Using a membrane on all three decks ensures that water from rain or snowmelt will drain away from the house. On the ground-floor deck, the membrane keeps water away from the foundation, protects the underlying framing and connections, and allows for dry storage underneath.
To protect against fastener show-through, the author added a layer of wood-fiber recover board, fastened to the structural deck with the same reinforced galvanized screw plates and 1 5/8-inch screws used to secure the TPO membrane.
Once the completed membrane had been flashed and leak-tested, mahogany decking was fastened to tapered pressure-treated sleepers.
The finished porch was trimmed out with PVC post and column wraps, moldings, and balusters, combined with mahogany stair treads, fascia trim, and railings.