I have a 110year old house in the Chicago area with aluminum siding over clapboards. I will soon have the aluminum removed and replaced with Wolverine Restoration vinyl siding. The new siding will be placed over 1/2" foamboard (seams taped) - over the old wood clapboards.

Questions:

1) This seems like the perfect opportunity to blow in insulation into the exterior walls. I used cellulose on my last old house but am considering professionally installed foam (e.g. Polymaster Retrofoam). Any opinions or concerns?

2) Should I also consider installing Tyvex house wrap over the old clapboards before installing the foam board and siding? I want to tighten up the house a little bit - but don't want to create moisture problems. Would your response differ if I decide not to blow in insulation?

All input would be GREATLY appreciated!

Thanks!
Ed

 

to your post. You raise interesting questions. First, what is Polymaster Retrofoam. Sounds like a trade name, but for what kind of foam? Is it an air barrier or vapor barrier? Is it blown in or sprayed? Seems to me that you don't want multiple vapor barriers, no matter what you use. I would think the Tyvex would be redundant, if the extruded polystyrene under the siding is properly applied and taped, since that would be both an air barrier and vapor barrier. How about using dense pack cellulose for the cavity fill? Just questions here, but I am interested in what an expert would say. Regards.

 

I'm going to try to answer all you questions. First the 1/2" foamboards will have very little or no insulation value to your home. It's primary purpose is to prevent condensation between the vynal siding and the wood clapboard. This is because vynal siding loses heat 2,000 times faster than wood. The probablity that dew point would be reach between the 2 without the foamboard is extremely high. Furthermore, these foamboard that go under siding in cold climates have a Perm rating higher than .5 and therefore would not qualify as a vapor barrier. And is not a air barrier.

Tyvek prohibits air infiltration and is not an air barrier or used in the air boundary. I would recommend install the Tyvek prior to the foamboard.

Air barriers are applied to the air boundary which parallels the thermal boundary. In other words a vapor barrier can be a air barrier. The importance of the air barrier has been well documented. Whenever you heat air it expands and when it cools, it contracts. Your house cannot get bigger or smaller as the air in the home expands and contracts. The air barrier seeks to control where the air goes out and comes into the home. An example of this is as the air is heated in the home and the expansion occurs, it will seek the path of least resistance. Let's say it's an electric outlet on an outside wall. The warm air in the house goes through the outlet into the insulation where it will condense. The number 1 source of moisture problems in walls today, bar none. You know those inexpensive electric outlet and switch sealer. They qualify as an air barrier and you will be surprised on how much they do for you. Since the air barrier seeks to control where the air goes and comes into the home, where does it go? Regardless how tight your home is or how expensive your windows and doors are, the expansion and contraction of air within a structure will find a way to go out and come in. By the way this is the primary source of air exchange in a home which is good for the occupants. The air barrier if properely applied directs this exchange towards the windows and doors where moisture is not a concern, unlike inside your walls, ceilings and floors.

Injected insulation vs blown-in insulation. And my favorite, product claims. Insulman and I agree completely on this subject. Regardless of the product and their claims, experience and quality of workmanship plays a larger role in determining the effectiveness of insulation. I've been on hundreds of sites where insulation was being installed involving injected and blown-in insulation. With injected the procedure to assure 100% coverage is to mix the chemicals in such a way that it expands slowly. In every case I observed the foam was coming out of the hole before the installer could get the nozzle out of the hole. I'm talking a few seconds. With blown-in, the procedure is to add more air than the product for a specific period of time and adjust the nozzle to add more material than air to fill the cavity, which was done every time I observed. This is why I favor cellulose over foam.

Both products claim that the need for a vapor barrier is unnecessary. Regardless what they both claim, several layers of paint on the walls and ceiling and certain types of wall paper would qualify as a vapor barrier. It might be a concern if fiberglass was being blown-in. this is because fiberglass has a very low absorbancy rate to moisture.

I'd like to end this post with a comment about 2 people, whom I admire and respect, Insulman and twelvepole. Insulman, what's it going to take to get you to comment again, you want me to e-mail this radiant barrier guy and encourage him to come back to this forum? Your view is much different than mine and I have learned a lot from it. I am looking forward to reading your posts again. We both better start looking out for twelvepole, twelvepole been doing some research. It won't be long before we start asking twelvepole for some advice. You checkout those links. twelvepole just one comment about the links, this guy from pbs, delete his link. Shrinkage will allow for drainage? Bad idea.

 

Thanks for the detailed response. The foam product I was considering - basede on the recommendations of two installers - was Insulpro's Retrofoam. It is fully expanded as it leaves the injection hose and is a shaving cream consistancy when applied. I was thinking it is more likely then cellulose to get into all the wall cavities. I may have to rule it out based on price - I'll get the bids back in a few days.

I have blown cellulose into several attics and also into the external walls of my former old house. It was alot of work - but I knew it was done right. I may have to bite the bullet and do it again on this house.

Bottom line - based on your (resercon) posting, it sounds like I should blow in the cellulose, then wrap Tyvek over the old wood clapboards before installing the foam board. Did I get it right?

Thanks!

 

Yes, I would recommend the cellulose and the Tyvek before installing the foamboard.