why does drip edge go over membrane?

On a pitched roof, my understanding is that the rubber underlayment should go down first, then the drip edge. I'd have thought that the drip should go first: then, any water captured by the membrane would run off over the drip. I can guess that putting the membrane first lets the it seal the drip nails. But, to what end, if there's no place for the water to go?
Can anyone shed any light on this?
Thanks
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On 9/28/2010 11:50 AM, George wrote:

looks like a couple of schools of thought here:
http://www.toolbase.org/Design-Construction-Guides/Roofs/drip-edge-placement
http://www.doityourself.com/stry/drip-edge
http://www.hometime.com/Howto/projects/roofing/roof_4.htm
http://www.gaf.com/training/ROOFING-VIDEOS/The-Importance-of-Drip-Edge.html
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Steve Barker
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On one of the HGTV shows, choosing the best home-improvement guy, the judge dinged one of the contestants for putting the drip edge over the roofing membrane. The judge wanted the membrane over the drip edge to guarantee all water was kept out, just like the OP thought was correct.
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On 9/28/2010 3:57 PM, hr(bob) snipped-for-privacy@att.net wrote:

the trend i'm seeing whilst googling, is to put the drip edge under the membrane on the eaves and on top of it on the gable ends.
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Steve Barker
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Drip edge at bottom of roof goes under the membrane. Any edging on the sloped edges typically goes over the membrane...but this is not essential - it can go either way.
R
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That's what instructions for the WeatherShield membrane say to do.
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It's a holdover from the building felt days. The edge on top on the sloped sections held the end of the building paper down - prevented it from curling back up - and prevented the wind from ripping it off. With self-adhesive membrane that is no longer an issue, so the location, top or bottom, of the edge doesn't matter on the slope. On the low edge drip edge should always be under the membrane.
R
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Hi George,

When I shingled our roofs, I installed the drip edge along the bottom of the slope first, then installed my roofing felt over the top. This way if water finds it's way under the shingles, in theory it should flow down on top of the felt, then over the drip edge. If the drip edge were on top of the felt, the water would go under the drip edge to the wood decking. I don't see why membrane would be any different.
On the sides of the roof slope, I installed the drip edge after installing the felt. This keeps any rain that may be blown under the edge of the shingles on top of the felt, and not blown under the felt to the wood.
On top of the drip edge at the bottom.
Under the drip edge on the sides.
Take care,
Anthony
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The OP asked about 'rubber membrane' which obviates the necessity of doing it the traditional way that you mention. If you think about it, if the wind is blowing hard enough to push rain sideways between adhered membrane and drip edge, I'd be more worried about the whole roof being lifted off.
R
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Interesting timing. I just returned from the library and the current issue of Fine Homebuilding answered this very question. There take was that the membrane should be under the drip edge, and wrapped over the top of the fascia (hidden by the drip edge). I never did it that way, but it makes a lot of sense, particularly in ice dam territory.
R
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Hmm... I suppose wrapping over the top of the fascia would prevent the issue of water going under drip edge to the wood decking. Good to know if I'm still around in 15-20 years when I need to reroof our house. :)
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