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Green Building Bible, Fourth Edition
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    • CommentAuthorNeil K
    • CommentTimeOct 11th 2008
     
    Our SIP house is now up and thoughts are now turning towards the plasterboard fit out inside.

    Something has just crossed my mind:

    Is there any advantage in putting in any foil based insulation to the inner face of the SIP before we put up the plaster board? Is there any advantage in putting up foil backed plasterboard?

    We will be dilligently hunting down potential air leaks and taping some joints too, so the whole 'build tight, ventilate right' philosophy is taken as a given.

    In general the plan is to fit the plaster board direct to the SIP panels. There are only a couple of walls where any studding needs to go up first in order to provide a cavity space for cables, so most of the walls and roof will be direct contact SIP to plasterboard.

    Glad of any thoughts on the subject......
    • CommentAuthorTimber
    • CommentTimeOct 11th 2008
     
    speak to the SIP mantacturer. They should have a full set of standard details and some 3rd party certification which will tell you how their panels should be used.

    You will need a vapour control layer of some form, and i would suggest the use of a 500g polythene vcl taped and jointed at laps. Foil backed pb is ok, but a separate vcl is better as all the joints can be sealed!

    As for additional insulation, you won't need it, and it might cause problems with how the sip panel works regarding condensation.

    Timber
    • CommentAuthortony
    • CommentTimeOct 11th 2008
     
    What is the U value of your SIP?
    • CommentAuthorsipman
    • CommentTimeOct 11th 2008
     
    Neil

    Standard technical details require the use of vapour check plasterboard, but in practice provided you install a MVHR system (which is a must) standard Plasterboard is acceptable

    depending on the "u" vaulue of your SIPs house, additional internal insulation would in normal circumstances be a waste of money (diminishing returns)

    I'm suprised joints need taping, all joints should have been sealed with expanding urethane by the erection team

    What heating system are you installing
    • CommentAuthortony
    • CommentTimeOct 11th 2008
     
    "Standard technical details require the use of vapour check plasterboard, but in practice provided you install a MVHR system (which is a must) standard Plasterboard is acceptable "

    That is unscientific crazy and asking for trouble in my opinion. MHRV will not stop moisture damage to structure when it is cold outside.
  1.  
    Yes, I agree with Tony. We have discussed the issue of MVHR and moisture migration on several occasions. It is contentious to say the least. Have a search for ASMET.

    Irrespective of this I would be worried about deviating in any way from the SIP manufacturers spec. They will have assessed the condensation risk and not following their recomendation would be very risky.
    • CommentAuthorSaint
    • CommentTimeOct 12th 2008
     
    I agree with Mike and Tony, by beefing up the insulation on the inside face of the SIP you could inadvertently push the dew point right into the middle of the SIP foam core where unless its XPS but more likely PUR or PIR you'll get interstitial condensation. Taping the joints might stop the vapour drive but squirty PUR foam unlikely
    • CommentAuthortony
    • CommentTimeOct 12th 2008
     
    Nothing will stop the drive but it is possible to stop the vapour -- use a vapour barrier.
    • CommentAuthorsipman
    • CommentTimeOct 12th 2008
     
    Condensation risk analysis SIPs Panel with afdditional insulation
  2.  
    Interesting. But...

    What happens if the added insulation is not adhered directly to the SIP panel [as in the detail drawing]? Ie. it's position is moved so that a cavity exists between insulants?
    What if a different insulation were used?
    What if the foil on the back of the plasterboard is damaged or deteriorates?
    • CommentAuthorTimber
    • CommentTimeOct 12th 2008
     
    what if indeed!

    Lots and lots to go into about this lot.

    I would strongly suggest you just follow the manufacturer's standard details!
    • CommentAuthorsipman
    • CommentTimeOct 12th 2008
     
    My comments that a vapour check plasterboard may not be required have been questioned, find below a link to a scientific document for discussion

    Neil it goes without saying, for insurance purposes,etc you should at all times follow manufacturers advice



    http://www.claysllp.co.uk/assets/x/50292
    • CommentAuthorMike George
    • CommentTimeOct 12th 2008 edited
     
    Edited

    Sipman, The linked deatil is only relative to a particular manufacturers product. I also think it is a little misleading in terms of the difficulty involved in adressing thermal bridging and punctures made by following on trades. It does not address my 'what ifs' above
    • CommentAuthortony
    • CommentTimeOct 12th 2008
     
    Nor is it independent -- seems strange to say no vb for domestic but needed fir commercial???
    • CommentAuthorTimber
    • CommentTimeOct 12th 2008 edited
     
    The issue that I see is that you don't need a 'vapour barrier' as such.

