Roofing advice: snow and ice
Eliza Jane Darling
March 11, 2013 in Design Dilemma
We're building a small cabin in the Adirondacks, where snow is a fact of life. Since we're starting from scratch we can build to purpose, but a central question is whether to design a roof that will shed the snow or bear the load. To complicate matters, persistent cycles of freeze-and-thaw seem to be increasingly common. Years ago "January thaw" was a fairly predictable event; nowadays we seem to get them every other week through winter and spring, so ice buildup is a concern.

Budget-wise, we can't afford the Welsh slate I'd dearly love to have; ditto clay or cedar, unless the investment meant a substantial savings (and fewer headaches) down the road. So we're probably looking at metal or asphalt shingle. Beyond material there are questions of pitch, ventilation, insulation and clearance, which may differ depending on how we want the roof to handle the weather. We know enough to keep the roof line simple and avoid valleys, and are currently thinking of a classic saltbox style (no dormers) where the main potential dam would be at the chimney.

Any thoughts? What's the dream roof in a mountain climate where the weather is turning a bit strange?
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14thstreet
We have regular black steel on our workshop in the back yard and the snow on the south side melts off before it can slide off in sheets. The north side slides off though more slowly, sometimes dropping larger chunks on the ground. There are pieces you can install on the roof on top of the steel to break this up, but we don't care for the look of those so we haven't installed those. We would add them if we had to, for function. We haven't had any issues with the gutters being pulled down yet (been thru 2 winters now). Our house on the other hand has steel shingles by Decra. They are hurricane rated, 50 yr warranty and all that so they won't blow off. The appear similar to asphalt from the road. They seem to handle the snow in a similar fashion as asphalt shingles. I would recommend either. We did full plywood sheeting & tyvek under both roof surfaces for strength.

Both of our roofs are vented along the peak with something like roll vent ridge cap, and of course the soffit is vented as well. Our insulation in the attic is blown-in fiberglass rather than regular cellulose since fiberglass will not settle as much over the years, thus providing better long-term insulation.

I might add, the workshop has a 4/12 pitch roof and the house has a 6/12 pitch roof. We had to make the workshop with a lower pitch roof than the house due to code restraints on "accessory building" height since we are within city limits.
March 11, 2013 at 2:01pm     
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PRO
Ironwood Builders
A few ideas...Ice damming is a problem, so the Grace's Ice and Water Shield on the eaves (a self adhering bituminous underlayment). Metal roofing over the eaves and then composition shingles above that. I would go with a steeper roof pitch than the typical salt box, minimum a 9-12, though I favor a 12-12 or even steeper in snow country. Don't worry about valleys...Ice and Water Shield 3' up both directions and a metal valley will keep things moving. A "cricket" at the chimney, a mini roof that is the width of the flue and has a ridge that runs from the flue, level back to the roof, covered with a torch down or self adhering bituminous sheet (properly flashed) will prevent leaks above the chimney.

There are some new plastic/rubber type products available that mimic Vermont slate in appearance and cost substantially less. http://www.euroshieldroofing.com/en/products/eurolite-slate.html I usually despise fake products, but these actually look pretty good, perform well and use recycled material..and cost less than a true slate roof. I would still do the metal roof over the eaves, as that is where ice dams form.

Ventilation depends on the interior architecture...if there are cathedral ceilings, we have a couple of ways of venting the roof...or not, and that decision gives us answers regarding insulation. With a steep roof pitch outside we can do a raised heel scissor truss and lower pitch cathedral ceiling inside. The raised heel makes the R-38 insulation we need stay off the eave vents. A combination of low and high venting will keep the roof cold and make for less melting when the cabin is heated in the winter. The same idea or application of insulation holds true if we do a stick built rafter and flat ceiling roof structure or a standard flat ceiling (if cathedral ceilings are not in the architectural plan) raised heel truss. To obtain the R value at the perimeter, a stick built roof would most likely be framed from 2X10...ergo more expensive than the truss material (and installation).

Another possible option is a "hot " roof. We do these regularly and building science and technology is better than ever. Using a 2X12 rafter and sprayed in place high density polyisocyanurate foam filling the rafter bays completely (absolutely no voids in the foam allowed...and no recessed lighting!), the roof is unvented. We can achieve as high as an R-48 or R-52 with this method and maintain inside and outside roof pitches as identical. Many contractors will do a version of this roof with rigid foam or fiberglass insulation. It does not work. I've torn them out and fixed them.

