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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorSimonD
    • CommentTimeOct 25th 2020
     
    Hello,

    I'm a complete newbie to the forum. I've been building a house on my own and I've just got to the stage of ordering the windows. The fabric of the building is about 4/5ths orginal brick/brick, some block too, 1920s bungalow which is to receive 140mm of wood fibre EWI. The new first floor is 140mm timber frame filled with sheeps wool and an additional 50mm wool wrapped to the outside of the frame. Windows are not mega high performance 3g units but they come in at a u-value around 1 for whole window performance.

    I've been looking at the detailing for window installation and planning to fit the windows on the ground floor within the EWI, which means they'll sit only about 10-15mm out from the from wall. My initial thinking was to build a plywood box into the window opening and fix the windows to this using brackets - the window would essentialy be butted up to the box rather than framed by it - then fit the EWI and lime render to finish. As an option, I'd also been considering an alternative where I install battens to the outside of the masonry cavity wall and fix windows to this.

    As far as this goes, can anyone with experience help me choose the most appropriate approach and the pros and cons of each option with the EWI?

    With the timber frame, I've seen many opinions of how to seal up the windows once fitted. These frame will be extended out slightly from the main structure 140mm frame, but only by about 30-40mm in order to allow for the timber sills to extend 30 odd mm beyond the finished cladding.

    My question here is mainly down to sealing the window frame. I've seen so many opions, ranging from simply to use silicon sealant, to using external and internal tapes, to using compriband type expanding tapes to the outside etc. that it's rather confusing the make the choice.

    I've got an idea of how I might approach it but I'd again like to put this out to the forum to ask for some input, especially in regards to adequately insulating any remaining space between the frame rough openings and the window frame.

    I'm also curious as to whether I should use some kind of pan flashing along the bottom of the window frame?

    Hopefully I'm not repeating to many questions already asked on here!

    Many thanks,
    Simon
    • CommentAuthorSilky
    • CommentTimeOct 25th 2020 edited
     
    for what it's worth...

    I did plywood boxes of variable depths ( 17 - 25 cm ) thrown out from the wall. I had a timber frame structure on the roof gable and old masonry with concrete like window surrounds on the lower floors.

    I used an construction of 54 x 54 battens fixed to the building with either screws or frame anchors. I then projected out from these battens to position the uprights of the facade so that that the inner edges line up with the battens. I then fixed horizontals in the outer facade so that they line up with horizontal battens above and below the window. Finally I cut the plywood box and fixed the plywood onto the battens and the outer frame to form a complete box. ( My way is bottom full width, then sides sitting on the base to the top, then top piece between the sides ). I used 21mm marine grade ply but will reduce this to 15 or 18 for the next batch, expensive stuff. In the timber frame area I fixed the outside of the box to a membrane covering the entire roof ( including gable ). I sealed the joins of the plywood boxes with facade sealant. In the masonry areas I didn't have a membrane ( air tightness is meant to be internal plastering ) so I just use a facade sealant between the interior of the plywood box and the internal wall , these will eventually be taped and plastered / tiled over etc..

    That in itself is a lot of work, I was getting about 2/3 window boxes done each day.. lots of details and checking of measurements to align everything with the openings nicely. When done correctly it at least gives a good preperation for fitting the windows..

    Fitting the windows... you can tape to the plywood box both inside and outside. The windows were actually supported on metal brackets screwed back into the battens on the wall ( so screwed through the plywood and into the battens ). This also takes some planning to get the brackets the correct length. I could have screwed through the window frame and straight into the plywood and on into the outer frame but prefer to use brackets, less disruptive to the window frame and less change of distorting the frame, more flexibility of positioning and correcting..also takes more time of course

    Don't forget about planning height allowace for fitting sills below..The plywood box also gives you a good place to plan your waterproofing under the window. ( https://www.youtube.com/watch?v=MYtbplsubBM ).

    I used a spreadsheet, so I could put all my opening sizes and then calculate where to position the battens and the facade. In my case the boxes were actually bigger than the wall openings, so I had to plan that relationship very carefully so that the sash would sit nicely in front of the opening.
    • CommentAuthorCWatters
    • CommentTimeOct 25th 2020
     
    Make sure the sills project out far enough so the drip groove on the underside ends up in the in the right place after EWI and render.

