The first step is to lay a
moisture barrier over your existing deck. Probably the best type
of product use is an EPDM sheet. Try to make sure there are no
seams in the sheet which could leak water. You can buy EPDM in different
widths with lengths up to 50' wide from specialist
suppliers such as
Conservation Technology who can also custom fabricate a
single sheet to avoid seams. They can also supply a complete
system that includes all required adhesives, sealants etc.
Alternatively if you have a plywood surface on your deck, you
may wish to consider one of the liquid rubber type products
which are generally applied by spraying, such as
Premium Liquid Rubber.
Then all you need to do is to snap our decking tiles into place over the top
of the membrane and in no time at all you'll have a great looking decking floor for your existing deck plus a dry area underneath. And perhaps best of all, you can do it all yourself. No need for expensive tradespersons and very little disruption or mess.