[GSBN] Ceiling Air Barrier

Enga Lokey enga at thelokeys.net
Fri Nov 21 06:26:15 CST 2014

Thanks again for all the great perspectives. Min, your comment was a reminder of how different people's perspectives can be. My biggest lament after doing initial energy improvements to my first home here in Australia (which had no insulation at all when purchased) was that I could no longer hear the rain on the tin roof once it was well insulated. In the land of drought, that is music!

Derek, my comment about mass is that the rafters were sized based on the weight they would have to hold. I am very much not an engineer, but I have used some of the software to select member sizes and a lightweight timber clad ceiling is different than a heavy ceiling  with batons and drywall. Your point regarding fire is taken.


Natimuk, Australia

enga at thelokeys.net

On 21/11/2014, at 11:03 PM, Frank Tettemer wrote:

> I'd advocate for drywall AND the membrane. The membrane, when installed with great care to seal all seams, is a good attempt at a perfect air barrier. I've used a product by CertainTeed called Membrain, which is a variably permeable sheet material, similar to your product, (in intention, at least).
> I have used this material would good results, in double-stud, dense-packed cellulose wall construction.
> To the ceiling, I would add drywall and a rough taping of the seams, to seal them, with a drywall 'mud'. This layer acts as a bit of a fire-stop. Or, at least a fire slow-down.
> On top of the drywall, (towards the inside of the ceiling), I would add the wood layer, for aesthetic purposes.
> Some building codes require a layer of drywall, under any other ceiling covering materials, such as wood, bamboo, rattan, etc., for fire resistance. II imagine that it could mean the difference between a fire-ruined interior, or a total fire-loss of the roof.
> My Canadian back-woods two-cents.
> Frank Tettemer
> Living Sol ~ Building and Design
> www.livingsol.com
> 613 756 3884
> On 20/11/2014 5:14 PM, Min Hall wrote:
>> Hi Enga - And now another two cents worth. Cathedral ceilings are not that great for the acoustics in a room and adding the dry wall(gib as we call it in NZ) certainly helps with this. It helps muffles external noise – rain, hail, etc. and it can also be part of an absorptive acoustic treatment – having drywall, then some more battens with 2 inches(50mm) of acoustic insulation and then your timber ceiling lining with ¼ to 3/8 inch (6-10mm)gaps between each board.
>> Just designing a house for a music buff and we are striking all these issues.
>> Cheers
>> Min
>> *From:*GSBN-bounces at sustainablesources.com [mailto:GSBN-bounces at sustainablesources.com] *On Behalf Of *Derek Stearns Roff
>> *Sent:* Friday, 21 November 2014 10:55 a.m.
>> *To:* Global Straw Building Network
>> *Subject:* Re: [GSBN] Ceiling Air Barrier
>> Enga, I was not advocating drywall plus Intello, but rather asking the man who knows, John Straube, if he could see any reason to use both. I was also asking his views on drywall instead of Intello. Intello is a great product, from what I read. I’m not arguing that you should change your plan, rather I hope to hear more about comparing the options.
>> I think the increased fire protection is the strongest reason to consider drywall. The roof/ceiling is the most vulnerable part of the building envelope, from a fire perspective. A secondary factor would be greater reliability/success rate in air-sealing penetrations. These considerations may also seem like belt and suspenders to some. My guess is that around here, the cost of installing airtight drywall, with all materials and labor, would be a bit less than installing Intello, materials and labor. Your situation could be different.
>> I’d like to understand your comment about needing to calculate the mass in the original engineering. Please say more.
>> Thanks,
>> Derek
>> On Nov 20, 2014, at 1:57 PM, Enga Lokey <enga at thelokeys.net <mailto:enga at thelokeys.net>> wrote:
>>    Thanks all of you for the discussion. Yes and no answers are so
>>    useless. They are very unhelpful in fleshing out the subtleties
>>    and "why's" of an issue and mostly used by those that don't really
>>    know what they are taking about but are strongly opinionated.
>>    Feile, your info about multiple blower door tests is something I
>>    need to be aware of when design some future studies. Do you have
>>    any links to that info? Derek, you are not the first to suggest
>>    the drywall idea. To me it sounds like belt and suspenders. Yes
