Teardrops n Tiny Travel Trailers

I asked this in my build journal but havent received any responses and am hoping to begin cutting tonight.

Starting to plan ahead for roof spars and insulation. I am planning on ripping down 2x4's for the spars because of avilabilty, cost, straightness etc.
I will go with 1" thick foam board for insulation.
My question is should I rip my spars to exactly 1" for a super tight fit of the foam board or rip them a bit thicker ( maybe 1 1/16 or 1 1/8) to have a little play for the foam bored?

Thanks for the input.

When I did mine, the spars were the same size as the insulation. Both were 1.5" exactly. I didnt notice any big problems when I applied the plywood. I did have to kerf the styrofoam to make the corners. I think the styrofoam stuff I used compressed a little so take that into consideration. Also be sure to have the insulation you are planning to use on hand to verify the thickness. I noticed at the store there were two different types of 1.5" insulation and each was just a bit different in thickness. I think i would recomend leaving just a bit of wiggle room.

I would leave a little wiggle room. I learned the hard way that the nominal dimensions of foam board aren't exact. My 1/2" foam turned out to be 9/16". I was going to stack three pieces in my nominal 1X2 (3/4X 1 1/2) spars. Ended up using only two pieces with an air gap to avoid bulging of my skins. My fault for not measuring them in the store, but that was all that was available at the time. It wasn't a total loss since the air gap made the overhead wiring runs a little easier.

Cool. thanks for the responses. I think i will go to the store and measure the 1" board and assuming it is accurate i will simply rip the 2x4's into thirds. After the loss of material from two cuts I should end up with spars just shy of 1 1/8".
Sound good?