Storage truss insulation - does this make sense?

[Eplebnista]

I have a 24 by 26 garage with cathedral trusses over a bay with a lift and storage trusses over the other bay. The cathedral trusses are insulated to R38 with cellulose. Walls are 2 x 4 framed and insulated with r-15 fiberglass batts.
The chords of the storage trusses are 2 x 6 in the center section and insulated with R-21 batts and the chords for the outer sections are 2 x 4 and insulated with r-15 batts. The center section is about 10 feet wide and the outer sections are about 8 feet wide.

Given that I only have R-15 in these outer sections, I am considering putting foamboard on the flooring in the outer sections and covering it with 1/2 plywood. If I use 2 inch foamboard this gets me close to a level floor and increases the R-value. Since my trusses are on 16 inch centers I don't load up the outer sections since heavy items don't squeeze through I am not worried about the weight.

I am in Maryland and plan to put in a mini-split primarily for air conditioning in the summer but would keep the garage at 50 degrees in the winter. The garage was built 5 years ago and is fairly tight.

My questions are:

1. Is the foamboard idea dumb? Any foamboard I would use would be rated for under foundation use and good to 25 psi.

2. Is the bump in the R-value worth it when the center section is always going to be R-21ish ?

Any thoughtful input would be most appreciated.

Thanks

 

[like2wheel]

I'm confused.
Isn't the center of the attic truss the `storage` part? That's how mine are designed.

I put foam in the center part to gain as much R value as I could in the 2x6 center & put R38 bats on the sides. No floor there.
Unless I'm misunderstanding your situation, I don't think the sides are engineered for storage .




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[Eplebnista]

You are not confused. The builder of the garage put flooring down in the outer "non-storage" areas. I have used those areas for smaller and lighter items - which is about all that can fit because my trusses are 16 on center.

I hate to lose that space, but I completely understand what you are saying. However, what I was describing was putting foam board under plywood where you have R-38 batts.