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  1.  
    I’m looking for feedback from people who’ve had wood fibre exterior wall insulation done on their homes and how they’ve found it.

    I’ve been considering this for our old stone farmhouse in Devon with a lime render over the top. The house had a significant damp problem due to the walls being rendered with concrete render and the internal walls papered and painted. Water got in and couldn’t get out. We’ve removed all the old render which has dried out the house and it’s a completely different environment now. We’ve also made good many of the holes and leaks that were causing water ingress. Breathable EWI seems like a good option to keep the building healthy and damp free.

    We’ve also dug out and lowered the patio behind the house that was above internal floor level and dug the side of the house out as the ground was halfway up it. No wonder it was damp. Internally, the floors are concrete and will, one day, be dug out and replaced with underfloor heating along with replacing the middle floor which is like a roller coaster and strip off all the old failing plaster and replacing with lime plaster. Meantime we have storage heaters, an oil-fired rayburn and a woodburner. We’re several years away from renovating the interior and I’d love to get the exterior sorted and insulated so we can reduce our high energy usage. The renewal of the old woodburner and installation of a new one in place of the oil fired rayburn this summer will make a big improvement to that as we a regular supply of wood. Oh and I put 300mm of insulation in the empty loft which has improved comfort significantly too.

    We’ve been looking at Warmshell as one option along with other makes of wood fibre insulation. We’re about to have several old single glazed windows replaced with new oak double glazed ones and have been in discussions with the window manufacturers, a local company who’ve already done several windows and doors for us, about getting them made to be most compatible with EWI. The advice from warmshell is to go with an aluminium cill with up stands to prevent weather and water ingress better and reduce thermal bridging.

    Warmshell have been talking back and forth with our window company about how best to install the windows, although the window company are a little hesitant as it’s all new to them. Their main worry is the possibility of water ingress affecting the wood fibre insulation and wonder if an exposed Devon farmhouse might be better with internal insulation but that’s a huge other box of worms to consider. The farmhouse needs new windows and re-rendering so to me it seems EWI would be the best option.

    We would need to extend the roof to provide additional overhang for the walls as there’s almost no overhang currently, but that wouldn’t be too big a job. I'd also really like to find a company that can do this and be able to claim some of the ECO money to subsidise the cost a bit but haven't found anywhere yet that does so with this type of insulation.
    • CommentAuthortony
    • CommentTimeFeb 9th 2015
     
    Not that bright to use organic and potentially degradable insulation on the outside. Further a wild thickness would be needed to meet building regs part L1b.
  2.  
    Really? I thought wood fibre was ideal for this as it's breathable, at least that's what I'm being told by a few people. Also, 120mm would get us to regs apparently.
  3.  
    Having viewed a timber frame house that was externally insulated with wood fibre boards, I would have concerns over durability despite liking the concept. The edges of the boards had "blown" as happens to chipboard that gets wet and this was clearly visible through the render.
  4.  
    That's very interesting, thanks very much for that. I've been told on another forum that EPS has only ¼ the permeability of wood fibre but that it's more about the permeability of the render. perhaps I should be looking at lime render over EPS instead of wood fibre.
  5.  
    Two thoughts on that; there have been reports of the render cracking around the outline of the fixings for EPS external insulation, believed to be caused by high wind loadings IIRC and the other point is ensuring the installer includes adequate protection from vermin around the base so mice don't turn your insulation into Swiss cheese!

    Using EPS or perhaps XPS you could also continue the insulation down below ground level (with the aforementioned protection) which helps to reduce heat loss at the floor/wall junction.
  6.  
    I'd plan to go down 50cm below ground if possible, though the house is built straight onto clay. would have to ask a builder if that's an ok idea. Wouldn't want to go to XPS on the house as I know that's not breathable at all.

    Interesting about the cracking, I wonder if mesh over the eps would help with that.
  7.  
    All EPS systems are fully meshed - if you miss a bit of mesh however you will get a crack.
  8.  
    Ah, so it's more about ensuring you watch the installers carefully and make sure everything's done correctly then?
  9.  
    One other issue I'm seeing is that everyone who installs EPS EWI seems to use a waterproof silicone render, which would make it unbreathable, I'll have to ask some of them if they can do lime rendering, I'm guessing it's unlikely with most companies as they simply won't have trained people to deal with lime.
    • CommentAuthorEd Davies
    • CommentTimeFeb 10th 2015
     
    Just 'cause something's waterproof doesn't mean it isn't “breathable” (vapour permeable). That's what so-called breathable membranes do for a living. Don't know about silicone render, mind you.
  10.  
    Posted By: Ed DaviesJust 'cause something's waterproof doesn't mean it isn't “breathable” (vapour permeable). That's what so-called breathable membranes do for a living. Don't know about silicone render, mind you.


