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Should Your Roof Have Synthetic Underlayment?

If your roof is old, it probably has asphaltic felt paper underlayment.  Felt is the most common type of underlayment in older homes, and it’s still frequently used today.

But is felt paper the best option?

Probably not.  When it works, it works well(ish).  But there’s a reason felt paper is used almost exclusively on cheap roof installations these days (several reasons, actually).

Felt can be dangerous


One of the biggest benefits to high quality synthetic underlayments like GAF Tiger Paw is it’s safer for roofers to walk on.  High quality synthetics are designed for extra-gripping walkability.  Felt paper doesn’t have that.

Safety is such an important part of being a roofer, that it’s no wonder some contractors have transitioned to using synthetic underlayments instead of felt.  However, not all synthetic underlayments are created equal.  Some are much thinner and slicker (and worse) than the good stuff — like Tiger Paw.

You’re unlikely to get a 50-year roof with felt


Underlayment acts as the secondary water-shedding layer beneath shingles.  But after 20-30 years, felt will usually have degraded so much that it does no such thing.  It’ll tear, crumble, fall apart, and undergo many other manners of degradation.

Synthetic underlayments are not immune to these issues either, but they’re much more robust.  That’s why manufacturers that offer 50-year warranties sometimes require a strong synthetic underlayment be used instead of felt.

Shingles can ripple under felt


Felt paper doesn’t lay perfectly flat.  For this reason, what can look like a great new roof can reveal uneven shingle patterning soon after installation.  Synthetic underlayment rolls out easy and flat enough that rippling effect on shingles isn’t an issue.

If felt is used on a roof and the shingles don’t lay correctly, some roofers will redo it.  But not all.  Sometimes you’ll be left with a bad looking roof.  Not always, but it’s a risk you may not want to take.

Synthetic underlayment is better over solid roof decks


Homes weren’t always built with plywood roof decks.  And they often used to have cedar shake roofs instead of asphalt composition shingles.

With wood shakes, felt underlayment is the right choice because of how it breathes.  Shakes should not be applied over top a solid substrate because they too need to breathe in order to dry out.  Felt couples greatly with shakes and skipped sheathing because they both soak up moisture and air dry.

A good synthetic underlayment won’t do this.  They have some measure of breathability, but their strength is more about durability and preventing outside moisture from reaching the roof plywood.

What about cost?


Upfront cost of synthetic underlayment is usually a little higher than felt paper.  But it comes with many important benefits that make synthetic underlayment the long-term less costly choice.

There’s a risk to roofers potentially injuring themselves when using felt.  There’s a cost to the potential of shingles rippling.  And when a roof is only rated for 20-30 years of performance if it has felt underlayment — when it could be rated for 50 years with a good synthetic — then that’s a big deal.

Overall, we use synthetic underlayment (typically GAF Tiger Paw) because it’s the best, safest all around option for everybody involved.  Your roof will perform better with it, and we like using it more than other stuff.  It’s a win-win all around.



Looking for a roofing contractor who will make sure your new roof has the right kind of underlayment?  Give us a call today ((253) 544-3651) or fill out our free estimate form.

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