# House wrap over foil faced foam?



## ToddnDarla (Jan 10, 2013)

We're looking at a siding job on a 1979 prefab. Ya, I know... Anyway, it looks like it has 1" foil faced foam on exterior of framing. I'm not sure if this is also the sheathing, or not. Does any one put house wrap over this? R-Board? Nothing? What possible breathing/drying issues might occur with vinyl siding over the top? Thanks for any input.


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## Philament (Dec 9, 2014)

I'm not a fan of foil faced insulation on the exterior in cold climates because of it's low permeability, and usually (but not always) it's polyisocyanurate which degrades in performance as it gets colder. If there's poly as the vapour barrier inside, which is usually done in cold climates like yours, then there could be problems because the wall has nowhere to dry. 1" of foam (if that's what it is) on the exterior is a little risky too check out your building code for minimum exterior R-value for the wall depth. 

If it's really well air sealed though and the house hasn't had any moisture problems, then putting house wrap on the outside isn't going to cause any problems. 
There was a similar discussion here where a house wrap vendor weighed in on the discussion: http://www.contractortalk.com/f33/house-wrap-question-165050/


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## ToddnDarla (Jan 10, 2013)

Thanks for the reply. That was a good thread, sorry that I missed it earlier. I will for sure check with the B.O. for his official opinion. Now I wonder if we should look at removing the foam? The cost always plays into these decisions too. I still need to see if there is wood sheathing under the foam, or not. There were some foolish things done to save a buck back in the day.


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## ScipioAfricanus (Sep 13, 2008)

Very doubtful that the "foam" would have been considered in the lateral loading calculations. At least I have never seen that. Probably likely that there is sheeting or let-in bracing on the wall.
Now whether or not foil faced insulation is used the foil should not be touching anything else like sheeting or siding or any other material as this will basically render the foil useless. It needs an air gap between the foil facing and any other material of about 1-1/2", which is I believe the average distance most use.

It could be the foil has holes in it for permeability but I am not convinced the holes are of much value for that. I like the idea of a continuous insulation like this though so I would recommend replacing the foil foam with non-faced foam then the WRB like Tyvek.

Andy.


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## ToddnDarla (Jan 10, 2013)

So here's another angle, anybody using this Tyvek Thermal Wrap
http://http://www.dupont.com/conten...ials/assets/DBI13_19197_Brochure_me01_web.pdf


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## ScipioAfricanus (Sep 13, 2008)

ToddnDarla said:


> So here's another angle, anybody using this Tyvek Thermal Wrap
> http://http://www.dupont.com/conten...ials/assets/DBI13_19197_Brochure_me01_web.pdf


Page is not available...what did you do to it?



Andy.


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## Philament (Dec 9, 2014)

I have not used the ThermalWrap product, but I see nothing in their data reports that indicates that it has been tested to any of the recognized thermal resistance standards, only sheathing membrane and air barrier. I would put the thermal claims in the realm of marketing hype like bubble wrap. 
Sounds like they're going for a radiative r-value much like the foil faced, which I have little faith in. As Andy mentioned, a radiative insulation gain needs an air space, an enclosed undisturbed air space at that or wind washing and convective currents can negate its benefits. And if it gets covered in dust or dirt the radiative insulating value is negated further. 
A bit heavy in nerd speak, but this research paper describes some of the effects. 
http://c.ymcdn.com/sites/www.nibs.org/resource/resmgr/BEST/best3_saber.2.14.pdf


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## ToddnDarla (Jan 10, 2013)

I was skeptical of the R-value as well. The install process also seemed to be heavy on details, and short on production. I know that details are very important, however, it seems to set you up to fail rather than realize any actual gains. Andy, sorry about the link. Don't know what happened. I'm trying to learn though, do I get points for that?


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