I don’t think I have seen it but I the way Brian and Marcel explained it does make sense.
Thank you.
It may be that since you are further North in Canada, you do not experience the mid-Winter temp swings that we occasionally get. Not uncommon for a 30-40 degree swing in Jan/Feb. Your Winter cold temps may be more stable.
Peter:
I stopped reading the article as I was finding statements that were off base or wrong.
“Research shows keeping the attic air temperature below freezing when the outside air temperature is in the low 20s can reduce the occurrence of ice dams. Research has shown sun exposure in the winter has little effect on attic air temperature. Warm air from living spaces below penetrating into the attic is usually the culprit in the formation of ice dams.”
HUH!!! Even if the attic air is cold, the roof shingle surface can get above freezing from solar heating and cause melting/ice damming."
Exactly.
I have an unheated uninsulated garage that has a North/South facing roof.
About the end of February when it is still very cold, the sun starts to shine on the North side near the ridge. The snow melts and water runs down toward the overhang and gutters.
Guess what?, ice damns form and can get quite high if we don’t get a good “spring thaw” day or two.
Of course it depends on the year and how much snow depth has accumulated on the roof.
Some years there are no problems and others make me consider putting in a roof melt system.
Solar contributes to the cause, but not the source of the whole problem. 
Who claimed anything different Marcel?
I can show you many homes where the Sun has little or nothing to do with it.
It does.
Please refer to the IRC Code Commentary.
Mike, read my French again.
Solar contributes but is not the main cause of ice damns.
I agree, a shed could have icicles, but the home with leakage and escaping warm air will be worse.
Your “French” is fine.
Sorry for any misunderstanding on my part.
On certain days, solar may be** the** cause of the problem even when the attic is well insulated and airtight. SEE “Cause: Snow thickness variation”
BTW: John Straube is now a principal in Building Science Corporation with Joe Lstiburek et al. I’ve known him for about 7-8 years now as he is brought into Nova Scotia as a speaker at our regular ENERhouse conference. In 2002, had to bounce some ideas off him when I was called called into a $9-10 million commercial renovation on a RUSH basis by the architects.
Older post, but relevant.
http://www.nachi.org/forum/f16/whats-your-narrative-one-48344/#post625384
If you saw a “ton” of ice hanging from the eaves, do you report it?
If yes, then what’s your narrative?
A ton of ice hanging from the eaves is definitely reported. This particular defect is also viewable in the summer months. I simply inspect any exposed rafter tails (in the attic) for moisture stains.
Illustration of David inspecting rafter tails in attic for moisture stains:
This ICE DAM illustration was developed to be inserted into inspection reports:
(Great illustrations inside reports help communicate findings.)
Ben,
Nice illustration, but I’d like to see the text edited. It states “Trapped water leaks through the shingles”. It doesn’t leak through the shingles, it should state something to the effect of…“accumulating water backs up and is forced right under the roofing material and into your attic or soffit cavity”.
And then gravity takes over, and this water infiltration simply drips down onto your living area walls, causing the nuisance staining and damage that can be observed throughout your walls.
[quote=“bgromicko, post:34, topic:50652”]
Illustration of David inspecting rafter tails in attic for moisture stains:
You failed to add my company logo on the back on my tyvek!
I see it…
Nice Text on my arse Larry, but where’s my logo?
Ya, I put that on the front of your Tyvek…
Thank you, Sir.