    Some windows are available with different width sills.
    • CommentAuthorSimonD
    • CommentTimeOct 27th 2020
     
    <blockquote><cite>Posted By: Silky</cite>for what it's worth...</blockquote>

    Thanks, that's all very helpful indeed!
    • CommentAuthorSimonD
    • CommentTimeOct 27th 2020
     
    <blockquote><cite>Posted By: CWatters</cite>Make sure the sills project out far enough so the drip groove on the underside ends up in the in the right place after EWI and render.

    Some windows are available with different width sills.</blockquote>

    Thanks, got that one covered with the depth of sills ordered, but easily overlooked, especially with companies that don't include the sills in their main quotations! Why do they do that?
    •  
      CommentAuthordjh
    • CommentTimeOct 27th 2020
     
    Posted By: SimonDWhy do they do that?

    Probably because there are so many different variations. Timber, metal, with or without corners, stone, concrete, etc and an infinite number of widths & depths.
  1.  
    Posted By: SimonDespecially with companies that don't include the sills in their main quotations! Why do they do that?

    Because it reduces the headline price making comparisons more favourable for them
  2.  
    Posted By: SimonD1920s bungalow which is to receive 140mm of wood fibre EWI............... then fit the EWI and lime render to finish.

    I would be nervous about the wood fibre EWI with lime render. Any future cracks or failure in the render would allow moisture into the wood fibre which would not be able to easily get out and would be disastrous in the long term for the wood fibre.
    Is the original build cavity wall? and if so is it / will it be properly fully filled?
    •  
      CommentAuthordjh
    • CommentTimeOct 27th 2020
     
    Lime render is quite normal with woodfibre insulation underneath. It's seen as one of the 'biobuilding' options and complete systems are supplied commercially by several companies internationally.
    • CommentAuthorSimonD
    • CommentTimeOct 28th 2020
     
    Posted By: djh
    Posted By: SimonDWhy do they do that?

    Probably because there are so many different variations. Timber, metal, with or without corners, stone, concrete, etc and an infinite number of widths & depths.


    Posted By: Peter_in_Hungary
    Posted By: SimonDespecially with companies that don't include the sills in their main quotations! Why do they do that?

    Because it reduces the headline price making comparisons more favourable for them


    Apologies, I meant that as more of rhetorical question. The sensible companies I found read the window schedule and looked at the drawings, thus sensibly assuming the use of sills but asking the question re depth, mitre corners/welded corners etc. The less sensible ones just didn't include anything or added it as an optional extra buried in an installation quotation - so some of it clearly about giving a favourable headline price. One of the least sensible ones quoted for sills even after we'd had a telephone conversation where I'd told them my required sill depth was more than their max available sill depth.
    • CommentAuthorSimonD
    • CommentTimeOct 28th 2020 edited
     
    Posted By: Peter_in_Hungary
    Posted By: SimonD1920s bungalow which is to receive 140mm of wood fibre EWI............... then fit the EWI and lime render to finish.

    I would be nervous about the wood fibre EWI with lime render. Any future cracks or failure in the render would allow moisture into the wood fibre which would not be able to easily get out and would be disastrous in the long term for the wood fibre.
    Is the original build cavity wall? and if so is it / will it be properly fully filled?


    As per djh, the lime render on woodfibre is part of a developed ewi system, although it's not the thin coat system typically sold as a pack by the woodfibre company (e.g. like Baumit with Pavatex). I will be using a traditional lime putty render.

    Re the cavity walls, no, they're not filled. They're narrow and in terrible condition - lots of debris in there. Plus, given the house's age, the external ground level around the house is higher than the internal oversite so the cavities essentially extend below ground level - in wet weather this gets very wet.

    My solution to this is that I've sealed up the cavity - sole plate plus glulam ring beam over the top of the wall (there for the 1st floor timber frame), modified all the underfloor vents to close the cavity there etc. etc. I've also installed plinth insulation the inside and will be adding it to the outside of the house below dpc by at leat 200mm below the timber floor joists internally (broken and chamferred at dpc level too) All a bit of a painstaking job but given my research, I think the best option under the circumstances. It's not perfect but as it's all wrapped and plastered externally, the cons are minimised as far as possible and reduce the inherent risks of retrofitting cavity wall insulation. That's the idea anyway...
  3.  
    Posted By: SimonD
    Posted By: Peter_in_Hungary
    Posted By: SimonD1920s bungalow which is to receive 140mm of wood fibre EWI............... then fit the EWI and lime render to finish.

