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    • CommentAuthordovecote
    • CommentTimeJan 29th 2012
     
    I am plumping for 80mm phenolic EWI on a 1960s block & brick cavity wall, but have come up against some questions.

    First is that there are a couple of roof slopes against adjacent walls with lead flashings. I am recovering the roof also and had assumed that the EWI & render would go back on first and the new flashings onto that. But the installer says no - they want the roof tiles to go on first, flashings onto the existing brickwork - then EWI over that, leaving a narrow 'channel' between the underside of the EWI and the topside of the roof tiles. Thoughts on this - possible thermal bridge?

    Second, I am replacing all my windows. The installer suggested that I put the new windows in flush with the existing external brick work and the EWI can overlap onto the frame - I can make the frames of the new window a little wider the compensate. Logistically this makes life a lot easier, but will this work safely? I was going to go for good quality softwood frames - should I consider something like an aluminium frame with its own built in insulation to avoid a thermal bridge?


    As an aside the cavity is filled with on-style foam insulation - not sure whether to suck this out or not.

    What is meant by instatntial condensation & dew point with respect to EWI?
    • CommentAuthorpmagowan
    • CommentTimeJan 29th 2012 edited
     
    I have the same issue in almost all respects. I am with you for number 1 point. I don't like the thermal bridge and so plan to flash on to the external wall insulation. My plan had been to tack flashing to the insulation and then render over this.

    Re the windows. I have already started boxing them out into the insulation layer to avoid thermal bridging. I am also supporting them on a layer of insulation so that they are not in contact with masonry. I am doing 200mm of plat EPS though so have more room. Overlapping on the frame is a good idea.

    Re the cavity wall. It is best for all the insulation to be external. This means that the mass of the walls is internal and once heated will buffer any changes in temperature from e.g solar gain, door being opened etc. Interstitial condensation occurs because your cavity wall insulation isolates part of the wall on the cold side. Once it is below a certain temperature then the warm humid air from inside your house will condense and water will form where the dewpoint is. If all the insulation is outside then everything is fine as the whole wall is warm and there is no issue of condensation.

    This is all as far as I know from my research but may be wrong. Others with more knowledge will be along shortly
    • CommentAuthortony
    • CommentTimeJan 29th 2012
     
    I too would put the windows in the insulation layer, oversized compared to the openings by say 20mm all round to loose a bit of frame and enlarge the glass areas (new windows generally give reduced glass area)

    I would carry the EWI down below the roof-line into the presumed loft? Then do the flashing (or secret gutter etc)to it before render
    • CommentAuthorpmagowan
    • CommentTimeJan 29th 2012
     
    Or if you pt on ERI (external roof insulation) then you could link the two together.
    • CommentAuthoraa44
    • CommentTimeJan 29th 2012
     
    Just don't do what they did here a couple of months ago. There is a house nearby that was being upgraded with EWI. At the same time they decided to remove the chimney. The chap who was dismantling the chimney found removing it brick by brick too slow so he put a rope round it and tied the other end to his pick up truck. Rumour has it that as well as the EWI, they also had to rebuild half the gable end.
    • CommentAuthorJanitor
    • CommentTimeJan 29th 2012
     
    Posted By: aa44The chap who was dismantling the chimney found removing it brick by brick too slow so he put a rope round it and tied the other end to his pick up truck.

    These people walk among us...

    :bigsmile:
    • CommentAuthordovecote
    • CommentTimeJan 30th 2012
     
    pmagowan, tony - thanks - useful comments

    I think I will look at doing the flashings same way as you.

    Am a bit stuck with the windows though - not much scope for them being in the insulation layer with only 80mm to play with - I still want a decent depth of reveal. But what is not clear to me is what the issue is as the existing windows sit on the same brick work - does adding EWI cause an issue?

    In terms of padding the frame with insulation - what do you use?
    •  
      CommentAuthorfostertom
    • CommentTimeJan 30th 2012
     
    Posted By: dovecotewhat is not clear to me is what the issue is
    It's because the window frame remains in contact with the masonry. The latter is at room temp, and conducts direct thro the wood frame to outside air. If the frame is moved outboard, there's no such direct contact.

