We have a closed in deck and I have been thinking it would be great convert into a bathroom. Is it even possible to put a bathroom on an old deck? The external deck has now got flooring board and carpet with underlay on top. But underneath it has easy access for plumbing. I’m wondering if you can put bathroom tiling etc on top of decking? The roofing is all part of the house roof and walls are closed in properly. The house itself is steel frame pole home about 11 years old. Photo shows the space With some of the original flooring still visible outside.