Dripping wet cedar soffits – cause? (not a roof leak)

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scandimod
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Dripping wet cedar soffits – cause? (not a roof leak)

Postby scandimod » Sat Jan 10, 2009 3:59 pm

Another conundrum from rainier/cooler climes; suggestions appreciated …

A few days ago we noticed that the 2’ wide cedar soffits were literally dripping wet along the entire north side of the house, where there is a row of clerestory windows between the beams. There was also moisture present to varying degrees on the other soffits, but it was hard to see because of the poor state of the soffit paint and/or its dark colour.

On this north soffit in the pics below, this past fall the cedar was restored and repainted with a light grey solid stain. The brown drips must be tannin leaching from the cedar.

The moisture source can only be a roof leak or condensation, but there is no way the roof, a 2 ply torch-on membrane, is leaking. I am guessing this is condensation related to the amount of snow we had in the last week of December. At least 2 feet or more on my roof, with melting in between, so a layer of ice would have formed somewhere. I suspect the soffit would have been very cold, especially since the 2â€￾ of rigid insulation on top of the roof (under the torch-on membrane) extends only to the exterior wall (to create a built-in gutter). Possibly making the soffit colder than the actual air temp, which would cause the condensation? Still, I would have thought that outside air circulation would take care of any moisture formation.

The air temps did increase this past week and we have been hammered by heavy rainfall, and most of the snow has melted off the roof. Now a few days later, roof, the soffits have pretty much dried off underneath, maybe because they have warmed up a bit? But now I’m wondering whether I should be shoveling snow off my soffits in winter to prevent this happening again … the thought of climbing a ladder every year to clean snow and stains off the soffits fills me with dread. Any thoughts about what likely caused this problem; has anyone else ever experienced it? Thanks.


Uninsulated soffit/gutter on north side (although there is vapour barrier and 5/8â€￾ roofboard beneath the 2 ply membrane across entire roof, including gutters)

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The problem

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Note how wet the unpainted cedar is

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Underside of fir beams also wet (some beams were restored with WoodEpox and are not yet painted/stained)

Image

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Joe
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Postby Joe » Sat Jan 10, 2009 4:09 pm

humidity?

if you wipe it, how long does it take to reappear?

how cold was it when you painted that area?

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Postby scandimod » Sat Jan 10, 2009 4:34 pm

That's what I'm thinking Joe - humid outside air that was warmer than the underside of the soffit. I don't see what else it could be. But I still don't get why air circulation would not prevent or minimize the condensation to begin with. The fascia board does create a bit of a pocket, but enough to trap air in that area?

I haven't tried to wipe it off; too cold outside and now it's snowing again :roll: Most of the moisture has disappeared since Wed when we first noticed it; there are still a few drips. I'm going to ask my roofer about this too, but I have a feeling he won't know the answer unless he's seen it on a similar style of house.

I would really like to know if anyone else in the PNW has seen this as I believe our region has been hit by the same extremes of weather. We lived in a similar style post and beam when I was growing up, and my Dad has a vague recollection he may have seen this before. However I think the last time we got this much snow in Vancouver was in the 60s.

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Postby Slim and Gabby » Sun Jan 11, 2009 9:19 am

I'd be willing to bet $$$$$ that's condensation! It looks like you're getting warming somewhere, maybe from a wall or window; I'd also bet $$$$ that, DON"T TRY THIS, if you turn off your heater and let your house become the ambient temperature, it will go away. I think the only way to get rid of this is some sort of hole in your fascia to let the warm rising air escape, or a fan to mix the cold air with the warmer air; yes, I know these don't sound like good plans of attack, I only offered them as hypothetical solutions, sorry!
What kind of heating do you have? radiant or forced air; radiant heat would be more likely to cause this as your heating the ground around your house, and any moisture is evaporating.
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Postby scandimod » Sun Jan 11, 2009 1:44 pm

I think it definitely relates to condensation - high moisture and the thermal conditions in that part of the roof. I too thought the heat might be radiating from the windows and causing the problem. The house is forced air heating and most of it is on a crawlspace; about a third on slab.

Here's an interesting theory my Dad emailed me this morning after I sent him the pictures. His sounds a more plausible scenario:

"The fact that the dripping is widespread suggests that it is not roof leakage, which probably would be localized. The fact that it is stained suggests that the dripping water originates within the decking, not on the lower surface, so the question is how does it get there in the first place? During high moisture level but above freezing conditions, as during prolonged snow or rain, the decking system, which has a slower heat and cool cycle than the outside air, will absorb or collect a good deal of moisture which eventually freezes and stays frozen until there is a significant and prolonged thaw, at which point the wood thaws out completely and releases its moisture, creating the drips. The remedy? Have the house moved to Palm Springs or, failing that, paint the soffit the same colour as the drip residue."

Thanks for those practical remedies, Dad ...

I can't imagine I'm the only one who has experienced this, but again you would have to make a point of looking at the soffit at the right time. Western WA had much the same weather as we did in December, I believe. A prolonged cold spell (-10C/14F at night, not much warmer during the day), then a huge snow dump, then torrents of rain.

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Postby reverb2000 » Sun Jan 11, 2009 7:04 pm

at some point you are going to pull these down because of rot. Go ahead and do it now and ck it out.