One more option is an exterior structural insulating panel system (SIPS) installed over a decorative rafter and wood ceiling interior. Edge detailing is important, as the insulation makes for a thick roof edge, but we have used false rafter tails at the eaves and transferred the roof plane to the top edge of the SIPS to make an exposed rafter and eave.

Gable end vents in a flat ceiling application or ridge vents for a cathedral ceiling make gravity flow work for ventilation. Power vents can really give better air flow, but my experience out in the country is that power is not always available when needed, and generators are set to provide basics, like lighting and refrigeration as opposed to roof venting. Solar powered vents work well..but the cells get dirty and things don't work well on cloudy days.

One last point about the traditional salt box design...eave and gable end overhangs were not deep enough for water to get away from the house exterior walls. Deeper eaves and overhangs, 2 feet or more, are the best way to prevent water hitting the sidewalls. In the photos, please note the snow "brakes" above gutters and the use of metal on the eaves. I've included a low slope cathedral ceiling photo to give you an idea of what a scissor truss ceiling would be like with a higher slope above.


[houzz=Tuscan Farm][houzz=Front Over Hang][houzz=2011 Showcase - Hillside Retreat][houzz=Lake Bluff custom residence]
March 11, 2013 at 2:49pm     
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feeny
Oh Ironwood. Will you just come out to Ohio and rebuild our roof? Ice dams are the bane of our existence. 70 year old slate roof laid over an original wood shingle roof. Too many gables and angles. Icicles galore..... ;-(
March 11, 2013 at 2:59pm     
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hr01
that would be quite the daily commute. But he seems like the kinda builder i would want also, and it doesn't hurt to ask lol David if you see this post check out what I said under "Kitchen/greatroom remodel"
March 11, 2013 at 5:36pm     
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Eliza Jane Darling
Much obliged for those detailed comments and experiences. We've made no absolute decisions on aesthetics as we're trying to do that in conjunction with functional considerations, choosing our compromises carefully. Our preferences tend toward the simple, spare and rustic, leaning more toward New England/Shaker/farmhouse/barn-home than Adirondack Great Camp or western-style log-home. The saltbox has turned out to be deceptively simple, for the colonial form, as Ironwood points out, has its problems (above and below; I note that many of the surviving 17th/18th-century ones seem to be sitting right in the grass - or in Adirondack parlance, the mud). Unfortunately the modernized versions are pretty hideous; it's a shape you can't "improve" too much without losing what you loved about it in the first place.

I'm intrigued by the "hot roof" system - would that work with a cathedral ceiling and does it limit your exterior roofing material choice? We're attempting to self-finance due to some ecological features of the land, which make it a bad bet for a construction loan (as well as being somewhat risk-averse ourselves in this crappy economy). Therefore we're building small, so interior real estate is key, and we've been contemplating a functional loft opening out onto the main sitting area rather than an enclosed attic.

That Decra steel roofing mentioned by 14thstreet is beautiful, as is the Eurolite slate. If I had my druthers I'd go with solar slate, but in addition to the expense this seems to be primarily available in Britain. With our budget, we'll probably wind up with corrugated tin off the old barn up the road.
March 11, 2013 at 6:05pm   
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PRO
Ironwood Builders
Eliza, by the way, a classic name...sounds like Bronte' or Dickens. The "hot" roof is specifically designed for cathedral ceilings where interior ceiling height is an issue. We use it with standard comp shingles and metal roofing. It isn't so much about the roof or the ceiling as the insulation and the movement of moisture through a roof construction. Humidity, or water vapor, travels through a roof system, inevitable as the tides. The key to a cold roof, a standard vented roof, is the air flow inside the attic space drying out that moisture before it settles into the framing or roof decking. Water vapor needs air to reach into a building...and it needs temperature differential to reach "dew" point, the point at which water vapor turns back to water. So, for water to damage a roof (that doesn't actively leak!) it needs to morph from vapor to water inside the roof, with the help of air and temperature change....condensation. A hot roof denies the air necessary for condensation to happen...ergo the solid spray foam fill of the rafter bays (and no recessed can lights!). Temperature differential cannot be controlled. The heat from the interior and the cold from the exterior, or vice versa, will always meet somewhere in the middle of a hot roof.

