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Ice dam and a leaky valley


frank19991999
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Hello,

I live in a semidetached house, the valley between the 2 houses faces north. In winter there is always an ice dam there, I added attic insulation, roof ventilation - soffit vents and a wind turbine- but nothing helps.

This winter after a snow storm we had a about 15 mm rain and the roof started to leak, along the wall in between the houses. I assume the valley is leaking.

2 questions:

1. Any suggestions regarding the ice dam ? Would a metal valley help ?

2. What option to repair the valley I have ?

Thanks much,

Frank

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Hi Frank,

Well, you probably already know this, but an ice dam is caused when snow high on the roof melts and that melted water drains down to the edge of the roof, refreezes, and begins to form an ice dam. More and more water drains down the roof and builds it up higher and higher, until it's large enough to hold enough water that the water doesn't freeze solid and remains liquid. It's that unfrozen water that drains back under the surface and into the house. The snow is melting because too much heat is escaping into the attic and the attic is too warm.

Adding insulation isn't going to help if there are too may air passages allowing heated air to rise into the attic. You need to seal holes that come up through the walls where pipes and wires are routed and ensure that the chase around any chimney's is sealed and insulated. At the same time, put gaskets on the wall switches and receptacles and ensure there is an airtight seal around the attic hatchway.

Once that's done, make sure that there's sufficient ventilation in the attic to keep cold air constantly entering the attic and then flowing up the underside of the roof. You'll know when you've got things right when there's no more than about a 3°F difference between outside air and attic air.

As for a metal valley, wide metal valley flashings used to be standard procedure back in the day when roofers really taught other roofers how to roof and folks didn't learn the trade by working for a roofer during their college vacations or between other jobs; so, if you're home is old enough, there might be one there anyway. If the home is of a more recent vintage, I should think that in your area, with the weather and snow that you get, underneath all of that roofing material, there should be at least a 36" wide layer of bituthene ice and water underlayment lining that valley as a last defense - on top of that should be a wide metal valley flashing before the cover is woven. Or, a W-shaped valley flashing if you plan to have an open valley.

Alternatively, you can line the valley with heat tape to prevent the dam from forming. Just be careful how you fasten it to the roof so that you don't puncture the valley. Office max sells some pretty good spring clips for papers that will hold a heat tape firmly in place, but you've got to be careful not to pinch the element.

Have you looked at how your attic ventilation is configured? Perhaps the issue is that there's not enough convective airflow up the underside of the roof due to too few eave vents or because of gable end vents which are defeating convective flow. Check out some of the other threads on this board that discuss attic ventilation for some tips.

ONE TEAM - ONE FIGHT!!!

Mike

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Not really, have it stripped out and done right. If it's been leaking as long as you imply, there's bound to be unseen damage there anyway.

Just explain to the neighbor that even if that water isn't dripping into his home, it's getting into his framing and is going to cause rot and will eventually cause structural integrity issues. Ask him which he'd rather do; split the cost of fixing that valley right, or listening to the ton of crap that'll get dumped on him by his significant other when the damage is eventually discovered and costs a whole lot to fix.

OT - OF!!!

M.

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For the heat tapes to work it's quite likely that you will also need to run them into the gutter and down the downspouts and leaders (the commercial "self-regulating" types work best). Also, there have to be correct drip edges / other appropriate flashings installed, and the gutters or other water control means have to be properly placed, pitched and fastened. Usually, the heat tapes will require a dedicated circuit.

However, assuming the roof membrane is intact and the roof edges, fascia and gutters are detailed properly, if properly designed and installed the commercial heat tapes will solve your problem, and can eliminate ice damming when other measuers will not.

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Well,

There you have it from someone who, like you, is in snow country. That sounds like a plan (I'd still be wondering about the condition of that wood though.).

Don't see much snow here; I got a call from a gent this morning who wanted to know if I'd be willing to drive up to Index, about 35 miles away, to look at a little riverside cabin. Being ever envious of folks with riverside cabins, I said, "Sure, when do you need me to do that." "Well," he replied, "It'll have to be in a week or so when some of the snow has melted - there's about 5ft. of snow on all sides of it right now." This is one weird state! Betcha if I drive up to Mt. Rainier this July when it's 90°F down here there will still be 30ft. high drifts adjacent to the parking lots at Sunrise.

OT - OF!!!

M.

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Yes,

A competent roofer should be able to strip out a valley, repair any rot, line the valley properly, and lace a new valley, without re-roofing the entire house. The issue you then have to deal with is a valley that's a different color than the rest of the roof. Even if you purchase the exact same brand, series, and color of shingle, there will be a difference and, if the valley is visible from the street, you might not like it.

I won't post a link to instructions or try and tell you how to do it here, because it's definitely not a project for a do-it-yourselfer or a roofer with minimal skills. Anyone accepting this job must know how to do this with his or her eyes closed or you don't want to hire them. You definitely don't want to hire the roofer based on the bid - you need to hire the roofer based on competence or you're liable to end up doing it all over again. You're going to want the roofers to provide you references from someone who they've done the identical repair for in the past, so you can check with that homeowner and ensure that the work was done correctly. Don't be shy about demanding a reference; if the roofer is competent, he or she shouldn't be shy about providing you the name of a past client whose had this done.

OT - OF!!!

M.

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I agree w/Mike completely, although there's some oxymoronic possiblities in the "any competent roofer" description.

Most competent roofers I know can't afford to weave in a valley. They have to sell full jobs to stay in business. It used to be relatively common, but not anymore around my 'hood.

It's not easy finding the sort of skilled tradesman that can weave a valley. Good luck.

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Hi,

I know of an 81-year old down in Florida who could do it in a matter of hours, but he absolutely hates the cold weather now. There's no way anyone could get him to go to Ontario in the wintertime.

Hey, wait a minute, the Chadster is just across the lake! Give him a call; he can probably build a machine that will do it for you.

ONE TEAM - ONE FIGHT!!!

Mike

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Frank,

It would be nice to see what you are talking about, but it is done just like any other repair. First, remove the roofing in the area effected, fix what's underneath, install metal flashing along with the rest of the roofing.

The idea is getting someone that is knowledgable, capable, and willing to do it right.

A Vally Flashing could include a "splash rib" down the middle, it acts as a barrier to stop the water from the opposite slope, from flowing under the roofing.

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