    As you say, you're stuck if using such thin insulation. Any gd reason why you're not using twice as thick/half the price/breathable EPS?
    • CommentAuthorpmagowan
    • CommentTimeJan 30th 2012 edited
     
    As Fostertom says the problem is thickness. I am going for 200mm EPS 70 platinum which gives me a good depth to sit the windows in. Also with the boxing sitting on insulation rather than mosonry another cold bridge is fixed. The best way to work it out is to draw a cross section of your window, insulation, wall setup. Then colour the wall to the inside of your insulation red, the window and frame and internal air can be orange. Now draw little arrows from the red side to the outside trying to follow the shortest paths. Assume that all orange is 1/5 the distance shown on your scale. You will then find that the cold bridges (shortest arrows) are all around the frame and glass. You then need to work out ways of reducing these, the best of which is more insulation. This is simplistic but gives a reasonable idea and I like colours!:wink:

    There is a computer programe that does this properly but it ends up looking like a confused rainbow.
    • CommentAuthordovecote
    • CommentTimeJan 30th 2012
     
    fostertom, pmagowan,

    I went for 80 phenolic because I didn't have the eves depth for anything thicker without it look very odd.

    So I understand - if I were keeping the existing windows, which currently sit on the external brick skin of the cavity, and then added EWI without moving the windows, would I end up with an issue that I did not have before or just not the best I could have? Or is it more subtle in that what was a cold external skin becomes a warm interior skin? If the latter then what are the effects - heat loss or active condensation where there was none before?

    What are the options for padding the window frame with insulation - same phenolic? Or are there windows with built in thermal decoupling.
    • CommentAuthorpmagowan
    • CommentTimeJan 30th 2012
     
    I think there are a number of things (all in my opinion of course). Ideally you would do the roof as well, extending the eaves. This allows improved air tightness too. Obviously this increases cost. One of the problems is, increasing the insulation but leaving gaps creates cold spots where condensation will form. A little like it does on single glazed windows. I presume this effect would be more concentrated if the insulation system was working well. The other thing is just the reduced overall effectiveness of the system compared to an ideal installation. Essentially everyone on here is likely to encourage you as close as possible towards the theoretical ideal (bearing in mind there are multiple solutions).
    You can get windows which have a thermal break in them. They are more expensive. I am placing my frames inside a ply box which will sit on insulation which in turn sits on the wall. This reduces the (biggest i think) thermal bridge between the massonry and the frames (both good conductors). The outside of the frame will be partially overlaped with insulation as will the inside. So the little arrows will only be able to go directly from the air through a thin rim of frame to outside (and through the glass of course). This is as good as I can reasonably get without cutting the frames in half and putting a thermal break in the middle.
    •  
      CommentAuthorfostertom
    • CommentTimeJan 30th 2012 edited
     
    Posted By: pmagowanYou can get windows which have a thermal break in them.
    which work in the inboard-outboard direction; what we're saying here is heat transfer crosswise to that, from outer perimeter of frame (in contact with masonry reveal) inward to the joint line between fixed frame and opening sash; and/or from frame perimeter turning outboard to the window's outer face.
    • CommentAuthorpmagowan
    • CommentTimeJan 30th 2012
     
    Yes Fostertom but that is mostly resolved by laying the frame box on insulation.
    • CommentAuthordocmartin
    • CommentTimeJan 30th 2012
     
    Dovecote,
    when I planned to use 75mm phenolic I was surprised to find that it was not readily available, 3 yrs ago.
    60mm K5 EWI was the thickest size stocked at several large distributors. The situation was the same last year when I started to plan another job. Apparently, I was told, orders have to be in place for several hundred m2 before the best known manufacturer will run off a batch.
    Have you found a source of 80mm?
  1.  
    Hi Dovecote, You might find some useful info here about a renovation we did in Ireland http://www.viking-house.co.uk/passive-house-renovation.html
    • CommentAuthordovecote
    • CommentTimeJan 31st 2012
     
    Hi docmartin

    I have had no difficulty in finding 80mm phenolic - but as part of a EWI package provided by an approved installer of Wetherby, Permarock and the like. My project is 200 sqm of wall. One installer mentioned that phenolic board was readilly available at most big merchants, but I did not think to ask after the thickness.

    dovecote
    • CommentAuthordovecote
    • CommentTimeJan 31st 2012
     
    Viking House - thanks for your info - interesting reading. Did you do the dew point calcs yourself or get an energy assessor in?

    Also interested in how you mounted the windows - by the looks of it they partly rest on the blockwork, but did you insulate between the frame and the blockwork and then overlap the EWI over the outward facing frame?
    • CommentAuthordovecote
    • CommentTimeJan 31st 2012
     
    pmagowan - thought I had posted this question last night but can't see it - so must have got lost on the ether.

