The Passive Solar Book

[ki4hpz]

The Passive Solar Book, July 2006, goes over exterior walls.  In this order.

Drywall
6 mil vapor barrier
2 x 4 studs filled with unfased insulation - his recommendation is 2 x 4 walls
1/2 CDX on the exterior
1" tongue and groove insulated blue board
Outside siding

Would you put a vapor barrier between the 1/2 CDX and 1" tongue and groove blue board? Any comments?

[Freeholdfarm]

A vapor barrier should always be on the heated side of the wall, which means his location is correct unless you live in a really hot climate.  However, I don't see how he can recommend 2x4 walls.  How old is that book?  I know I've seen it, probably read it at some point, but don't own a copy.

Kathleen

[ki4hpz]

The book just came out. This is the latest edition. Would you not use house wrap?

http://www.amazon.com/Passive-Solar-House-Complete-Heating/dp/1933392037/sr=8-1/qid=1159857363/ref=pd_bbs_1/102-8640075-7303306?ie=UTF8&s=books

[glenn kangiser]

House wrap manytimes performs OK, but if it doesn't and water gets behind it then you are in for possible mold problems.  Many places have had to be remodeled or worse in a few years due to housewrap.  30# felt has performed reliably for many decades and generally does not have the problems of the new wraps.  If using a wrap, a rain screen wall is good insurance.  Felt wrinkles when wet and makes a drainage plane -then returns to shape when dry.  

We have a lot more info here on this site -- search tyvek.

[ki4hpz]

Between what layers would you put house wrap? I live in the north georgia area.

Thanks

[glenn kangiser]

If I was to use a house wrap I would only use it on the outside and only with a screen wall.  The problems it can cause could cause replacement of all materials from foundation to way up the wall.  I wouldn't use it myself in actuality - I'd use felt.  

The problems with the house wrap come in where any water gets behind a penetration or hole in the wrap and gets between it and the wood.  The wrap will pass vapor but not water.  Imagine a sheet of plastic against the wall.  Take a hose and fill it with water -simulating a good leak.  What happens to the water?  It spreads all over the place trying to find a way out -- It may damage everythng in it's path and cause major mold.

Felt on the other hand starts to wrinkle when it gets wet- it expands a bit.  Wherever it wrinkles makes a drain - if there is not room for a drain it starts to conduct a bit more water wicking it out of the damp area.  It passes more vapor than the wraps along with water by this method.  When it removes the water it drys and goes back as it was, ready for another incident.  The wraps do not have this ability.

In the summer in your area the heated side could be the outside as humidity is high and the inside is cooled.  In this case it could be a vapor barrier on the outside but then again so could felt without as much need for a screen wall space and without much danger of the winter moisture problems.  It's hard to beat an old proven material.

It is a great idea to wrap the house with one great big envelope and the corporations have spent lots of money promoting their easy to use product.  They just don't mention the possible problems.

[Freeholdfarm]

This may sound like heresy, but in a hot, humid climate, I wouldn't put a vapor barrier in the walls at all.  I think it would just be asking for mold and rot problems.  I would use an insulation that was relatively impervious to moisture -- or leave the insulation out altogether, except in the roof.  

Kathleen

[glenn kangiser]

That is another option, Kathleen, and one that has been good over the years in some areas.  You don't see many 100 to 400 year old houses with vapor barriers.  Maybe painted plaster walls would act as a bit of a barrier on the inside.

This new idea of making things 100 percent air tight has created a whole new set of problems - some with not too good a solution.

I think the felt and insulation is still a good idea though - prevents your heating or cooling from getting away.

[John Raabe]

Today I would do 2x6 framing (24" o/c if possible), unfaced batts and the exterior foam covered with taped house wrap and spacers for a drainage plane under the siding as Glenn mentions. In really cold climates I would do an interior 6 mil poly VB but not in mild or cooling climates. In cold climates the foam could be put on the interior under the drywall and taped for both an air and vapor barrier.

The taped housewrap will serve as an air barrier and that will stop the vast majority of moisture migration problems.

While the book may be recently reprinted (is it by Ed Mazria?), that wall is from the late 70's and early 80's. I know because I used to preach the same sermon myself.

[Sassy]

Speaking of passive solar - our weather has been 56 degrees or cooler for the past 3 days & today the high has been 66, it's also been overcast & rainy.  The interior of the underground cabin has stayed at 70-71 degrees without using any heat...unless you can consider "hot flashes" heat   - Glenn keeps threatening to attach a fan to me   ...

So, the thermal flywheel effects of the ground storing heat from the sun makes our place quite comfortable & cheap to heat.   8-)  

[ki4hpz]

I found on page 49-50 of James Kachadorian's book that house wrap is not need if you use 1" tongue and groove blue board. The blue board acts as additional insulation and seal against penetrations.

[Amanda_931]

Not sure what part of the country you're from (at one stage we thought that putting general locations in our posts--glamorous Middle Tennessee, California Gold country, Ahmpit of the Cape, for instance--was a good idea, which is why a few of us do it.), but Kachadorian at the time the first edition of the book came out, had mostly worked in New England.  Might or might not be good for, say, USDA chill zone 8 in Moore County North Carolina.

[Freeholdfarm]

Sassy, your comment about Glen wanting to attach a fan to you make me laugh -- sometimes I feel like I could replace the furnace, myself!  Unfortunately, at least so far, I've only had hot flashes during hot weather . . . not during the cold weather when they might have actually been appreciated!

Kathleen

[glenn-k]

We actually saw her raise the temperature in the room while we were in there with no other reason for the temp increase.  It was colder outside.  Heaters we off -sun was already past the window hours ago- We have a small weather station with a sensor about 8 feet from her chair.

She's one hot mama. :-/