Best low-slope roof system for 1:12

jpherronJanuary 1, 2007

I have a large shed dormer on the back of my house that's started having some leaks, and I need to have the current roll roofing replaced. the dormer is 50x15, 1:12 pitch, with a stone chimney and 2 vent stack pipes (otherwise nothing special). There's a small section (about 3 foot) at the top of the 8:12 roof for the rest of the house, so there is a roof slope change to consider. The roof is high up off the ground (it's on the back, and there's a walkout basement), so it is not visible at all. I'd like to find a roofing system that will hold up well, hopefully be reasonably priced, and can be put on now, in cold temps. I'm in central Indiana, and the temps right now are highs in the 30s-40s.

I have an estimate to have the current roof torn off, 1/2" foamboard applied, with .6 EPDM, for $3300 plus any replacement decking. This seems a bit high to me, but I don't know for sure. Is this reasonable for rubber? Are there other options that would be better/cheaper?

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I do not know of a better system for your situation than the EPDM, properly installed. Too often, the installation is not correct and the material gets bad publicity. Other than mechanical damage or damage from petroleum oils, EPDM is as durable as it gets, provided it is installed so that it stays in place.

    Bookmark   January 1, 2007 at 1:17PM
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So, are there any issue with putting EPDM on this time of year? I thought there might be an issue with the adhesive in low temps.

    Bookmark   January 1, 2007 at 3:24PM
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EPDM can be either glued down or mechanically fastened.
If teh area is not to large you could try resource Conservation Technology, Baltimore, MD.
They will make up a panel with tabs along the seams on the back for fastening.
If you provide a good drawing they can even turn-key all the materials and ship them to you.
The issue with EPDM in residential is that the manufacturers are not interested in the residential market, just the commercial market.
It is not very hard to install, the biggest problem is getting a seamless membrane up onto the roof. It gets heavy very quickly.
There are a number of places that will sell you factory seamed pieces of various sizes and materials, but they are not set up like Resource Conservation with a fastener tab along the seam.
EPDM is more expensive than torch down bitumin, but it lasts much longer.

    Bookmark   January 1, 2007 at 3:42PM
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Thanks, brickeyee, the mechanically fastened EPDM is an interesting possibility. I asked this same question on a forum mostly geared toward roofing professionals, and got a much different impression from them about the difficulty of doing this myself (although it's pro roofers, so it must be taken with a little grain of salt). They suggested that a. the bid I got was actually low, and b. that a mod bit (but cold-applied) would be better, but more expensive.

I'm pretty handy in general, having done extensive kitchen remodels, flooring, basements, etc. But I've never done a roofing project.

One issue that they brought up was the chimney. They said flashing a stone chimney would be very challenging, and should cost a lot of $$. What's there now is a mess of roofing cement, and since it's not visible anyway, I would think of doing something equally inelegant, if I was to DIY.

Do you have a feel for how the tabbed EPDM would price out? I'm seeing about $1/ft for materials from the pros, but I would imagine this kind of material might be pricier?

    Bookmark   January 1, 2007 at 7:33PM
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Just in case you get the EPDM and later have flashing problems, never use asphalt based roofing cement with EPDM, the asphalt oils will ruin the EPDM. Urethane sealants such as NP-1 are compatible, but cost more and are less convenient to apply.

    Bookmark   January 2, 2007 at 7:52AM
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I've taken some pics to give people a better idea of what I'm looking at. brickeyee, do you think the chimney would make it too difficult to try a DIY rubber roof install?

Here is a link that might be useful: Roof pics

    Bookmark   January 2, 2007 at 1:45PM
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Knowledgeable installers can deal with the chimney with no problem. They probably will cut a groove around the chimney for a metal counterflashing that comes down over the upturn of the EPDM at the chimney. The counterflashing will cover the top edges of the upturned EPDM, but probably will not actually touch it.

Here is a link that might be useful: counterflashing

    Bookmark   January 2, 2007 at 4:48PM
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Please let me toss my experiences into the ring.

We have a contemporary home,, with one section,of the roof of about 800 sq ft., to be a pitch of about 1.5/12....Now, on there previously was the wide roll roofing stuff (3').... It lasted 10 years, started to buckle in places,, leak by skylights etc.

Well, anyways,,, eventaully had the whole roof done. Met with approximately 8 contractors. They all provided different opinions and recommendations for an appropriate product.

Three recommended a shingle, with no problems whatsoever based upon their years of past experience.

