Looking for advice on metal roofs
Our new home design includes a simple shed roof (passive solar home) with a chimney (4/12 pitch; approx 2400 sq ft). We’d like to put on a roof that is “no maintenance”, highly durable, light in color, and is Class 4-rated. We’ve looked at standing seam and stone-coated galvalume shingles. First question – are there other good alternatives to these roof types? Second question – how much difference does the gauge of the metal make and are there guidelines for choosing a metal roof gauge.
Our roof will face North and we hope to capture some rainwater via rain barrels to use for garden irrigation. Thanks in advance for your advice.
Mike S.
Omaha NE
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Roofing is fire rated as Class A, B or C, with A as the highest. If you want to use your roof for rainwater collection, I would recommend the standing seam.
Thanks, Robert. With Class 4, I was referring to impact resistance. I'm in one of the top four hail states.
Michael,
In general, any roofing should be "no maintenance" -- although clearly the inexpensive asphalt shingles sold these days develop algae problems so quickly that many homeowners have gotten used to washing their roofs regularly to address algae build-up.
Leaving the question of algae aside, metal roofing is a good choice. Personally, I would stay away from metal shingles -- it doesn't make much sense to take perfectly good metal roofing and cut it up into little pieces so that it resembles a different kind of roofing.
Conventional through-fastened metal roofing panels -- the kind used for decades on barns -- are a less expensive alternative to standing-seam metal roofing. Through-fastened metal roofing works best on simple roofs (gables and sheds) that aren't all cut up into little triangles and pierced by dormers, valleys, and intersecting architectural features.
Heavier gauges of metal roofing will probably last longer than thinner gauges. But any metal roof should outlast an asphalt shingle roof.
Exposed fastener roofs may have performed well on barns.......
lots of drying potential
I think they would be MUCH more risky on a highly insulated and air conditioned building.
John,
It sounds like you think that through-fastened metal roofing lacks drying potential.
Well, that's debatable. Such a roof clearly has more drying potential than a standing-seam metal roof.
It's also very easy to install metal roofing on 1x3 or 2x4 purlins -- that increases the drying potential.
John, is the roof you're imagining vented?
Martin & Lucas,
I agree that
Purlins and or vented roof would be better IF using exposed fasteners.....
The story I hear is that the fasteners become loose over time and the "washers" break down from UV exposure...lots of flexing etc. (is that not true?) (perhaps a Texas myth?)
Not a problem in a barn
Not so sure about a home
John,
I know that modern roofing screws with neoprene washers are much less likely to become loose over time than the old roofing nails with lead washers.
Back in the day, corrugated metal roofing was applied with long, washer-headed nails that were installed through the ribs (high points) of the metal panels and would deflect in wind loads and loosen from swelling and shrinkage of the underlying wood. Eventually they would leak and sometimes allow panels to blow off in a big wind.
Modern ribbed metal roofing is installed with short neoprene-gasketed screws on the flats of the panels. These fasteners have greater holding power and are not subject to wind torsion like their elder brethren. Such metal roofs can be as water-tight and last as long as a standing seam roof at less cost. And their exposed fasteners help keep snow and ice on the roof and prevent the avalanches common to standing seam roofs which can do considerable damage and cause havoc for shoveling walkways and drives.
The primary advantage of a metal roof over composition roofing is for potable rain-water collection, except for terne or galvalume roofs which may contribute heavy metals. Factory painted metal roofs are attractive and durable but more difficult to repair or renovate than shingled roofs, or even climb up on to clean the chimney.
My rookie experience:
With that low of a pitch I would go standing seam. I would not want snow sitting on exposed fasteners no matter how fancy. I want a 50 year roof.
I have corrugated metal on a 12/12 camp and standing seam on a low pitch barn for this reason.
The heavier guage standing seam is not worth it for me because I wouldn't stand on either guage, or run a stove pipe through it. But that's me.