    Indeed, figures for vapour and liquid permeability closely guarded by render manufacturers - I wonder why:devil:
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 10th 2015 edited
     
    Fantastic project - great - got any pics? would help to get a better idea of what might turn out to be critical factors.

    Your project, as so far described is no special technical case - standard EWI solutions will do fine. These systems are extremely reliable, with little risk of water penetration if done properly - that's why the suppliers are so relaxed about offering warranties, requiring no more than their regional rep to come to site to have a word with whoever's doing it to make sure they more or less understand. The rep (Parex anyway) also comes to look at the job to advise fixing system etc, before the materials order is placed.

    No need to go to wood fibre, for breatheability. Although much more breatheable than EPS, the latter is plenty breatheable enough, and the patent nylon mesh reinforced thin-coat renders that go with it, whether the basic acrylic type or the silicone or mineral types, are also plenty breatheable. Wood fibre should be problem free - it's very widely used for standard EWI in Europe - tho in UK it's priced into luxury territory.

    How flat is the exterior wall face? Is it easily covered with flat boards? If basically flat and the individual stones not too knobbly, then EPS EWI at least can be fixed with adhesive alone, no need for long screw ('mechanical') fixings. While you're at it, don't settle for less than 200-250mm thick.

    The danger area for water penetration is where the unbroken EWI render meets other things - principally windows. This can't be done carefuly enough - lots of info on that on this forum, can run through it if nec. Pressed metal cills are good, if the styling suits. They don't need upturned ends.

    Windows - do consider custom-sized Scandinavian-style triple glazed ones from e.g. Russell Timbertech - phenomenally cheap, ready glazed, factory finished, pressed metal cills available. Prob less than half the price of locally made DG, and superior quality. Can have 'fake' glazing bars applied easily. Again, the way and position to fit them is well discussed on this forum.

    EPS EWI is fine to run right down to and below ground level (XPS etc not necessary - and not breatheable) - strongly recommend you did a trench and run it down as far as the foundation bottom (but not an inch further). If that goes to significant depth, this may relieve you of having to disturb/insulate your ground floor slabs - the whole chunk of subsoil inside this underground 'coffer dam' of downstand perimeter insulation is then insulated. Visualise the greatly increased path-length that heat has to travel, down through the slab, down below the bottom of the EWI, curving back up to external ground surface. Subsoil in such 'thickness' (the path-length) is an excellent insulator. After a year or two to equilibriate, there will also not be much heat loss straight down. The trench can become a french drain, further guaranteeing the house's dryness - backfill with Leca (lightweight expanded clay aggregate - balls like maltesers) or similar expanded glass granules. These add good insulation to the perimeter downstand. In fact, if your walls don't downstand deep to foundation bottom, your perimeter insulation can instead take the form of a 300 thick 'wing' of Leca (topped with 200 topsoil over Terram) spreading a metre wide of the wall - or a bit of both.
    •  
      CommentAuthordjh
    • CommentTimeFeb 10th 2015
     
    Two points we've learned:

    (1) It's usual to extend the EWI over the front of the frames to improve the insulation, especially if they are inward-opening windows. Most external aluminium covers on windows, including ours, mostly defeat the effectiveness of this.

    (2) It can be tricky sealing the corners of metal sills where there's a junction of the sill, the window, the wall and the EWI. Either try to actually build a sample well in advance, or simply copy an already built example exactly.

    FWIW, we have woodfibre insulation for the little bits of EWI around our windows. We haven't noticed any problems so far. We have lime render and the rest of the wall structure is straw bale, so there's probably a bunch of complicated moisture management going on.
  11.  
    Foster tom thanks for such a detailed reply, lots for me to take in and consider.

    some photos of the house:

    Back of the house after taking off most of the render. The windows are yet to be replaced. Once that's done, we'll make good the bits of stonework that require repair and put a scratch coat of lime plaster over to even it up. You should be able to see that, apart from the corner section where we did some underpinning, the house basically sits on clay, there's no real foundations to it.
    http://i63.photobucket.com/albums/h139/Mr_magicfingers/Luckaborough/IMG_4374_zpse3f6cfb5.jpg

    There's a 1980's cavity wall extension at the end of the house, with a conservatory. Eventually the conservatory will go and patio or bifold doors will go in their place. The plan is to finish all exterior work and then wrap the house in EWI.
    http://i63.photobucket.com/albums/h139/Mr_magicfingers/Luckaborough/IMG_4909_zpsfsx1unde.jpg

