I need roofing advice
I need advice on roofing. I live in death hot/humid zone 9. I am not working this summer and have to repair my roof on my 1600 sq ft. mobile home.
I will replace some rotted decking with 1/2″ plywood, and install Grace self-adhesive underlayment.
I am recycling 4″ thick Dow blue Styrofoam. They are 2 ft x 2 ft.
I’m not sure the best way to attach them. (?)
To protect the Dow Insulation from the elements, I was thinking of spray foam roof because of the low weight. (?)
If I have an R-35 above my roof deck, is it OK for me to have a NON-vented roof cavity ?
Roof cavity has blown-in cellulose. I think 14″ at peak, and 8″ where it tapers.
Please stop me if I am about to do something really regrettable.
Thanks for any advice !
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Replies
Jacq,
Where are you located? Your reference to "climate zone 9" has me confused. Here is a link to the Department of Energy's climate zone map: https://www.greenbuildingadvisor.com/sites/default/files/images/H-T%20Zones%20with%20Cities%20ABC+.jpg
Assuming that you live in a hot climate, your plan will work.
Rigid foam is usually attached to plywood roof sheathing with cap nails. For more information, see How to Install Rigid Foam Sheathing.
It's fine to build an unvented roof assembly, as long as you follow a few principles. More information here: Insulating Low-Slope Residential Roofs.
Closed-cell spray polyurethane foam can be used for roofing, as long as the right density material is used, and as long as the foam is installed by a qualified contractor. For more information on spray foam roofing, see Spraying Polyurethane Foam Over an Existing Roof and Roofing With Foam.
If you want to save money, you could skip the Grace peel-and-stick underlayment, and just use asphalt felt.
I apologize. I see now, I was using my old outdated gardening zoning. If I am understanding the map you provided I seem to be in zone 2A. Im inbetween Austin & Houston Tx.
Thank You for the advice, I can sleep now knowing the details are in place.
warmest of regards !!!
In your climate even WITHOUT the R35 above the roof deck and a full-fill of cellulose you can do away with roof venting. But with the R35 foam above the deck it'll be even better, if hard to measure in the cooling & heating bills.
Air sealing an older mobile home can be challenging, but with judicious use of closed cell spray foam you can usually take the leakage down by quite a bit working it from below the floor, where most of the holes are. Latent cooling loads are high in your area, and cutting down air infiltration has a huge benefit on comfort. Sealing the ducts as well as the house are important for fixing air-handler driven air infiltration.
Shading the windows from the exterior is probably the most cost-effective retrofit cooling load reduction you can buy, especially if the windows are clear-glass single panes. On the south side awnings can work, but on the critical west and east sides exterior pull-down shades or shutters are in order.
Very good advice !
I didnt realize I need to consider the screw spacing for attaching foam to decking.
The blocks are 2ft x 2 ft. any suggestions on pattern of screws ?
or should i try & glue them as bigger sections & then consider screw spacing ?
thanks