Synthetic underlayments question

What do I look for in a quality synthetic underlayment? Fellow roofers what’s important to you when selecting?

Traction is the main thing we look for. Unless it’s sitting out in the heat for months at a time that is the most important thing for us. I miss good felt. Synthetic doesn’t wrinkle and is UV resistant for long periods of time but other than that is has many disadvantages.

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I like something that will hold a chalk line.

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Can you tell me the disadvantages?

Axiom can you put a chalk line on decent synthetics? Does the underlayment need to be dark in color?

Something that is waterproof vs. Water resistant. I also prefer something breathable. No matter what synthetic you choose you are relying on the rim of the plastic cap keeping the water out. We do a lot of older work with plank decks I personally still use 30# whenever I can.


Disadvantages of all synthetic that we have used is it is not truly waterproof. Wind chatter will separate it slightly from plastic caps and let water in. Other problems we’ve had are shrinking in valley areas, which force you to either pull nails from uphill side or cut to make it lay down tight. Also it doesn’t show frost as well as felt does.

The synthetics that I have used that hold a chalk line the best is Certainteed DiamonDeck and Malarkey secure start, these have some type of fiber in the surface kinda like hair.

I also prefer felt most of the time but the felt available (available to me anyway) nowadays is very poor quality.

I like the synthetics because not being black they are much cooler to work over and I am not very fast so I need something that will hold up to the elements for over a month sometimes.

I personally have not had an issue with synthetics leaking before roof installation but I do most of the work and am always there to supervise at a minimum.

Dont use greyish certainteed with blue prints on it.doesnt hold even on 7/12 ,slides like its 45 degree joke. Gaf has nice big azz roll twice the size of regular synt and it covers same 10sq or so.super thick and really has some grip compare to other shitters

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