>>    your pants are doubly certain not to fall down, but when it comes
>>    to drywall and air barrier, the extra drywall is alot of extra
>>    materials, time and labour (plus mass that would need to be
>>    calculated in the engineering originally). I personally am too
>>    lazy for that. But, maybe I just don't understand something
>>    important there. Would the Intello not be a redundant and a waste
>>    of money at that point?
>>    You guys rock! Thanks,
>>    E
>>    Natimuk, Australia
>>    enga at thelokeys.net <mailto:enga at thelokeys.net>
>>    On 21/11/2014, at 4:05 AM, Feile Butler wrote:
>>        We detail the airtight membrane stapled to the ceiling joists
>>        for the flat ceiling sections, with ample insulation above. As
>>        noted previously, hats to seal services passing through are
>>        critical. However, if there is space, a nice detail is to
>>        allow for a 25 - 40mm (1" - 1.5") service void below the
>>        airtight barrier to avoid concern about services breaking
>>        through (we always use this detail on walls). The
>>        plasterboard/T&G is fixed to a minimal amount of battens. This
>>        is particularly beneficial if anyone wants to add services in
>>        the future as they will be independent of the airtight membrane.
>>        On the sloped sections, sometimes it is difficult to get
>>        enough insulation within the depth of the rafters. In this
>>        situation, we staple the airtight membrane to the underside of
>>        the rafters. Then we fix semi-rigid wood fibre boards (e.g.
>>        Gutex or Steico) through the membrane into the rafters and fix
>>        our plasterboard or T&G to the wood fibre boards. It is an
>>        effective detail and has been tested with very good results.
>>        We have also fixed very small lath-like battens on to the
>>        membrane in situations where it needed to be a bit more
>>        robust, e.g. horizontal battens fixed through the membrane to
>>        vertical studs in a timber frame wall where cellulose was
>>        pumped in after.
>>        I'm a big fan of Intello as it is a cellular membrane and
>>        checks vapour in both directions - so if the weather
>>        conditions mean that reverse diffusion is required, this can
>>        happen. The micro-porous membranes are not so capable.
>>        You have mentioned being careful at penetrations/junctions - I
>>        still use the pen test every time - can you put pen to paper
>>        and trace around each section of your building. If you need to
>>        lift your pen - this is an area that needs some consideration.
>>        I did hear an interesting point from a services engineer who
>>        also carries out a lot of blower door tests. People worry
>>        about screws/nails/staples diminshing the effectiveness of the
>>        airtight membrane. But the fixings fully fill the holes, so
>>        this is not really a concern. However, in houses where there
>>        were multiple blower door tests carried out, it was noticed
>>        that the results were getting slightly worse every time (now -
>>        the figures were probably miniscule). But it turned out that
>>        each time the membrane was put under pressure from the blower
>>        test, it moved and strained against the fixings, enlarging the
>>        holes that little more.
>>        Regards
>>        Feile
>>        feile at mudandwood.com <mailto:feile at mudandwood.com>
>>        www.mudandwood.com <http://www.mudandwood.com/>
>>        ----- Original Message -----
>>        *From:*Derek Stearns Roff <mailto:derek at unm.edu>
>>        *To:*Global Straw Building Network
>>        <mailto:GSBN at sustainablesources.com>
>>        *Sent:*Thursday, November 20, 2014 2:28 PM
>>        *Subject:*Re: [GSBN] Ceiling Air Barrier
>>        It’s wonderful to have your input, John. I wonder what your
>>        opinion is of airtight drywall under (closer to the outside
>>        world) the tongue and groove wood ceiling. The advantages
>>        would be greater fire resistance and greater thickness and
>>        stiffness that might suffer less damage to the airtightness
>>        during the subsequent steps in the construction process, than
>>        would an unsupported layer of Intello (unsupported until the T
>>        & G is installed). There are disadvantages as well. Would
>>        drywall plus Intello ever make sense?
>>        Thanks,
>>        Derek
>>        On Nov 20, 2014, at 6:45 AM, John Straube
>>        <jfstraube at uwaterloo.ca <mailto:jfstraube at uwaterloo.ca>> wrote:
