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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorgravelld
    • CommentTimeSep 29th 2016
     
    EWI skirt insulation (my name for it, I'll change the title if there's a more commonly agreed one) is where EWI is applied from the DPM and down toward the foundations of a house.

    This is an approach at odds with many EWI installations, which terminate the EWI at the DPM, leaving a significant bridge.

    This is a subject I think is pretty important to retrofits and it's something I'd like to do in my own, so when @MarkyP said he was doing it I was interested. He said:

    Posted By: MarkyP
    in a nutshell - existing long bungalow with poorly fitted CWI to around 75mm thick with blockwork/rendered walls. Planning to fit an additional 100mm - 125mm (thickness limited by existing eaves overhang) of enhanced EPS (the grey stuff in the pic James posted above) then finish with a render coat. The pic above I'd seen before on other threads, planning to do the same and dig out down to top of footing and take EPS right down. I will take 125mm ESP down to DPC level, then maybe 100mm or 90mm below down to top of footing to allow a step/drip detail. Will use the slab method below ground to keep the rodents out. EPS will be adhesive fixed. EPS is cheap and I will be DIY fitting it and possibly DIY rendering it so I've decided to actually EWI the new extension while I am at it which is being built now with blockwork CWI walls. The EWI will help me address a bunch of limitations of the CWI including cold bridging by ties and catnic type lintels, and the various gaps in the insulation and huge mortar snots bridging the cavity left by the brickies. I did my best to check the cavity as they went along but I've no doubt there are a few undiscovered sins hiding in there. The archtitect, the brickies, the joiners, BCO - everyone, they all think I'm a bit bonkers doing this. I've had a mixed bag of quality in terms of the trades on the job but all of them without exception have no idea about detailing for enhanced thermal performance.


    My questions are:

    Is the drip detail important? If there was a French drain around would this not be enough?

    I am currently thinking about a loose fill EPS approach for the wall using trusses, boxing in a cavity and filling with bead. However, I don't want trusses to touch the ground for fear of rotting. So I either continue with the alternative 'standard' stick some board on the wall approach (my worries around sealing all interfaces probably matter less underground) or I work out something different to timber to use for the trusses... maybe a bit mad but I wondered whether concrete trusses and boxing in could be done?

    Did architect spec the work? I guess not, given what you said. If not, how did you spec it? How did you draw up the plans to present to whoever did the work?

    Were you concerned about digging to the foundations (or was this dug anyway?)

    How do you deal with existing drainage, e.g. gutter or soil pipe going into a drain?
  1.  
    pixs mentioned
      DSCF2253-12.JPG
  2.  
    and single skin EWI extension floor/wall detail
      floor to wall detail2.jpg
  3.  
    I dont think the drip or external dpc break is necessary as water is unlikely to wick up the EPS.
    It does however create a nice break and a darker colour below it is less likely to suffer from discolouring
    due to rain splash back etc.
    You could achieve it by just pinning a small drip bead on top of the eps at the required height and rendering it in
    running the mesh down on top it.
    • CommentAuthortony
    • CommentTimeSep 29th 2016
     
    I would rather see eps below dpc
  4.  
    yes, I do that now, easier to get hold off and cheaper and fine to use from discussions on here
    • CommentAuthorringi
    • CommentTimeSep 29th 2016
     
    Posted By: tonyI would rather see eps below dpc


    But check the water table, also if you put in a french drain, it must have somewhere to drain to. If you are on clay, it is likely to remain filled with water.
    • CommentAuthortony
    • CommentTimeSep 30th 2016
     
    It tends to be very dry near most houses, but even if there is ground water and the water table is high it would need to be pumped away as any soakaway would not work unless on a hill but then there probably wouldn't be a high water table.
    • CommentAuthorgravelld
    • CommentTimeSep 30th 2016 edited
     
    I thought the point of a french drain was to have some way at the bottom of diverting water into a proper drain?

    I think we are on clay. How do people go about surveying this type of thing?
  5.  
    Posted By: gravelldI think we are on clay. How do people go about surveying this type of thing?

    dig a hole where you want the drain/soakaway or what ever, (to the relevant depth) put some water in it and see how long it takes to disappear. Of course if the hole fills with water by itself then that a whole different game!
    • CommentAuthorgravelld
    • CommentTimeSep 30th 2016 edited
     
    Thanks. Assume you should do it at different times of year, and how quickly should it drain?
    •  
      CommentAuthordjh
    • CommentTimeSep 30th 2016
     
    Posted By: gravelldI thought the point of a french drain was to have some way at the bottom of diverting water into a proper drain?

