Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)

Categories



Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

Buy individually or both books together. Delivery is free!


powered by Surfing Waves




Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.




    • CommentAuthorMHicks
    • CommentTimeOct 23rd 2016 edited
     
    Our BC man came round for his pre-slab pour check last week and all went smoothly, in the end...

    Anyway, he suggested that the DPM be left protruding "2-3 inches" beyond the wall and then before we put the EWI on we should lap it UP the wall, he reckoned this would prevent moisture ingress into the masonry. I wasn't at all sure about that and checking it was on my list of things to do but then our blockers turned up at dawn and went and cut the DPM flush with the outside wall surface and blocked up from there.

    I wondered: what is the right way to deal with the DP in a solid wall with EWI? Should the DP continue through the EWI to the outer skin (not sure how I'd manage that now...)?
  1.  
    The general wisdom presented here with retro-fit EWI is that there is no need to have a break at DPC when using EPS as the EPS will not track moisture across the DPC. I Don't see that this would be different with new build.

    I have trouble seeing the BCs logic when he says that 2-3 inches folded up would prevent moisture ingress into the masonry. - How?
    • CommentAuthortony
    • CommentTimeOct 24th 2016
     
    I see no ships, carry on -- turning it up 50 to 75mm wont do anything anyway!
    •  
      CommentAuthorfostertom
    • CommentTimeOct 24th 2016
     
    Except trap and direct inward any moisture that might be running down the masonry face e.g. following EWI failure in the only way it ever happens - sloppy detailing around window openings. Much better to let it run on down uninterrupted.
    • CommentAuthorgravelld
    • CommentTimeOct 24th 2016 edited
     
    Posted By: fostertome.g. following EWI failure in the only way it ever happens - sloppy detailing around window openings. Much better to let it run on down uninterrupted.
    Another reason to full fill re. my earlier idea :tongue:
    •  
      CommentAuthorfostertom
    • CommentTimeOct 24th 2016
     
    Full fill is no less susceptible to faults around windows, and no less serious in effect.
    • CommentAuthorgravelld
    • CommentTimeOct 24th 2016
     
    What kind of faults?
    • CommentAuthorEd Davies
    • CommentTimeOct 24th 2016
     
    What do you mean by “full fill” here? Some sort of frame filled with EPS beads or the like?
    • CommentAuthorgravelld
    • CommentTimeOct 24th 2016
     
    External frame full filled... Truss, boxed in, full fill under pressure.
    • CommentAuthorEd Davies
    • CommentTimeOct 24th 2016
     
    Right, thought so. Just hadn't seen “full fill” used that way - normally people mean filling a cavity between bricks or blocks.
    • CommentAuthorMHicks
    • CommentTimeOct 24th 2016
     
    Thanks. I couldn't see any sense in what he was saying.

    The consensus very much seems to be that external EPS needs no break. I look forward to trying to persuade our BC that it's OK though... It's 100mm cavities and dense concrete blocks as far as the eye can see down here. Timber frame is still a crazy new thing.
    •  
      CommentAuthorfostertom
    • CommentTimeOct 24th 2016 edited
     
    Posted By: gravelldWhat kind of faults?
    You've still got a 'void' filled with beads effectively same as 'void' formed of sold EPS, with same weatherproof skin having v low tolerance of inward liquid leakage thro that. So, just the same the skin has to be flawlessly, robustly sealed where it meets windows, cill etc. Except that your skin, if render, moves with a substantial board backing which expands/contracts with a mind of its own, rather than intimately bonded to solid EPS. More risky, I'd say, tho prob not v risky, at that.
    • CommentAuthorgravelld
    • CommentTimeOct 25th 2016
     
    Posted By: Ed DaviesRight, thought so. Just hadn't seen “full fill” used that way - normally people mean filling a cavity between bricks or blocks.
    Agree, I thought that when I wrote it. Just trying to differentiate between fill and sticking/fixing blocks against a wall.
    • CommentAuthorgravelld
    • CommentTimeOct 25th 2016
     
    Posted By: fostertomYou've still got a 'void' filled with beads effectively same as 'void' formed of sold EPS, with same weatherproof skin having v low tolerance of inward liquid leakage thro that. So, just the same the skin has to be flawlessly, robustly sealed where it meets windows, cill etc. Except that your skin, if render, moves with a substantial board backing which expands/contracts with a mind of its own, rather than intimately bonded to solid EPS. More risky, I'd say, tho prob not v risky, at that.
    Agree you still have to meticulously seal. I don't really see how the render issue, isolated, is much different though. Wouldn't EPS blocks possibly buckle against each other, pushing themselves out?

    If you have a timber frame instead wouldn't that be a bit more forgiving?

    I'm partly an advocate of leaving the EPS bead unglued too, so the combination of that and the bead under pressure I would hope would at least keep the insulation against the wall (but as you say, still problems at interfaces).

    This is all about managing failure as much as it is about doing it right in the first place.
    •  
      CommentAuthorfostertom
    • CommentTimeOct 25th 2016
     
    Posted By: gravelldWouldn't EPS blocks possibly buckle against each other, pushing themselves out?

    If you have a timber frame instead wouldn't that be a bit more forgiving?
    EPS blocks are fairly elastic. True that 'unmatured' they can take on a strong bend while lying loose, thro unequal weather exposure or internal stresses. But once you've got them glued in place they'll 'give' and stay more or less in installed shape, rather than pulling away from the substrate. Foam filling the joints, and the joint to the window frame, also holds things together - the block will 'give' rather than pulling away at the joints. So by rendering direct onto the EPS at the window junction, the render and its seal to the frame should stay unmoving in contact.

    Compare with a batten-and-board backing to render (because you can't render direct onto EPS beads!) - anything timber moves around a lot, with moisture variation and built-in stresses and unanticipated loads. Unless the assemblage is strongly fixed to the window frame, this means there will be perpetual movement across the joint to the window frame. Even if by strong fixing you prevent that movement actually at the window frame joint, the movement will simply show up at the next weakest point. If you think to get round that by using cement particle board instead of OSB, not only will it cost a lot but you'll be warned to leave plenty of movement joints because the framing/battening will still be moving relative to the less moveable board, which can cause buckling effects.
    • CommentAuthorgravelld
    • CommentTimeOct 25th 2016
     
    Really helpful, thanks Tom.

    If you had cladding rather than render, does that change things much?
    •  
      CommentAuthorfostertom
    • CommentTimeOct 25th 2016
     
    OK, so then the cladding acts as a first defence against driving rain but you still need a flawless durable waterproof joint in behind. If done with flexible dpc, then that can absorb movement; whether a mastic sealant joint will endure is a matter of judgement. Have to get the overlaps of a dpc-type solution right, so whatever happens everything drains outward and down.
Add your comments

    Username Password
  • Format comments as
 
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press