I'm glad to hear you are going with a lighter color. I was not that smart about it and went with black. Which will be fine if I turn them into solar furnaces:) They get HOT.
With 40 decades of facilities engineering behind me, I vote for standing seam with concealed fasteners for metal roofs. All the natural forces at work on a metal roof tend to ratchet exposed fasteners out over time. On a building that had over an acre of roof, the architect specified 40' long panels in the mild climate of Southern Oregon. Thermal expansion cause these sheets to change their overall length more than 5/8". Exposed self-tapping screws w/ neoprene washers were installed in the flats. That was mistake #1; the holes in the roofing should have been slotted with really big neoprene washers (I doubt that they exist). Mistake #2 was 1/2" plywood (circa 1980) sheathing. These (Tek)screws need a minimum of 5/8" plywood, according to the roofing manufacturer. Cycling between 20 and 105 degrees over the seasons, the roofing turned traitor and the screws lost the battle within the first 10 years. Standing seam costs 25% more but the payback is less than 10 years. Their fastening system allows for thermal expansion and contraction without putting undo lateral force on the srew.
That is what I'm thinking as well. Even if a roof is vented I'm not sure letting deep snow sit on the fastners is a good idea. When the spring melt starts the roof over my garage traps an inch of standing water in the slush that is trapped between the deep snow and the roof. Water drains very slowly out of that slush. Also, a steeper roof aught to shed snow in smaller quantities more frequently rather than in one crushing avalanche. I'm thinking an 8/12 pitch should be sufficient but that's just my gut talking. Any thoughts?
RetiredCivilEngineer,
It sounds like mistake number one was trying to put an acre under roof. What was the color of the roofing? I suspect that was mistake number 2. Roof color is the primary determinant of solar gain and hence expansion.
If the architect had specified four 10' panels rather than a single 40' panel, there wouldn't have been a problem. Don't blame the roofing material for poor design.
Exposed fastened steel roofs are common up here in Eastern Ontario and Western Quebec. Standing seam roofs are not very common up here, in fact they are kind of exotic. There is lots of snow and we usually end up with a bout of rain, at times heavy, in winter falling on these snow covered roofs. It's prudent to put tar paper down on the roof deck, more prudently both Bakor and Soprema make a modified bitumen recommended as an underlay for steel roofs (Which could be used as an air barrier too!).
Some of the roofing profiles can be used down to 2/12. From my experience the shallower pitches are the only way you are going to avoid an avalanche of snow(though the snow could turn into a free flowing glacier in spring time). Snow barriers are readily available from the steel roof suppliers for steeper pitches.
As someone has mentioned the simpler the better with steel roofs. That coming from someone who has installed steel on a complicated roof! Also I would make the steel roof a true cold roof by using 1x3 or 1x4 strapping. You can fasten the steel to 5/8" plywood but strapping the roof deck will allow you a little more flexibility when you are thinking about the related building science issues.
Cheers,
Andrew
Malcolm Isaac put an exposed fastened steel roof on his PHPP designed house in Wakefield, Quebec. Check out the following page.
http://passivehouse.ca/buildings/newbuildingprojects/singlefamilyhouse
He has some construction pictures on Flickr showing how the strapping for the roof was done. Sorry I can't access Flickr so you'll have to find the pictures on your own.
Andrew
Andrew,
The Wakefield, Quebec house is a nice house. Thanks.
Here's the link to construction photos of Malcolm's house which includes some pictures of the roof.
http://www.flickr.com/photos/malcolmi/sets/960305/
Andrew
Interesting house, and it sure looks nice, but way too much work insulating it for me. What is the deal w/ all the concrete blocks lying on their sides in the foundation? Is that how some folks establish footers and bearing walls? Interesting, and simple. j
JKlingel
I'll email Malcolm and see if he can respond to your question. Malcolm I think would be the first to admit that their are easier ways to build a Passive House!
Andrew