A Non-Vented Flat Roof - Contractor Talk - Professional Construction and Remodeling Forum

Dog Gone · 10-02-2009, 02:52 PM

Mid-century Modern home has flat torch-down roof. There are about 10" between roof decking to interior ceiling. Insulation (mineral wool) rests on the interior ceiling and is approx 4 " thick and provides minimal insulation (R-11?). This space is currently accessible only by removing facia/rim joist on soffit. (Roof is relatively new). Roof has both soffit vents and top vents.

Is it safe to fill cavity completely with additional insulation and close the venting ports so it's a non-vented space?

Welcome any ideas to improve R-value up there without removing roof or ceiling.

mics_54 · 10-02-2009, 03:14 PM

Quote:

Is it safe to fill cavity completely with additional insulation and close the venting ports so it's a non-vented space?

Welcome any ideas to improve R-value up there without removing roof or ceiling.

realistically? no, and I can't imagine how given the constraints and information

**genecarp** · 10-02-2009, 03:17 PM

I would go with iceynene only, if you are going to take away the venting, the container must be completely sealed, any air could cause condensation. G

Dog Gone · 10-02-2009, 03:24 PM

Thanks for your input. What about this...

If I were to remove the facia/rim joist and insert (slide in) continuous baffles... couldn't I blow extra insulation under them and leave current venting points?

There's a good 6" of venting space now so I could add significant R value.

OR... what about sliding in additional rigid insulation board???

mics_54 · 10-02-2009, 03:48 PM

One soulution would be to remove all insulation, remove the facia, slide ridgid foam ito the spaces. It needs to be snug...a long space would make this impossible and dont tear the vapor barriers. This would obviously present some difficulties like cieling fixtures, nails etc etc.

Introducing sprayed foam would also be possible completely filling the spaces. That would also present some problems like over filling resulting in bulged ceiling. Any future leaks would go completely unnoticed and we know what happens then.

I just don't see how it's possible with out removing roof or ceiling.

davitk · 10-02-2009, 09:03 PM

Yes, "hot roofs" (non-vented) are now acceptable per the latest UDC, as long as the insulation completely fills the space leaving no voids. The material can be of any type, as long as the interior has a vapor retarder.

If it were mine I would hire an insulation contractor who specializes in injection foam.

**joasis** · 10-03-2009, 06:24 AM

Low expansion, open cell foam. The rock wool will absorb the expansion......what a PITA!