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Doug Dolphin Posted: Sep 16, 2007 03:52 PM	combining spray foam & batt insulation Last summer our 100 yr old house was lifted & had a full basement poured. Upon completion of framing it in, we had 2" of cc spray foam recently installed. However, the stud cavities were not completely filled, leaving an approx. air space of 2" between foam & inside surface of the studs. I still have the R20 batt insulation that we used last winter (which, in our part of Québec easily hits the -30 and below zone). Would it be cost effective to split the batts, fill the remaining cavity space and add a vapor barrier? Or is this overkill? Thanks for your time.
Gerry Wagoner Posted: Sep 16, 2007 09:29 PM	The closed cell foam should provide a vapor barrier. Are the walls open? If so, I much prefer adding cellulose to the cavity to fill out the walls. This will bolster your total insulation, AND add good sound retention to the exterior wall. You will notice, there is no carcinogenic warning label on a bag of cellulose. There is one on Fiberglass "insulation". Have fun, oG
Posted: Sep 17, 2007 07:08 AM	...but since you have the glass laying go ahead and use it...save the time and press em in there and be done with it.. (the airspace inside the wall will be about 1 degree difference of the airspace on the room side of the wall,,) you do not want to install an additional vapor barrier, the 2" cc app should give you that and 2 vapor barriers on the wall is not so good.. ...olger,,,a warning lable from the state of california,,,everything gives you cancer!!!,.,
mason Posted: Sep 17, 2007 09:46 AM	The closed cell foam will allow the batts to work more efficiently and 2 inches may be sufficient to prevent condensation.( according to Mark Bomberg's research on behalf of the NRC). But, to be safe, I would conduct some moisture vapor transmission analysis of the proposed application to be sure.
Rob Granger Posted: Sep 17, 2007 04:12 PM	Mason, Being new to this industry how do I complete a vapor transmission analysis?? Rob
mason Posted: Sep 17, 2007 04:51 PM	The best tool is something Oakridge National Labs developed called WUFI. Some SPF suppliers have copies so ask them. If not, you could ask your HVAC contractor. They should have the ability to do the calculations. Also, download SPFA's technical document AY 118 Moisture Vapor Transmission. It has a pyschrometric chart to perform the calculations along with instructions and sample problems. The only problem with this type of calculation is that it only provides a snapshot and doesn't take into consideration the wetting and drying of an assembly during different times of the year (or day) like the WUFI software does. So this calculation tends to be overly conservative.

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Doug Dolphin

Posted: Sep 16, 2007 03:52 PM

combining spray foam & batt insulation

Last summer our 100 yr old house was lifted & had a full basement poured. Upon completion of framing it in, we had 2" of cc spray foam recently installed. However, the stud cavities were not completely filled, leaving an approx. air space of 2" between foam & inside surface of the studs. I still have the R20 batt insulation that we used last winter (which, in our part of Québec easily hits the -30 and below zone).

Would it be cost effective to split the batts, fill the remaining cavity space and add a vapor barrier? Or is this overkill?
Thanks for your time.

Gerry Wagoner

Posted: Sep 16, 2007 09:29 PM

The closed cell foam should provide a vapor barrier. Are the walls open?

If so, I much prefer adding cellulose to the cavity to fill out the walls. This will bolster your total insulation, AND add good sound retention to the exterior wall. You will notice, there is no carcinogenic warning label on a bag of cellulose. There is one on Fiberglass "insulation".

Have fun,

oG

Posted: Sep 17, 2007 07:08 AM

...but since you have the glass laying go ahead and use it...save the time and press em in there and be done with it..
(the airspace inside the wall will be about 1 degree difference of the airspace on the room side of the wall,,)
you do not want to install an additional vapor barrier, the 2" cc app should give you that and 2 vapor barriers on the wall is not so good..

...olger,,,a warning lable from the state of california,,,everything gives you cancer!!!,.,

mason

Posted: Sep 17, 2007 09:46 AM

The closed cell foam will allow the batts to work more efficiently and 2 inches may be sufficient to prevent condensation.( according to Mark Bomberg's research on behalf of the NRC). But, to be safe, I would conduct some moisture vapor transmission analysis of the proposed application to be sure.

Rob Granger

Posted: Sep 17, 2007 04:12 PM

Mason,
Being new to this industry how do I complete a vapor transmission analysis??

Rob

mason

Posted: Sep 17, 2007 04:51 PM

The best tool is something Oakridge National Labs developed called WUFI. Some SPF suppliers have copies so ask them. If not, you could ask your HVAC contractor. They should have the ability to do the calculations. Also, download SPFA's technical document AY 118 Moisture Vapor Transmission. It has a pyschrometric chart to perform the calculations along with instructions and sample problems. The only problem with this type of calculation is that it only provides a snapshot and doesn't take into consideration the wetting and drying of an assembly during different times of the year (or day) like the WUFI software does.

So this calculation tends to be overly conservative.

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