Help me pick a roof
Hello, my house is in need of a new roof. It is a 1,700 sq foot, story and a half salt box with garage (18 square). It has a relatively steep pitch on the long salt box side. The house also has cathedral ceilings in half of it and these are not insulated as well as the areas with a true attic. Therefore, ice damns are a potential problems. I live in upstate NY, where we get around 70″ of snow per year and routinely see single digits above and below zero. During the winter of 2015, we had lots of snow and cold, and I had some ice damning, but nothing horrible.
I am currently getting roofs quoted two different ways. Asphalt shingles with full ice and water shield and metal roofs, again with full ice and water shield.
A few of my questions are:
1) I was originally attracted to a metal roof because of it’s ability to shed snow, but if I do full ice and water shield on a asphalt roof, do I need to even worry about this? Can I just let the snow sit on the asphalt even if ice damns begin?
2) One contractor quoted me an exposed fastener metal roof (ideal roofing’s Americana panel), while another contractor says he does not like any exposed fastener metal roof. Are exposed fasteners really that bad?
3) My end goal is to never have to worry about ice dams, clearing the roof is very difficult because of the angle and length. Would asphalt with full ice and water shield do this? Or do I need the snow shedding ability of metal?
PS-I have already added all the insulation I can in accessible areas, I am not going to rip out the ceiling of the cathedral areas to get more insulation in there.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Chris,
Now is the ideal time to fix your ice dam problems once and for all by installing one or more layers of rigid foam about the roof sheathing. This approach may not be cheap, but it is (by far) the best way to go.
For more information, see How to Install Rigid Foam On Top of Roof Sheathing.
Chris,
Q. "I was originally attracted to a metal roof because of it's ability to shed snow, but if I do full Ice and Water Shield on a asphalt roof, do I need to even worry about this? Can I just let the snow sit on the asphalt even if ice dams begin?"
A. I'm not a fan of the "full Ice & Water Shield" approach. It disguises the problem rather than addressing the heat flow that is melting the snow on your roof. For more information, see this article: Prevent Ice Dams With Air Sealing and Insulation.
Q. One contractor quoted me an exposed fastener metal roof (ideal roofing's Americana panel), while another contractor says he does not like any exposed fastener metal roof. Are exposed fasteners really that bad?
A. Either type of roofing -- exposed fastener metal roofing or standing-seam metal roofing -- can be troublefree or a nightmare, depending on the skill of the installer. It's far more important to choose a competent roofer with good references than to worry about the type of roofing going on your roof. So choose your roofer wisely. I've installed a lot of exposed fastener metal roofing, and these roofs perform just fine.
Q. "My end goal is to never have to worry about ice dams. Clearing the roof is very difficult because of the angle and length. Would asphalt with full ice and water shield do this? Or do I need the snow shedding ability of metal?"
A. If you never want to worry about ice dams, you should install one or more layers of rigid foam above your roof sheathing, followed by another layer of roof sheathing and new roofing.
Chris:
I've had metal roofing for 35 years, the same Ideal Americana panels you mention. I'm on my second roof. The first was galvanized, not baked on enamel. It likely could have lasted many years more but visible rust made for an eyesore. Back then we used galvanized nails with bushings. This roof never leaked (save for a flashing issue around chimney), as far as I know. I originally had roll roofing (no money and in a hurry) on plywood deck. I used 1x4 furring strips above this for the metal roof attachment, so it is possible that if I had a few small leaks I would not have known it. But I did check the attic regularly and saw no leaks. I now have a colored roof, fastened with screws on the same furring strips. Been fine for 7 years.
Like Martin I would have no qualms about this type of roof if properly installed. I have a 2 story house with a gable roof, -too high to shovel and I never have. The snow slides off when it's ready. I don't however, have any issue with ice dams that make leakage more likely. I'm sure hidden fastener roofing is higher end, but can also leak if there is standing water behind an ice dam, and is also much more expensive I believe. The Ideal is quite reasonable.
In the US climate zone 6 parts of upstate NY fully half the total R needs to be on the exterior of the roof deck for adequate dew point control in an unvented assembly. In zone 5 it only needs to be 40%.
If the cathedralized ceiling portion is 2x6 w/ R13s you can blow insulation in from the exterior bringing it up to about R20 in the cavity, in which case you'd be moisture safe at the roof deck with 3" of exterior rigid polyiso in zone 5, or 4" in zone 6.
If it's 2x8 rafters blown full of fiber you'd be at about R28, and would need 4" of exterior polyiso in zone 5, or 6" in zone 6.
With any foam-over (even at less than current code min for total R) the ice damming risk is much reduced, since there is less temperature striping at the rafters to get the process started. If the rafters are 2x10s or bigger and you continue with the roof deck vented from below (since the exterior foam needed on the exterior for dew point control may be way too thick & expensive) even 2" of foam would cut the thermal bridging at the rafters in half, reducing the ice damming potential by quite a bit.
