Expert: Richard Taylor, AIA - 6/2/2007

Question
we have a flat roof on our Illinois house that is replaced every 10 years or so.  I would like to put some kind of deck on it but don't want to rip off the deck when replacing the roof. It has to be something that can withstand Chicago weather without causing the roof to deteriorate and that is easliy removeable.  All I have seen so far is interlocking tiles (a possibility but costly)-any other thoughts on how I can creat an attractive, removable  surface?  Our roof is a bit of an irregular shape so the new outdoor carpets really won't work and I worry that they trap moisture against the roof>

Answer
Lolla - thanks for your question!

You've probably already hit on the easiest and least expensive solution, the tiles you mentioned.  There are other methods, but they involve some construction and aren't as durable as tiles.

For example, when we build decks over flat roofs we usually build the deck as a separate structure, with the deck built in panels that are small enough to be removed for cleaning and repairs below.

You have another issue to consider first, however.  Assuming that the roof wasn't originally designed as a deck, and that you're not using it as a deck now, you probably don't have the structure in the roof to support a use as a deck.

Building codes require that structures supporting people be designed for a "live load", which means the weight of everything except the deck itself.  The live load requirement of an outdoor deck is generally two to three times the live load requirement of a roof alone.

In addition, the (concrete) tiles you're considering will add significant weight on the roof.

So without some additional structural consideration, your roof (and the walls that support it) may not be nearly strong enough to be used as a deck.  If you have any questions about this, you should contact a local structural engineer or architect to evaluate it.

Don't forget that a roof deck also must meet codes for railings and stairs - you want to keep yourself and your guests safe!

Hope this helps!

Richard Taylor, AIA