[GSBN] air barrier

Thu Nov 20 07:33:55 UTC 2014

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

Regards

Ian

Ps  we specify thick (for max R value) polyester blanket and never use blown
glass fibre based product

  www.adobesouth.co.nz   Ian Redfern
 Adobe South
 A:    5 Lancewood Rise, Onerahi, Whangarei
 P:     09 436 4040      M: 027 490 2324
 E:     ian at adobesouth.co.nz

From:  <jfstraube at gmail.com>
Reply-To:  Global Straw Building Network <GSBN at sustainablesources.com>
Date:  Thursday, November 20, 2014 2:55 PM
To:  <GSBN at sustainablesources.com>, Global Straw Building Network
<GSBN at sustainablesources.com>
Subject:  Re: [GSBN] air barrier

Hi Enga
Things like this are my specialty so I am comfortable weighing in. Yes a
large (to minimize laps) roll of strong sheet (to resist wind gusts) like
intello or more affordable Tyvek or Hardie wrap or whatever would be great
sandwiched between the wood ceiling and the rafters. Care? is needed at
partition walls light fixtures and wiring and plumbing penetrations but it
certainly is and can be a good way to make an air barrier.

Sent from my BlackBerry 10 smartphone on the Bell network.

                                                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.

Enga Lokey
Natimuk 
Australia

enga at thelokeys.net

On 18/11/2014, at 2:31 PM, douglas nichols wrote:

> Hi Ian
> 
> I've come upon this similar tie in when attaching gable trusses with a tall
> energy heel.  Sheeting over wood bond beam up onto the  truss heel with
> continuous ply makes for a very strong connection (sheer and uplift) and I
> have not had to do any special crack protection.  That being said, proper
> straw bale to wood plaster techniques are crucial.  My process is:  fill any
> gap between wood bond beam and straw bales with straw clay,  next 2 ply stucco
> paper over the sheeting (slip plane is a must I feel in these large exterior
> sheeting / plaster scenarios), 6 inch lap of lathing onto straw (if your not
> lathing entire building),  and continuous slip coat from straw to lathing.  I
> use wet clay slip pushed into the bales and then add straw (lots of it)  to
> the clay to go over the prepped area this gives a very similar monolithic
> substrate (with high tensile strength from all the straw) for the next plaster
> layers.  You can always bed some big pieces of fiberglass mesh (or other type)
> in the brown or finish coat (I've started doing this at all corners of
> openings to reduce cracking).  Out of curiosity how will deal with overhang?
> Will the top cord of the truss run long?
> 
> Doug Nichols
> Natural Building Instructor
> Community Rebuilds
> Moab Utah
> www.communtityrebuilds.org <http://www.communtityrebuilds.org>
> 
> 
> Date: Mon, 17 Nov 2014 15:26:10 -0700
> From: ian at lopezsmolensengineers.com
> To: gsbn at sustainablesources.com
> Subject: [GSBN] Plaster detail at Bale/Plywood Interface
> 
> Hi everyone,
> 
> I'm currently helping with the design of a one-story SB house with a
> rectangular footprint and a simple shed roof.  The SB walls will be
> constructed with a wood bond beam that's in the horizontal plane around the
> whole perimeter of the house, supported on wood posts.  Prefabricated wood
> trusses will then bear on top of these beams.  The trusses will have a "right
> triangle" shape to create the shed roof and a flat ceiling on the interior.
> 
> On the higher side walls of the trusses, the owner would like to have plaster
> continue all the way up to the underside of the roof (actually, to the
> underside of the roof sheathing), with minimal trim/flashing, etc. at the
> interface/transition between the straw bales and the plywood.
> 
> I've already mentioned to him that there's the possibility that that plaster
> will crack at this interface (due to the differences in substrate material,
> plaster thickness, etc), and I've suggested that there be a control joint in
> the plaster, or a piece of trim with flashing or something.
> 
> I'm just wondering how the rest of you prefer to deal with this detail...
> 
> Thanks very much,
> 
> Ian Smith, P.E.
> Boulder, CO, USA
> 
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