Since I got the roof and the deck roof 99% complete, and it was definitely helping with the heat, I decided it was time to insulate the roof under the deck. The deck roof already cut the temps by 5-10°, but I knew all along it would need actual insulation.
I bounced around several ideas, including joists with traditional insulation, concrete (including aircrete), and a few other options. I stumbled across an idea and after doing the math and researching, I landed on high density styrofoam. The type I purchased was rated at an R10. When you add some foam to the corrugation as gap filler, additional insulation, and adhesive for the polystyrene; I figured the end result would be between R12-15. Coupled with the solar roof over the deck, I was hoping it would have a substantial effect as the outdoor temps rise.
You might be thinking “styrofoam for decking?” but this is the type that is designed to go underneath a concrete slab. It has a high compression strength and can take lots of weight. It was in 2×4 panels and I was able to buy the perfect quantity. The only waste were a couple of very small pieces cut to fit around the upright poles.
Even though it has a high water resistance rating, the roof was already watertight underneath, and I put an extra layer of RedGuard for extra protection; I decided another layer of protection wasn’t a bad idea. I added a layer of synthetic roof underlayment over it. It was cheap, extra insurance. The day after getting the insulation and foam onto the metal container roof, the indoor temps were were they should be. It got to almost 100 degrees with a heat index of 106 outside and the living room HVAC (the room under the deck) didn’t even kick on until almost noon. Easily a 15° improvement. Eureka.
After laying the underlayment and taping the seams, I added flashing around all sides. I then tested my theory on the next layer. That part is tongue & groove roof decking material or sheathing. I only got four sheets because the night I was picking it up, it started storming – badly. I was fortunate to get materials loaded up and make it back in one piece. The wind was so strong that it required driving at under 55mph instead of the usual 70mph. The wind did pick up one piece of roofing panel that was only partially attached due to the need for a taller ladder to reach the last securing points. But rain or not, I got up there and straightened it out after the wind died down. I waited until morning to try the decking with the t&g. It worked well.
I will finish the last pieces in the coming weekend or two. Another layer of roof underlayment will go over the wood decking to add waterproofing. Then deck boards go on top of that to finish it all.
I used concrete and bolts to fill in the container corners. These will anchor post mounts and hold the posts for the railing, which I’ve already cut and gotten ready. But it was hot, it was lots of work and I ran out of water, so I had a beer and the dog and I hung out on the deck as the sun went down.
McGowen Container House (and more) 