Expert: Richard Taylor, AIA - 3/7/2009

Question
Dear Richard,

We bought a brick attached house built on 1925.  In the front, there is a
sunroom (brick), the roof of which is flat rubber, approx. 8 ft x 20 ft, and
accessible from the 2nd floor master bedroom.  We would love to reclaim this
small roof and enjoy it as a relaxing balcony/deck.  However, from initial
research we conducted, it seems that putting a wire mesh, cement and tiles
over the rubber roof will cause leaking problems and damage the rubber.  Is
there a way to make our plan for a balcony come true?  Some additional
information about the roof (we can send pictures if it will help): the roof has
an external drain hole in the corner.  However, when it rains, there are
puddles of water here and there, which they evaporate or I broom away.

Your help will be greatly appreciated!

Answer
Hi Maria - thanks for your question!  I had a question similar to yours not long ago, so I'll copy that answer for you below:

You have a couple of issues to address here; the first is structural. The loading requirements for a deck are much higher than for a roof alone; be sure the structure is designed to accommodate that load. That means the roof structure, the connection of the structure to the house (very important) and the columns. It also means the foundations below the columns. Have this all checked out by an experienced pro. (Maria - check your roof; it probably wasn't built to handle the loads you want to put on it.)

You'll also have to meet code with the railings. This is a critical design issue, as you don't want to change the character of what you have too much.

The roof you'll be building has three basic parts. The first is the structure itself; the second is the waterproof membrane, and the third is the deck surface.

There are a couple of ways to build this, I'll describe the one we use most frequently. The roof structure should slope from the house to the edge (where the gutter should be) at a rate of about 1/8" per foot. You can achieve that by cutting a slope into the top of the rafters. (Maria - this might be a problem with your existing roof.)

Plywood decking goes over the rafters, which is then covered by a single-ply roofing membrane - typically a "rubber roof" - which is glued to the decking (check with the manufacturer on the proper substate). The posts for the railing should already be in place; use the prefabricated rubber "boots" provided by the membrane manufacturer to flash around them.

Now you have a waterproof roof, how about the deck surface? If you install it directly on the membrane it will be sloped and you'll punch holes in the rubber. Instead, use "sleepers"; sleepers are sloped 2 x members that sit on top of the rubber roof. They are cut with the opposite slope to the rafters, so that the bottom edge follows the slope while the top edge is level.

(Maria - you need a concrete base to put cement and tiles on; you can't put tile on the wood roof you have.)

The sleepers are the nailing base for the decking...but here's the important part...the sleepers are NOT nailed to the roof. The sleepers just sit there, held in place by the weight of the decking boards. No need to nail at the edges; there's plenty of weight to hold the deck down even in strong winds. Some designs even build the deck in sections, so that they can be lifted up for cleaning the rubber roof below.

I also like to glue a small strip of rubber roofing to the bottom of each sleeper for extra protection of the membrane below.

The details are the important part; how you handle the posts, the railings, the gutter, the flashing to the existing wall, etc. Do these right to keep the project looking good and working properly. You can get a lot of help on the details from the rubber roof manufacturers (the big ones are Carlisle and Firestone).

The above is a generic description; you'll need to do a little more homework on this to get it planned just right. You might try www.jlconline.com for more info.

Hope this helps!

Richard Taylor, AIA
www.rtastudio.com
www.rtaplans.com