Henry’s Ice & Water Shield Under Or Over Drip Edge?

First thank you for taking the time to read my question. This is a long debated topic in which I have read endless articles about. Some people like the company Grace debates that having the IWS (Ice and Water Shield) on first is best because if the gutters build up with ice and lift up the drip edge the IWS would protect the wood. Others say that having the IWS over the drip edge would be better because it allows the water that found its way under the shingles to run over the drip edge and into the gutter.

Could you explain what you have found works best for placing the IWS over or under the drip edge for shingles that will get both snow and rain? Please explain your reasoning as to why it is best.

In addition, could i just use Feltex underlayment synthetic fully over my IWS just for added protection?

-Roof pitch 6/12, Architectural shingles

For maximum ice dam protection, ice and water shield first. Let it hang over your fascia by a bit, say an inch, than install the drip. You can also put a small strip of ice and water over this to seal it, but unless you have severe ice damming issues I wouldn’t bother.
Covering your ice and water with synthetic won’t have any protection benefit but will make replacement of your roof next time around more pleasant.

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Thanks Patchap! I’m glad you mentioned the fascia over hang because I was thinking of doing it. I was also thinking that if i placed the IWS over the drip edge it would make it difficult to replace later on.

As for the valleys, I would assume I would do the eaves first with IWS than run the IWS down the valley to go over the IWS that I placed on the eaves?

Could you check my order please to make sure it sounds correct?

  1. Place IWS on eaves than the valleys.

  2. Place the Feltex synthetic underlayment about three inches above the IWS (eaves) and stop about three inches in on the valleys (or should i just cover over the IWS in the valley)?

  3. Last put W Valley Sheet Flashing over the valley so it covers the IWS and the three inches of underlayment?

Thanks again

We always do ice and water first, wrapped over face of the deck, and then the drip edge.


Why not both?

Put a target sheet of IWS down on the deck and folded down onto the fascia. Install drip edge per the norm and then install IWS out to the edge of the nailing flange of the drip edge and up the slope of the roof decking and terminating at an area sufficient to prevent ice damming.

Belt / suspenders. Debate is now over.

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In order to work Ice & water shield needs to be adhered to wood, it leaks around the nails if it is installed over metal.

I install the I&W first then I install the drip edge then I strip the drip edge in with 6" window flashing (anyplace where there is I&W shield) or I&W shield.


“I install the I&W first then I install the drip edge then I strip the drip edge in with 6” window flashing (anyplace where there is I&W shield) or I&W shield."

Axiom, you bring up many good points. Do you also run the IWS a little over the fascia? Also, would it be best for me not to nail the IWS down on the wood where the drip edge will go, so it has less nail holes?