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About Richard Taylor, AIA
Expertise
Ask me about all aspects of house, remodeling. , and room addition design and construction. Ask me about historic homes, renovation, and restoration. Ask me about materials and techniques, and about how you can get the best value for your design and construction dollar. Ask me how you can make your home a very special place. I can't, however, answer specific structural engineering questions in this forum - that's something you'll need on-site observation for.
Experience
I own a five-person residential architectural firm, and have been designing custom homes, remodelings, and room additions across the country since 1983. Check us out at Richard Taylor Architects and RTA Plans. I have written and been published extensively on the subject of residential architecture. .
Organizations
American Institute of Architects, City of Dublin Architectural Review Board, Past Editor of SPLASH (a CAD program), Past Editor of Open Directory Project, Boy Scouts of America
Publications
Business First of Columbus, Suburban New Publications, About.com, Cleveland Plain Dealer, Columbus Dispatch Residential Architect
Custom Home Architect
Remodeling Architect
Education/Credentials
Bachelor of Environmental Design (Architecture) Miami University 1983
For more about home design, check out my blog at Richard Taylor Architects Looking for great Luxury Home House Plans? Try ours at RTA Plans.
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You are here: Experts > Arts/Humanities > Visual Arts > Architecture > Installing a deck over a roof
Architecture - Installing a deck over a roof
Expert: Richard Taylor, AIA - 9/23/2008
Question
We have a 71 year old (stone) house with an attached porch. The porch floor is slate with wooden columns. The columns have wood encased beams that support a roof. This roof has a decorative railing and there is a door that leads out of our master bedroom onto the roof. The columns (and we suspect the beams) are rotting. We are going to replace them. We would like to make the "deck" above the porch a usable deck space. We will replace the wooden columns and beams, but are concerned with what kind of roofing to use. We would like to put some sort of an engineered decking and railing on the roof. We are concerned that by putting anything on whatever roof we choose it will void the warranty (and will leak). We have talked about no nailing through the roof and only attaching the decking at the edges, but are concerned about high winds, etc that would make this unstable. Do you have any recommendations. I have attached a picture of the existing structure. The roof deck would be around 26 feet long by 10 feet deep.
Answer
Hi Betsy - thanks for your question!
Looks like a lovely home - there's a lot of value in the historic character of it, make sure you maintain that when you replace the porch.
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.
You'll also have to meet code with the railings - the ones in the photo don't. 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.
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.
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
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