My contractor that built my deck has also installed a self design
underdeck roofing. His father,an engineer, designed it. Basically it
consists of 2x2 furring strips nailed and caulked onto the inside of
the floor joists and plastic panels caulked into place between them .
Then exterior plywood was installed as a ceiling. The system is leaking
in several places. They have attempted to repair it twice. Now they
want to use caulk to fill the spaces between all the deck floor boards.
In my experience, any system that relies on caulk as the primary means
of preventing leaks is doomed. I would tear up the deck, put down a
layer of plywood, then rubber, then sleepers, then decking. another
alternative might be to use something like roofing steel for a ceiling,
with provisions for drainage.
It depends where you live. In most places caulk
is an inadequate way of rainproofing a roof.
Together your contractor and your designer
built a roof which leaked contrary to their
intentions. What has changed to suggest
either would now do better what they failed
to do before?
In my experience, you are doomed to have leaks in that setup. There
are just too many places for water to gain access. I have seen one
system used under a deck that could be used. If you were to cut
sleepers (0-3" for example) and attach them to the under side of the
existing deck joist (creating a reversed slope). Then use a corrugated
roofing material (metal or plastic) installed in reverse to the
sleepers on the underside.
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