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Question about a drippy roof
Old 08-10-2009, 01:13 AM   #1
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Question about a drippy roof

A couple months ago we replaced our sidewalk FuturaStone with stamped concrete, so now we can actually see the drips and puddles that have probably been there for 20 years.

Nearly every morning, when the overnight temperature hits the dew point, we have puddles under the gutters at the same two places. I finally climbed up on a ladder for a look at what I thought would be leaky gutters.

The problem appears to be a flaw in our roof construction. Hawaii building code tends to be less stringent than the Mainland because there's no freeze/thaw cycle, and I'm sure that Castle & Cooke an occasional monolithic MegaCorp builder is tempted to cut a corner or two when they're cranking them out by the hundreds.

I've posted photos below. It looks like our roof rafters have been cut off vertically and the fascia boards nailed flat on them (so they're vertical too). A 1"x2" has been nailed to the top of the outer face of the fascia and the gutters have been mounted right under the lip of the 1"x2". The roof sheathing probably stops right behind the 1"x2" and the paper (on top of the sheathing) comes out to the outside edge of the 1"x2". The composition shingles only stick out about an inch beyond the paper and the 1"x2" over the gutters.

It looks like water condenses on the roof (on the shingles or the photovoltaic panels) and drains down to the edge of the shingles. Instead of dropping off the edge of the shingles into the gutter, however, at these two spots they seem to work their way back up under the shingles (capillary action? holes in the shingles?) to the paper. From there the moisture seems to flow down the face of the 1"x2", turn under its bottom edge to flow to the fascia board, down the fascia board, turn under its bottom edge, and drip onto the sidewalk.

Some mold has grown onto the 1"x2" but the wood is pretty well sealed with paint and it still feels solid. It probably dries every day (the shingles easily hit 100 degrees or hotter), cools overnight, and then gets wet an hour or two before sunrise. The water doesn't seem to get far enough back up the eaves to cause problems with the walls (we've had this stretch of wall open and we'd have seen water damage), so I think the only reason I care about the water flow is because we see the sidewalk puddles.

Aside from the ugly, is there a hidden problem? Is this area supposed to have drip-edge flashing on the 1"x2" to make the water go into the gutter? I could stuff a foot or two of drip edge between the 1"x2" and the paper, and hopefully that would make the water hit the gutter. Any other solutions?
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Old 08-10-2009, 04:00 AM   #2
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Nords - In california we have to have flashing on all edges. I would think that without flashing the wood 1 x 2 would rot away. If is not installed properly (bulges, etc) it can wick and cause rotting as well. I'd take the pic to Home Depot and see what they advise.

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Old 08-10-2009, 06:15 AM   #3
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What Rambler said: drip-edge flashing
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Old 08-10-2009, 09:14 AM   #4
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I mentioned in another thread my neighbor's problem with a poor flashing job. This is probably a 20-25 year old home, so years of this problem have caused major sidewall rot. A corner support post had rotted away and the deck was no longer well attached to the house, and the sidewall has major holes in it. Maybe you won't get this damage, or maybe it hasn't gotten bad enough to notice yet, but the problem next door is extensive. I'd fix yours before you see this kind of issue in your house.
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Old 08-10-2009, 11:52 PM   #5
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Drip edge is nice, it can also protect wood from the splash of rain drops hitting water in the gutter, and splashing upwards.

But houses were built for many years without metal drip edge. If your roof is at least a 4 in 12 slope or so, projection of the bottom edge of the first course of shingles should cause the water to drip into the gutter, not roll back and up/under.

If this roof area was heading into a strong prevailing wind, then it might have more of a tendancy to creep around the projected edge. But are you really sure it is not coming from a hole/cracked shingle/whatever a bit further up the roof? Especially since it is on just two areas on the same exposure.
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Old 08-11-2009, 07:58 AM   #6
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Nords,

Looks like the issue is due to water condensing on the PV panels, then slowly dripping onto the roof in the problem areas. Not a lot of flow, so when it gets to the edge of the roof it tends to cling rather than drip. This is caused by the meniscus (surface tension) of water molecules, they want to bond together, and follow each other- i.e. a siphon. This is common in low slope roofs. When it rains, and water is rushing off the roof, it probably drains just fine, until the rains are over, the roof is drying out and flow subsides to under a trickle-the point where surface tension wins out over gravity. You need something to break the siphon action. Drip edge flashing forces the water to follow a steeper downward path with a sharp change in direction; by disturbing the flow path it breaks the meniscus, which gets the water moving again, the steeper vertical component increases velocity and the small high-angle cross section of the slick metal edge prevents it from clinging-unlike a nice fat, low- slope, rough-surface shingle - more than likely doubled at the eaves (starter strip) -which actually decreases the exit angle ever so slightly, slowing down the flow and exacerbating the clinging problem.

Good thing the 1x2 is still sound. It would be a big job if you had to replace it, too. I would spray the affected areas of the roof and 1x2 with a bleach solution or antifungal, install the drip edge and then scrape, sand, and repaint the exposed fascia as needed when everything dries out thoroughly.

Let us know this project turns out; I enjoyed the future stone makeover.
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Old 08-11-2009, 11:11 AM   #7
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Thanks for the suggestions, everyone. Drip edge it is. I think I even have the correct color left over in our attic from some other job.

Quote:
Originally Posted by Telly View Post
But are you really sure it is not coming from a hole/cracked shingle/whatever a bit further up the roof? Especially since it is on just two areas on the same exposure.
Yeah, that's a nagging concern. Both on the south side, but one is well shielded by a projecting adjacent portion of the roof and the photo area is only a couple of feet out of 60.

We've drilled a couple dozen holes into the roof's rafters/beams to hold the PV panel brackets. Hit 'em all first try, used lots of roof caulk, never had a problem with any of them, and the underside of this part of the roof is our living room's cathedral ceiling. So if we screwed up then we only did it once and it's not leaving any stains or rot along that part of the slope. Rot would be even more plain in the eaves, but the cloth must be drying out every day.

The shingles in that area are wet underneath but I guess that doesn't show whether the water came from on top or from underneath. Lucky we live Hawaii-- if this was a freezing climate then we'd have the ice dams from hell. And whether the water comes from above or below, a piece of drip edge should take care of it.

Ironically the job's going to wait a few days until Felicia is through thrashing us. Forecast calls for at least 2-3" of rain in the next 24 hours. We have our eye on another roof repair from last winter (bad corner flashing) that should get a great leak check...
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Old 08-11-2009, 11:42 AM   #8
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Drip edge it is. I think I even have the correct color left over in our attic from some other job....
Isn't that like storing your umbrella in the car?
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