To All,
I am going to add a 10×20 foot front porch to our home, supported by pillars, with traditional railings, etc. The only thing unusual about this project is that I want it to have a completely flat roof!!! Does anyone have experience with flat roof construction…such as what type of membrane to use, the best drainage systems, and what special supports would be needed??
If you know of any articles or books on the subject…please let me know. I will certainly be interested to hear of your ideas and experiences.
Thanks,
Sicuranzo
Replies
A perfectly level flat roof is an invitation to disaster. It will be leak-prone all its life. All roofing materials for flat roofs require at least a pitch of 1/4" per foot of run.
I like EPDM. It is without a doubt, the best roofing material available. It's appearance is akin to a rubber innertube so it ain't pretty enough to tale to the ball but she'll keep the snow and ice away.
Piffin,
Thanks for your good ideas for my flat roof project. The 1/4" pitch info is just the number I was looking for. Also, I will look for EPDM, sounds like a good product. I don't care if it's not pretty...no one dances on my roof! Does is stand up to high heat??? We only get about 12 inches of rain per year, but it can average 115 degrees here during the summer.
Also, my porch roof will be about a 10x20 plain rectangle. Any ideas for drain placement, type needed, etc???
Thanks for you help.
Sincerely,
Sicuranzo
I'm with piffin, 'cept be sure you don't fudge that 1/4" per ft - try to give it a bit more, cause syuff is never as straight as we'd like it to be and you don't want any ponding.
Bob,
About my flat roof project. Thanks for your reply. I definitely will use the 1/4" pitch rule. I also will give it more...I've got plenty of room up there and no one will ever see it. You're right, I definitely want to avoid ponding. Do you have any other ideas about drains; type, placement, etc??? This porch roof will be about a 10x20 plain rectangle.
Anyway, thanks again. If you come up with any other suggestions, please let me know.
Sincerely,
SICURANZO
Sicuranzo --
Tar & gravel used to be cheap, but now it is expensive in this area. Liquid tar has run into environmental regs and workers' insurance. I'd ask your local roofers what they're familiar with.
In the local tar&gravel roofs, typically the drains go through the roof inboard from the edge, but outside the building walls. In sunny Paso Robles, you'll probably have long overhangs, so there's plenty of room to do this. The intent is that no water goes over the edge of the roof. There are no conventional gutters.
A common maintenance problem is that the drains get blocked, water goes over the edge, and eventually the rim joist gets damaged. The first solution to pay attention. Large-diameter drains help, too.
You might consider a nice detail from Japan. I've seen these in Eichlers in the Peninsula. They're often called "rain chain" in English, and "riku" (I think) in Japanese. Instead of the usual pipe to conduct water from the roof to the ground, there's a hanging chain of cup-like things, and a gravel bed below. You could build a bed of river cobbles, and let it help move the water away from the house foundation. Combine that with some Zenny landscaping, and you're all set. http://www.hidatool.com/rain_chain.htm shows a picture, and Hida is a retailer. Other retailers can be found by searching on "rain chain". I've also seen a Western version using ordinary chain with fairly large links. The water tends to stick to the chain as it falls. It probably doesn't corral the rain as well as the cups, but with only 12" of rain per year, the difference may not be much.
Jamie
I installed one of those rain chains for a customer at his request. Pretty but also non-functional in my opinion. I stood in the rain and watched it. Instead of the water splashing on the ground and spattering on just the bottom 16" of siding, It spattered off of every single ball to wet the siding all the way from top to bottom.
If you don't want gutters, talk to the roofers about making up a gravel stop style metal edge to trim this porch with. Have it made with about a one inch stand up and then bend it in a couple of select locations so you are controling the place where the water comes off the roof, lioke a scupper does. Internal drains are way too complicated for a porch roof. Leave that alone.
Excellence is its own reward!
I agree with Piffin and Bob. I don't think I've ever seen a truly flat roof, and I can't imagine a reason to try and build one.
When I was roofing, I would find one occasionally and the first thing I would have to do is inform the builder o owneer that I had to upcharge him for shiming or installing wedge-ply to slope a drain.
Excellence is its own reward!
Never seen a flat roof? C'mon to California! In the suburban San Francisco area, there are tens of thousands of 'em. In the fifties and sixties, it may have been the most-common residential roof. They're tar&gravel, although lots of them now have been covered with a couple inches of spray-on polyurethane foam which both insulates and seals. Of course, we only get 20" of rain per year, so your results may differ.
Another thought --- if your interest in a flat roof is because you want to walk on it, you really have a different problem. Roofing materials will not generally hold up to being walked on. You can build a roof and/or deck combo that will handle this, but it is an entirely different proposition from making a roof whose only job is be waterproof.
Hi Jamie,
Thanks for your support on doing a flat roof. I lived in San Francisco and loved them there....so like you, I know it can be done. I would like to make it tar and gravel. Thanks for the info from you and the others. I can certainly understand the need for 1/4" pitch..which I can easily do. Also, I will try to find the product EPDM for the membrane.
One other question for you however...what about drains for the water run off??? I live near Paso Robles, California and we only get 12 inches of rain a year, but I still need some ideas on best placement of drains, type, etc. (My porch will be about a 12x20 plain rectangle) Any ideas???
Thanks for your help.
Sincerely,
Sicuranzo
Jim,
Thanks for your reply to my questions about building a flat roof. I know it won't be perfectly flat! The others gave me the guideline of 1/4" pitch...and that is the number I needed.
Hey, but thanks for the reply. I'll let you all know when it's finished!!!
Sicuranzo
Never seen a completely flat roof?
I helped fix a real winner once. An architect had talked the local school board into a flat roof with ####twist - There was a 2" lip around all the drains so the roof held water. The theory was that the water would slowly evaporate during the summer, and help keep the building cool.
Naturally it wasn't long before they hired us to tear out all those lips around the drains and re-do the roofs.
I know I'm narrow minded. But I can afford to be - I'm right.
Must've been a disciple of Frank L Wright, right?Excellence is its own reward!
put a little pitch in it and use a metal roof. It will make your porch compliment your house. I've never seen a membrane roof not leak in a short period of time, especially if there is a seam involved. Seems like there is always some area where the seam seal isn't quite right. Also, putting any penetrations in a roof is inviting leaks. Yeah they work great for about 5 years then its time for the roofing tar, or caulk. let the water drain off of the edge of the roof and use gutters to control the runoff.
Hey Steeltheone,
Thanks for your ideas about a flat roof...metal with a slight pitch sounds good.
found a great link http://www.metalroofing.org/