    The side of the house, the ground used to come 5' up the side, this was all dug out and the old kitchen window changed to a door out to the garden.
    http://i63.photobucket.com/albums/h139/Mr_magicfingers/Luckaborough/IMG_5038_zpsrjw3gpme.jpg

    House was thatched until the 60's, you can see the change in building material from where the new roof was put on.
    http://i63.photobucket.com/albums/h139/Mr_magicfingers/Luckaborough/IMG_5004_zps29704af7.jpg
  12.  
    There's no way we'd go with 200-250mm of insulation, that's just not going to go well with the house, it would mean digging up the side patio area and give massive extra thickness to the windows. The walls are already 600mm thick. Also, I really doubt, in a house like this, that the extra insulation would make that much difference, you'll never make this house sufficiently airtight to make it worthwhile. I'm aiming for 100-120 max.
  13.  
    Also looked at the Russel Timbertech site, I'm sure they look great in a modern building but they seem to either do sash windows, which we don't have or very modern tilt windows which don't suit the cottage.

    We've been very pleased with the oak double glazed units we've had so far from our local joinery company. One advantage is that if there's any issues, the company owner comes out and ensures they're corrected personally.

    Interesting that you say up stands aren't needed on the cills, everyone I've spoken to so far seems to think they're essential. What's your reasoning for not having them? Can you suggest an alternative method for insuring a good seal at the window reveals?
  14.  
    DJH, yes we're planning to have the insulation come round the reveal and over the window frame, we're specifically having the window frames made thicker so that, when it's done, the frame still has the correct proportions. Good to know you're not seeing water ingress with lime and wood fiber, that's encouraging.
  15.  
    Posted By: mr_magicfingersI'm aiming for 100-120 max
    That's where I would be in a renovation too, unless I was made of money that is, and, indeed, it is what I put on top of my roof - (no loft and is beam and block so really is EWI for a roof).
  16.  
    mr_magicfingers - are you going to put a parge coat on the outside to help with air tightness through the stone/rubble wall or will you EWI straight on top of the stone and expect the EWI to provide the air tightness?

    Also when the EWI is put up make sure that just dot and dab is not used. IMO there should be a contiguous solid line of adhesive at least on one horizontal edge of the insulation boards to prevent air circulation between the EWI and the wall which would negate the effect of the EWI (I insist on 1 horizontal edge and 1 side continuous bead of adhesive on each board with the rest of the board dot and dab)
  17.  
    Peter, yes, as I mentioned, the plan is to put a coat of lime over the stonework once we've repaired any damage that's been done over the years. That would give us a fairly flat surface that would also be the same level as the render on the new section of the house and allow for a seamless overlap so that it all looks even when finished.

    Thanks for the information on the fixing. I'll talk that through with the fitters when we decide what we're doing.

    It's all probably a year away, as we have some other work to do to the house before the outside is finished all round but I want to start getting the ideas straight in advance as so much is dependent on it, such as the window fitting and reveals etc.
    • CommentAuthortony
    • CommentTimeFeb 11th 2015
     
    Two choices over the join, I straddle it with a whole sheet or put a straight join there with a movement joint, which I would go for.
    • CommentAuthorRick_M
    • CommentTimeFeb 11th 2015
     
    Posted By: Peter_in_Hungary(I insist on 1 horizontal edge and 1 side continuous bead of adhesive on each board with the rest of the board dot and dab)


    I don't quite understand this?

    I went for grids of adhesive. Also if your wall is not flat your adhesive lines have to be correctly sized to ensure they all contact. The EPS I used had air pathways right through, it was cheap. Very breathable, I'm sure
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 11th 2015 edited
     
    Beautiful house - where in Devon? (Dartmoor cob farmhouse, me).

    Posted By: mr_magicfingersThe windows are yet to be replaced. Once that's done, we'll make good the bits of stonework that require repair and put a scratch coat of lime plaster over to even it up
    That suggests the windows will be fixed within the stone zone, insulation to follow. Really important to mount the new windows within the insulation zone, not touching the stone (except for cantilevering mounting brackets or timber/board similar), or you create a big thermal bridge around the window perimeter, which will be the house's concentrated magnet for condensation, seeing you'll have eliminated the all-over magnet that the walls presently are. That's another good reason for minimum 150 EWI thickness - to accomodate the window's thickness plus a bit of external reveal.

    Parging is gd idea, for airtightness (make sure it's really continuous) - but expensive - though some cost will be recouped by easing fixing of EWI.

