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.




Energy Assessment: When to do air tightness testing?

Bottom of Page

1 to 20 of 20

  1.  
    • CommentAuthorSprocket
    • CommentTimeJan 27th 2011
     
    We are roughly at first fix on a small barn conversion.
    Uncoarsed stone rubble walls, Newlath membrane, then breathable VCL, then battened out.
    Roof insulation is in. All sealed at top of wall + wall plate etc and down to floor
    Cabling and pipes are in and VCM penetrations hopefully sealed.
    Everything is well taped and/or glued. It *ought* to be pretty air tight.
    But wall insulation + board + plaster not in yet.

    We are wondering if it would be a good idea to check air tightness as soon as doors and windows are in. That way if something is leaking we can do something about it without having to remove wall boards etc.

    What do folks think? Is it a waste of time before final interior finish?
    And what sort of person/company should we go to for this sort of thing?
    I don't really need a certificate. I just want to know how air tight it is and if it leaks then where does it leak.
    And I am wondering how expensive testing is likley to be?

    TIA
  2.  
    I don't know how much it costs, but there's a lot to be said for checking airtightness at least twice. Once when air barriers, windows & doors are fitted & again on completion. That way you can fix the structural problems before they're covered up & any problems found on completion can be more easily traced.

    David
    • CommentAuthortony
    • CommentTimeJan 27th 2011
     
    where is the air barrier?
    • CommentAuthorRobinB
    • CommentTimeJan 27th 2011
     
    Cost us £200 ish - would have like to do it at both stages but waited 'til plastering was done. For that money we got 1/2 day and a chance to go around with their smoke wand, find and seal a couple of weak points and retest and got the cert. we needed for building control.

    I imagine an early test would be a great project for students on a related course with access to the kit.
    • CommentAuthorSprocket
    • CommentTimeJan 27th 2011
     
    Well, some encouraging comments already. Moreso than I expected.
    Tony, I think our air barriers are

    1) The outer layer of newlath DPC on the walls. Tricky stuff to seal at edges but we did our best to seal overlapped sheets with Orcon-F and then tape.
    2) We did not think that was enough so on top of this we added a layer of heavy duty breathable VCL. Taped at edges.
    3) The VCL goes up over the top of the wall and is glued and taped to the wall plate. This also covers any minor cracks between wall plate and top of wall. The membranes go right into window reveals and doorways too, so there is no exposed stone anywhere inside.
    4) The roof is sarking board (a paraffin impregnated particle board with T&G edges) with all joints taped. Usual membrane outside of that too, also taped. Underneath the sarking board we have PUR insulation but it's just push-fit. Noggins at the edges are a tight fit to rafters and sarking and wall plate, all sealed with more Orcon-F.
    5) Floor has just the base slab. Still to do floor insulation here (will be 140mm sintered glass below 70mm screed for UFH). The VCL in the walls will be joined up with the floor DPM I think - still to sort out exactly how.

    Once doors and windows are here we should be sort of air-tight. Perhaps I should wait until the floor insulation and screed are in? I don't know what sort of test result we should really expect without the internal finishes though. How will I know if the result is good enough?
    • CommentAuthortony
    • CommentTimeJan 28th 2011
     
    Test it at that stage then.
  7.  
    Posted By: Sprocket1) The outer layer of newlath DPC on the walls. Tricky stuff to seal at edges but we did our best to seal overlapped sheets with Orcon-F and then tape.
    2) We did not think that was enough so on top of this we added a layer of heavy duty breathable VCL. Taped at edges.
    Perhaps it's just terminology, but I'm concerned you might have your membranes the wrong way round.

    Is the "newlath DPC" a non-vapour open polyethylene or polypropylene damp proof membrane? Is the "breathable VCL" directly on top of this? If so, why have a breathable layer directly on top of a non-breathable one? Is the idea to prevent moisture getting stuck between the two membranes? Or are you saying that you have the "newlath DPC" on the inside & "breathable VCL" on the outside?

