Low-ceilinged small bathroom in Zone 4, built in 1930: How to insulate?
Greenconfusion
| Posted in Energy Efficiency and Durability on
The home has a metal roof with good dow corning underlayment. It is sloped and is a low ceiling at outside wall. I wanted to use Closed cell spray to Insulate . I have been closing up all soffit vents. I have to gable vents on house. My concern is having roof deck rot. Should i leave a 1/2 inch gap and vent to attic ? The area is a wrap around porch connected too main house that has been closed in over the years. The ceiling joists rest on top plate of main house.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Green,
Your description is unclear.
It's OK to install closed-cell spray foam on the underside of the roof sheathing. If you do that (without making any changes above the roof sheathing), you'll end up with an unvented roof assembly. So there is nothing to vent.
As long as your roof sheathing is sound and dry at this point, and as long as your roofing doesn't leak, you won't get sheathing rot.
Im glad to hear that , i hope to flash and batt to finish .
Green,
For more information on the flash-and-batt approach, see Flash-and-Batt Insulation.