Maybe 1" RIGID INSULATION ? ANY PICTURES OF EXISTING CONDITIONS?

Would appreciate advice on the best option. Top 2 of the day are the 2" rigid foam panels (greenstar) or the spray foam that would completely enclose it with no venting.

Thank you for your help.

dont use spray foam... use the rigid insulation r-20 to r-30 in the roof ... r-19 in walls .... good luck

Start with the R value desired and the space available in the framing. Without that information we are forced to guess.

The truss framing appears shallow. If the roof is to have vents top and bottom an air space will be needed against the sheathing leaving even less space for insulation. I can't stay for sure but I doubt there will even be enough space for closed cell spray foam with no venting therefore foam board doesn't seem a viable alternative either.

If the contractors aren't pointing these things out to you, I suspect there is something you haven't told us about the R value required. Is there insulation board above the roof sheathing?

Using software you might be able to use the performance based method and decrease the R value for the roof by increasing the R value of the walls but in your sunny climate I doubt thats a smart approach.

In New England, a similar R value is required for a roof so if that space will be occupied it is framed with rafters instead of trusses. It would be ironic if you had to furr out the framing to meet the energy code.

The manufacturers of Greenstar brand reflective covered EPS referred to by the OP claim it provides the equivalent of R38.

Pretty amazing for two inches of expanded polystyrene with an R value of 4 per inch, plus two inches of airspace.

And pretty damn amazing when you consider that even the tech expert for the Reflective Insulation Manufacturer's Association International says the enclosed empty space is rated at R4 per inch. Colour me green with scepticism.

If you choose to go with a vented attic, be sure the attic kneewalls are treated properly.

For an independent on-site recommendation, speak with a qualified energy consultant in your area. Your utility provider should be able to direct you to appropriate experts.

Thanks for the advice. We were hoping to have the insulation done this month, however because there is just so much confusing information we will likely wait to meet with an energy consultant from the power company as suggested by Worthy. They will not schedule a consult until x number of billing cycles.

JDS- There is no additional insulation between the shingles and the roof.

I know of no building code in the US that recognizes "equivalent" R value for a reflective radiant barrier (other than the R value for the air space) although the barrier will definitely lower your energy costs. Maybe there is a performance trade-off you haven't told us about or a code amendment for your jurisdiction.

I would have expected the designer and/or builder to have anticipated providing space for the code required insulation before starting the foundations. Why are insulating companies proposing R 20 if the code requires R38? What R value was shown on the building permit drawings? Your entire post is a conundrum.

Even with no venting and closed cell spray foam you will need at least 2x6 roof framing which looks to be the case although it would be helpful if you told us the space available.

I suspect there is something important you haven't told us about this project.

For instance, if you are using the Prescriptive compliance method and if the roof insulation is full height over the exterior wall top plate, the R38 requirement can be reduced to R30. Is that the case? This reduction does not apply to the U-Factor, Total UA Alternatives or Performance compliance methods.

Another way to reduce the Rvalue requirement is to use software that allows tradeoffs between different parts of the envelope.

Any of these insulation design methods must be calculated and recorded and approved in the building permit documents. You should not be discussing the required roof R value with contractors.

I suspect that by the time the required R value is actually achieved in that space, it will no longer meet code for habitable space due to loss of head height. Thus the OP attempting to dance around that issue with snake oil ''equivalent'' marketing BS. If this is new construction, the issue lies squarely at the feet of the architect who designed an unlivable area. Perhaps conventional framing would have yielded a better result and that was rejected due to cost cutting?