As it turned out, we went with a heavy gauge arch. shingle, GAP, an ice and water barrier pretty much a portion of the area, step flashing with new skylights,,,about 7 years ago. The work was done in early fall,,,,and roof sealed wonderfully come winter here in the Northeast USA. Also, please note,,, over the past couple of years,, we would have up to at times a foot of snow on the roof,,, and in some places,, especially down by the gutters,,,,3-4 inch layer of ice.

To this day, it still looks almost brand new,, has worn well,,,no leaks,,, and could not be any happier....The price was well under some of the other methods,,, it wil last probably at least twice the timeframe of the cheapo roll roofing, etc....

Just beware, the membrane system,, can leak,,,if you trees nearby,,, watch out for falling branches, and watch out for the price tag as well...

I get up every morning, and thank the contractor that recommended and did the work; there is nothing like the feeling of a leakfree roof.

Best of luck.

By the way,, a local friend of mine,, had his shed dormer done with a shingle,,, and I bet the pitch of hgis roof is just like yours,, and has never had a problem in over 23 years to this day.

    Bookmark   July 16, 2008 at 3:15PM
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A very low pitch roof can also be done in metal. At 1/12 pitch, you are right at the threshold where standing seam becomes impermissible (I mean true standing seam with a rolled lock seam), and soldered flat seams must be used. A soldered flat seam metal roof won't be cheap, and must be done by an artisan, but it lasts a very long time. It's on the very upper end in terms of cost, especially if done in maintenance-free copper.

    Bookmark   July 18, 2008 at 7:47AM
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Location plays a big part in low pitch roof type selection.
If you get significant snow you end up doing a lot of work to prevent water from getting under lap shingles.
Double coverage roll tends to have a limited life.

Bitumen (torch or cold) still has a lot of field seams that require sealing. The material is also very thin and easily damaged by debris (falling on the roof or being stepped on when already there).

EPDM can usually be had in large enough pieces for residential with factory seams.
It is also from 0.040 thick and more.
EPDM against brick requires a wooden nailer, then the EPDM is held in place with straps and screws, and the edge covered with counter flashing.
I use copper set in grooves in the mortar joints of brick walls.
It can even be done on stone walls but it is a lot harder to cut the grooves.

EPDM can be glued down, ballasted down, or mechanically fastened.
The last one I installed has a 500 lb AC condenser in the middle of an 18 x 10 area that holds it down and is screwed and clamped at the edges.
Resource Conservation makes up pieces to order and leaves a flap at each seam that you can anchor through as the roof is installed using special washers and screws. You end up with no exposed fasteners.
Some commercial work drives fasteners through the EPDM and then covers the area with the edge of the next piece.
Field seams are more likely ot cause problems and the uncured EPDM used to make the seams is a real PITA to handle.
It sticks to EVERYTHING. You, the tools to cut it, etc.
I much prefer a factory seamed panel that can be cut down to exact size.
The EPDM industry is not interested in residential work, so finding a good installer can be a problem.
In Europe it is used for residential and many details of installation can be obtained.

Tar based products cannot touch EPDM without causing damage.
Old roof decks need an isolation membrane or a layer of plywood (1/4 inch is fine).
When I need to run EPDM up to shingles I use 1/8 inch plywood up under the last course of shingles, install the EPDM, the use flashing between the shingles and the EPDM.

The best edge treatment for EPDM is to wrap it over the edge and fasten to the fascia using aluminum bars, sealing tape, and screws.
Use stainless hardware here.

    Bookmark   July 19, 2008 at 11:01AM
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Hi all,

I am reading up on this subject, and if you have any more ideas for our application, I would appreciate it. We are planning to install a 5' x 7' sauna onto the back of our house, and the HOA wants us to match the home's arch shingles. There isn't enough slope to do that so we're looking at other options.

We considered a metal roof, but we don't think they'll approve it. Are there membrane materials that we could install the arch shingles over somehow? That would be the most likely thing they would approve (exact match to house), but if nothing like that exists, what other options should we look at? It needs to look pretty high end so just a membrane alone won't fly.

Our house is contemporary style, and we live in GA so snow/ice/cold is not an issue.

Thanks for any advice!


    Bookmark   August 1, 2008 at 7:34PM
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In my opinion gluing synthetic rubber and neoprene membranes together is not a wise DIY project. It's difficult, messy, and extremely dangerous. It would be at the top of my list of the greatest bargains in home repair right above floor sanding.

Hire a good installer so you can forget about it and worry about something else. Stop eating between meals. It'll pay for the roof, extend your life, and impress your wife.

    Bookmark   August 3, 2008 at 12:14PM
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