I am in the process of designing a Timberframe home and considering usings Sips to cover the roof. Many of the Timber manufacturiers recommend roof sips. I am located in MN. and have seen three timber projects w/sips that have very considerable ice dams. I want to avoid this at all costs. Any suggestions?

I think a SIP roof will work for you well. As a matter of fact, SIP walls between your timbers will work well too. As far as the ice dams are concerned, there are at least two ways to deal with this problem. One, put a cold roof over the SIP roof. Two, go through a winter to see if you have a problem. If you do, take some pictures and next spring add some electric roof deicing products like Warmzone to the problem areas. (LINK) There are some systems that only activate when there is ice present to save electricity.


Steve Etten
www.GrandCountySIPs.com
SteveEtten@GrandCountySIPs.com

OK, now I'm confused!

With a SIP thick enough for a roof panel, how does enough heat penetrate to melt the snow and create an ice dam? 

To me, this seems counter to the whole SIP idea.

Very respectfully,
but very confused,

Larry

Larry,

Great question. It had me confused at first too, but I think I’ve come up with a theory.

First of all, I’ve noticed it only on the south side of my house and then I saw water dripping from the eves during sunny days. Most houses have a flat interior ceiling with insulation between the rafters and none under the roof, helping to keep the roof un-insulated and cool.

With a SIP roof, the insulation is directly under the roofing material. Now when the sun strikes the roof, it heats up the roofing material, melting the snow, then refreezing to form ice at the eves at night. The sun’s heat is prevented from penetrating the roof by the insulation. The heat is not penetrating the roof from below, but is being generated by the sunlight. It’s similar to the sun melting ice and snow on a highway. If the highway were insulated from the cold dirt underneath it, it would warm up faster and melt the snow faster. The problem, of course, is at night when the water would again freeze. A cold roof can help this because there is airflow between the SIP roof and the cold roof, preventing heat buildup from the sun. I hope this helps.

Steve Etten
SteveEtten@GrandCountySIPs.com
www.GrandCountySIPs.com

Steve did a good job of explaning how the sun can cause an ice dam. Normally, they are caused by heat escaping the structure. And, when working with SIPS the only way that I can see that happening is an improper installation where heat is escaping from the seams of the roof panels(think Alaska). Or possibly, they used a panel that was way too small(thinkness).

A good article on Ice Dams can be found here.

Steve,

Thank you for a cogent reply.

JC,

Thank you for the link.



The explanations make perfect sense -- it's all obvious when you know the answer!


Two follow-up questions:

With a SIP roof, there would seem to be little risk of short term damage to the interior (assuming that the joints were taped); with a SIP roof and with 2 sections of a membrane at the edge, would an ice dam present any significant risk to the building or outer clading?  (With a well constructe SIP roof, could ice dams be safely ignored?)

From what I've read, I gather that the shingle color does not have a significant effect on the max. temp in an attic during the summer.  What of the reverse?  Would light color shingles absorb enough less energy to make a difference in the surface temp. on SIP roofs in the winter?

VERY respectfully,
Larry

I hear a good reason to use steel SIPs is they provide a secondary water barrier in case of back ups or storm damage to permanent roof

Larry,

When I built my SIP home three years ago, my contractor recommended to use ice and water shield all the way to the peak of the roof. Living here in Grand Lake Colorado with many sunny winter days, he said it would be a good idea. I wasn’t sure what he meant by that, but now I think I do. I used medium green shingles to minimize snow slides off the roof. I haven’t noticed any damage at all so far, and I haven’t heard about other people having problems, so, so far so good. If I notice anything, I’ll replace any damaged shingles and do something else. It really depends on how bad a problem you have. If you just have a few icicles, I might be tempted to ignore it. On the other hand, if you have a substantial ice dam, I would put up some heat tape. A lot depends on where you live, the direction your roof faces and how many sunny days you have. Most of my ice forms at the bottom of the valley of my dormer. That’s the only place where there’s any ice formation. If you don’t have any valleys, you might not have any problems at all.

When I lived in Iowa, it was usually recommended to use white or very light colored shingles to reduce the heat in the attic and also help reduce the heat in the house during the long, hot summers. I think a lighter colored shingle or metal roof would help reflect some of the sun’s energy and minimize the heat build-up.

Kind of an afterthought; how do you nail shingles to a steel SIP roof?

Steve Etten
SteveEtten@GrandCountySIPs.com
www.GrandCountySIPs.com

Larry,
Please remember that seam tape is an 'Insurance Policy'. It's not a replacement for a properly sealed SIP joint.
No. As Steve explained, anytime you have snow on a roof, and it melts and refreezes, the potential exists. Shingle color? I don't think that it'll matter. Some days you have sun/temps that will melt the snow. So, the snow is going to eventually melt, and in a lot of situations, refreeze. Shingle color is not going to stop the inevitable.

Steve, where in Iowa are you from? I spent way to many years in Nebraska.

Most ice dams are caused by heat loss via air leakage through the upper most thermal boundary and air barrier. Certainly if you have a south facing roof you can get some ice daming because of daytime snow melt, night time freeze-up. Likley if you are getting ice dams on a sip panel roof its because whom ever did the install did not get a proper airseal. Wanna totally avoid ice dams? Put on a standing seam steel roof.

It only takes ~32 degrees and a tiny bit of heat loss to get ice dams. The heat from the building warms up the snow to 33 degrees, it runs down to the 31 degree eves and refreezes. No air flow needed.

There is a reason that most northern climate houses have vented attics with the same temperature in the middle and over the eaves.

I used 8" OSB SIP panels on my roof along with a darker brown standing seam metal roof. I live in Michigan and have been through (2) winters. The only time we get any kind of icing is when it is sunny out and the snow melts slightly and then tiny (like 3"), very thin icicles form on parts of the eave. My attic is sealed and conditioned. For the most part, the snow slides easily off the roof ( 6/12 pitch). Where my house sits allows me to just let it fall. We shovel out the entryways and there you go. No ice dams though.

10 inch SIP roof going on 9 years in the mountains of Wyoming. Standing seam metal roof

Not 1 ice dam ever. We have snow on the roof most of the winte, up to 2 feet( low pitch)