[Strawbale] 5 perms / no ventilation, and top-of-wall (Mark Piepkorn)

[Frank Tettemer]

Rob, I've just realized my mis-understanding ... you wrote:
'In *predominantly cooling climates*, air leakage would tend to
be from the outside-in at the top plate wall/ceiling junction ... SNIP

And I mistook your comment to mean in a *cool climate*, (such as ours).

and of course you're right.  In a climate where cooling is needed, the 
flow of infiltration is reversed, just as you've said.
(In our *cool climate*, during the heating season, hot air attempts to 
escape from the house)
And I do agree that anticipating that attempt at infiltration, at the 
wall-ceiling junction, is just what is needed. 
John Straube, I believe, has indicated that this seal be an air barrier 
but not a vapour barrier, in that thread-forming post that you offered, 
Mark .  Or am I mis-understanding that, too? 

So we have the potential for an opening (crack) due to separation of 
plaster and beam, up near the top of the wall. 
But what if the straw bale wall did not meet at a beam? what if the beam 
was well inside the wall assembly, (or), outside the wall assembly?  And 
what if the wall assembly penetrated the ceiling vapour barrier, going 
through the ceiling into the attic space?  And the plaster render was 
troweled onto the inside of the strawbale wall, with ceiling membrane 
brought down the bale wall six to eight inches and pinned to the bales.  
The inner plaster seals well with the ceiling membrane, and we've slowed 
down (or stopped) the in/ex/filtration.  Above the ceiling membrane, the 
plaster is laid onto the bales, up and over the top of the wall, and on 
down the outer surface of the wall, un-interrupted by the exterior 
soffit .  This is hard to describe.  Am I making sense?

Frank



Rob Tom wrote:
> On Mon, 12 Mar 2007 19:30:31 -0400, Frank Tettemer 
> <frankt at webhart.net> wrote:
>
>>
>> But cracks are cracks, and in plaster renders, very hard to prepare for
>> or plan for. Or prevent.
>
> Frank;
>
> I think that the strategy is to assume that cracks will occur at the 
> wall-ceiling junction and having anticipated them, devise a means to 
> ensure that continuity of the air barrier at that crack.
>
> That is the basic princsiple behind the use of control joints.
>
>
>> I visualize the home, with it's inner air pressures, and think about
>> this whole question from that avenue of exploration.  And "typical house
>> stack-affect" makes me tend believe that ( on a non-windy day), internal
>> house pressures from stack effect (in a cold climate)
>> are busy moving *hot air* and moisture vapour *outwards*, through any
>> passage available, towards the great outdoors, about anywhere on a wall
>> from the neutral plane, on up.
>>
>> And from *below* the neutral plane, *cold, dry air* spends its time,
>> slipping *inward* through any cracks.
>
> That is what physics tells us to be true.
>
>>  I'm not so sure that what
>> you've said is true, Monsieur Tom.
>>
>> Rob Tom wrote:
>>> "In predominantly cooling climates, air leakage would tend to
>>> be from the outside-in at the top plate wall/ceiling junction butthe 
>>> outside/inside differences in temp & humidity  (and hence the 
>>> concerns WRT)
>>> aren't as great in that situation."
>>
>> I'm thinking: "airleakage goes from inside to outside, near the top of a
>> wall assembly, and then one can address airleakage on that basis".
>
> Assuming that the perceived un-truth is the reference to the reversal 
> of infiltration/exfiltration locations WRT to the neutral plane in 
> cooling situations, I would refer interested parties to:
>
> --> the ASHRAE Handbook of Fundamentals,
> ---> the chapter on "Ventilation and Infiltration"
> ----> "Thermal Buoyancy, Stack Effect"
> -----> "Cooling Season"
>
> Basically, indoors is cooler than outdoors. Coolth tends to drop and 
> the warmer air replacing it infiltrates above the neutral plane.
>
>> But replacing these plaster coats with tyvec or tarred felt is not a
>> good option, to me.
>
> I haven't looked at the book to which Duck Foo'd was referring so I 
> don't know what it suggested but I wouldn't imagine that they're 
> suggesting that plaster be replaced with Tyvek or tarred felt.
>
> For one thing, the Fire Marshall wouldn't like it one bit.
>
>
> === * ===
> Rob Tom
> Kanata, Ontario, Canada
> <A r c h i L o g i c   at  c h a f f y a h o o   dot   c a >
> winnow the chaff from my edress in your reply
>
>
>
>
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