[Greenbuilding] Mold questions

[Jefro]

Hi Keith, thanks for the response.

The point you and Rob make is well taken, but I'm not sure we could 
transition to a slab at this point, 90% of the way through engineering.  
Nor do we want to, actually---we chose a joisted floor for several 
reasons.  I'm interested in the idea of conditioning the crawlspace, but 
not sure how realistic that is.  I had wanted a basement early on in the 
process but it was deleted due to cost.

Regarding mold in cellulose, several of the sites I read about mold have 
talked about it growing on organic materials including cellulose, such 
as the paper backing on wallboard.  Most sites also mentioned that mold 
can grow on just about anything as long as moisture and oxygen are 
present.  When you see it in fiberglass, do you see it in the glass 
itself, or in the paper backing?

Your note about barriers is very interesting, and I will take it very 
much to heart and discuss it with our contractors.  For the exterior, we 
can caulk all sheathing seams and wrap in tyvek; for the interior we can 
certainly use foam to seal around all protrusions and then plaster over 
the foam.  Does that sound sufficient? 

I am also learning more about our humidity, which will be different at 
the new property (4 miles inland) than it is at our existing house (1 
mile inland).  The new property will be warmer on average and will have 
better airflow and a lower water table.  Will know more in the next few 
weeks.  I dearly wish we could have been on the land for a year before 
building so we could study all of this, but it just hasn't worked out.

For the roof, we are planning to insulate the rafters with either 
cellulose or denim batts, making sure to leave a space for airflow 
between insulation and sheathing.  The air is to be provided by vented 
soffits and a ridge vent, or at least that's how I have been picturing 
it.  The roof is a rock simple gable-end design with nothing fancy, just 
two flat planes at 8:12 joined at the ridge.  Overhangs are about 4 
feet.  I'm not sure what you mean by using SIPs, would they comprise the 
top layer between rafters and shingles, or would they attach under the 
rafters?  Very likely beyond our budget in any case.

Thanks again for all the advice


Keith Winston wrote:
> You've gotten a lot of good advice here, Jefro. I'll add some emphasis:
>
> The "just don't" that Robert wrote means -- don't use a crawl space! The 
> only way crawlspaces work well in a potentially humid climate is if they 
> are fully conditioned, and that's problematic for a bunch of reasons. 
> Figure out how to build on a slab, or a (conditioned) basement. Much 
> more at (the much-vaunted) buildingscience.com.
>
> As mentioned, ditch vapor barriers altogether, and think in terms of air 
> barriers. Caulk all relevant framing members, gasket/caulk sheetrock & 
> electrical/other protrusions, etc. More at buildingscience.com.
>
> Finally, why do you think mold loves cellulose? Do you have any concrete 
> data to that effect? I've seen mold in fiberglass far more than 
> cellulose. I would echo the idea that your wall cavities need to be kept 
> dry (consider secondary drainage planes behind your siding), and that 
> cellulose is fine in a well-built wall.
>
> Your roof details are a trickier issue: how are you thinking of building 
> it? I tend to like a hot-roof design, with the insulation against the 
> roof itself (as opposed to in the ceiling/attic floor). As with walls, 
> the air-barrier question becomes very important with roofs, especially 
> in a humid climate. You might consider SIPS or foam for the roof. Doing 
> a ventilated roof is very very hard if you've got any complexity of 
> design at all (i.e. dormers).
>
> Good luck! You are on track by asking such good questions.
>
> Keith
>
>
> Jefro wrote:
>   
>> Hi Robert, thanks for the response
>>
>> Not sure what "just don't" refers to.  Don't ventilate the crawlspace?  
>> Or don't use a vapor barrier under the house?  The building department 
>> here recommends neither insulation nor vapor barrier in a crawlspace, 
>> and while I was very skeptical at first I'm starting to see the logic.
>>
>> Our climate isn't quite "southern humid".  Average air temp here is in 
>> the low 60s so we are more similar to Vancouver than to most other 
>> places in the US.  I agree about not using vapor barriers at all, but 
>> short of cutting holes in the sheathing I'm not quite sure what to do; 
>> that's the main reason I posted to the list.  We had originally intended 
>> to be building with bales and using permeable earth plasters on both 
>> exterior and interior, but that plan has changed considerably. 
>>
>> We have been looking at cellulose because it is recycled and natural, 
>> but building a solidly performing house that will last a hundred years 
>> is much greener than using recycled materials and rebuilding every few 
>> decades.  I am not very familiar with Roxul but will do some research.
>>
>> thanks again
>>
>> Robert W. Tom wrote:
>>   
>>     
>>> On Mon, 28 Aug 2006 04:29:00 -0400, Jefro <jefro at jefro.net> wrote:
>>>
>>>     
>>>       
>>>> Mold is a big concern for us, as my wife has asthma and we both have 
>>>> allergies.
>>>>
>>>> - We are planning to use cellulose insulation.  Mold loves cellulose
>>>>       
>>>> - I am concerned about getting vapor barriers right.
>>>>       
>>>> (well-ventilated) crawlspace
>>>>       
>>>>         
>>> Ggggnnnaahhhhh !
>>>
>>> Sounds like a Disaster in the making, with a capital "M".
>>>
>>> A "well-ventilated crawlspace" in a humid southern (US) clime surely 
>>> has to be on Joe
>>> Lstiburek's  (a good Canadian, eh ?) "Top Ten" list of dumb things to 
>>> do. If not, it should be. So just don't.
>>>
>>> Similarly with the cellulose:
>>>
>>> If there are any doubts about the ability of the designers and 
>>> builders to detail the air barrier so that bulk moisture transport via 
>>> air leakage is minimised, I'd say look for some other insulation that 
>>> has a capacity to drain and is not susceptible to moisture. (ie Roxul 
>>> mineral wool)
>>>
>>> As for vapour barriers; vapour diffusion through the broad surfaces of 
>>> buildings never has and never will be a problem in a mild southern 
>>> (US) clime... so "getting the vapour barriers right" means not using 
>>> them.
>>>
>>> The sheathing materials (plywood) and Portland cement plasters in 
>>> themselves are of sufficiently low vapour permeance that they will 
>>> likely behave as effective vapour diffusion retarders, and possibly 
>>> even dangerously so.
>>>
>>> ===* ===
>>> Rob Tom
>>> Kanata, Ontario, Canada
>>> <archilogic at chaffyahoo dot ca>
>>> winnow the chaff from my edress in your reply
>>>
>>>
>>>     
>>>       
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