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Housing - New Build: What level air tightness can be got just by using spray insulation?

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    • CommentAuthorringi
    • CommentTimeAug 25th 2016
     
    I am in the process of doing a thought experiment….

    What level air tightness can be got just by for example Icynene between all the wall studs with little effect make towards air tightness apart from round opening, windows, etc? E.g. can all the timber work be done by normal trade’s people, and then the “bad workmanship” sorted out by using spray insulation?

    What design changed would be needed to enable this? (For example not doubling up on studs, or putting 2by2 horizontal timbers on the outside of the frame before fitting the sheathing board.)

    PS are there issue with racking resistance by putting the sheathing board on horizontal timbers rather than directly on the studs?
    •  
      CommentAuthordjh
    • CommentTimeAug 25th 2016 edited
     
    I'd have thought you could get pretty good airtightness either from sprayed on foam or from blown in cellulose, as long as you sealed the openings and used a multi-layer structure as you suggest.

    I don't know what the implications for racking of using cross timbers would be, though I guess probably not good. Larsen trusses or double studs would be other ways to avoid leaks through the structure. Or put one or the other of the cross timbers or racking boards on the inside, but not both.
  3.  
    The concern with spray foam is shrinkage so I wouldn't rely on it for airtightness, that's not to say there isn't problems with other forms of insulation like cellulose, rockwool or glasswool settling and if rockwool/glasswool isn't cut accurately and pushed between studs the wrinkling can reduce performance. If low density insulation is laid flat above a ceiling, convection currents within the insulation reduces the performance.
    The racking board should go directly onto the studs.
    •  
      CommentAuthordjh
    • CommentTimeAug 25th 2016
     
    Posted By: Viking HouseThe concern with spray foam is shrinkage so I wouldn't rely on it for airtightness

    Are you talking about rigid or flexible foams?
    •  
      CommentAuthordjh
    • CommentTimeAug 25th 2016
     
    Your certainly have much greater dependence on the skill of the installer if you rely on the insulation for airtightness. It's easier to see defects in a membrane or plaster layer, so perhaps that's why they're used even when it might be possible to do without them.
    • CommentAuthorgravelld
    • CommentTimeAug 25th 2016
     
    Icynene is VERY springy, I was surprised when I handled some a few months ago. More like the springiness of a soft foam seat, than expanding foam, which (unless you use one of the fancy ones) sets pretty rigid.

    I would've thought, and same with cellulose, if inserted under pressure they would deal with movements in the structure.

    In fact I would be more likely to trust that than rigid EPS or similar board with filled expanding foam gaps - too much to go wrong imo.

    But that's just a hunch.
    • CommentAuthortony
    • CommentTimeAug 25th 2016
     
    comments, i) insufficient thickness = insufficient insulation, ii) how will it join to other insulation barriers? iii) horrible to mess with afterwards.
    • CommentAuthorringi
    • CommentTimeAug 25th 2016
     
    Posted By: tonycomments, i) insufficient thickness = insufficient insulation, ii) how will it join to other insulation barriers? iii) horrible to mess with afterwards


    Thickness is easy, just need to use Larsen studs etc, we all know how to make wide walls with limited thermal bridging from the studs. Larsen studs could also hang from the roof. (However cost many an be issue....)

    I don't see a problem with "join to other insulation barriers" as the spray insulation could be continuous over all the walls and roof. (Tape etc will be needed for the windows to seal them to the ply boxes.)

    As to "mess with afterwards", is this not also an issue with warmcel type insulation, I can't think of any insulation that is easy to install without gaps and does remains where it is put in wide walls, that does not have that problem.
    • CommentAuthorringi
    • CommentTimeAug 25th 2016
     
    Posted By: djhYour certainly have much greater dependence on the skill of the installer if you rely on the insulation for airtightness. It's easier to see defects in a membrane or plaster layer, so perhaps that's why they're used even when it might be possible to do without them.


    I was assuming that the insulation is put on in layers, and being expanding would tend to fill any gaps.
  10.  
    I have 350mm timber I-beams with 15mm OSB3 external racking boards. It is fully filled with Icynene and I achieved average air tightness 0.47 ACH. I haven't used any tapes or membranes.
    •  
      CommentAuthordjh
    • CommentTimeAug 25th 2016 edited
     
    Posted By: PeterStarckI have 350mm timber I-beams with 15mm OSB3 external racking boards. It is fully filled with Icynene and I achieved average air tightness 0.47 ACH. I haven't used any tapes or membranes.

    So the joints between the OSB sheets are not airtight?

    I'd call that conclusive proof. Well done!

    Edit: what did you do at windows and doors etc?
    •  
      CommentAuthordjh
    • CommentTimeAug 25th 2016
     
    Posted By: ringiI was assuming that the insulation is put on in layers, and being expanding would tend to fill any gaps.

    I was mainly thinking about cellulose, which is all done in one go, rather than foam. I don't know much about how Icynene is installed.
  13.  
    Posted By: djhSo the joints between the OSB sheets are not airtight?

    I'd call that conclusive proof. Well done!


    The OSB boards are square edge and they are not fully supported along the joins so not airtight.

    The Icynene was sprayed in three passes, each layer expands around 100mm.
    • CommentAuthorringi
    • CommentTimeAug 25th 2016
     
    Posted By: PeterStarckI have 350mm timber I-beams with 15mm OSB3 external racking boards. It is fully filled with Icynene and I achieved average air tightness 0.47 ACH. I haven't used any tapes or membranes.


