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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorGareth J
    • CommentTimeApr 5th 2021
    Hi all,

    I’ve been trawling through threads here for a while now but now have something specific that would be great to get some advise on. Apologies if it’s been covered before.

    I’m currently modifying/somewhat restoring a mostly 1800s stone and earth walled cottage here in North Cornwall. On the cards is something to replace the failing ~1” of Tyrolean render applied sometime probably about 50 years ago. It’s done a decent job overall and protected the house from driven rain pretty well. Generally where I’ve removed it, as part of modifying the lean-to that’s on one side, it’s really dry underneath, as is the earth between the stones in places I’ve had to dismantle.

    However, in places the render is failing and letting water track behind and even, on really bad driven rain days, (which we get here for extended periods) we have some leakage in the lean -to. Digging some of the south gable end (which has been rebuilt with blockwork at some point) plaster off shortly after such a rain session and it’s saturated, the blocks underneath are saturated and as it dries out the joints in the blocks are ghosted on the outside – implying to me that there is moisture within those blocks/mortar joints too. Seems to me like the mortar here (at least) is pretty porus. There is also some damp indoors at low level, this corresponds to underground bits - Parts of the house are built into the ground which doesn't help and those which are, “foundations” on the outer skin of stonework are only at the level of the subsoil, rather than the full depth of the interior rooms. As was the tradition.

    I have been considering digging off the failing mortar, and redoing with lime but am not actually convinced this is a good idea.

    I’ve been reading the “loosing faith in lime” thread with great interest as I think that I had come to similar conclusions (thought not as well thought through or articulated) before reading, regarding permeable wall coverings. Eventually I want to put something on the outside that is impermeable to driven rain, flexible enough to cope with a sagging old building and, ideally, though not essentially able to let moisture out – I could aim to control wall moisture entirely from within...

    That leaves me to consider other options including EWI, a cladding system, or patching the worst bits for now and planning “something else” in future.

    I love the ideal of EWI but I have reservations – mainly, I dont like the idea of adhering a product, with some "adhesive" of unknown lifespan to the outside of the building, the building is far from straight or square and I dislike how much I know it will cost. Of course the advantages will be obvious.

    I also can’t afford roof alterations, so any covering needs to either taper in at the gable ends, which would be ok, or be very thin. The soffits can take up ~100mm.

    I have been looking at Tyvek’s “drainscreen”
    Or similar competitor products, which look like they might be able to achieve what I would like, mold to the shape of the house, and with expamet and render, provide a good, flexible outer skin without taking up much depth. Areas that could afford the space could even be battened and insulated - if that were allowed regs/fire wise.

    Has anyone experience with these type of products? Are they actually appropriate? Can’t see much with respect to UK suppliers.

    Thanks in advance and apologies for the long first post!
    Welcome, Gareth.

    Are you 'hands-on'? Would you be doing the EWI (at least the insulant if not the render) yourself? Could you do the roof extension yourself? It's what I hope to be doing on mine. The roof is 120 years old and, of course, really 'ought to be replaced'. However it has had a lot of fettling over the years and it's not being replaced now. I look at it like this: I don't really 'do' roofing, but I can follow patterns, as witnessed by fairly large areas of re-slating over the years. Probably the biggest cost will be the new rafter(s) at the verge and the extended rafters at the eaves. I can wrangle wood, and the scaff will be up for the EWI. Best case, I can get a roofer to piece in. Worst case, I 'follow the pattern' and do it myself (with breather membrane 'because I can').

    I take your concerns re lime. Though I have seen may examples, even exposed, where it has 'worked' I have heard of many more where it hasn't. Some of the worst cases have been where new owners have removed 'that horrible render' and gone back to 'the original stone', not knowing that the stone, being of poor quality, was probably always rendered because it performed badly in driving rain.

    I think I'd really try to steer you down the EWI route because, whatever the aesthetics and moisture issues (important as they are) I believe an un-insulated house wants insulating. Taking the opportunity to insulate while you *have* to do something with the walls anyway seems like a golden opportunity.

    I am sure others will be along soon with more, and I'll follow up with more if you want.

