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Housing - New Build: SIP house sole plate detail, help needed

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    • CommentAuthorseveral
    • CommentTimeMar 1st 2013 edited
     
    Hope someone can offer advise on this. I am building a sip house and the soleplate detail is similar to drawing A.

    My concern is simply this, any defects in the aluminium trim(ie, at joins etc) could lead to water getting in and sitting on the DPM under the soleplate.

    So, is it better for the DPM under the soleplate to be lapped back up the external face of the SIP like drawing B?

    thanks in advance
    • CommentAuthorTimber
    • CommentTimeMar 1st 2013
     
    Can't see it making any difference really, but I guess that B might be better. Make sure the flashing works!!

    Alternatively slide the SIP to the outside/make the upstand less wide, so there is less of a lip on the masonry, although I assume that the detail is as it is for aesthetic reasons?
  3.  
    Hi Mark

    Here is how it is done on our house.

    The renderboard and ventilation gap overhangs the foundation and completely eliminates the aluminium profile and any potential problems with it in your detail.
    • CommentAuthorseveral
    • CommentTimeMar 2nd 2013
     
    yea, I can see I should have been done slightly differently to eliminate this issue, but unfortunately, this is how it's been done and is in place now. I just want to be 100% sure what to do with the DPC before closing everything off. At this moment in time, I think it probably is best to fold the DPC back up on itself.
    • CommentAuthorTimber
    • CommentTimeMar 2nd 2013
     
    No, don't do that! Not up the outside of the SIP/soleplate. You would be better off just cutting it off.
    • CommentAuthorTimber
    • CommentTimeMar 2nd 2013
     
    Have you seen the technical bulletins on the UKsips website? A bit on the lightweight side, but a good starting point if you have limited experiences with SIP.
    • CommentAuthorEd Davies
    • CommentTimeMar 2nd 2013 edited
     
    Timber, is that because any water that runs down the inside of the breather membrane would be trapped behind the DPC? You'd hope that most water behind the breather would be vapour but presumably condensation does happen sometimes. Have you changed your mind in the last 13 hours about this?
    • CommentAuthorseveral
    • CommentTimeMar 2nd 2013
     
    so .....leave as is, lap up on the outside or just cut back?
  9.  
    Posted By: Ed DaviesTimber, is that because any water that runs down the inside of the breather membrane would be trapped behind the DPC?


    Looks like it would be trapped behind the aluminium profile in any case. But I would have thought that with a sips panel there shouldn't normally be moisture migrating out through the panel?
    • CommentAuthorTimber
    • CommentTimeMar 2nd 2013
     
    Cut it off.

    Ed - yes, also if the breather membrane and/or flashing is detailed correctly, water could track behind and get pushed towards the SIP with DPC turned up the outer face.
    • CommentAuthorEd Davies
    • CommentTimeMar 2nd 2013 edited
     
    Posted By: Chris P BaconLooks like it would be trapped behind the aluminium profile in any case.
    Good point. Perhaps that should be pulled a little away from the bottom of the SIP and the soul plate to allow those to “breathe”.

    But I would have thought that with a sips panel there shouldn't normally be moisture migrating out through the panel?
    Shouldn't be much, I agree. But if one was confident there was absolutely none then why bother with breather membrane rather than just something cheap and water-proof. If there can be any vapour behind the membrane then there can be condensation there, at least for a short while. You don't want that to trickle down and pool somewhere it can't get out and can cause rot.
    • CommentAuthorPaulJ
    • CommentTimeMar 2nd 2013
     
    I would go for A but when fitting the flashing, (assuming it is not yet in place) fill the gap between flashing, DPC and sole plate with some low modulus mastic
    • CommentAuthorseveral
    • CommentTimeMar 2nd 2013 edited
     
    ok how about this? cut back the DPC under the sole plate just so it's hang an inch or so past the the sole plate...

    Raise the aluminium up by 10-15mm off the brick and then place another DPC behind the aluminium to catch any water that *might* (but shouldn't) get through joins.

