Need advise on roofing an addition.


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Old 03-03-05, 06:32 AM
rjc116
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Question Need advise on roofing an addition.

Im am adding a porch with gabled roof that will tie into the existing roof. What is the method to cutback existing shingles and add the valley flashing to assure a watertight job.
 
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Old 03-03-05, 07:15 AM
J
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First of all you will have to remove more old shingles than you think. You will need about 3' torn off to full shingles, up from the heart of the valley. This should leave an irregular "stagger" pattern where the old, full shingle end. You will be installing Ice & Water Shield and/or "w" valley metal in the valley and will need to cut back the existing underlayment (felt), leaving enough to make a 6" lap (good idea to use some plastic cement here). Now you just shingle into the valley from the existing shingles and trim.
Jim
 
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Old 03-03-05, 07:21 AM
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Assuming the ridge of the gable will die into the main field of the existing roofing.....

The gable shingles will need to lap under the main roof shingles. (Closed valley). Once your valleys and ridge are established, cut the existing shingles along the new valley and remove the existing shingles 2 to 3 feet back from the valley (not cutting..but more of a selective demolition removing nails and pulling full shingles)...install valley underlayment...roof the addition, then tie-iin the existing roof, trimming to close the new valley.

If your using an open valley (exposed metal), instead of a closed valley, the procedure is essentially the same...trimming both sides to complete the valley.

Major rule of thumb for valleys.......NO NAILS within 6" either side of the centerline!

Good Luck!
 
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Old 03-03-05, 02:22 PM
J
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I was taught that the steepest side of the valley always laps onto the lower sloped side. If they are the same slope, you get to pick. I always make the winward side lap onto the leeward side...if I know which way the predominate storm winds blow from.
Jim
 
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Old 03-03-05, 06:25 PM
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Ahhh yes grasshopper...but only half true...
Confucius say "steeper OR larger volume of water"
which the taller side would have.

Larger volume of water will win the fight when they meet at the valley and could push the flow and debris up under the lap as opposed to helping it flow away from the lap over the underlying section.

"when you can snatch the pebble from my hand..it will be time for you to leave"
 
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Old 03-04-05, 04:52 AM
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Uh oh.....my two pennies is I've Always run the steeper side, or even just the larger side. down onto the smaller side or lower-pitched side. I've done this due to my experience fixing leaks over the years. I started fixing others leaks long before ever doing loads of complete re roofs. Whether the area is steeper or larger or both, it encourages more water migration sideways at the valley. Have redone bunches of leaking valleys, and although there's usually "something else" going on with them as well, this "smaller onto larger" or lower-pitched onto steeper" have been factors. In the end, there are preferences like this which may not make a difference as long as there's redudancy built in. In other words, it's jes the way I like to do it.
 
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Old 03-04-05, 09:10 AM
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Lets say you have a 12/12 pitched small (window or vent) dormer in the field of a 8/12 sloped roof.

Would you have the dormer roof on top?....No.
The larger volume of water on the main slope would (could), defeat the valley lap at the dormer.

Not to say it will always fail, as Dodge stated there is, or should be sufficient overlap and/or redundancy in the valley, and there could be other defects with the valley...

...However, many a leaks at the valley that no one else could seem to find, have been solved by reversing the valley to the correct configuration.

Coincidence?......Maybe not!
 
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Old 03-04-05, 10:50 AM
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Shinster, I "think" we agree, although when trying to explain it, I started to confuse MYSELF.
When I'm installing roof, I prepare, then shingle all smaller areas, dormers etc. THEN shingle up past them on the larger areas.
When shingling two or more areas when one of them is of the low-piched variety, I always roof the lower pitched one first, then shingle the rest
so that............water rushing down in greater volume or at a higher velocity would not tend to migrate sideways in the valley....running under the lower-piched or smaller-dormer type area.
There, I've said it, all over again, I think.
 
 

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