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Tar paper over Ice & Water Shield (under comp)?

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BuilderBumm

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Discussion starter · #1 ·
We are working with a customer on a big remodel in a windy / wet location. Their roof is a 3.5 / 12 pitch. They are insistent on having a composition roof installed over new 3/4". I've been "trying" to convince them to install a mechanically seamed standing seam metal roof, but they like the look of comp better.

Our roofer is reluctant to install comp on a 3.5 / 12 pitch, as the National Roofing Association says 4 / 12 or steeper, only.

I am suggestion that they cover the entire roof with ice & water shield. The roofer then said that we should cover the I&W with a double underlayment. Sounds good to me, as there is a lot of wind at that location and the pith is not within the standard.

My questions are:

1st, is it necessary to add the layer of felt or tar paper? I'm not asking about the convenience factor for the next roof that will go onto the house down the road. I'm asking about no leaks for this roof.

2nd, what 'underlayment' should we recommend, what weight & what overlap? In the past, I've never been a big fan of the 2" overlap. I've always figured that a double overlap is way more bullet proof.

What do you think? I appreciate any and all comments.
 
#2 ·
Use a quality synthetic felt (diamond deck/ titanium over the ice guard) make sure the laps dont lay over one another and you will be golden.

Im assuming you are making sure that the ventilation is up to snuff as you are putting down 2 vapor barriers and will otherwise lock in a lot of moisture.
 
Discussion starter · #3 ·
A&E Exteriors said:
Use a quality synthetic felt (diamond deck/ titanium over the ice guard) make sure the laps dont lay over one another and you will be golden.

Im assuming you are making sure that the ventilation is up to snuff as you are putting down 2 vapor barriers and will otherwise lock in a lot of moisture.
Click to expand...
What do you mean "make sure the laps dont lay over one another"?

Yes, for the size of the attic, we have just the correct amount of top vent, and considerably more than the formula for the bottom vents.
 
#5 ·
I still use felt. I half lap. I do consider the next roof and convenience. Manufacturers dont figure on using both paper and ice. The paper is supposed to be a second line of defense and since wind damage is more prone to low slopes the Double coverage can hold up better. If you want to be super safe go 30# over 15#
I would imagine synthetic manufacturer are ok without the 19"lap but check.
 
#8 ·
I have seen alot of guys start putting felt paper over the ice and water. The reason is removal. When it first came out, everyone put shingles right over the ice and water. Then down the road, it came time for a new roof. Those shingles bonded to the ice and water. In order to remove the shingles, you have to cut the roof sheeting out and replace it all.

I don't know if that is what he is thinking about.

I did have a low pitch roof, the customer would only go with shingles. The manufacturer told me to do 2 layers of ice and water, staggering laps.

I don't know if it was the right thing or not. It still doesn't leak though.
 
#9 ·
BuilderBumm said:
What do you mean "make sure the laps dont lay over one another"?

Yes, for the size of the attic, we have just the correct amount of top vent, and considerably more than the formula for the bottom vents.
Click to expand...
The horizontal laps should be about a foot differend between the 2 layers of underlay
 
#11 ·
#14 ·
Raise the roof? Are you nuts. Many roofs here that are flat are because of mean height of the roof is maxed.
Shortening the exposure with ice will last for a long time. I have done plenty of variations that hold up. I have never had a problem.
 
Discussion starter · #20 ·
Frankly, I've been telling this customer that they should let us do a metal roof for them. I have ill feelings about today's composition shingles. It seems that the warranties "look" great, but in reality the warranties are pretty light weight and it looks as if today's composition shingles don't last very long - no matter what the warranty is.

Do today's shingles need replacing far sooner than one would expect? ie: a 30 year shingle only lasts maybe 20 years, a 40 year shingle might only last 25 or maybe 30 years. Is that a correct statement?
 
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A&E Exteriors
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