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Green Building Bible, Fourth Edition
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    • CommentAuthorCranbrook
    • CommentTimeAug 12th 2020
     
    Currently looking in to ideas for a possible upcoming extension and would like to consider an insulated raft, especially as I've never done one that's insulated before.. also, as the extension will be single storey with a vailted roof, I'd like to consider using 140mm blocks (as mentioned on a different thread with reinforcement every other course) covered with eps and then a silicone render... Can anyone give me any pointers with this proposition?
    • CommentAuthorGreenPaddy
    • CommentTimeAug 12th 2020
     
    Look at this building regs link BRegs Part C - page 31 specifically

    https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/431943/BR_PDF_AD_C_2013.pdf

    Minimum thickness for solid walls 215mm in light weight agregate. No doubt other routes are possible, but you need to demonstrate that to your BCO.

    Light weigh units are also much better for the construction guys, who end up with knackered forearms and wrists by the time they're 55 years old, working with dense 7N blocks.
    • CommentAuthorjamesingram
    • CommentTimeAug 12th 2020 edited
     
    Above appplies to areas of 'severe' exposure so depends on location.
    Done the 140mm solid wall with EWI a few times , not on a raft foundation though
    as long as the wall isnt above a specific height or length it complies with reg
    A1/2 2C6
    "solid walls constructed of coursed brick or blockwork should be at least as thick as 1/16th of storey height."
    thereforw 2.4m/16=150mm


    table 6.33 suggest 190mm minimum heights <3.5m and lengths <12m
    but...
    if you adhesive and mechanically fixing 200mm eps to this its also easy to sell the fact that this will give additional rigidity to the wall. you're actually building a walls 340mm thick
    (360+ with plaster and thincoat external finiish) from one way of looking at it.

    I've got 3 BCOs onside with this before.

    I've used 140mm fibrolite as they're easier for working with and give a good plaster key.
  1.  
    heres a few drawings I use to show BCO at start of 'building notice' job.
    I just do EPS down to footing top now
      floor to wall detail.jpg
    • CommentAuthorjamesingram
    • CommentTimeAug 12th 2020 edited
     
    a rather confusing roof to wall detail :bigsmile:
      wall-roof junc2.jpg
  2.  
    if you can get hold of an old copy of the AECB silver standard they show the EWI solid wall detail drawings far better.
    • CommentAuthorgoodevans
    • CommentTimeAug 12th 2020
     
    Posted By: CranbrookCan anyone give me any pointers with this proposition?
    Yes - the only route is to use an Engineer - if you have large lintels or have any other use for structural calcs - tag this on to the commission.

    Structural engineers are good value for money (it is a strangely low paid profession - I went into computing with my degree in civil engineering) - just being able to use 140mm blocks saved the fees of the engineer for my build.

    If you make it simple for the engineer and ensure no wall is longer than around 5 meters without lateral bracing (a right angle or "T" junction when looking down on plan) you should be able to avoid the use of "wind posts" and the calcs associated with those. Whisper me if you would like more specific advice or my engineer details (no site visit should be necessary).
    • CommentAuthorCranbrook
    • CommentTimeAug 12th 2020
     
    I like the look of that James

    Is there any way to eliminate cold bridging at the junction between footing and block?

    Also, with the fibrolite, when you say good plaster key, I assume you still have to render first?

    What do you cover the eps with at plinth level?
    • CommentAuthorgoodevans
    • CommentTimeAug 12th 2020
     
    Just crossed with James - I had gable ends so needed to go up 6.5m - that may be why I needed the engineer.
    • CommentAuthorCranbrook
    • CommentTimeAug 12th 2020 edited
     
    Posted By: goodevans
    Posted By: CranbrookCan anyone give me any pointers with this proposition?
    Yes - the only route is to use an Engineer - if you have large lintels or have any other use for structural calcs - tag this on to the commission.

    Structural engineers are good value for money (it is a strangely low paid profession - I went into computing with my degree in civil engineering) - just being able to use 140mm blocks saved the fees of the engineer for my build.

    If you make it simple for the engineer and ensure no wall is longer than around 5 meters without lateral bracing (a right angle or "T" junction when looking down on plan) you should be able to avoid the use of "wind posts" and the calcs associated with those. Whisper me if you would like more specific advice or my engineer details (no site visit should be necessary).


    Yes structural engineers are invaluable, and yes they are definitely good value for money, trying to get mine to send me an invoice alone is like getting blood from a stone. That being said, my engineer is winding down and isn’t interested in keeping up to speed with newer schools of thought, hence the reason I’d like some information before getting him to do the calcs
    • CommentAuthorCranbrook
    • CommentTimeAug 12th 2020
     
    Posted By: goodevansJust crossed with James - I had gable ends so needed to go up 6.5m - that may be why I needed the engineer.


    I’d be keen to have a gable to enable me to have a vaulted ceiling..
    • CommentAuthorgoodevans
    • CommentTimeAug 12th 2020
     
    Posted By: CranbrookIs there any way to eliminate cold bridging at the junction between footing and block?
    This is typically a problem area - you need structurally strong units that are good insulators - with the insulation doing down to the footings on the outside to mitigate the heat loss and the damp environment I would keep to blocks and know you have done your best.