    I would be nervous about the wood fibre EWI with lime render. Any future cracks or failure in the render would allow moisture into the wood fibre which would not be able to easily get out and would be disastrous in the long term for the wood fibre.
    Is the original build cavity wall? and if so is it / will it be properly fully filled?


    As per djh, the lime render on woodfibre is part of a developed ewi system, although it's not the thin coat system typically sold as a pack by the woodfibre company (e.g. like Baumit with Pavatex). I will be using a traditional lime putty render.

    Re the cavity walls, no, they're not filled. They're narrow and in terrible condition - lots of debris in there. Plus, given the house's age, the external ground level around the house is higher than the internal oversite so the cavities essentially extend below ground level - in wet weather this gets very wet.

    My solution to this is that I've sealed up the cavity - sole plate plus glulam ring beam over the top of the wall (there for the 1st floor timber frame), modified all the underfloor vents to close the cavity there etc. etc. I've also installed plinth insulation the inside and will be adding it to the outside of the house below dpc by at leat 200mm below the timber floor joists internally (broken and chamferred at dpc level too) All a bit of a painstaking job but given my research, I think the best option under the circumstances. It's not perfect but as it's all wrapped and plastered externally, the cons are minimised as far as possible and reduce the inherent risks of retrofitting cavity wall insulation. That's the idea anyway...

    I understand that woodfibre with lime putty is used as EWI but I would always be nervous about any damp/wet getting to it. With something like EPS which is tolerant of both wet and damp these worries go away.

    The cavity sounds like a problem - it is always difficult to stop the gale going through - but it sounds like you have given it a good go. Have you drilled a few strategic holes into the cavity to see if there is still a cold wind in there?

    Can you lower the ground level outside - or put in a french drain (with an outflow) to mitigate the water table outside during wet weather?

    If you are wedded to woodfibre EWI what about using EPS for the first 1m from ground level as this won't care if it is a bit damp occasionally.
    •  
      CommentAuthordjh
    • CommentTimeOct 28th 2020
     
    Posted By: Peter_in_HungaryI understand that woodfibre with lime putty is used as EWI but I would always be nervous about any damp/wet getting to it. With something like EPS which is tolerant of both wet and damp these worries go away.

    Lime is pretty good at letting damp back out again once the source goes away. Woodfibre is hygroscopic and can buffer a lot of moisture without problems as long as it doesn't sit there for long periods. Both woodfibre and lime will let water drain down through them as well, albeit slowly. It is essential to protect the top of the construction and preferably have a good roof overhang.

    If you are wedded to woodfibre EWI what about using EPS for the first 1m from ground level as this won't care if it is a bit damp occasionally.

    Having said all the above, I do agree with this bit and especially for any insulation that is below ground level. I wouldn't use woodfibre or anything organic underground and the first two or three feet above ground certainly gets wetter than the rest of the wall due to splashback. We have 600 mm gravel to minimise splashback and our render on bales starts about 300 mm above (it varies a bit).
    • CommentAuthorSimonD
    • CommentTimeOct 28th 2020 edited
     
    Posted By: Peter_in_Hungary

    I understand that woodfibre with lime putty is used as EWI but I would always be nervous about any damp/wet getting to it. With something like EPS which is tolerant of both wet and damp these worries go away.

    The cavity sounds like a problem - it is always difficult to stop the gale going through - but it sounds like you have given it a good go. Have you drilled a few strategic holes into the cavity to see if there is still a cold wind in there?

    Can you lower the ground level outside - or put in a french drain (with an outflow) to mitigate the water table outside during wet weather?

    If you are wedded to woodfibre EWI what about using EPS for the first 1m from ground level as this won't care if it is a bit damp occasionally.


    Posted By: djh
    Lime is pretty good at letting damp back out again once the source goes away. Woodfibre is hygroscopic and can buffer a lot of moisture without problems as long as it doesn't sit there for long periods. Both woodfibre and lime will let water drain down through them as well, albeit slowly. It is essential to protect the top of the construction and preferably have a good roof overhang.

    Having said all the above, I do agree with this bit and especially for any insulation that is below ground level. I wouldn't use woodfibre or anything organic underground and the first two or three feet above ground certainly gets wetter than the rest of the wall due to splashback. We have 600 mm gravel to minimise splashback and our render on bales starts about 300 mm above (it varies a bit).


