Another tidbit for exterior insulation retrofits
jklingel
| Posted in Energy Efficiency and Durability on
Cold Climate Housing Research Center, zone 8, just published this, and it may be of use to anyone retrofitting exterior insulation. http://cchrc.org/safe-effective-exterior-insulation-retrofits
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John,
I've just started to read this -- looks highly interesting. Thanks!
Sure thing. It will be interesting to see how this develops.
Cool. (or maybe I should say Cold.)
Maybe I'll find out I'm all wrong about exterior insulation.
Thanks John
Just a couple of reminders (unless I read too fast): They simulated older, non-super-tight house walls. It IS dry up here, too, so this may not apply to places that actually get wet in the winter.
The results of this study are applicable to homes in Fairbanks, Alaska, so we should be cautious about generalizing these results for homes in other climates.
I found these sentences quite interesting: "The humidity at the sheathing was very high for all test walls during the first winter (40% interior RH and positive pressure). ... The walls with thin exterior insulation were essentially at 100% humidity all of the first winter, with or without a vapor barrier. In contrast, the walls with thick exterior insulation were able to stay under 100% relative humidity. The test wall with 65% exterior insulation and a vapor retarder was even able to remain under 90% relative humidity. Notable for both graphs is that the test walls with a vapor retarder took longer to dry during the summer than the test walls without a vapor retarder. This matches expectations, as walls without vapor retarders can dry more easily to the inside. However, this drying capability did not spare the test walls without vapor retarders from abundant mold growth on the sheathing."