    Thanks for all the help btw, I really need to get this sorted asap
    • CommentAuthorseveral
    • CommentTimeMar 4th 2013 edited
     
    I ended up cutting it off (10mm to 15mm from the sip), now the building inspector thinks it should go back on and by lapped up the SIP. And I spoke to the sip company who also said the same.

    I'm still totally unsure, architect is away. Feel like I've proper messed this up now. :cry:
    • CommentAuthorTimber
    • CommentTimeMar 4th 2013
     
    Don't lap up SIP!

    Make sure the breather membrane is well lapped with flashing.

    Lapping the DPC up the outside will hamper the breathability of the sole plate and the OSB sheathing. Might not be a problem, but it would certainly be detrimental vs cut off given the circumstances. The detail as shown above would not have any downside that I could see vs the lapped detail.

    UKSIPs technical bulletins all talk about drainage and ventilation to ensure durability.

    What level is the surrounding ground level?
    • CommentAuthorseveral
    • CommentTimeMar 4th 2013
     
    think it's 2-3 bricks down.

    How can the sole plate breath though when the aluminium trim is fixed directly to it?
    • CommentAuthorCWatters
    • CommentTimeMar 5th 2013 edited
     
    I see no problem with the aluminium alone other than the joints (eg "A"" looks fine to me). I'd overlap the joints in the aluminium and put a patch of membrane say 300mm wide behind each joint as per the first "C" above.

    If the building inspector isn't convinced then perhaps ask if breather membrane should be used as per your first "C" above for the whole length. The membrane needs to be covered by the aluminium as it isn't normally considered UV stable in the long term.
    • CommentAuthorseveral
    • CommentTimeMar 5th 2013 edited
     
    the building inspector suggested using a flash band(bitumen type thing) around the sole plate, behind the aluminium. My concern is that I've cut back the DPC now too far and cannot get back what I've cut off.
  19.  
    It depends what you are asking the dpc to do. I think what you have done looks OK. Dpcs are usually to stop rising damp. It looks as if you have other measures to deflect falling/blowing damp. I do think that if it were lapped back up the SIP, tere's arguably too much scope for a worst-case ' bowl of water' for the SIP to sit in.

    Nick
    • CommentAuthorseveral
    • CommentTimeMar 5th 2013 edited
     
    So with that in mind, what does happen to any water running down the sip? If the DPC is not to be lapped up because of water coming down, what happens to that same water if the DPC like it is? I has to go somewhere.

    So should a gap be left between the flashing and the brick for ventilation? ie, raise the level of the flashing slightly to maintain a 10mm gap between underside of the flashing and brickwork, or would this become a void for insects etc etc.

    Or what about having some breather membrane behind the aluminium as well?

    The flashing keeps the water running off the building, the DPC stops rising damp, but nothing is in place to deal with water that either gets behind the main breather, or behind the flashing, this is the water that will sit on the sole plate. And if it's such a bad idea to lap the DPC back up, then that means there is a chance of water getting there.
    • CommentAuthorCWatters
    • CommentTimeMar 5th 2013 edited
     
    I think you and the building inspector might be worrying a bit too much. I don't like the idea of using bitumen as it will seal in any water.

    Take a look at what other SIP manufacturers recommend in this area. If anything they just use a regular DPC strip (similar to your cut off DPM) or they fold the DPM down the outside of the blockwork not up the SIP.

    http://www.woodspec.ie/media/woodspec/content/sectionbdetaileddrawings/detail_b_6.2.123.jpg
    http://www.builditgreen.co.uk/media/BIG-standard-details.pdf
    http://www.thesipcompany.com/pdf/W1.pdf

    If any water runs down between the SIP and the membrane then it will wick between the SIP and DPC regardless. What I mean is I don't think having a blockwork "shelf" makes any difference to this particular issue.

    The important thing is that the membrane (or in your case the mambrand and aluminium) extend below the DPC level so that any water running down the outside of the membrane is deflected outwards. The joints in the aluminum apper to be the main issue and I'd either overlap them or put short lengths of aluminium behind butt joints.

