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Is using R-19 batt insulation with Kraft-faced vapor retarder, Visquine vapor barrier, & drywall okay?

Question:

I am using 2x6 studs with R-19 batt insulation accompanied with Kraft-faced vapor retarder, a Visquine vapor barrier, and drywall. Is this the best option? Or should I instead use an R-21 and no vapor retarder? Will I need the R-21 for southern WI? Or will it not add much in terms of insulation over and above the R-19? And seeing how I will have a Tyvek housewrap and a plastic barrier already, how important is that Kraft-faced vapor retarder? I would like your recommendation on the best wall insulation option for this case.

Answer:

According to the International Building Code 2000, Wisconsin is mostly within the 6,000 Heating Degree Day (HDD) belt, except a small corner in the Northwest portion. Six thousand HDD is considered cold-climate condition. The recommended vapor barrier for the interior wall is either to use a 3-mil. polyethylene (Visquine) or a vapor-retarder paint on the interior. As such, you do not need both the Kraft-faced paper and Visquine for the R-19 design you mentioned. Housewrap is not a vapor barrier, it is primarily an air infiltration barrier. If you use housewrap, follow the manufacturer's installation instructions. As far as using R-21 vs. R-19, it depends. You should look at the payback for this upgrade and ask a heating contractor to evaluate it using Manual J software or perhaps your local electric or gas utility. Also consider if you use the extra insulation, it may allow you to install a smaller furnace thereby off-setting the expense. The links below will give more in-depth information on the topics discussed here: