Horizontal roof valley - how to flash?
#1
12-11-16, 10:15 AM
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Horizontal roof valley - how to flash?
I have a complex shaped roof part of which has a horizontal valley about 8 feet long. Either end of the horizontal valley transitions to sloping valleys, and each of those transitions is itself complex, not continuing in the same direction. The original flashing appears to be only roll roofing. The roll roofing appears to have shrunk and lifted up over time, resulting in numerous holes. Over time several layers of wet patch roof repair were applied as temporary fixes.
I want to reroof the area, probably need to replace underlying wood in that part too. What would be an economical flashing solution apart from roll roofing? I believe a single continuous sheet of flashing material is required to traverse the entire length of the horizontal valley and also cover the complex transition plus several inches at either end.
Alternatives I can think of include metal sheets (e.g. galvanized steel) which can riveted and soldered at the complex transitions, or perhaps an ice and water barrier with overlap taking on the role of soldering. I'm looking for experience or advice on materials and method for this unusual flashing problem.
P.S. I've been searching the web for examples of flashing a horizontal valley, but I can't find any. It guessing that horizontal valley design is not popular due to difficultly of flashing.
I want to reroof the area, probably need to replace underlying wood in that part too. What would be an economical flashing solution apart from roll roofing? I believe a single continuous sheet of flashing material is required to traverse the entire length of the horizontal valley and also cover the complex transition plus several inches at either end.
Alternatives I can think of include metal sheets (e.g. galvanized steel) which can riveted and soldered at the complex transitions, or perhaps an ice and water barrier with overlap taking on the role of soldering. I'm looking for experience or advice on materials and method for this unusual flashing problem.
P.S. I've been searching the web for examples of flashing a horizontal valley, but I can't find any. It guessing that horizontal valley design is not popular due to difficultly of flashing.
#2
12-11-16, 11:16 AM
Member
Sounds like your discribing what's called a dead valley.
Post a picture so we can see what your seeing.
Post a picture so we can see what your seeing.
#3
12-11-16, 11:45 AM
Group Moderator
A single piece of ice and water shield down the middle is a must, followed by another layer of it on each side to extend it higher. Then a continuous metal flashing should be layed on top. Shingles and fasteners should be kept as far as possible from the exposure. If you plan to solder transitions, copper would be a good choice.
Alternatively, a single piece of glued down epdm could be used, but you need some one skilled who can glue up the transitions and such.
Alternatively, a single piece of glued down epdm could be used, but you need some one skilled who can glue up the transitions and such.
#4
12-11-16, 12:53 PM
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#5
12-12-16, 10:10 PM
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Joe caption - Picture of roof from google view. Right is color coded: red is dead (flat) valley, yellow are descending valleys. The other not color coded whitish features are all ridges. The bottom left corner room has a 14" raised floor, so the ceiling, and therefore the roof too is also raised a little higher. I wonder if the raised floor was an after though, and the roof quickly revised to accommodate. The house is 80 years old.
Last edited by Craig Hicks; 12-12-16 at 11:39 PM.
#6
12-12-16, 11:33 PM
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XSleeper - Ice and water looks impenetrable, that's no problem. But worry whether it can do the transition.
The transition at either end of the flat valley is a saddle shape - 1 ridge and 2 valleys intersecting at a point. (The general case of a saddle shape has 2 ridges and 2 valleys, in the particular case you could say that one of the ridges was 0 degrees). There are 3 angles around the saddle intersection point, and their sum is greater than 360 degrees. That means a piece of flat paper cannot be folded into a saddle shape. If the piece of paper is cut, and the cut is opened to a v-shape, then the paper can be made into a saddle shape with the v-shape leading to the saddle intersection point. So two pieces of paper can be cut and folded to cover the saddle, but they will have zero overlap (or in practice tiny overlap) at the saddle intersection point.
The saddle shape is hard - to get a layer covering it something needs to be moulded into the the shape. If there were a liquid bonding agent that worked to perfectly fill the tiny intersection point and cperfectly join all seams coming out from the intersection point, that would do it. I suppose a smalll piece of lead or copper could be hammered into a saddle shape to cover the saddle intersection point and then soldered on.
About EPDM - I have seen specs saying it cannot tolerate oil (e.g., tar, bitumen).
"Anti-freeze, acetone and alcohols are just a few substances that do not affect the ethylene propylene diene monomer. It is not, however, resistant to oil and reacts adversely to the slightest exposure." [http://www.rubbercal.com/sheet-rubbe...-rubber-epdm/]
The reaction of EPDM to "tar, bituminous" is rated the lowest value (4), meaning not suitable, in this table: Rubber Chemical Resistance, Rubber Chemical Compatibility, Page 6 - Mykin Inc
Could that be a problem when covering with tar based shingles? It certainly seems that it would be a problem with tar.
