More on Walls and Floor...

I just got back from an epic coastal hike.  Two friends arrived from Brooklyn NYC on wednesday night and by thursday afternoon we were on Rialto Beach on the Olympic Peninsula.  We traveled 20 something miles up the coast over gnarly rock and boulders to Shi Shi beach where my friend was waiting with an amazing campsite and a leather pouch full of red wine.  It was a bit stressful at times because the distance was much harder to cover due to the terrain, but we pulled through.  I did not take any photos, but my friend Scott Hollis covered our destination.  Check out his photo stream here.

When I finally got home I borrowed my girlfriend's computer (because I don't even have a working computer with internet access) and I saw some emails about my floor, wall, roof post.  First of all I was ecstatic to see that people were responding, but also that the blog is working to spread my projects and initiate feedback.

My friend Tyler Smith is an architectural engineer and works for a building envelope engineering firm in Portland, Oregon.  When he read my post he took it straight to his boss and they had some discussions about the design.  He later called me back and we had a bit of a conference call.  He said it was a great learning opportunity for him to cover external wrap insulation with his boss and it was very helpful for me to get building engineer's input.

Advice from buildings engineers:

1.  Do not use polyiso foam.  They claim that the stuff acts like a sponge and if you mount it over the housewrap to the plywood sheeting it will hold moisture and there will be inward solar vapor drives that will push the moisture from the insulation into the wall.  They recommended using xps (extruded polystyrene) because it is waterproof and to get the foam board xps insulation that has vertical grooves in the insulation so when moisture condenses it can have an avenue to get out.

Tyler also mentioned that once the Polyiso is impregnated with water it no long has any insulating value.  In all types of insulation the closed air space creates the insulating capacity.  Once the air spaces become filled with water, the water transfers heat well and the wet insulation will become a bio-mass that actually, in our climate, will stay cold and your heating system will have to work against it.

2.  The wall wrap material is not sufficient for the floor moisture barrier.  It is gonna rip.

3.  They recommend using an impervious membrane on the floor and walls, but not on the roof.  A friend of mine has been encouraging me to use a vapor permeable house wrap so that when moisture builds in the walls it can escape.  The engineers claim that you do not want moisture entering in your walls or floor and that the only way to prevent that is to put a heavier, impervious membrane.  I was advised that the interior wall paneling that I am going to use, (woven cedar mat) will have plenty of airflow to dry out the wall if water were to enter.  Because the foam is sitting directly over the wall it can hold moisture and they would highly recommend using something that will not allow water build up to pass through.

After all that great advice my friend stayed late at work and sketched these wall/floor cross-sections for me.  Thanks so much Ty.

The email ended with this recommendation:

"I was also trying to think of a way to exterior insulate the floor, similar to the walls, then using some kind of woven high-strength permeable material as the 'siding' under the insulation (like this stuff http://www.all-rite.com/underbelly-material-p-407.html).  However, then you'd need an air/water barrier above the insulation, which you'd want to tie into your walls somehow"

If there are any further comments please do not hesitate to add them to ad them directly to the posts, thanks...