    The general rule of thumb is whatever is on the inside of the wall should be five times more resistant to moisture vapour transfer than whatever is on the outside.

    Now if we took a normal Timber frame wall, it consists of breather membrane and OSB on the outside, so you need something at least 5x more vapour resistant than OSB. Normally polythene is used because its cheep and easy.

    If you put the OSB sheathing on the inside of the wall and leave only the breather membrane on the outside, the OSB is generally at least 5x more vapour resistant than the breather membrane and so the balance still works.

    With a SIP panel, the inner and outer face are of the same construction and so NO differential is formed, and a vcl is required.

    (Edited to make my ramblings a bit clearer!)
    • CommentAuthortony
    • CommentTimeOct 12th 2008
     
    Sorry dont like it. -- SIP it not worth taking any chances as if it fails SIP is the structure.
    • CommentAuthorTimber
    • CommentTimeOct 13th 2008
     
    Read again Tony,

    I am explaining why a sip panel SHOULD have a vcl! No differential is formed between the inner and outer face of the panel, and as such vcl should be used!
    • CommentAuthorMarkH
    • CommentTimeOct 13th 2008
     
    I get a bit nervous when people talk in doom laden ways about interstitial condensation - we're re-roofing next spring and will have 90mm PIR board between rafters and 50mm PIR board over the rafters. This seems to go against advice re condensation. Our designer double checked with a well know insulation manufacturer and they said that condensation would only be a risk with a 30 degree difference between inside and outside - this seems OK, but is it?
    • CommentAuthortony
    • CommentTimeOct 13th 2008
     
    yes 30 degree difference is very rare!
    • CommentAuthorsipman
    • CommentTimeOct 13th 2008
     
    Neil

    would be interesting to know the recommendations from your SIPs supplier
    • CommentAuthorNeil K
    • CommentTimeOct 23rd 2008
     
    All,

    Thanks for the comments. I certainly seem to have opened another can of worms! Sorry for the delay in getting back on this, so as a start I will answer a number of the questions posed:

    U values: Walls 0.17, Floor 0.16, roof 0.19
    Heating: Underfloor heating to be fed with an air source heat pump
    Air Management: Whole house air recovery system is going in.
    Joint sealing: The erection team were OK, but a few areas were under foamed..... literaly the 'hapeth of tar'. Subsequent attempts to re-foam end up with a bead on the face with little penetration into the cracks. I plan to caulk the remaining gps and tape over.

    In terms of the recommendations of the supplier; I have been in touch and received the following:

    "The plasterboard can be fixed directly to the SIPs structure, or it can be fixed via battens. This is fully dependent on what services there are locally. Double layering of plasterboard allows the first layer to be "chased" for electric wiring, but battens will be needed where there is any pipework.

    I have attached a copy of the BBA agrement certificate, which outlines the properties of the panels in item 10.2 regarding interstatial condensation. It would appear that it might be best to use a vapour barrier behind the plasterboard, or use foil-backed plasterboard. Any plasterboard fixing detail shown indicates the panel being fixed via 38 x 25mm battens.

    Any further insulation would obviously improve the u-value, but I cannot comment on which type or their various performances. We have a client at present who has calculated that an additional 65 - 70mm insulation under the roof panels will offer a potential u-value of 0.12."

    So whilst they have been responsive in terms of changes to details that have caused me concern I am not hugely confident that the above represents a definitive view that covers the concerns that the forum have raised.

    The other item that seems to have been glossed over is that the SIP construction does not mean that OPB is the only material exposed in the building. At joints there is clearly the potential for the joining timbers at the panel edges to be exposed to any dampness that could build up behind a vapour barrier.... am I worrying unnecessarily about this?

    So my present proposal based on the comments would be:
    Mechanical Ventilation - YES
    Deal with any drafts by caulking the odd SIP joint and tape.
    Polythene onto walls and hold in place with 15mm battens
    Screw foil-backed plasterboard to battens

    As options I may look for a reflective vapour barrier so glad of any comments, and I am considering painting the exposed timber with PVA before covering with the barrier. Would I be better to put the barrier on top of the battens to create an internal air-space between the barrier and the SIP...... do you sometimes wish you'd never asked?