    Have a look at your door threshold details - supporting the threshold can be tricky - it has to overhang the eps below. Plan ahead here - in then end I ended up with solid block walls under the thresholds with a massive thermal bridge. Given my chance again I would have has a small section of full fill cavity under the threshold with a small thermal bridge under each jamb.
    •  
      CommentAuthordjh
    • CommentTimeAug 12th 2020
     
    Posted By: CranbrookIs there any way to eliminate cold bridging at the junction between footing and block?

    That's what the 'raft foundation' aka 'passive slab' does, of course. There is no thermal bridge with such a foundation and a single block wall with EWI. AS an alternative to conventional cement blocks, you could also consider Poroton-type honeycomb clay blocks as widely used on the continent, or even Durisol blocks, which can be DIY.

    Compacfoam or similar can be very useful at thresholds.
    • CommentAuthortony
    • CommentTimeAug 12th 2020
     
    It is all in the design, it is possible to design out thermal bridges. Passive house have published a very useful technical guide, I have it if you want to borrow it
    • CommentAuthorjms452
    • CommentTimeAug 13th 2020
     
    Posted By: Cranbrook

    Is there any way to eliminate cold bridging at the junction between footing and block?


    these worked nicely in our single skin EWI porch (building control exempt) and brickies got on with them ok.

    https://perinsul.foamglas.com/en-gb
    • CommentAuthorjamesingram
    • CommentTimeAug 13th 2020 edited
     
    Posted By: CranbrookI like the look of that James

    Is there any way to eliminate cold bridging at the junction between footing and block?

    Also, with the fibrolite, when you say good plaster key, I assume you still have to render first?

    What do you cover the eps with at plinth level?


    AECB suggest a ultra lightweight block below ground to reduce Therm.bridge ,but this would get wet so not make much difference surely?

    'Good key' for internal wet plaster , and external EWI adhesive if used

    I use the thin mesh coat render rubbed up to a good finish below DPC then paint it black and a plastic drip bead to seperate the above and below dpc height
    Also I dont bother running DPC through EWI EPS anymore
    above DPc Its and silcon thincoat troweled finish

    re gable end height , it does say that rule (H/16) applies 'per storey'
    if a tie is used above 2.4m I presume you can just go up another 2.4m

    the jobs ive done with this method have all been single storey rear extension 3-4m out / 6-8m width,
    vaulted roofs up to just below 1st storey windows. BCO hasnt questioned gable infill height.
    if you think about it, its only a small triangle section, connect via wall starter to the existing building and strapped to the roof via gable straps using the standard method (all inside the tea cosy EWI layer)

    Windows and doors I make a cement board box all 4 sides (aquaboard) and sit the units out into the surronding EWI (i used ply in the past but since looking into issue re fire travelling in EWI a clear fire break material makes more sense at this weak spot)
    I did this with some upvc sliding patio doors on one job and havent had and issue re movement in 9 years
    • CommentAuthorCranbrook
    • CommentTimeAug 13th 2020
     
    What thickness cement board do you use James?
  3.  
    •  
      CommentAuthorfostertom
    • CommentTimeAug 14th 2020
     
    So it's about fire spread, not fear of wet getting at ply or (as I've done it) OSB3?
    • CommentAuthorjamesingram
    • CommentTimeAug 14th 2020 edited
     
    Yes Tom , it seemed prudent to use this rather than ply .
    I use Upvc windows, as they are sitting into the EPS
    if for some reason they caught alight (say kitchen fire, ive seen melted upvc windows in such a fire) the cement board would be a bit more of a fail safe barrier against the eps than wood.
    internally the plasters and plasterboard reveals are doing the job , externally the class O mesh coat render.
    •  
      CommentAuthorfostertom
    • CommentTimeAug 14th 2020
     
    Yes, I guess we (or I) should up the game, even tho 2 or 3 storey EWI without a semi-resistant outer cladding to form a chimney cavity, is a totally different situation from multi-storey.

    I should specify Class 0 render and additionally consider flame retardant EPS - what do you think about the latter? More expense.

    A thought - if the render is Class 0, might be a danger that it would for a while at least form that semi-resistant outer skin rather than falling to pieces?
    • CommentAuthorjamesingram
    • CommentTimeAug 15th 2020 edited
     
    Yes i agree , small buildings with ease of escape are very different.
    I was under the impression any EPS boards for EWI already had flame retardant in.
    Apparently its a nasty chemical, I'm unaware whether it leechs out or off gases in any way so I guess issues only arise in manufacturing or post use disposal.
    I was also under the impression all the thincoat mesh render build ups where class O anyway.

    Once the fire broke into the ESP I could imagine the EPS (fr) melting back and the heat and flame travelling across in the structure underneath the exterior finish destroying the whole render system. Im am just offering a laymens guess though.
    • CommentAuthorjms452
    • CommentTimeAug 15th 2020
     
    Posted By: fostertom consider flame retardant EPS - what do you think about the latter? More expense.


    I like EPS for breathability but if fire is a concern I think phenolic is about the best low k value insulation.
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