    Into a soakaway or an exisiting waterway for preference (with permission)
    •  
      CommentAuthordjh
    • CommentTimeSep 30th 2016
     
    Posted By: gravelldhow quickly should it drain?

    There's a standard, I believe. Don't remember what it's called.
    • CommentAuthorPeterStarck
    • CommentTimeSep 30th 2016 edited
     
    Posted By: gravelldThanks. Assume you should do it at different times of year, and how quickly should it drain?


    There are details of the percolation tests in Part H.
    • CommentAuthorringi
    • CommentTimeSep 30th 2016 edited
     
    If your soil is clay, it will drain slower, but you can still have clay soil that is not very water logged. However as soon as you give the water somewhere to go that is easier then the clay, the water will take the easy option. Therefore a French drain can be a “water magnet”, not what you want next to your open cell insulation.

    You can get insulation designed to work however wet the ground is.
    • CommentAuthorgravelld
    • CommentTimeSep 30th 2016
     
    Thanks.
    • CommentAuthorBeau
    • CommentTimeOct 1st 2016
     
    Posted By: djh
    Posted By: gravelldI thought the point of a french drain was to have some way at the bottom of diverting water into a proper drain?

    Into a soakaway or an exisiting waterway for preference (with permission)


    Yep put ours into a grey water drain. On top of a hill and water table can get to within 200mm of ground floor level.
    • CommentAuthorgravelld
    • CommentTimeOct 21st 2016
     
    A thought when reading the other IWI/EWI thread after Wookey's post...

    Has anyone ever installed *just* skirt insulation, not alongside EWI? Just wondered what sort of details you would put in and how to make it future proof for tieing in to future EWI.
    • CommentAuthorwookey
    • CommentTimeOct 21st 2016
     
    Yes. RobL has done skirt-only. Using foamglass.
    • CommentAuthorgravelld
    • CommentTimeOct 21st 2016 edited
     
    • CommentAuthorRobL
    • CommentTimeOct 21st 2016
     
    Yes, I put in perimeter wall insulation, 'skirt only'. It's definately made the solid floor of our house warmer.
    I started using XPS, and have about a 3metre length using that. I quickly decided it wasn't easy use, and swapped to foamglass to do the rest. XPS bends and gives when you fit it, and needs to be pinned and glued well - better than I did it anyway. In contrast, foamglass was simple to fit - any wall imperfections - just grind the foamglass against the wall, and it wears away the corresponding bit of foamglass - then you get a perfect fit!
    It's been a few years since I've fitted it - and the XPS bent away at the top - I think its the earth shifting, changing the pressure behind it. It's easy to fix, but doesn't inspire confidence. In contrast, the foamglass needs no attention.
    I fitted the insulation a brick and a half below the dpc- thinking that one day we'd ewi. I intended to get commercial ewi 'one day', then fix the missing one and a half bricks worth of foamglass in place afterwards. We haven't done ewi.... yet.... I intended the ewi to overhang by at least 10mm.

    Foamglass is friable - if water gets into the open cell structure and freezes, it damages the surface. So it needs protecting. I made the top surface have a slope on it, so water would run off quicker. Then any of the exposed surface has bitumin painted on. And the bits that might get damaged have fake lead flashing stuck on. If we ewi, i'd put the lead flashing on all the way around at the bottom, it's easy, and it works pretty well.
    •  
      CommentAuthorfostertom
    • CommentTimeOct 22nd 2016
     
    V interesting wisdom. But Foamglas is v expensive isn't it? Compared to EPS anyway. Wd the low price of that, rather than XPS, have swayed yr judgement?
    •  
      CommentAuthordjh
    • CommentTimeOct 22nd 2016
     
    Posted By: RobLIf we ewi, i'd put the lead flashing on all the way around at the bottom, it's easy, and it works pretty well.

    How do you deal with the corners of the walls? We have the fake lead stuff around at slab level, covering the timber soleplates and the tops of paving slabs that protect the EPS of the passive slab. It all worked fine except that we never found a good way to make corner joints, so they are a bit of a bodge.
    • CommentAuthorgravelld
    • CommentTimeOct 22nd 2016
     
    Thanks Rob, so how does the top of the insulation appear? Don't suppose you could post a photo?

    I must admit if be disappointed leave the DPC. That's because when I thermal imaged my wall, the DPC is the worst bit, so it may be psychological. Also I thought heat loss would be worst where exposed to the air rather than below ground, although i also realise the surface area would be much less.
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