    Basically, I am curious as to whether the whole window frame (including ply cladding) sits in the EWI layer or is it partly resting on the blockwork (with insulation between the ply and the blocks)?

    What are your thoughts on going below the DPC as per Viking House design - the simulation looks convincing.
    • CommentAuthordocmartin
    • CommentTimeJan 31st 2012 edited
     
    Dovecoat,
    will your phenolic EWI board have a fibre glass sheathing both sides? When this is removed K5 EWI has a rather friable consistency. On the other hand the bond to basecoats is excellent; the somewhat smooth appearance of EPS has always worried me in this regard.
    Apart from the peculiar hollow sound when knocked, the final result of K5, fibreglass mesh/basecoat and JUB acrylic seems to be very robust.
    Martin.
    • CommentAuthorpmagowan
    • CommentTimeJan 31st 2012
     
    Dovecot, the ply board boxing is in order to extend the frames so that the main body can be in the insulation zome while a small amount of ply is in the massonry zone. So yes, my ply is resting on 'the blockwork' but with an insulation board between it. I used 80mm (i think) PUR (i think) for the first window for a test. It seems to be working well (still in the no-glass stage) and the insulation is holding it in place with the help of squirty foam. I will have less ply up the sides but also less insulation. Essentially my windows will be completely isolated form the non-insulated structure and will stand alone as far as their overall u-value goes.
    • CommentAuthordovecote
    • CommentTimeJan 31st 2012
     
    Thanks pmagowan.

    docmartin - the phenaolic slabs are faced with "plain glass tissue", which means fibre glass I guess. Did you have any particular standard of mesh? Permarock offer a 'standard' and extra robust versions.
    • CommentAuthorTimSmall
    • CommentTimeJan 31st 2012
     
    Posted By: pmagowan
    Re the cavity wall. It is best for all the insulation to be external. This means that the mass of the walls is internal and once heated will buffer any changes in temperature from e.g solar gain, door being opened etc.


    Be careful with this bit... I think your statement is only valid if your cavity ends up being pretty much completely air-tight from the outside (it probably isn't). I suppose you could try and use a blower (extractor fan would do) and smoke sticks or smoke machine etc. to try and ensure your cavity is air-tight prior to fitting the EWI...



    With 200mm of EPS outboard, you are probably best off full-filling your cavity with something like EPS bonded beads.

    I recently had a quote for £99 for having 'platinum' bonded EPS full-fill on a 3-bed 20s semi (70mm cavity) (plus £1700 for removing the partial fill of white wool first - they said that they'd need to do it to make sure it was done properly, and insisted that it was impossible with out 'professional tools' I said 'no thanks' - BTW, they gave me the £99 figure before they knew about the white wool, so it wasn't some sort of loss-leader).

    If your cavity is at all leaky, then you will risk thermal bypass stealing all the heat from your masonry, especially when it's windy. Icynene might be even better in this respect.

    In general, you don't need much EWI to ensure that interstitial condensation doesn't happen. For vapour-open insulation materials, I've seen a figure of a minimum of 25% the thermal resistance of the wall being in the external insulation order to prevent interstitial condensation. 50% for less vapour permeable...

    Tim.
  2.  
    <blockquote><cite>Posted By: dovecote</cite>Viking House -Interested in how you mounted the windows - by the looks of it they partly rest on the blockwork, but did you insulate between the frame and the blockwork and then overlap the EWI over the outward facing frame?</blockquote> Yes that's how we did it, have a look here http://viking-house.co.uk/passive-windows.html
    • CommentAuthorborpin
    • CommentTimeJan 31st 2012
     
    Posted By: Viking House
    Posted By: dovecoteViking House -Interested in how you mounted the windows - by the looks of it they partly rest on the blockwork, but did you insulate between the frame and the blockwork and then overlap the EWI over the outward facing frame?
    Yes that's how we did it, have a look herehttp://viking-house.co.uk/passive-windows.html" rel="nofollow" >http://viking-house.co.uk/passive-windows.html
    Seen those before and the windows just seem to be sitting on the insulation. What holds them there? Brackets back to the frame?
    • CommentAuthordocmartin
    • CommentTimeJan 31st 2012
     
    Dovecote,
    the heavier weight mesh was chosen; sorry I do not have the details available.
    Regards, Martin.
    • CommentAuthordovecote
    • CommentTimeFeb 6th 2012
     
    Folowing question - soffit boards - should you put the EWI and render on first then fit the soffit boards back or should you apply the EWI & render with the soffits in place, so that the EWI ends at the underside of the soffit board?
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