The transition at either end of the flat valley is a saddle shape - 1 ridge and 2 valleys intersecting at a point. (The general case of a saddle shape has 2 ridges and 2 valleys, in the particular case you could say that one of the ridges was 0 degrees). There are 3 angles around the saddle intersection point, and their sum is greater than 360 degrees. That means a piece of flat paper cannot be folded into a saddle shape. If the piece of paper is cut, and the cut is opened to a v-shape, then the paper can be made into a saddle shape with the v-shape leading to the saddle intersection point. So two pieces of paper can be cut and folded to cover the saddle, but they will have zero overlap (or in practice tiny overlap) at the saddle intersection point.
The saddle shape is hard - to get a layer covering it something needs to be moulded into the the shape. If there were a liquid bonding agent that worked to perfectly fill the tiny intersection point and cperfectly join all seams coming out from the intersection point, that would do it. I suppose a smalll piece of lead or copper could be hammered into a saddle shape to cover the saddle intersection point and then soldered on.
About EPDM - I have seen specs saying it cannot tolerate oil (e.g., tar, bitumen).
"Anti-freeze, acetone and alcohols are just a few substances that do not affect the ethylene propylene diene monomer. It is not, however, resistant to oil and reacts adversely to the slightest exposure." [http://www.rubbercal.com/sheet-rubbe...-rubber-epdm/]
The reaction of EPDM to "tar, bituminous" is rated the lowest value (4), meaning not suitable, in this table: Rubber Chemical Resistance, Rubber Chemical Compatibility, Page 6 - Mykin Inc
Could that be a problem when covering with tar based shingles? It certainly seems that it would be a problem with tar.
#7
12-12-16, 11:45 PM
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joecaption
#8
12-14-16, 02:41 PM
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Mixing EPDM and shingles, questions to and answers from an EPDM dealer
I wrote to an EPDM dealer asking questions about mixing with shingles. Q&A posted here FYI:
Questions:
This message concerns your instruction page:
RUBBERALL® Membrane To Shingle Transition
Installation Manual
(1) When placing shingles on the EPDM membrane, can they be nailed with the nail passing through the membrane? Does the membrane self seal around the nail? Could movement of the membrane relative to the nail cause a rip which could propogate?
(2) Over the EPBM layer, should shingle to shingle securing with tar be avoided?
Answers:
Two good questions.
1) Yes you do nail through the membrane. The shingle over the top keeps any water from coming in around the shingle nail or staple. There is not enough stress on the membrane under the shingle to cause a rip.
2) It would always be better if the single did not have the self -sealing asphalt tab. However since the asphalt is not very molten it has never been seen to cause deterioration on the membrane. Again if there is any weakening of the membrane in the area of the asphalt tab the deterioration has never be observed to grow beyond the single. The single over the membrane is always the water proofing membrane.
3) Please do note that the lower single edge should be kept an inche or so above the transition from a pitched roof to a low slop roof to be certain the edge of the shingle does not cut the membrane if there is movement in the roof system.
Questions:
This message concerns your instruction page:
RUBBERALL® Membrane To Shingle Transition
Installation Manual
(1) When placing shingles on the EPDM membrane, can they be nailed with the nail passing through the membrane? Does the membrane self seal around the nail? Could movement of the membrane relative to the nail cause a rip which could propogate?
(2) Over the EPBM layer, should shingle to shingle securing with tar be avoided?
Answers:
Two good questions.
1) Yes you do nail through the membrane. The shingle over the top keeps any water from coming in around the shingle nail or staple. There is not enough stress on the membrane under the shingle to cause a rip.
2) It would always be better if the single did not have the self -sealing asphalt tab. However since the asphalt is not very molten it has never been seen to cause deterioration on the membrane. Again if there is any weakening of the membrane in the area of the asphalt tab the deterioration has never be observed to grow beyond the single. The single over the membrane is always the water proofing membrane.
3) Please do note that the lower single edge should be kept an inche or so above the transition from a pitched roof to a low slop roof to be certain the edge of the shingle does not cut the membrane if there is movement in the roof system.
#9
12-14-16, 05:08 PM
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Found an old thread on this site, showing a picture of a cricket built to run water out of an otherwise dead (flat) valley: http://www.doityourself.com/forum/ro...w-orleans.html
#10
12-15-16, 09:31 PM
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Ref: A solid example of a cricket for a dead valley
cricket1.jpg Photo by Sk8zero81 | Photobucket
The cricket frame is built right into the rafters. Really it is changing the roof design.
The cricket frame is built right into the rafters. Really it is changing the roof design.