I know you are joking about the tin from the barn down the road...but others might try it if I don't discourage it. Not for a roof, OK? Reclaimed corrugated roofing can be used on sidewalls with attention to detail and the use of a rain screen (see Benjamin Obdyke's Homeslicker). The stuff is nailed or screwed in place with gasketed fasteners...and making sure every last hole is sealed is impossible.
March 11, 2013 at 8:15pm     
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Eliza Jane Darling
Definitely kidding! I have looked into reclaimed materials for decorative interior elements, but I'm a bit leery that the trade is driving the destruction of our rural barns. I have no proof of that, though I did notice that two local (big, beautiful) barns that seemed structurally sound disappeared recently, with nothing replacing them. I suppose that's another discussion; I just have a thing about old barns.

On the hot roof issue - glancing around the web there seems to be some contention as to whether they cause ice-damming at the eaves. Is that a matter of using enough insulation to keep the roof cold? "Hot roof" almost seems like a misnomer; "hot" refers to the conditioned attic space, rather than the exterior roof itself, if I'm not mistaken. At any rate having slept on it, I would definitely like to have a useable loft, even if it's a partial one, particularly because I'm only 5' tall. I could use a hobbit-space for a library/study up above without taking up more spacious real estate down below, where my (taller) husband needs to maneuver comfortably too.

Yes, the name is old-fashioned, much like my taste in architecture (and come to think of it, music). It's a real challenge to adapt some of the classical forms to modern technology and knowledge without obliterating their character altogether.

Thanks very much for this detailed discussion - wish you were in New York rather than California!
March 12, 2013 at 6:30am   
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S. Thomas Kutch
Eliza, Dave (Ironwood) has given you some excellent advice. The only thing I differ with him is the Grace Ice and Water shield being just the 3'. I've always recommended to just use it on the whole roof, especially if this is a residence that there are periods of time where you're not there. The great characteristic about the I&W shield is its self sealing capabilities.........every penetration into the roof deck is a potential water leak, the ice and water shield seals around penetrations, be it a shingle nail, staple or metal roofing attachment, it's sealed..... I've used it on a number of homes from Florida with driving rains to the mountains in NC and Colorado and have never had a complaint about leaks .....either from rain, snow or ice dams. There are certain areas where you may want to save some bucks...........the roof isn't one of them. Some will say it's overkill and maybe it is, but it my opinion and my client's opinions.......it's been well worth the investment in the long run. Just something to think about.
March 12, 2013 at 8:07am     
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Eliza Jane Darling
Thanks Thomas, that sounds sensible. Building to budget is a necessity but we don't want to be penny-wise and pound-foolish, compromising on structural elements that will mean costly repair or high energy costs down the road. I would rather get the structure right - built to climate - and live with plywood floors for awhile, than pour limited funding into the finish work.

We're facing a (sort-of) similar dilemma with electricity. Running the feed on poles through our wooded lot would be cheaper than burying the cable. But I can guarantee that a softwood will take the line down (through wind or ice or both) within a year, and beyond the 100ft off the road for which the electric company is responsible, that'll be our problem to fix. And don't even get me started on the septic issue (the land is almost entirely rock, ledge and wetland), which is the bane of our existence.

Really this piece of land is a pain in the arse, but it's beautiful and iconic, and holds considerable sentimental value; I've known it all my life and feel very lucky that we were able to buy it. I'm sitting just across the lake from it now in my rental house. Have attached a photo of it, taken in autumn. Locally we call it "The Big Rock," for obvious reasons.
March 12, 2013 at 9:18am     
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hr01
It's a beautiful spot i see why you love relaxing there
March 12, 2013 at 10:26am     
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PRO
Ironwood Builders
Eliz and STK, yes I left the Ice and Water Shield off the majority of the roof! We've been using a product called "Tiger Paws" lately, a polypropylene membrane used like the old building paper (tar paper) that rolls out and plastic cap nails down. Cheaper by far than a full roof of Ice and Water Shield..and that goes back to my comments about roof pitch. We use full Ice and Water Shield protection in low pitch roofs, 5/12 and under. In snow country I want a 9/12 minimum and a 12/12 is preferable. Ice and Water Shield is a 4' wide product and I call it out on 2' eaves on a 12/12 pitch, taking the product to just 1' beyond the plate line. I did not fully detail the roof, as another line of bituminous membrane is necessary to extend up the roof above the plate line an additional foot minimum. Three feet in valleys with a 1' overlap at the center. I do agree that the very best roof would have a full cover of Ice and Water Shield even at a 12/12 pitch.

