insulation and vapor barrier confusion

[dorothyinak]

Just when I think we finally have an easy, no-brainer project.....

We were planning a 6mil vapor barrier on the inside (have tyvek on the outside) hoping that will keep the moisture going in the right direction.  Went on-line to find tips on making sure we seal it up tight, and was feeling fine til I read this from a Building Science Corp. article:
One of the problems in the building industry is that we have a spreading "cult-like" mentality that worships at the "church of polyethylene". This cult views the answer to all moisture problems as the installation of a polyethylene vapor barrier condom on the inside of buildings. This cult is responsible for many more building failures than building successes. It's time that the cult deprogramming started.

Homer, AK is definilty a cool, wet marine climate....we have our share of 70 degree days in the summer, but generally, wet and cold for the winter and wet in the summer.  Most of the info I've seen supports the total encapsulation of the interior walls in plastic, but not sure after this and reading some of the older posts.

Thoughts?  I was also thinking of using the Kraft facted batts and the 6 mil poly, since I thought it looked easier to install, and it may be awhile between installing the insulation and finalizing the vapor barrier......is this overkill?

[glenn-k]

Based on most of the online research I have done, I don't think that sounds like too good an idea.

Most of the best information is in this topic -

http://www.countryplans.com/cgi-bin/yabb2/YaBB.pl?num=1140662724

[jraabe]

I used to do builder training with Joe Lstiburek, founder of Building Science Corp. He (they) do pretty good science and even better marketing. Joe knows you have to hit a builder over the head with a 2x4 to get their attention and then tell them something really scary to get them to change the way they build.

This may have some merit when you are trying to move building science. (And even more merit when you are trying to get federal and state funding.)

However, Joe can get people unnecessarily worked up with his chicken little act. That part of the show hasn't changed for over 25 years!

If you are in a heating dominated climate (Homer, AK qualifies!) you will have very good luck making the interior side of the insulation as vapor and air tight as possible, and then make the outside surface relatively more breathable. You basic plan is well proven. Two things will help perfect this for your climate:
• Have good ventilation and ideally heat recovery ventilation to maintain good interior air quality. Fresh outside air to any combustion equipment (don't rely on interior air for fireplaces and wood stoves).
• Install the siding with a rain screen so that wind driven moisture is not held against the wall. This can be 1x4s or lath strips over Tyvek, or wrinkled heavy tarpaper (30#) instead of Tyvek. Either will break the capillary action of moisture and let the siding dry out. I think the heavy tarpaper will likely be the most cost effective and easiest to install.

PS - I used kraft faced batts and 6 mil poly on my walls when I built the Solar Saltbox in 1982. I used 15# felt over plywood sheathing and under cedar siding on the outside. We've never had a bit of moisture problems yet (in a Puget Sound climate).

[jraabe]

Here is the wall Building Science would suggest for your climate:

[dorothyinak]

How does one get the fresh air into the fireplace, when things are wrapped so tight?   Is this something to add to the woodstove, or just to consider with whole house ventilation (acually the ventilation I was thinking of in kitchen and bath were all about getting the moist air out, not letting fresh air in.

I think we will go with the tar paper and siding over that.

-D

[John Raabe]

Ventilation can mean something as simple as cracking windows or get as elaborate as UV treatment of incoming air.

In a well sealed house you can do things like turn on a bath fan and the kitchen fan and pull smoke down the chimney and out into the room. This is not a good idea.

Combustion appliances - wood stove, gas water heater, etc. should have a good sized fresh air intake directly vented to the firebox.

I do not have that. I have an old pre-certified cast iron wood stove. I have an air intake in the door next to the stove but this does not always provide enough air. When the dryer and fans are running I can still get backdrafting on the stove (but only when there is no fire). Stinky but not particularily dangerous.

This is not just a problem with super tight houses. Almost all houses today have similar problems. You don't have to deal with this in a leaky turn of the century farmhouse - but they have other problems such as astronomical heating bills.

The best advice is to get a certified wood stove and install it with a combustion air duct sized for the unit. Have as few bends as possible in the ducting. For a gas heating system consider direct vent units that use outside air and are installed on an outside wall.

[DemianJ]

I'm trying to figure out the details for the walls for my 20x24 cottage near Charlottesville, VA and was wondering if anyone sees any problems with the following layers (particularly foil faced foam under tyvek and whether I should do an interior vapor barrier to reduce the wet aire forced into the wall from the inside):

Inside to Outside-->

Latex Paint
Sheetrock
5 mil Poly (??)
Blown Cellusose b/w 2x6 16 oc
3/8 OSB
1/2" foil faced Polyiso foam sheeting
Tyvek (or # 30 tarpaper)
1"x3" Furring Strips
8" Lap Cedar Siding (back primed and latex painted)

I found this article on the UMass BM&WT website (thanks, Glenn!; lot of great info there) warning about impermeable foil faced foam in cold climates, but wasn't sure about my temperate climate where heating is only slightly more of a concern than cooling.  I'd like to use the foil to reflect the radiant heat from the wood sun as well as the summer sun (the house has full southern exposure).

[/url]http://www.umass.edu/bmatwt/publications/articles/insulating_on_the_outside.html[url]

Thanks,
Demian

[glenn kangiser]

I think if you are using the furring strips doing the screen type wall you will eliminate most of your problems from the start.  Tyvek's worst problem from what I've read seems to be when water rather than vapor gets trapped inside and can't get out.  The heated side vapor barrier will keep liquid water from condensing on the colder outside walls.

