0 Helpful?

Due to aesthetics, R-20 (4 1/2 inches of rigid foam) above the roof is my limit

Due to aesthetics, R-20 (4 1/2 inches of rigid foam) above the roof is my limit. Would Roxul plus an airspace in the rafter bays be a good choice for the remainder of the needed R-value?

Jesse, 80% of home is concrete slab with remaining 20% being crawl space I closed in - conditioned basement. In a high water table area with no vapor barrier under slab or crawl. De-humidifier runs constantly.

I plan to include air space in rafter bays under sheathing along with batt insulation for remainder of needed R-value. Is an airspace necessary with R-20 foam above roof sheathing?

Asked by cameron morris
Posted Jul 1, 2014 8:31 AM ET
Edited Jul 1, 2014 9:34 AM ET


1 Answer

Select your preferred way to display the comments and click "Save settings" to activate your changes.

It looks like you intended to post this on a different page. In most cases, it makes sense to maintain just one thread for a series of questions, rather than starting a new thread each time.

Here is a link to the original thread:

It would be a good idea to post all answers back on that page.

Answered by Martin Holladay, GBA Advisor
Posted Jul 1, 2014 9:36 AM ET

Other Questions in Green building techniques

To vent or not to vent?

In General questions | Asked by Eric | Nov 28, 15

Insulating a non vented vaulted ceiling in Canada

In Green building techniques | Asked by Kirsten Quist | Nov 28, 15

SIP walls insulating the floor joists

In Energy efficiency and durability | Asked by Brian W | Nov 28, 15

Locating manifold of a radiant floor heating system

In Mechanicals | Asked by Carroll Ayer | Nov 28, 15

Can PEX pipe be reused after a fitting is removed?

In GBA Pro help | Asked by K C | Nov 27, 15
Register for a free account and join the conversation

Get a free account and join the conversation!
Become a GBA PRO!