    What is a breathable vapour control layer? Is it a vapour control layer with variable vapour resistance (e.g. Intello Plus) or an intermediate vapour resistance (e.g.Tyvek SD2)? Or do you mean a breathable sarking/sheathing membrane?

    Non-vapour open vapour control membranes should be on the inside/warm side of the wall. Breathable sarking/sheathing membranes should be on the outside/cold side of the wall.

    David
    •  
      CommentAuthordjh
    • CommentTimeJan 28th 2011
     
    and is there any insulation?
    • CommentAuthoranglia
    • CommentTimeJan 28th 2011
     
    If you're not installing an MVHR system, you should aim for a result between 3 and 5M3/hr/M2@50pa
    • CommentAuthortony
    • CommentTimeJan 28th 2011
     
    err

    lets say below 5 but why not aim for below 1?????
  11.  
    Posted By: angliaIf you're not installing an MVHR system, you should aim for a result between 3 and 5M3/hr/M2@50pa
    I don't think this necessarily follows. I think its pointless having MVHR if you're in the 3-5M3/hr/M2@50pa range. However, even if using natural ventilation, you should aim to get as low as you can so that ventilation can be controlled using trickle vents, humidity sensitive vents, etc. Build tight, ventilate right, as they say.

    David
    • CommentAuthorSprocket
    • CommentTimeJan 30th 2011 edited
     
    Thanks everyone - it's good to have someone to talk to about this stuff.

    The Newlath 2000 (not breathable) is outermost (next to rubble wall). It's waterproof but is covered in 'dimples', intended (I think) to let the inner facing stone surface ventilate slightly and stop water building up.
    Originally that was going to be only thing between wall and insulation but the Newlath was looking tricky to fold over top of wall and I wanted something to seal the top of wall inside and the tiny movement gaps/cracks where wall plate (timber) adjoins wall (via cement mortar). The newlath is also tricky to seal well to anything else including itself. So we added a layer of more flexible Intello-plus. It covers whole wall behind battens, joins to floor membrane and folds over top of wall where it is glued and taped to the timber wall plate. Top edge of wall only has Intello, no Newlath there.

    Insulation: yes, but not in yet. Plan is for 100mm of PUR between wall battens, then ~25mm air gap, then a multi-foil (continuous/taped with same in roof; insulation that doubles as inner VCL, not breathable so if moisture did get into insualtion area it can only get out outwards) then another ~25mm air gap, then 12mm plaster board, skim finish.

    MVHR: Yes, Xpelair Xcell 270BP. I presume that means we need more air tightness?
    Sure, I'll aim for zero ;-) but wasn't sure what to reasonably expect at this stage. If I get 3 should I be worried now or can I just expect the final finish to get us < 1.0 ?

    Heating (UFH from GSHP) is specced for winter losses including 0.5ACH. I think/hope there is a bit of headroom there though.
  13.  
    It's not good having two non-vapour open membranes, one inside & one outside the PUR/wall battens. Any water vapour making it through the multi-foil could condense on the cold side of the timber battens & will not be able to escape due to the Newlath membrane. The Intello-plus is not intended for use on the cold side of the insulation & will not be able to function as designed because it is over the Newlath membrane. So there is a real risk that the battens will rot due to water accummulation.

    As a rule, you should avoid having battens near the cold side of a non-vapour permeable construction & timber should be able to breathe towards at least one side of the construction. Is it too late to remove the battens, fit PUR against the wall & batten over this? Instead of using multi-foil, could you fit PUR between these new (warmer) battens & put some more Intello-plus on the inside to aid drying of the battens towards the room?

    David
    • CommentAuthorwookey
    • CommentTimeJan 31st 2011
     
    David - I think the battens are on top of both membranes so they are not trapped between. The two membranes are right next to each other. I think it's OK to have a double-membrane like this when one is not sure of the itegrity of the 1st one. I agree that intello is overkill here - I don't think it'll do it's clever thing right up against another membrane on the cold side.

