[GSBN] Ceiling Air Barrier

Frank Tettemer frank at livingsol.com
Fri Nov 21 06:03:56 CST 2014

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
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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> derek at unm.edu <mailto:derek at unm.edu>
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