Snow in the attic

Specific Inspection Topics Exterior Inspections
1

We don’t usually get snow falls of more than a foot, but the last weekend’s storm dumped 16 inches and it was a blowing storm to boot. So at this afternoon’s inspection, there was a pile of snow underneath each attic vent. Probably about a gallon bucket of snow each. The roof was replaced in July, along with new pan vents. My question is, does this sound normal, taking into account the amound of snow and the wind? My first thought was the wrong type of vent for the slope of the roof, but maybe you guys that see more
snow on a regular basis can comment. Thanks in advance.
Stu

2

Stuart;
Did the house have a ridge vent?
What kind of soffit vents were they?
Was there any gable vents?

It has been known on occasions for prevailing winds under the right scenario, applied with the normal stack affect of Attic Venting, that a negative pressure will result under those wind conditions and suck snow up, through, and in the Attics. Very rare occurrences, but been known to happen.

There always are a perfect condition for what one, does not want to happen.

Marcel :slight_smile: :slight_smile:
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3

Twice I have seen this one was the strong wind came from the same side as the vents and I think caused a negative pressure in attic and sucked in the snow . The other was Turbine vents . I have been told this can be a concern with them .
Roy Cooke
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4

Marcel and Roy,
The soffit vents were the louvered strip-type, about 2 inches wide and about 4 feet long per section, cut into plywood soffit. No ridge vent, or turbines, just 7 pan vents and one disconnected powered roof vent with a pile of snow underneath each one. The wind was about 20-30 mph during the storm. I was thinking there might be different heights or profiles of vents, like with ridge vents. I couldn’t see them from the ground because they are buried in the snow. I guess I can call it out as it was, and mention that under certain weather conditions this may happen again. The last time we had this much snow in one helping was in 1995. Any other thoughts out there? Thanks for your help.
Stu

5

We used to see snow in the attics regularly with the ridge vents that had inadequate baffles (very thin and airy type not the brillo pad type) but that has been corrected by the manufacturer.

I’ve not seen it up here in northern Michigan where the roof vents leak snow…probably an odd negative pressure thing like the others said.

6

Stuart,

The moisture is coming through the roof vents. This is not common, but I would not consider this rare either. Moisture can get through any opening under the right conditions. I’ve had rain come down my chimney and soak my carpret. Conditions had to be just right for that to happen and they were.

7

Thanks Larry and Erol.
Stu

8

Have seen it a couple of times as well, no real concern. Did not even write it up.

9

I see it once or twice a year after a blowing snow storm or a really hard rain. If there isn’t really alot inside, I don’t write it up. Common sense will tell you with any roof opening, some minor moisture can get in.

10

Thanks, Bartman
Stu

11

Wait a minute. Snow is water, in the spring or before, the snow is going to melt. Wet insulation is no insulation. Of course it is a concern. Advise your clients to get up there and remove as much as possible before it soaks the insulation and soaks down onto the drywall. Water will find a way into the home if given any chance what so ever.
Larry

12

I have seen it happen with gable vents if a parallel wind with roof ridge.

Have seen it with mushroom cap vents and other vents. Certain wind conditions will create it.

13

We are talking about a minimal amount here, and it usually melts very slowly and evaporates without even leaving a puddle or causing any staining. To advise clients about it would more than likely cause more hysteria than it would be worth in my books. If you’re going to try and document every possible scenario that comes along…we’ll good luck with that.:wink: </IMG>

14

Have you found any like I and others seem to have found .
I too thought it was so little why be concerned .
This is a judgment call and I feel I and others have done exactly what we should have done .
I see condensation on windows that needs to be controlled and I see condensation on windows that is Minor and say nothing.
Roy Cooke.

15

The pan vents you mention are a poor means of ventilating any roof, they let a minimal amount of air out of the attic and they can become (as you have learned) a source of air intake to the attic.

Some rules for adequate ventilation are;

  1. only one intake source, preferrably the eaves with a strip vent or vented soffit, which is located as low as possible (eaves)
    2)only one exhaust point, preferably the ridge on conventional roof lines, again continous WITH AND EXTERNAL BAFFLE AND A FILTER ON THE INSIDE
    3)if a power vent is installed the other exhaust sources become intakes, if the power vent is set up to operate with humidity it can pull in the weather.
    4)overlapping or multiple attempts at curing a ventilation problem can and will create what is called a ‘short circuit in the ventilation’ which often negates the performance.

Suggestion, if you want to learn about ventilation check our Certainteed’s roofing and ventilation training courses. Get the video that shows smoke tests it can be an eye opener.

16

where does a person find these video’s

Cookie

17

I gotta say, I really appreciate all the feedback I’ve gotten on this subject. I had considered most of the information before I posted my original message, and it always encourages me that first and foremost, the NACHI membership always helps each other out on these message boards. The snow storm we had was unusual for this area, and it caused unique situations, such as snow blocked plumbing vents, covered up furnace flues, major ice damming and a few roof collapses. The snow in the attic was an anomoly, because of the very strong winds during the whole snowfall. This was the only house (out of 20) I inspected during the next 2 weeks that had any snow on the inside. Thanks again to everyone that weighed in.
Merry Christmas.
Stu

18

20 inspections in two weeks. I’m moving down to your area!

19

Come on down.
Stu

20

The snow in our attic did not come through vents. It ran in a line matching the ridge row/center beam of the roof. It was 6-9 inches deep, one foot wide and about 30 feet long down the center of the attic floor. With the very high north winds and our house facing north/south it appears that the wind raised up the shingles along the very top ridge of the roof and then the snow just fell straight down into that straight line. Anyone ever hear of that happening?