    It seems that newlath is a fairly stiff (and not at all flat - I can see why sealing is tricky) lath-replacement substance to allow plastering of damp walls. As 0.5mm thick plastic sheet I presume is it totally vapour-proof, so a second sheet of easier-to-fit plastic on the inside shouldn't cause any problems. I guess a sheet of intello will be OK too, just much more expensive.
  15.  
    Posted By: wookeyDavid - I think the battens are on top of both membranes so they are not trapped between. The two membranes are right next to each other.
    Sorry, my post was ambiguous. There are three membrane/foil layers involved. The Newlath is on the cold side with the Intello-plus. The multi-foil is on the warm side. My concern is that the battens are on the cold side trapped between the Newlath/Intello-plus & the multi-foil. There are at least three ways forward:

    1. I would prefer to see a vapour open breathable sarking/sheathing membrane on the cold side & non-vapour open vapour control layer on the warm side. Perhaps rain penetration is an issue, but even so a breathable sheathing membrane should be able to provide the necessary protection without stopping vapour transfer.

    2. If this is not possible then the next best thing is to mimick a warm roof structure. Place the insulation against the Newlath/Intello-plus & fit the battens over the top. The battens will now be much warmer & less vulnerable to decay.

    3. In its current location, the Intello-plus is redundant from a vapour control point of view. The airtightness role could be performed just as well with 0.3mm polyethylene directly over the Newlath membrane. The insulation could be fitted against this with battens on top. The Intello-plus could be re-used as a vapour control layer on the warm side instead of the multi-foil, allowing the battens to dry towards the room when conditions are right.

    David
    • CommentAuthorSprocket
    • CommentTimeJan 31st 2011
     
    Yes, I see what you mean. The intello could probably have just been a plastic sheet.
    Oh well, I don't fancy removing it now - it's all taped and glued at the top. I guess I can live with it.

    The battens are fortunately not in contact with the membranes. The rubble walls are so crooked that it was simpler to fix at top and bottom to rafters and floor so there is a 20~80mm air gap. They rest on Perinsul block (sintered glass to insulate the edges of the heated floor). The Intello comes through over the top of the Perinsul but the Newlath goes straight down behind it. Sorry, it's not so easy to describe so I've probably still missed a few details.

    This is a pretty small barn. The idea was to learn what we can before doing the big one next door so this is all useful stuff to think about and learn from. The current spec is pretty much the standard build-up from the TLX multfoil brochure but because of the rubble stone wall we added the newlath. It didn't occur to me how much that might change things.
  17.  
    Posted By: SprocketThe battens are fortunately not in contact with the membranes. The rubble walls are so crooked that it was simpler to fix at top and bottom to rafters and floor so there is a 20~80mm air gap. They rest on Perinsul block (sintered glass to insulate the edges of the heated floor).
    I like the Perinsul block detail.

    Do you plan to put anything in the 20-80mm air gap? Could you fill this with some flexible insulation? If you leave an air gap then the battens won't be much warmer than the Newlath membrane, they'll be just as prone to condensation & there's a risk of thermal bypass (air getting around the insulation).

    David
    • CommentAuthorSprocket
    • CommentTimeJan 31st 2011
     
    We hadn't planned to fill it. But then we hadn't expected it to be so large either. This gap didn't figure in any of the drawings. I have been wondering about how much the air will move the Intello; although the Newlath is pretty firmly fixed to the wall.

    What sort of thing would you suggest? Something like mineral wool?

    - Andy
  19.  
    I wouldn't recommend mineral wool behind the PUR/battens due to the risk of condensation. I'm imagining some kind of compressible closed-cell material like the foamed polyethylene or nitrile rubber used for pipe insulation. It's available in sheets & would be quite easy to fit behind the battens, but you would also need to do behind the PUR boards if you wanted to reduce the thermal bypass risk.

    David
  20.  
    In my experience having two airtight layers with one as a 'backup' causes more problems than it solves.

    The issue is that it makes leaks very difficult to trace back to their origin. Air gets into the space between the two layers and can travel long distances before entering through the inner barrier.

    I'd propose treating the inner barrier as the air barrier and not even attempting to seal the outer membrane.

1 to 20 of 20

  1.  
Add your comments

    Username Password
  • Format comments as
 
Back to Discussions Top of Page
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press