    Thanks Peter,

    Do you know where you leaks where coming from as 0.47 ACH is only just within the limit we should be aiming at for new homes.

    What the cost of Icynene like?

    Also is there a reason you used 15mm OSB3 rather then a thinner OSB3?
  15.  
    We were aiming to be better than the PH requirement of 0.6 ACH so didn't look too hard for leaks. We found two which were an opening sash not tight enough and at the top overlap of the lift slide doors.

    The Icynene cost was just under £10000 for all external walls, roof and ground floor ceiling.

    I could have used 12mm but I tend to over engineer everything!
  16.  
    Peter well done on a great airtightness result!
    Here's something on Foam shrinkage https://www.youtube.com/watch?v=ieLm9NwE22c
    • CommentAuthorSilky
    • CommentTimeAug 25th 2016 edited
     
    looking at the comments under the video there seems to be a general consensus that this wasn't PU foam, so I hope not a problem for Icynene type product? I've been wrestling with this topic for far too long now and still haven't decided. I need to retrofit insulation over a mixture of substrates ( in-filled woodframe / solid masonry / hollow clay blocks ). Really keen to have ventilated facade with cladding. Main concerns are air tightness ( infiltration ) in the insulation layer ( not wind tightness which will be by external membrane ), robustness/longevity of the insulation ( has to be at least 30-40 years in my opinion, ideally a 100! ) including vulnerability to water damage and/or vermin. If I was building new I would go for hollow clay blocks, 40 cm thick and recently even considered having the walls demolished and re-built.. would have been the best plan if I wasn't already half-way through the renovation. So back to the original thread.. even if there is a small ammount of shrinkage with Icynene the very long term risk could be minimised by using rigid boards under-sized to the framework and then using Icynene to fill between the boards and the frame. This is one of the solutions I'm considering, seems to be a popular method state side ( judging by some youtube videos ) and Icynene is also available there as a DIY product ( expensive ). Any opinions on this?

    edit : spelling
    • CommentAuthorgravelld
    • CommentTimeAug 25th 2016
     
    That video is worrying, buy there's no info about what product it is.

    If be interested in any claims Icynene have about shrinkage.

    Peter what was the cost per m3?
    • CommentAuthorringi
    • CommentTimeAug 25th 2016
     
    Posted By: Viking HouseHere's something on Foam shrinkagehttps://www.youtube.com/watch?v=ieLm9NwE22c" >https://www.youtube.com/watch?v=ieLm9NwE22c


    Any ideal on what types of foam shrink?
    • CommentAuthorringi
    • CommentTimeAug 25th 2016
     
    Posted By: PeterStarckWe were aiming to be better than the PH requirement of 0.6 ACH so didn't look too hard for leaks. We found two which were an opening sash not tight enough and at the top overlap of the lift slide doors.


    Thanks, so the leaks where nothing to do with the Icynene.
    •  
      CommentAuthorSteamyTea
    • CommentTimeAug 25th 2016
     
    You could see if they can do a different mix of PU and spray a sealing coat on first. PU sticks to PU very well generally.

    They could also put in a melamine filler to make it more solid and fire resistant (if they don't already).
    •  
      CommentAuthordjh
    • CommentTimeAug 25th 2016
     
    Posted By: ringiDo you know where you leaks where coming from as 0.47 ACH is only just within the limit we should be aiming at for new homes.

    Why do you think we need an airtightness result any better than that? I don't know of any standard that looks for better than the PH 0.6 ACH and the only results that are better that I know about are obsessive people who got lucky.
    • CommentAuthorFlubba
    • CommentTimeAug 26th 2016 edited
     
    The foam in the video is Urea-formaldehyde insulation, well known to shrink and cause issues in houses where it was used as cavity wall insulation.
  24.  
    Posted By: gravelldThat video is worrying, buy there's no info about what product it is.

    If be interested in any claims Icynene have about shrinkage.

    Peter what was the cost per m3?


    I was quoted £9950 for 212m2 @ 350mm and 74m2 @ 250mm
    •  
      CommentAuthorSteamyTea
    • CommentTimeAug 26th 2016
     
    When we were making cushion tooling, we worked on 3% shrinkage by volume. It was greater in corners though.
  26.  
    The only problem I know of regarding Icynene shrinkage is if the surface is too cold it doesn't stick so well and does pull away. Normally it is very difficult removing Icynene, just ask my other half who did all the cleaning up. Have a look at my blog.

    http://eastkentpassivhaus.blogspot.co.uk/
  27.  
    Here's a link to the BBA certificates if that helps.

    http://www.icynene.ie/certification/
    • CommentAuthorgravelld
    • CommentTimeAug 26th 2016
     
    Thanks Peter.
    • CommentAuthorringi
    • CommentTimeAug 26th 2016
     
    Is there a way to use icynene on a “house wrap” enclosed wall that does not have sheathing boards?
    •  
      CommentAuthordjh
    • CommentTimeAug 26th 2016
     
    Posted By: ringiIs there a way to use icynene on a “house wrap” enclosed wall that does not have sheathing boards?

    You mean can it be used on the outside of a wall, as EWI?

    If so, then I guess the answer is yes, but it would need a separately-supported weather screen outside it to keep sun, wind, rain, creatures etc etc off it. It would be semantics whether you called that structure 'sheathing boards' or not.

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