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Postby scandimod » Sun Jan 11, 2009 7:23 pm

The only rot I ever experienced on this 50 year old roof deck resulted from years-long roof leaks. The entire deck was exposed when I reroofed a few years ago so, we had a good look at any rot at that time and addressed it.

I think this condensation is a temporary phenomenon relating to atypical, extreme weather conditions. Wetting and drying cycles with the seasons are normal in our climate; otherwise all the MCM houses in the PNW would have rotted away by now. I'm just trying to understand exactly how this works.

Hopefully my roofer and perhaps the local roofing association can shed some light. It may be that terminating the rooftop insulation at the exterior walls is not a good idea.

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Postby reverb2000 » Mon Jan 12, 2009 4:15 am

looking at the pics again, I think your roof is leaking. The leak is building up at the unpainted cedar area and doesnt drain fast enough. It may be building up and continue to leak after the rain...either way, just open it up and look...and make sure and post pics. I bet you could have pulled some boards down in the time you spent on this thread. I do that sometimes...spend more time figuring out a solution, before I am totally sure what the problem is.

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Postby scandimod » Mon Jan 12, 2009 11:17 am

Trust me, it's not a roof leak, it's condensation. I live in one of the rainiest climates on earth and I would soon know if it was leaking. I'm also intimately familiar with the composition and application of my roofing material. A hot mop/torch-on system is practically bulletproof and mine will probably outlive me. Also there are actually 4 membrane layers at the outermost edge of the roof due to a process called stripping.

"Pulling down" boards?? There is no way to remove the roofboards without first cutting and removing the roofing membrane over top of them.

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Postby Joe » Mon Jan 12, 2009 11:45 am

you might consider having a conversation with neighbors who have similar soffit.

did you wipe it? If so, did it come back?

does this happen all around the house? Just in this one spot? only by windows? does it face north, south, east, or west.

does your window near the soffit have condensation?

I know it's more humid in the NW during the winter time. You may want to track the humidity and see if it relates to the moisture.

if it's going to be dry for a few days, throw some water into the soffit and see what happens. I don't think it's a leaks. the photos don't indicate it.

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Postby Joe » Mon Jan 12, 2009 11:52 am

does your roof pitch towards the north soffit? possible a leak somewhere else and is running to the edge?

I know torchdown rolled roofing is good and can pond water, but maybe there's a leak in a seam somewhere?

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Postby reverb2000 » Mon Jan 12, 2009 4:51 pm

cut one of the those soffit boards, you dont have to cut the roof, if the roof is leaking you will see the water path. That hot tar roofing system isnt that great. If there are any roofers here they will echo this. Flat roofs now are done with a commercial rubberish membrane. It will last forever ( or 70 yrs). More expensive, but well worth it.

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Postby scandimod » Mon Jan 12, 2009 7:03 pm

Joe your suggestion to pay attention to humidity is a good one. Yes there has been some degree of moisture ranging from a very light film to actual drips all around the house, which I have noticed in previous years. Never as bad as this time though, as far as I know. The moisture is definitely less on the gable ends where the insulation goes right up to the roof edge, although it's an angled soffit (widens towards the ridge) so that may also be a factor. I always thought that the bit of moisture I could see was from warm house air leaking at the top of the ceiling to the outside. They didn't seal the wall/ceiling joint too well 50 years ago, and these types of houses are especially challenging to seal at the top of the wall because of all the V grooves.

The other thing is that the moisture has been harder to see because of the condition of the soffit (we are in the process of restoring the soffit around the entire house).

The drippy north soffit in the photos has been steadily drying out after a warmer spell over the past week or so, despite continuous rain, dispelling any notion that the moisture is from a roof leak.

reverb, I don't have a "hot tar" roof, which I take to mean tar and gravel (although the old one was). I describe the torch-on system in my separate post about the roofing materials. It WAS expensive, although it may not be the Cadillac of all roof systems. My roofers assure me it will last at least 30 years. They should know; they are one of our area's top roofing companies.

Finally the base and cap sheet seams are overlapped at least 3" (which you can see in the pics) and when they torch on the cap sheet, they make sure there's a bit of visible bleed along the seam to seal it. The cap sheet and base sheet are melted together, and the base sheet is melted on to the materials below. Practically indestructible, at least for a long while.

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Postby reverb2000 » Sun Jan 25, 2009 4:03 pm

S. mod...how did this situation turn out?

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Postby greenmod » Sun Jan 25, 2009 5:43 pm

I'm in Olympia, WA - so I experienced the same weather as you up there in Van. I also have a very similar roof design (torch down, insulated over actual house, not overhangs). You can see my snow post here:
http://www.lottaliving.com/bb/viewtopic.php?t=13689

We have not seen the condensation issue you are describing, but we did end up shoveling snow when it started melting. We also have much larger overhang than you do (5 feet) so maybe ours wouldn't trap air? I wonder if it relates to your eave windows. Is it only where you have windows? Ours were drywalled/sided over (and insulated) so we didn't have heat escaping in that area. We just opened up 2 this weekend.
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Postby moderns-r-us » Mon Jan 26, 2009 1:04 pm

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