation
  2.  
    Apart from thermal mass benefits it is much easier to get a quality build with single block, no chance to cut corners with the cavity insulation by leaving gaps and not placing properly against the inner skin, no skimping or improper placing of wall ties and no mortar snots bridging the cavity.
    Edit to say also single block is quicker (= cheaper) to build
    • CommentAuthorOsprey
    • CommentTimeDec 17th 2024
     
    I am sure PIH is correct, but am being conservative on this. Neither I, builder nor architect has experience with that approach (nor 150mm full fill EPS beads either, but its more in their comfort zone. I would also fear resale value if the extension construction method was radically different to the rest of the house.
    • CommentAuthorMike1
    • CommentTimeDec 17th 2024
     
    Posted By: OspreyI am sure PIH is correct, but am being conservative on this. Neither I, builder nor architect has experience with that approach... ...I would also fear resale value if the extension construction method was radically different to the rest of the house.

    Almost all buildings had solid walls until the 1920s, so they're not exactly radical, even if insulating them externally only started following the 1970s oil crisis (the same time as cavity wall insulation). It's a system that's widely used in almost all of Europe. Mainly because, outside the British Isles, cavity walls are rare (except in Belgium, the Netherlands & Denmark).

    In the UK, wall insulation wasn't widely adopted until the Building Regs mandated it in the 1990s, and as Peter implies, it's these that are tricky to get right, with a consequently higher risk of them going wrong.
    • CommentAuthorrevor
    • CommentTimeDec 20th 2024
     
    Posted By: Peter_in_HungaryApart from thermal mass benefits it is much easier to get a quality build with single block, no chance to cut corners with the cavity insulation by leaving gaps and not placing properly against the inner skin, no skimping or improper placing of wall ties and no mortar snots bridging the cavity.
    Edit to say also single block is quicker (= cheaper) to build


    Whist this has merit one must not discount cavity wall construction. We went down that route with our refurb and extension of our circa 1750's farmhouse. I worked with the bricklayer every day and I would install the insulation. We did get issues but not of our making and that was to do with the insulation. I had bought 100 mm PIR tongue and grooved boards and early on found they were not fitting together properly a number were tapered and ends not square so left gaps on the joints. Had to stop build as I had to wait for replacements. If a builder had been doing the job do you think for one moment they would have stopped work, no way, cost them money they would have carried on and that is where a lot of issue is. I have a builder friend who helped me to get me started and he said that if he has problems with materials he will try and replace but if it means stopping the job he will carry on and do the best he can with what he has got. He cannot be paying his men when not working.

    The plan with the stone built structure was to externally insulate and render. I went to look at a job similar to what we planned and fortunately we had had very heavy rain, The gable end of the house we went to view was soaking wet and you could see the joins outline of the boards. We decide not to go down that route so we externally levelled the wall with lime render battened out and cross layered 2 x 50 mm board left a cavity and cedar clad. A cavity is a saviour where we are, cat 4 weather exposure.

    Posted By: Mike1Almost all buildings had solid walls until the 1920s,


    Don't know when cavities were first used in construction but our last house late Victorian semi built 1898 had cavity.
    •  
      CommentAuthordjh
    • CommentTimeDec 20th 2024
     
    A drainage plane is far more important than a cavity for wind-driven rain protection. That is a waterproof layer on the outside of the main structural wall, either with a small cavity or some textured material in front of it to allow water to drain down, and then some kind of wind-stopping layer at the outside. The outermost layer can be anything from a brick wall, through a solid timber wall to a hit-and-miss timber construction with a (air pressure) balancing space behind it. [I investigated the subject when we built in case I needed to add extra protection to our lime-rendered walls.]

    Cavities were known about from very early times and started to be used in late Victorian times especially in exposed places, but were only widely adopted during the 1920s.
  3.  
    ''Don't know when cavities were first used in construction but our last house late Victorian semi built 1898 had cavity.''

    Yes, mine from the early 1890s has a 'proper' (circa 2 inch) cavity, though a lot of it is full of rubble at the bottom and HUGE amounts of up-to-130-year-old bird-nesting-material in the upper part.

    The other side of this is how long solid walls went on. Until about 2013 the latest solid walled property I had seen was in S. Yorks, from 1939. Then in 2013 I met the resident of a detached house in Nottinghamshire. Their whole estate was built of 9 inch solid brick in the 1950s, and I have since learned of several other estates in Nott'mshire built the same in the same era.
    • CommentAuthorMike1
    • CommentTimeDec 21st 2024 edited
     
    Posted By: revorDon't know when cavities were first used in construction but our last house late Victorian semi built 1898 had cavity.
    Like most innovations, it takes a while for them to spread. Just looked it up and Historic England say that the first experiments were in the 'early Victorian period' - so around a century before they caught on.

    It seems to have taken longer in London where "The London Building Byelaws of the early 1920s made it compulsory for one leaf to be a full brick wide and this may be part of the reason why relatively few cavity walls were built in London at this time."

    It goes on to say that "the use of cavity wall construction became increasingly common particularly for the house building boom of the inter-war years where developers saw its economic advantages over solid wall construction."

    The article has some interesting illustrations of the what they did before the invention of the metal wall tie:

    https://historicengland.org.uk/images-books/publications/eehb-early-cavity-walls/

    Posted By: Nick ParsonsThe other side of this is how long solid walls went on. Until about 2013 the latest solid walled property I had seen was in S. Yorks, from 1939. Then in 2013 I met the resident of a detached house in Nottinghamshire. Their whole estate was built of 9 inch solid brick in the 1950s, and I have since learned of several other estates in Nott'mshire built the same in the same era.
    Interesting too!
  4.  
    When I was living in England one of my houses was a old gate house (cottage) built about 1830. This cottage was built to match the manor house and had cavity walls with 3" cavity with substantial cast iron wall ties with a large bulge in the centre as a drip point. The mortgage surveyor (valuer) called it 9" solid wall construction 'cos he didn't bother measuring anything and the outer skin was of flemish bond with snapped headers.
    (On his recommendation the mortgage co. also insisted on a chemical injection DPC despite it having a slate DPC. whereas the actual problem was a leaking gutter and down pipe Grrr.)
  5.  
    (On his recommendation the mortgage co. also insisted on a chemical injection DPC despite it having a slate DPC. whereas the actual problem was a leaking gutter and down pipe Grrr.)

    Oh, thank God those days are largely gone. Common-sense seems to be more common now ('Address the damp' rather than 'Full PCA damp-proofing'). The worst thing was when they insisted on a DPC when *it wasn't damp*!! Madness and such a waste of time, money and effort (not least the effort of undoing the incorrectly-applied work.
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