Installing stone veneer over 2-inch rigid insulation
We live in climate zone 5A and we unfortunately purchased a log home that only has 3.5″ pine walls with no insulation (we thought there was insulation at the time of purchase per the manufacturers website). Anyway, we want to install 2″ rigid insulation on the outside of the log walls and use stone veneer. I am trying to understand the wall section though. My thought is:
3.5″ pine wall
2″ rigid insulation
tyvek
metal screen with scratch coat
stone veneer
We are going to put a ledge angle at the base on the stone should only be about 8ft high. But how should we attach the stone metal screen through the 2″ insulation??? Is there a product similar to the plastic “‘studs” within ICF walls that veneer can attach to? If a product like that exists then we could cut the rigid board to 16″ strips and install these stud type members for the metal screen to be secured to. Any thoughts???
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Nicole. Martin Holladay responded to an owner who had a similar objective. The post is four years old, so he may want to amend some comments. Note his link to an article on installing rigid foam. I'm not sure how minimum r-values apply when overlaying a log home, but I'm sure someone else will comment.
"As you probably know, the two weaknesses of most log homes are the low R-value of the walls and the fact that the walls leak a lot of air.
It's very important that you establish an exterior air barrier on your log home. You can do this with plywood, with housewrap, or with the rigid foam layer. No matter which approach you take, you have to aim for an airtight installation.
I don't know how bumpy or out-of-plumb your walls are. But if they really are both plumb and co-planar, you are lucky. In that case, you may be able to achieve an air barrier with a layer of rigid foam. I would advise that you use polyisocyanurate. Here is the controversy: rigid foam may shrink, so some builders are wary of depending on the rigid foam to be your air barrier.
In any case, the foam needs to be thick enough to keep the interior of the foam above the dew point in your climate, and the seams need to be carefully taped with a high quality compatible tape.
If you are leery of the dimensional stability of the rigid foam, you should establish your exterior air barrier with taped housewrap or taped plywood before proceeding to install the rigid foam.
Your final question is: what material will you use as your WRB? Your WRB may be the same as your air barrier, but in some cases you will have different materials for these two layers. Study up on GBA -- there are plenty of articles on these questions.
Read more: https://www.greenbuildingadvisor.com/video-how-install-rigid-foam-insulation-outside-house#ixzz4Oo6IKAqC "
Nicole,
You are taking on a big challenge. There are many factors that may trip you up, so you may want to reconsider your plan.
As my earlier advice (quoted by Steve) points out, you have to (a) establish an air barrier, (b) provide an adequate layer of insulation with a decent R-value, and (c) make sure that your wall is vertical and co-planar. And that's just for starters.
Assuming you can do all of that, your next challenge has to do with the fact that log walls settle as they age (because logs shrink), while a stone wall doesn't settle at all (and is inflexible). That makes stone veneer the worst possible choice as siding for a log house.
Most stone veneer jobs are tied back to the wood wall that supports them with masonry ties. As your logs shrink and settle, the logs will pull your stone wall apart.
I suggest that you seriously consider a different type of siding -- perhaps wood lap siding, cedar shingles, or fiber-cement lap siding.
As it turns out, my husband and I came to the same conclusion last night. So I thank you both for your advice. We came to this conclusion for different reasons than listed above, but all the more reason not to apply the stone to the wood logs. Our logs are in fact flat, but as a structural engineer I was unable to be comfortable with any type of connection going through the 2 inch insulation and back into the wood logs carrying stone. The new wall system that we are considering is listed below. My only question is where to place the vapor barrier??? I am finding conflicting information as to if it goes against the wood logs (behind the insulation) or on the outside of the insulation. Please advise. As I noted we are in the Pittsburgh area (zone 5A).
3.5" wood logs
vapor barrier here???
2 inch rigid insulation
vapor barrier here???
1x furring for a 3/4" air space
and cedar siding
Thank you in advance for your advice.
The wall does not need a vapor barrier anywhere, but it does need an air barrier.
Using a flexible broadsheet housewrap between the logs and foam (detailed as an air barrier) will help a lot, as will taping the seams of the foam.
The window flashing and drain plane needs to be defined too.
Nicole,
The rigid foam is your vapor retarder. (For more information on this issue, see Do I Need a Vapor Retarder?).
If you do a careful job of sealing your rigid foam seams with high-quality tape, the rigid foam can be a fairly effective air barrier. Don't forget to seal the perimeter of each wall with tape or canned spray foam.
Every wall requires a water-resistive barrier (WRB) -- usually housewrap. In your case, the WRB should be installed between the rigid foam and the furring strips.
One of your challenges will be developing a flashing plan for your windows. There are a variety of options -- what you do depends on whether your existing windows will stay where they are, or whether the existing windows will be re-positioned, or whether you will be purchasing new windows.
The amount of work to install 2" of rigid foam vs. 4" of rigid foam would be pretty similar, I would recommend installing more than 2".
If you use 2x4 furring over 4" of rigid you can use a dimensional 2x6 as a jamb extension to trim out the sides of your doors and windows (4" + 1.5" = 5.5").