We don't know what you have now, R. The most affordable method for a DIY enthusiast is to place uncoated fiberglass insulation over any existing insulation. We don't know what you have now, neither the value nor the type of R. That would be a useful factor in determining how much more you should add. I would reconsider your plans and place ALL of the insulation under the roof terrace, then close the vents OR place ALL of the insulation on the attic floor.
If you don't have mechanical materials in the attic, I would keep it fully ventilated and use all the loose insulation on the attic floor. Loose fill insulation is cheaper and is also one of the best ways to insulate. If you want to create a conditioned attic, I would place all the spray foam under the roof and encapsulate the beams. Don't use stiff foam here, as it's likely to cause problems.
He has 5 years of experience writing and editing for a variety of web and print publications, and currently specializes in home improvement projects, such as roofing, remodeling and repairs. Ventilation is necessary, although perhaps less so if you have a slate roof that “breathes” to the outside (compared to other types of “torch-closed” roofs).
I've also thought about attaching only the part that most needs insulation, which is the section that's not behind the knee wall and below the ceiling beam.
Another approach we've discussed is to place the 2X8 “off the roof”, meaning that the 2X8 doesn't overlap the 2X6 for all 6, but maybe just for 4 or something like that. If you are going to leave 1 to leave air space under the roof cover and you have 2 x 6 inch beams, 6 of CCSP will provide you with an air seal and a cover of approximately 4 inches to mitigate the formation of thermal bridges between the beams. We also plan to keep the roof deck ventilated with 1 inch of airspace, regardless of the insulation method chosen.The top of the roof is above the roof beams (and the insulation), so it's not that much either important. Whether you plan to install it yourself or hire a trusted roof insulation contractor, insulating your home will lower your energy bills, reduce carbon emissions, and keep your home warm in winter and cool in summer. If you want to insulate the roof terrace, you're right to say that you have to seal the ventilation grilles and create what's known as a conditioned attic. So the question was: why worry about ventilation? The contractors suggested using foam insulation directly on the underside of the roof.
Available in fiberglass or cellulose, this type of insulation is often placed in hard-to-reach places, such as an unfinished roof or attic, through a long, flexible tube. After doing some research, my plan was to use baffles to allow ventilation from the ceiling vents to the top of the roof and to place some gable vents.