Regarding "hot" vs. "cold" roof technology...a cold roof is exposed to the air on it's underside by air venting. Heat loss through the ceiling is whisked away by the ventilation, preventing condensation...the roof is "cold" on it's underside. A hot roof is unvented, the insulation is warm from the interior and the cold pressing inwards from the exterior is what causes (with air) condensation in the roof....a "hot" roof is exposed to interior heating on it's underside. Hope this clarifies things.

Ice damming occurs when warm roofs melt snow and the resultant snow melt hits the unheated eaves. Most old house have or had minimal insulation. An R-48 should go a long way towards preventing interior air temperatures from melting roof snow. Global warming trends are causing your freeze thaw issues...these will effect the entire roof and the critical time is as the water continues to flow and the air cools down again for the night (or day!). Steeper pitch and metal eaves speed up the flow of water and the metal makes the ice slide nicely. Other, more expensive strategies than a band of metal on the eaves exist. I have not done radiant electrical on eaves, but know it to be a method of preventing ice damming (did an entire driveway once though!).

About head room in the loft. The IRC building code, which New York has adopted, requires the minimum average head room of a ceiling to be 7'. The spring point of the wall to sloping ceiling can be no less than 5'. This will be easy to achieve with the steeper roof pitch.

Septic systems in poor soils are commonplace here in Sonoma County...Our soils are very unkind in many areas. Moire, serpentine, clay, metamorphic rock, lava fields, decomposed granite...and pretty much everything else. The hills are the hardest and everyone wants a view! All septic systems work by the same principles, evaporation, transpiration or aspiration. Some of the very newest (and not yet approved in CA) rely on a natural ecosystem to do these three things...a filtered swamp....yummy! An engineered mound system would be a good fit with your soils. Basically a pressurized system in an artificial "mound" of imported dirt. The goods are gravity fed to a tank, filtered and then pumped to the mound. Oh, and like the roof, I'm simplifying things a bit! The soil allows the liquids to slowly transpirate into the harder sub-soils, grasses on the mound aspirate some of the sewage and the air around the mound evaporates the water. Tanks and filter cleaning are required on a regular basis, as is mound integrity inspection. But you get a viable septic system and as a California approved construction (toughest environmental laws in the land) your local building department should accept the design.

House styling is important....For snow country and not Mountain Lodge or Adirondack style, look to the granite and white clapboard style houses of New Hampshire and Vermont..Slate roofs for sure!

I suppose I am too detailed and verbose...but hard information and preparation are crucial parts to planning a home build. Your site is incredible..and I wish I could travel to help!
March 12, 2013 at 2:44pm     
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Eliza Jane Darling
"toughest environmental laws in the land" - Wish it were so, Dave, but we're in the Adirondack Park, which is one of the most strictly regulated pieces of real estate in the country. The problem isn't so much the type of septic but its location, given that there's a funny little "wetland" (i.e., seasonal stream) running awkwardly right across the property (which dips into a valley behind that rock in the photo). We need a 200' setback from the wetland (no exceptions regardless of system type), which is either going to take us up a steep ledge on either side of the valley, or through a copse I'd prefer not to cut, as the previous landowner did a hatchet-job in the valley and I'd like to keep as many trees standing as possible. We're going to look at it with fresh eyes this spring, as we're now planning on building much smaller than originally planned, which opens up more possibilities for tucking the cabin away in discreet corners that previously looked unusable (we had also planned on a carriage house, which means car as well as foot access, but have since scrapped that idea). We might still build something larger later, but for now we'd like something cozy and efficient that could be used as a guest house in the future.

I quite like the look of this little cottage I found on Houzz:




I can't say exactly what the roof pitch is here, but the design should be amenable to something like a 12/12, and clearly extended eves wouldn't detract from the style, either. One challenge I can see is the door directly beneath the valley where the two rooflines meet, which looks like trouble in the winter - but the door could be moved, for example to one of the ends instead...?
March 13, 2013 at 5:41am   
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