Can I insulate under the roof deck, in my attic? My roof has only two vents (gable). What materials can I use?
no soffits, no vents at eaves, only vents are the gable vents
Noooo. Insulating under the roof decking will do nothing except decrease the life of your roof.
The best thing to do would be to install a solar powered roof vent fan that operates on a thermostat. Place the power vent mid way between the two gable vents.
For more information:
Read "Should we use open cell or closed cell SPF insulation on the underside of our attic roof in southeast Louisiana?" a Q&A answered by Rick Goyette.