Triply #75 base sheet

Hey guys I am new here.I am a DIYer. I have done a few roofs about 15 or 20. I was wondering has anybody ever used triply #75 base sheet in place of tar paper? I have done it a few times and it seems to work great no wrinkles or bubbles. Does anybody see a problem using it in place of #30 felt? It is fiberglass reinforced.

very good.
thats a waunderfull base sheet.


I was just wondering if there is a problem using it under asphalt shingles. I was at a local home center and they said that is made only for under flat roofing rubber?? Home depot sells it right next to their #15 #30 felt (doesn’t mean it is ok to use it)

its just fine joe.


It is fine, but seems to me that is is way too much overkill for the underlayment, unless you are not confident that the shingle roof will be weather-tight.


It is not that I don’t trust the shingles. But the tri-ply lays out perfectly flat. If I remember right it is like $26 for 3 square roll where #30 felt is $18 for 2 square roll. So to me it is a no brainer heavier paper not much more $$. No bubbles. The only draw back is you better have a broom handy they sand the crap out of it.

If that is all the price difference is, then go for it. I would too.


I just got a reply from Gaf-ElK they said triply is not a suitable shingle underlayment but it will NOT void the shingle warranty. I emailed them back for a reason why it is not suitable but yet doesn’t void the warranty.

Humm, proceed with caution joe

Good Luck.

The reason it should not be used is it is not UL tested or listed and is not class A fire rated. If the building inspectors knew this they would fail it. It would also possibly remove the fire rating of the shingle. My reply was if the roof is on fire I think the least of my worries is warranty. Unless the house next door is where the fire came from.

Using 75# base sheet on steeper roofs might be a bit dangerous they are usually very gritty or sandy on lower pitched roof should be safer anyhow, but I doubt shingle manufactures would allow it because they test with felt paper not base sheets. Read what it says on the back of the package for installation instructions and go by that, that way in the future if something happens you installed the shingles properly and have covered yourself.

I know this question is 8 years old, but I want to make a comment that no one here has made. GAF Tri-Ply #75 Base Sheet is probably not a good idea for underlaying shingles because it is not waterproof! Hold a section up to direct sunlight, you will see a myriad of tiny dots of light. I had some left over from a small flat roof repair and used it (on a 1-square shed) for a temporary roofing, planning to apply shingles over it shortly after. During moderate showers, the roof leaked significantly. I took it up to let the sheathing dry, this is when I noticed the permeability. This is not due to damage, it’s the case with the entire roll.