    Neil
    • CommentAuthorTimber
    • CommentTimeOct 23rd 2008
     
    if you use an air barrier, fit it directly to the sip and then batten and board. The othe way means that services will penetrate the vcl and so you loose some of the benifit!

    As for moisture at gaps, a vcl will help prevent this and the breather membrane on the outside will stop external moisture getting trapped in panel joints.

    The U values seam top notch to start with so i don't see a huge point in adding extra!

    Timber
    • CommentAuthoralbacore
    • CommentTimeOct 27th 2008
     
    Neil K. wrote: "Joint sealing: The erection team were OK, but a few areas were under foamed..... literaly the 'hapeth of tar'. Subsequent attempts to re-foam end up with a bead on the face with little penetration into the cracks. I plan to caulk the remaining gps and tape over."

    We have exactly the same issues with our new sip build. Can I ask what caulking material you plan to use and what tape? Do you have a recommendation from the manufacturer? Presumably not all tapes are equal?
    • CommentAuthorNeil K
    • CommentTimeOct 31st 2008
     
    Albacore,

    Bloody annoying isn't it? I could have cheerfully throttled the bu&&ers for all the 'saving' they managed!

    In terms of materials: I am just about to start on this and was planning to follow the line in the thread at: http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2409&page=1#Item_0

    It seems as though a permenantly sticky mastic is going to be best for the odd gap (as opposed to caulk which I now understand dries), but I am planning on making sure I clean the face of the SIP panel of the goo after applying. I will be using a pallette knife to drive it into the gaps. I have sourced reinforced aluminium tape from tapes direct. Looks good, but no idea if it is yet.

    As to whether it all works.... lets pick this conversation up in a few years and see :bigsmile:

    I've been thinking of sharing my experiences on line with this whole process. When I get to type it up it might be a good idea to compare notes?

    Neil
    • CommentAuthorSally M
    • CommentTimeNov 4th 2008
     
    Neil,

    I have read all the comments with huge interest! I am starting the foundations on my house shortly and have ordered my SIP house that is due to go to manufacture. I am also planning underfloor heating (supplied by air source heat pump), MVHRS....and other 'eco' renewable sources. Maybe I need to ask in the contract that all joints are to be sealed neatly!

    My challenge today is that the house I designed, does not naturally lend itself to a SIP construction. This has led to a delay while we try to resolve some of the engineering problems.

    Can I ask who your SIP company is?

    Will watch this space and see how you get on!!! :smile:
    • CommentAuthorsipman
    • CommentTimeNov 4th 2008
     
    Sally

    all the joints should be closed and sealed by the SIP erection team, they should also have a tool called a rookie-tookie to ensure they can pull the panels tight together.

    under no circumstances should you have to seal any joints, the panels should be cut in the factory to the exact size and if any panels do require any alteration on site it should be a slight reduction due to panel creep.
      DSCN4904.jpg
    • CommentAuthorSally M
    • CommentTimeNov 4th 2008
     
    Hi Sipman,

    You seem to know your stuff!!!! This is reassuring to me. It is all a bit scary, as this is a huge investment to us and I want to make sure that I have planned things and tried to predict problems.

    The issues for me at the minute are that the architect and the structural engineer have never worked on a SIP house and seem to be applying traditional building methods. I think the SIP company are getting frustrated with the last minute changes but we have only just become aware of certain design problems. To further complicate things we are trying to achieve code level 6. I feel like I am spinning about 20 plates at the minute!

    Is this normal?

    Sally
    • CommentAuthorsipman
    • CommentTimeNov 4th 2008
     
    Normal

    an engineer with experience of SIps would certainly help,
    • CommentAuthoralbacore
    • CommentTimeNov 5th 2008
     
    All the gaps in our sips structure came where the edges of the panels were reinforced with timber to frame an opening -ie above and below the openings. Part of the problem seemed to be that foam applied at assembly seemed not to stick to the timber and with many windy days, we had more foam distributed around the garden than where it was meant to be. Where panels were joined with splines, the foam seemed to work much more successfully.
    • CommentAuthortony
    • CommentTimeNov 5th 2008
     
    how do you get the thing air tight???
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