>>            I am going to disagree with Ian here. What he has
>>            described, we would describe as a roof underlayment, not
>>            an air barrier. It is installed in line with the slope of
>>            the pitch and is therefore not able to be used as an air
>>            barrier if the attic is ventilated like normal wood frame
>>            pitched roofs. The asphalt impregnated paper material is
>>            very difficult to seal at laps and joints to make it an
>>            air barrier. when the wind blows, the laps open up and air
>>            rushes through. It is almost impossible to seal tight
>>            around pipe penetrations and other joints. Even if it
>>            could be sealed, most materials like this will rip if they
>>            are airtight when a big wind gut comes along. Thankfully
>>            they are not airtight, and work great as a temporary water
>>            protection, as stated, and continue to catch all the rain
>>            leak from holes and laps in the roofing and direct these
>>            leaks harmlessly to the outside. But an air barrier they
>>            are not.
>>            An air barrier at the ceiling plane level should be under
>>            the insulation and rafter, and ideally there should be
>>            some experience with testing the system in real buildings.
>>            The Intello solution is definitely one such solution—
>>            tested with blower doors and IR cameras all the time.
>>            On Nov 20, 2014, at 2:33 AM, Ian Redfern
>>            <ian at adobesouth.co.nz <mailto:ian at adobesouth.co.nz>> wrote:
>>                Good evening Enga,
>>                First a question : are you installing a fluffy blanket
>>                type insulation above and against the tongue and
>>                groove sarking i.e. between the purlins, or if the
>>                sarking is under the rafters the insulation the
>>                insulation will be between the rafters ?
>>                Assuming this scenario, we have for decades used a
>>                heavy weight black bituminous kraft breather paper
>>                building wrap across the slope with generous laps fish
>>                scale like to shed moisture during construction - one
>>                advantage is that these mask out any splits or loose
>>                small knots in the sarking as well as providing the
>>                essential weather resistance at a critical stage of
>>                the build (who wants water stains on their sarking)
>>                Another advantage is that it is non reflective so no
>>                glare for the building team - the roof underlay is
>>                over the purlins and usually installed by the roofing
>>                gang = this is another story
>>                From: Enga Lokey
>>                Sent: Wednesday, November 19, 2014 20:46
>>                To: Global Straw Building Network
>>                Reply To: Global Straw Building Network
>>                Subject: [GSBN] air barrier
>>                G'day all,
>>                I have been getting conflicting info on a ceiling air
>>                barrier, so I would love it if some of you that have
>>                experience in this realm would like to weigh in on the
>>                confusion.... or solution. I realise that a tongue and
>>                groove cathedral ceiling is a potential nightmare for
>>                air exchange. I realise that drywall can be installed
>>                airtight. It is claimed that air barrier wrap such as
>>                Intello can be used between the rafters and the
>>                ceiling lining boards to create an air barrier, thus
>>                the lining boards leak like a sieve and the roof
>>                cavity does not get air from inside. Can anyone
>>                confirm if an air barrier used in this position would
>>                be effective? With usual detailing of air-sealing at
>>                penetrations and wall/ceiling interface of course.
>>                Thanks for any bits of wisdom.
>>            John F Straube
>>            jfstraube at uwaterloo.ca <mailto:jfstraube at uwaterloo.ca>
>>            www.JohnStraube.com <http://www.johnstraube.com/>
>>            _______________________________________________
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>>        Derek Roff
>>        derek at unm.edu <mailto:derek at unm.edu>
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