If material cost is a concern, look around for reclaimed or factory-seconds foam eg:
https://albany.craigslist.org/search/maa?query=rigid+insulation
With any metal roofing you may need to install snow anchors to reduce the risk of roof avalanches burying someone in the yard.
Chris, unless I missed it you never mentioned whether your current roof is a "hot" roof (unvented) or a vented roof. Venting plays a big role in ice dams. Installing a few properly located vents might be helpful in the uninsulated areas. Otherwise adding insulation on top (with integral sheathing layer for nailing) will be key to keeping the heat inside away from the snow.
I once worked with a Waterproofing Consultant whose solution to most problems was to encase the structure in bituthane / ice & water barrier. I suppose it works but its bot a graceful solution and seems to be a bit overkill / wasteful. Good luck.
Hello everyone, thanks for the info.
First off, yes my roof is vented. It has full soffit vents running the length of the bottom and a ridge vent on top. I just don't know how well they did with proper vents in the cathedral areas, did they maintain a good air gap? I can't see in there, so who knows?
Both roofing contractors said just a modern ridge vent is really going to help, as I guess my current one is pretty limiting.
For the price difference between asphalt and shingle, just over $4K for my roof, I probably could get 2" of foam and new plywood installed and then a new asphalt roof. That would give me better insulation, but I still don't have the snow shedding abilities of metal. If this added insulation does not solve the ice damn issue there still is potential for them. With metal, there will be little/no snow on the roof, so no ice damns, right??
I really don't agree with people saying full ice/water shield being a bad idea. It adds like 400 dollars to the roof vs. other solutions costing 10 times as much. Is there any downside to full ice and water shield on a vented roof? The cost is so minimal....
Chris,
My price to cover the entire 18 sq roof with Ice and Water Shield would be around $1300 plus labour. Something doesn't add up.
Chris,
While Ice & Water Shield may prevent ceiling leaks, it won't prevent ice dams. Nor will it lower your energy bills.
A layer of rigid foam will help prevent ice dams, while also lowering your energy bills.
If you decide to install the rigid foam, remember that this approach will require you to seal the air inlets near your soffit vents, and to seal the air outlets near your ridge vents.
I was quoted a 450 difference between ice and water shield on the first 6 feet vs the whole roof. The first 6 feet on the "short side" of the roof is probably more than half the area. Also, 6 feet on the garage is probably around half of that roof. Maybe that is why?
So would installing rigid foam over my current sheathing, then installing new sheathing and shingles be ok? What about the fact there is an air gap behind the current sheathing?
Chris,
I urge you once again to read my article, How to Install Rigid Foam On Top of Roof Sheathing.
Note that you need more than 2 inches of rigid foam in your climate zone (Zone 6). You'll need at least 5 inches of rigid foam in order to keep the lower layer of roof sheathing above the dew point during the winter.
If you go this route, you'll need to do a very good job of air sealing the bottoms and the tops of the ventilation channels. The best way to do that would probably be with a two-component spray foam kit. As long as you seal these channels, the air space will do no harm.
Martin, I cannot read the article, it is for paying members only. 5" of foam is a non-starter due to price. I don't have $20K to throw at a roof.
Chris,
Look into purchasing used rigid foam. You can probably buy 5 inches of used rigid foam for the same price as 2 inches of new rigid foam.
And if you are about to spend $4,000 or more for a new roof, you might want to invest $15 in a one-month subscription to GBA. If our articles give you even one good idea, the knowledge might save you a lot more than $15.
Metal is actually no guarantee that snow will slide off. My
standing-seam is actually quite slick, and when it's cold enough
big sections of a snow-pack will cling to the steep 12:12 part
on the front for days, maybe weeks on end. Water adhesion is
funny stuff, it can manifest itself [or not] in all kinds of
crazy ways on smooth surfaces depending on temps and which
way they're trending during precipitation.
But yeah, when it finally warms up and lets loose, *whump*.
_H*
Chris,
I must say, (no one is paying me to say this) I find it fantastically ridiculous that you won't spend the money on even a one month membership to GBA so that you can obtain the info you need,. I can affirm that it will certainly be the single best $15 you have ever spent on your house. I'm in the middle of building a zero-energy home right now, and have been a member for some time. I can vouch for the fact that so many of the questions I had when it came to building this house, were answered via articles, blog posts and the Q&A section of this website.
Your question has been answered more times than I can count on this site, so pay up sucka and you'll breath a little easier
Oh and put a couple layers of foam on your roof, you don't need ice and water on the whole roof, and use metal too (exposed fastener or not).
I would like to second Brad's enthusiasm for a GBA membership. It is well worth it. And anyway, asking for too much free advice is uncouth... and uncool.