    Attached is drawing showing several things:
    1. How to leave extg window perimeter frames in place, as the start of a boarded reveal lining extending outward to the new outboard windows. That way, extra wall thickness looks OK and you can go join extg splayed reveal to new outboard parallel.
    2. External cills made of EPS, indistinguishable from traditional stone (thick slate? in your case). We just rendered it in with the rest, coat of matching silicone paint, but if doing it again, I'd have fitted one of those metal cills over the top surface.
    3. EPS extending down as deep as poss, french drain, Leca fill - would be more of the horizontal 'wing' in your case.
    4. At eave, we filled the triangular space on top ogf the wall, with blown-in Warmcell, which is great for fully filling every crevice and is fairly airtight at that, thus connecting the ceiling airtight membrane with the extg wall's external render as airtight layer, as well as capping the extg external wall top with insulation continuous with EWI and ceiling insulation.

    Posted By: mr_magicfingersI really doubt, in a house like this, that the extra insulation would make that much difference
    It would!
    Posted By: mr_magicfingersyou'll never make this house sufficiently airtight to make it worthwhile
    You're doing everthing right to make it airtight.
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 11th 2015 edited
     
    Posted By: mr_magicfingersRussell Timbertech ... they seem to either do sash windows, which we don't have or very modern tilt windows which don't suit the cottage
    No, I suggest their basic (non-PH) sidehung sash windows £325/m2 glazed and factory finished, Uw1.1 - no longer on their revamped website but I'll be upset if they've stopped doing em - if so there are others. Pic attached, full size panes, stick-on glazing bars inside and out).

    Posted By: mr_magicfingersyou say up stands aren't needed on the cills
    Treat render joint to the cill-tops same as you will to the window face - http://www.wemico.com/assets/04307-wemico-brochure.pdf p22 Window frame seal beads - plus a substantial bead of top grade silicone into the controlled-width gap bethween it and frame/cill-top face.

    Posted By: Peter_in_Hungarythere should be a contiguous solid line of adhesive at least on one horizontal edge of the insulation boards to prevent air circulation between the EWI and the wall which would negate the effect of the EWI (I insist on 1 horizontal edge and 1 side continuous bead of adhesive on each board with the rest of the board dot and dab)
    Agree - this in effect makes a grid of adhesive.
  18.  
    Tom, thanks very much for all that, I'm going to have to do some more research evidently.

    I'm over near Torrington, I see you're exeter based, do you have any recommended installers for EWI in this part of the world, it's always good to get recommendations.

    I'll contact Russel and ask about those windows.
  19.  
    looking at the diagram, suggests you're basically sealing the eaves in the loft. I thought you were supposed to keep airflow through the loft space to avoid condensation?
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 11th 2015 edited
     
    There are bat entry holes. Filthy up there!

    BTW, yes extg wall top is nicely insulated over - but what about the gable wall tops? With good EWI, the heat lost from rooms, into wall, then upward and curving back into the stone-cold loft, becomes v significant - another concentrated condensation magnet.

    So on this job we EWI'd the inside face of the gable walls as well as the outside face, right to the top (not bothering to render). That killed the heat loss into the loft but of course still left to top of the gable walls uninsulated, not to mention the chimney breasts.

    Always much better to 'EWI' right up and over OSB sheathing over the rafter tops, taking tiles off and replacing on top - gets over so many problems and fiddly stuff.
  20.  
    You see now we're getting into much bigger money: removing tiles and basically redoing the roof. You get way beyond the point of financial sense on some things like this. I'd guess you would add probably 7-10k by redoing the roof over and above the cost of the rest of the EWI. I'm never going to see that sort of return in the life I'm likely to spend at the cottage (probably 20 years). It's a case of finding what you can do, what's reasonable and affordable and making the best of that.

    Sure, adding a foot of EWI all over, putting a new roof on and basically turning it into a passive house is great in concept, but for the money, I could do a lot of other things. Much of my fuel is free as we own a piece of woodland and I have more than I'm likely to ever burn. This is about making the place healthier and more comfortable than it was but not going beyond our means.
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 11th 2015
     
    Insulation over the rooftop makes great sense if the roof covering needs workj anyway - note that we didn't do that in the detail drawing I posted - but it would have saved I guess £1500 of messing in doing it at ceiling level.

    It's not 'a foot' of insulation - and even if it was the extra cost of doubling or 1.5ing the EPS thickness is a tiny part of the cost - fixing whatever thickness then rendering, together dominate the cost. So thin is really false economy/spoiling the ship ...

    In 20yrs time you'll be cursing that you've committed yourself to burning your pension - all your wood fuel resource that will be priceless by then. Why not arrange now to burn almost nothing, save yourself 20yrs hard labour harvesting it or paying someone else to? Please don't say you're about to pay magabucks for a wood chip boiler or even a sophisticated gassifying woodburner! Spend more wisely while you have the opportunity.
   
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