    Wot Nick said +1
    If the soffits need extending then this can often be done by bolting a short sister joist alongside the existing without the need for any jointing. But if you can manage 100mm under the existing soffits then this would be enough for 80mm EPS (or 100mm if it goes) and this will make a big difference to the thermal performance of the house and the thin film render used with EWI will keep out the rain.

    I have put EPS EWI on a couple of stone earth buildings with very good results. The walls were not particularly straight so I put on the EPS by putting a thick bead of adhesive end to end on the top and bottom of the 100mm x 50mm sheets and put half a dozen good sized dobs in the middle then pressed the sheet on to the wall as a best fit with the adjacent sheets (no gaps between the sheet edges) when the adhesive had set the protruding edges were sanded down prior to the mesh/render coat going on. The result was a wall not plumb straight, but one that had as much 'character' as the original - but this worked. I could not use the mechanical fixings usually used on EWI because the stone is basalt and impossible to get a drill in but so far no problems but I used a bit more adhesive coverage than would normally be used.

    Don't forget that EPS and the render systems used with EWI are (a bit) breathable. I have not had any problems with the 2 stone buildings on which I have put EWI.
    • CommentAuthorMike1
    • CommentTime6 days ago
    Not quite sure what you mean by 'stone and earth', but if you're taking rammed earth / cob or similar, then I'd be very careful.

    I did some internet research on insulating pisé walls (a type of rammed earth with stones) a couple of years ago - you can find a thread here: http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16045

    As mentioned in my last post there, "there is currently no recommended guide for [the use of natural clay and stone building materials] recognised by professionals, nor any means of measuring and guaranteeing performance recognised by scientists. This lack traditionally leads to the application of inappropriate renovation and construction methods and/or the preference for other building materials that are less ecologically efficient but benefit from standardised testing procedures. At best, companies rely on their empirical knowledge."

    That empirical knowledge often seems to focus on installing internal wall insulation consisting of a thick layer (5cm or so) of lime mixed with hemp, which is believed to closely match the hygrothermal performance of the original wall, plus lime external render. Which is probably what I'd do.
    • CommentAuthorGareth J
    • CommentTime6 days ago
    Thanks for the welcome and the detailed replies.

    I am hands on and do a fair bit myself, including stoning, pointing and, reluctantly, a bit of plastering but I dont have the time to put to a full diy EWI job. If I go that route, I've got to really think through the underground bits now, before I backfill the "foundations" and redo the path. Damaged plaster will have to be patched and some waterproofing product put over it. Until I have the courage and time, or cash to throw at someone else doing it.

    Regarding underground, I am considering laying dimple sheet up against the foundation/wall and back filling with french drain gravel. Could put some insulation behind the dimple sheet before the gravel I guess but not sure of the effectiveness in that application.

    I appreciate your honesty regarding the failings of lime. I feel too many are evangelical about it's use without thinking through which aspects of lime are beneficial in which areas and whether the use is really appropriate or not. In particular, a "breathable" wall exterior without some kind of drainage plane is always going to struggle to get rid of the water within it when subjected to more days of driving rain than not.

    That's what led me down the drainage wrap route, looks like it could be a useful product if used in this way but I struggle to see any UK suppliers of DuPont's offering or others. Bonuses for me would be its flexibility, ease and speed of installation, low profile where it would need to be, could be used with EWI underneath and would let me use standard, non fussy, render. Lime if if I decided the look was worth it. Is it just not "a thing" in the UK?

    My roof is pretty new and looks good, messing with the eaves is a no go. In terms of faff, cost and the fact I dont want to mess with the well settled ragg slates. But that's not prohibiting me from doing something I'm sure.
    • CommentTime6 days ago
    Gareth said: "Regarding underground, I am considering laying dimple sheet up against the foundation/wall and back filling with french drain gravel. Could put some insulation behind the dimple sheet before the gravel I guess but not sure of the effectiveness in that application."

    Sounds like a sensible plan.

    and he said "I struggle to see any UK suppliers of DuPont's offering or others"

    https://www.dupont.co.uk/building/where-to-buy-tyvek-building-solutions-in-the-uk-and-ireland.html ?

    Or Dupont themselves if nobody admits to being able to sell it.
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