    Note the aluminium is appears to be raised up off the blockwork, probably to stop water wicking up behind it? Perhaps check what that gap should be (at least 6mm?).
    • CommentAuthorseveral
    • CommentTimeMar 5th 2013 edited
     
    The whole reason this issue came to rise was because of the joints in the aluminium, they were butted joints, even the corners, with simply a silicone seal. I was not happy with this, it does not make any sense to have a silicone seal keeping water from the soleplate, in an unaccessible place. So this is the reason why I cut off the DPC, for worry that if a joint does start to fail and I don't notice, it will not sit on the DPC against the soleplate. Then I realised that the whole soleplate ledge thing is not really a good design because it allows water to sit there. Most of the soleplate's I've seen have the outer brick at a lower level and have the breather membrane extend down below the DPC/soleplate.

    I'm hoping I can at least get the joints in the aluminium welded, to make a permanent joint. Also, the aluminium was sat directly onto of the bricks, no gap other than slight various in brickwork.
    • CommentAuthorTimber
    • CommentTimeMar 5th 2013 edited
     
    Sounds like poor detailing all round then TBH as you have identified! Not at all how it should be done.

    I agree about the flashing and the butt joints. Silly design.

    What is currently installed? Perhaps the detail in you post quoted below is the best of a bad bunch - but as mentioned not the best practice way of doing it.



    Posted By: severalok how about this? cut back the DPC under the sole plate just so it's hang an inch or so past the the sole plate...

    Raise the aluminium up by 10-15mm off the brick and then place another DPC behind the aluminium to catch any water that *might* (but shouldn't) get through joins.

    Thanks for all the help btw, I really need to get this sorted asap
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    • CommentAuthorCWatters
    • CommentTimeMar 6th 2013
     
    Not sure about welding. Would thermal expansion be an issue? Perhaps fit another length of aluminium say 500mm long over the joints?
    • CommentAuthorEd Davies
    • CommentTimeMar 6th 2013 edited
     
    Bit late now, I know, but would it have been a good thing to trap a strip of breather membrane between the DPC and the sole plate then wrap it up the side of the SIP and tape it to the main breather membrane on that? E.g., put the taped join under the attachment point of the aluminium flashing. Protects against water getting passed the flashing and also windwashing into any gaps between the SIPs and the sole plate.
  26.  
    Hi!

    I've been trying to look at the various attachments folk have uploaded, but none of them work for me on either this PC or Mac or other browsers....can anyone else view them? Or do 'old' jpgs get stripped from the forum?

    I'm currently discussing floor insulation for my SIP build that will be sitting on a piled RC slab, so keen to see exactly what people are commenting on.

    My intention was to have 200mm insulation that would sit higher than the top of the sole plate to reduce thermal bridging in that junction. With a further 70mm of screeding on top of that.

    If anyone can view any of the jps, I would be very grateful!
    • CommentAuthorEd Davies
    • CommentTimeMar 12th 2015
     
  28.  
    Hi Mark
    Are you concerned at all about the high level of cold bridging with SIPs construction?
    If you calculated it at all the junctions, it'd probably double the U-value!
    Its difficult to eliminate the wall/floor cold bridge with SIPs because both sides of the SIPs are load bearing and need to rest on concrete.
    Sole plates below the screed level on a cold slab aren't a good idea, there was a court case in Sweden as a result of Sole Plate rot that nearly took down a major house insurer. In Sweden its all warm slabs now with the insulation underneath.
    • CommentAuthorringi
    • CommentTimeMar 17th 2015
     
    Why can't something like the Marmox Thermoblock be used below the SIP?
  30.  
    Posted By: ringiWhy can't something like the Marmox Thermoblock be used below the SIP?
    You can't fix a SIPs sole plate to a Marmox Thermoblock.
    A standard 65mm Marrmox Thermoblock has similar insulating value to 45mm of EPS, we usually use 200mm of EPS at the wall/floor junction, so you'd need 4.5 rows of Marmox Thermoblocks for a similar effect.
    The double sole plate and double stud where panels meet is 9 times more conductive than the the middle of the SIPs.

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