    Thanks both for the input on this and yes, the design incorporates all these things to what should be a sufficient extent.

    The hygroscopic nature of the woodfibre working in sync with the lime render to allow moisture to pass through the fabric is exactly why i chose to use it. Whilst I have looked at eps and it's 'breathable' characteristics, I'm not convinced of its ability as an ewi system to provide the same beneficial breathable wall system as the natural products.

    With woodfibre insulation it is recommended that the minimum height above ground is 300mm and there are details to deal with less height which I have to do in my case due to external ground level as we can't dig out too much due to the shallow foundations. The detailing in our case uses a gravel splash area in the area under and slightly away from the bottom of the woodfibre insulation. There is a plinth insulation extending down from dpc to below ground level externally using XPS insulation suitable for below ground use and rendering. There is a perimeter layer of insulation between the plinth and the lowest level of woodfibre at 30cm above ground. Internally the plinth insulation I'm using above the oversite is EPS. As we're backing into a hill, there are plans to dig a french drain somewhat like a moat around the house about a meter out from the foundations (in heavy rain we get a stream coming down the back steps to behind the house so I need to divert this with the drain).

    We do also have large overhang of roof (over 50cm around most of the roof but as much as 1m at the front in some parts due to the design) but with the nature of the building our ground floor ewi extends out from the 1st floor cladding. To protect this, I've formed some bespoke flashing using the metal standing seam roofing material left over from the roof installation with sufficient upstand behind the cladding, drip edge and slope. This will be doubled up with extra membrane underneath the flashing and above the ewi.

    I'm hoping that covers it...:smile:
    •  
      CommentAuthordjh
    • CommentTimeOct 28th 2020
     
    Personally I would use EPS rather than XPS since it is somewhat vapour open, cheaper, reduces the different types of insulation and apparently performs better in the wet underground.
    • CommentAuthorSimonD
    • CommentTimeOct 28th 2020
     
    Posted By: djhPersonally I would use EPS rather than XPS since it is somewhat vapour open, cheaper, reduces the different types of insulation and apparently performs better in the wet underground.


    That's a good point. EPS had been my default but I had been diverted towards xps when discussing it with a 'technical' rep at one of the insulation supplier I'd spoken to. Luckily I haven't bought this part of the system yet, so thanks for the heads up. I'll revisit the decision.
    • CommentAuthorSimonD
    • CommentTimeNov 10th 2020
     
    Posted By: djhPersonally I would use EPS rather than XPS since it is somewhat vapour open, cheaper, reduces the different types of insulation and apparently performs better in the wet underground.


    Posted By: SimonD
    Posted By: djhPersonally I would use EPS rather than XPS since it is somewhat vapour open, cheaper, reduces the different types of insulation and apparently performs better in the wet underground.


    That's a good point. EPS had been my default but I had been diverted towards xps when discussing it with a 'technical' rep at one of the insulation supplier I'd spoken to. Luckily I haven't bought this part of the system yet, so thanks for the heads up. I'll revisit the decision.


    Just thought it could be a useful reference on this one. I believe it was actually one of the woodfibre insulation manufactures who in their system detail provides for xps insulation to be used as plinth insulation below dpc and into the ground. I also spoke to a Kingspan technical rep, who recommended xps 'greenguard' as more appropriate than eps.

    However, exactly as you have suggested, there is mounting evidence that EPS probably does the job better overall below ground, so a good few quid saved there. Here's a link to a US article about the differences between the two below ground:

    https://mcsmag.com/grade-slab-building-insulation/

    I found a few other threads one the web supporting this general view.
    •  
      CommentAuthordjh
    • CommentTimeNov 10th 2020
     
    Posted By: SimonDxps 'greenguard'

    Hmm, well he would recommend that wouldn't he? :bigsmile: It seems to be wildly over-specified in terms of its load-bearing capability.

    In terms of underground longevity, the thing that convinced me about EPS was when I discovered it is used to build railway and motorway embankments. It can be cost competitive with aggregate apparently.
    • CommentAuthorSimonD
    • CommentTimeNov 11th 2020
     
    Haha, yes he would indeed. Perhaps he thought I'd be driving my digger over it :-)

    That's pretty impressive as an 'aggregate.'
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