You may want to check - cedar and redwood doesn't like paint too well.  A vapor transmitting stain such as Defy may be better-it keeps out about 98% of the moisture and lets damp wood dry, or if you want paint possibly a pine, fir, hemlock etc. siding.

[John Raabe]

I think you have a good wall there and agree with the stain suggestion of Glenn's when using cedar or redwood.

You could use high-density cellulose or a BIBS installer and up the R-vaule of the cavity a bit.

If you have pretty much of a drywall interior and have done a good job of airsealing you can eliminate the poly and use a two coat PVA primer as the vapor barrier. Production builders doing EE housing do this combined with caulking and sealing strips for the airtightness.

[DemianJ]

Thanks for the tips.  I'll have to look into the Defy stain.

I was considering the high density cellulose, but was wondering if it might be better to use the non-damp material held in place by the interior poly since I wasn't hiring a professional and the article below expressed concerns about a non-professional getting the moisture content exactly right.

http://www.umass.edu/bmatwt/publications/articles/cellulose_insulation.html

I hadn't considered the BIBS option until now.  I'll have to price it.

Thanks,
Demian

[John_M]

After doing some research...sure sounds like that spray in insulation (icynene) takes care of a lot of concerns with moisture in the walls and roof.

Anyone have this done and have an idea on cost??  They always advertise that "...it only costs a littel more than fiberglass insulation..." and then you get a quote and it is like $3000 more!!!

[glenn kangiser]

Okie BoB did it.  He loves it.

[John Raabe]

Icynene does a very good job of airsealing and high-R insulation in one step. It needs to be done by a licensed installer and so is not a DIY project.

It is also considerably more expensive than other alternatives in most building areas. In some places the extra costs are not returned in future fuel savings.

I would have your installer do a careful cost comparison with other insulation options. If you do a Google search on "icynene cost comparison" you will find some spreadsheet templates and reports from installers.

Again, a very good product but an expensive one. In some situations the extra airsealing and quietness aspects of the product are more important than energy savings so that should be factored in as well.

[John_M]

What about the do it yourself kits.....

http://www.tigerfoam.com/index.php

http://www.foampower.com/

Do they seem like a cost effective alternative??

[Okie_Bob]

As Glenn recalled, I did use Icynene and absolutely love it. Also, John is correct, you can NOT install it yourself. In fact Icynene can not even be purchased unless you are a certified installer. The guy that owned the company I used told me the cost of the trailer that houses and transports the pumps, etc, cost him in excess of $100,000 plus he had a 1 ton pickup pulling it. That helps explain the cost differential in having it installed. In my case, I have a metal roof and that was a major factor in my decision, it cuts down noise dramatically. But, the sealing feature and good R value was important as well.
As to exact cost, I didn't even look at any other type insulation so can't give you a differential. I would guess it is maybe twice as expensive as fiberglass batts. But, that is just a guess. They figure it by the sq-ft-inch ie, total square footage to be covered by the thickness you want to end up with.
My building is 24 X 50 and roof is 4:12 pitch. I had the entire roof covered level with the 2X4's used in the trusses. I had the 2X4 stud walls completely filled in on the apartment in one end of the garage. The apartment is 24 X 16 so all walls in the apartment are filled with Icynene.
Total cost was about $2700 as I recall. So if you have a bldg that is 16 X 24 then add the extra roof of 24 X 34 you could figure backwards and get an idea of the cost per sq ft.
I suspect the cost would vary depending on how easy it is to get to your location, etc.
One other thing, in my case, since I have a large two car garage on one end of my building that had the roof only covered with Icynene you need to be aware that Icynene installation is a very messy afair. The slab in the garage portion is still covered with overspray from the installation. The installers were pretty good at covereing windows, etc with plastic but, I still have overspray everywhere and it is NOT easy to clean up. If you are doing a house and cover windows and remove all your tools etc, this is not going to be a problem. Just beware, it gets on everything!
Hope this helps. Any questions, please let me know and I'll respond as soon as possible.
Okie Bob

[Okie_Bob]

Guess I should add, my walls are 2X4 filled with Icynene and sheetrock on the inside. On the other side of the 2X4's working outward, I have plywood then 30# felt and on top of it all I used Hardiboard planks. I am very pleased with the results and see no evidence of any moisture problems and the apartment is heated and cooled quite efficently with a small window unit I built into the north wall. The Icynene makes the apartment so tight that it just feels great being inside it.
Okie Bob

[DemianJ]

I did some more research and decided to put the housewrap under the foam (i.e., the wrap is against the OSB) and the foil face of the foam facing the rain screen airspace.  It's supposedly more difficult to attach the wrap with foam underneath it and I'm guessing that covering the foil with the wrap would reduce the reflection of radiant heat (and maybe hasten the degradation of the wrap over time?).

http://www.buildingscience.com/resources/walls/drainage_planes.htm

[DemianJ]

And here's an extremely thorough article addressing all the questions I had regarding foam sheathing and housewrap.  I ended up choosing their "Wall 1" design before I found this article (but it would have helped with my agonnizing if I'd found it sooner).

http://www.buildingscience.com/resources/walls/Guide_to_Insulation_Sheathing.pdf


Lots of other helpful articles on wide range of building subjects:
http://www.buildingscience.com/resources/resources.htm

Demian

[Okie Bob(Guest)]

I was reading this post as it came to the top once again and wanted to share some cost info on Icynene I came up with over the weekend.
For 2 x 4 stud walls my neighbor was quoted  $1.15 per square foot. For 2 x 6 walls it goes to $1.25 per sq ft.
Thought that might help everyone.

[John Raabe]

Thanks for the good information. I think both Damian and Okie Bob have developed high quality wall systems that should work quite well.