Flat roof, leaking, center channel to blame?


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Old 12-20-20, 01:30 AM
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Flat roof, leaking, center channel to blame?

Hey all,

Wondering if anyone has some advice for the flat roof of my house.
It is a gravel style, tar paper with seams and I assume was torch-on. That said, it was a lighter colour than I've seen elsewhere, and had almost no gravel on it (after 20 yrs).
In the summer, we did a full coat of silicon roofing compound, applied exactly as per instructions. We had had a minor leak in the bathroom where I suspected the roofing was thin and there was a little bit of pooling water. All rain storms since the silicon coating seemed to cause no problem.
Now we had a rain storm this week, and there is significant water coming in, at a new location, into the living room. Running down the inside of a wall onto a door frame and then out onto the floor from the frame. Big issue.
All I can guess is that it's related to this weird central vent (?) that the roof was made with. I can't find anything online about this kind of roofing design. Any suggestions would be most appreciated. It's covered with a tarp for now. Pretty bummed there's a new leak given the effort that was put in, and having never seen a leak issue in this location.



Really not sure if this is a vent, or some other kind of channel.. I don't imagine its an internally draining gutter, because no water from the roof surface can get into the channels!
 
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Old 12-20-20, 07:21 AM
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Around here, the separator between two houses is built up 6-18" and roofed over, so it becomes part of the roof - and a positive separation. It looks like that aluminum thing is intended to flash whatever the separating wall is.

Can you look closer or get a better picture of how your roof is tied into that? It could just require some new roofing cement to seal it up. Though admittedly, I've never seen something that looks like that either.
 
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Old 12-20-20, 10:16 AM
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How is the roll roofing sealed at the raised edges? Also with the raised edges, I would think there is a drain somewhere on the roof. If not there could be 2-4 inches of standing water on all the roll roofing seams, including outer edges, until the water evaporates. Is this the case?
 
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Old 12-20-20, 10:46 AM
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Thanks for the replies.

There are drains close to the corners which are flush with the roof deck and drain out via external drain pipes.
The most standing water that could remain is perhaps half an inch in places though these places are distant from the leaking area.
the roof does go up higher around the edges by a couple inches, and drip cap sits over the top of the edges. No sealant at all.

The center channel seems to be laid over the top of the roofing material and then attached with rivets/screws. There was no sealing material just metal sitting on top of the roof. If there was poolig water next to the channel it would be an obvious target for caulking just in case that is a leak source.
Thinking about it I imagine there may be an open channel under this metal channel which would allow airflow into the roof cavity. If the metal channel itself has aged and failed somehow it would seem obvious that heavy rain could penetrate without pooling water needing to be involved?

 
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Old 12-20-20, 11:12 AM
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I think that aluminum ridge cap needs to be removed so as to see what is going on under it. Its certainly not part of a normal method.
 
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Old 12-20-20, 01:28 PM
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Thanks for validating how abnormal it is. Chatting a friend there's a suggestion the original construction method may have been a concrete foundation and basement and then 2 prefab long rectangular boxes craned on top. This channel would be the join if that's how it was built.

it is storm season here for a few months so that means rain very often..that'll make it hard to time and removal of the aluminum channel. I think it does need to eventually come off but I'm thinking about creating a wider larger umbrella capping with metal and installing that over the top of what's there. This may not be the most usual approach but I think it would continue to allow venting while protecting the whole setup from rain storms and water ingress.
Any ideas or thoughts?
 

Last edited by pnwpaddler; 12-20-20 at 01:30 PM. Reason: Added note about rainy season
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Old 12-20-20, 04:19 PM
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It sure looks like a ridge vent. These are used to vent attic spaces on a shingle, pitched roof, and never on a flat roof. If in fact, your house is 2 separate buildings built together, then an expansion joint should be installed at the intersection. Don't try to build a cap or umbrella over this mess. The leaks are coming from the vent channels in the ridge vent. Any water that builds up on the roof, say, like if your drainos get blocked, will just pour in. Any attempt to seal it would be short lived. My advice is to rip it out, nail a piece of .P.T. 1x6, and install a 12" wide piece of roofing, similar to what you have on your house. Use adhesive, not a torch, Keep the drains clear and let me know how you make out.
 
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Old 12-20-20, 05:30 PM
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Just remember that the location of the source and destination of a roof leak are seldom one above/below the other.
 
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Old 12-20-20, 10:58 PM
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Many thanks for the replies from both of you. Indeed I've wondered about source location vs where it's showing up in the house.

If we roofed over the ridge vent I wonder if then we would need to install new vents across the roof to allow breathing? Some googling has shown me there are purpose-built vents made for flat roofs.
 
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Old 12-21-20, 07:40 AM
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You must get the roof vent intended for a flat roof. That is, the ridge vent assembly needs to be higher so water cannot overflow from the roof into the roof vent even if water is dammed up by snow.Properly built flat roofs are not perfectly flat, in order to prevent water from forming puddles. Now that you have a leak you should go over the entire roof with a fine toothed comb to check for signs of cracking or of peeling apart of the layers.
 
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Old 12-21-20, 11:57 AM
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It's a good idea to look for roof problems in areas not always directly above where the water shows on the interior. If you have access to the attic/crawl space, then you could follow the water marks back to the leak. Otherwise, take measurements to plot the entry point of the water inside, then co-relate this area to the outside. If your roof failure isn't in that area, then go uphill from there. Most of the time, water gets in where there are roof penetrations, such as vents and skylights. Also check the perimeter flashings at the parapet walls. Your roof looks in good shape for 20 years. That's the average life span for your roof. BTW, your roof type is a Modified Bitumen, and not a Tar and Gravel. Modified is much easier to repair than T & G. And much less cost to reroof, as there's no gravel to scratch off and dispose.
 
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Old 12-23-20, 01:20 PM
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Thanks AllanJ and gumbodoggy - salient advice I very much appreciate.

In a way it seems like the original roofer's decision to locate this vent along the centre of the roof, where it is -not- built up high at all (like it is around the edges) is fairly questionable!

Its good to hear the roof lookedin good shape for 20 years. And that's helpful to know it is modified bitumen. I'm reaching out to local roofers about repair, but of course they're run off their feet.
 
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Old 12-27-20, 09:21 PM
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Following up here, the current plan is most likely to rip out the old roof rent, and resolve the issue.

One suggestion has been to build up alongside where the vent is, so that there is an angled portion, like there is on the outside edges of the roof where there is drip cap, place some new roofing material to create a downslope, and then place a new vent along the channel again (this one would be raised approx 3in from roof deck height. This would ensure runoff goes away from the vent instantly, while providing the same intended functionality of the original vent. Any thoughts?

Another suggestion was to do a new roof section over this area, and instead place in new roof vents around the roof, ones that are designed for flat roofs, removing the centre vent channel entirely.

Interested to see if anyone would have an opinion. Thanks all.
 
 

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