For the low wall around the deck extension, I used 3/16-inch foam board and cut kerfs to enable a smooth curve.
I attached it to the edge of the base, flush with the side wall. The exterior siding will extend along and around the deck wall.
For the deck proper I used the same 3/4-inch rustic planking as the interior floor, though the deck is to be stained gray. (The glass of wine — a nice 2013 Husch Mendocino Sauvignon Blanc — is to show scale :)
The inside of the deck extension is clad in vertical 1/4-inch basswood, which is narrow enough to go ‘round the inside curve nicely.
Decking done! Almost. I’ll stain it tomorrow.
Lastly, I brushed wood glue into the kerfs to fortify the curve and make the foam board more sturdy. When that’s dry, the deck will be able to withstand the gusty winds of the coast.