The Best Roofing Underlayment, Compared on Cost per Square
Five products, cheapest first. One of them seals around the nails driven through it and four of them do not, which is the only distinction that really matters.
The table
Five underlayments, by material cost
Per roofing square, which is 100 square feet of roof surface. Material only, before any labor.
Underlayment is the layer nobody sees and almost nobody asks about, which is exactly why it is the first thing trimmed to win a bid.
1. No. 15 asphalt felt, cheapest thing that meets code
$5 to $9 per roofing square material only, before labor. A square is 100 sq ft of roof surface.
Asphalt-saturated paper, the material every roof used before 2010. It meets code under a steep-slope shingle roof and it costs almost nothing, which is why it still turns up on a builder-grade job.
The catch. It tears if anyone walks on it wrong, it wrinkles when it gets wet, and a wrinkle telegraphs through the shingles above it. Leave it exposed for a weekend of Carolina rain and it is scrap.
2. No. 30 asphalt felt, felt that survives being walked on
$13 to $22 per roofing square material only, before labor. A square is 100 sq ft of roof surface.
The same material at roughly twice the weight. It is noticeably tougher underfoot, holds up better to a few days of exposure, and is what felt should be if you are using felt at all. Required under tile and slate, and sensible on lower slopes.
The catch. Still paper and asphalt. It still wrinkles, it still absorbs water, and it weighs four to five times what a synthetic weighs for the same coverage.
3. Synthetic, 25-year rated, best value on a full reroof
$15 to $20 per roofing square material only, before labor. A square is 100 sq ft of roof surface.
Woven polypropylene. Four to five times lighter than felt and five to ten times more tear resistant, it does not absorb water, it does not wrinkle, and it has a printed walkable surface. For the price of No. 30 felt it is simply a better product.
The catch. UV exposure limits are real and vary by brand, typically measured in weeks rather than months. It is also slick when wet, which is a crew safety issue rather than a performance one.
4. Synthetic, 50-year rated, what we specify as standard
$20 to $25 per roofing square material only, before labor. A square is 100 sq ft of roof surface.
Heavier synthetic with a longer warranty and a better exposure rating. The step up from the 25-year product costs a few dollars a square across a whole roof, which on a typical house is the cheapest upgrade on the quote.
The catch. It is still a water-shedding layer, not a waterproofing one. Nails go through it and the holes stay open, which is the entire reason leak barrier exists.
5. Self-adhering leak barrier, the only one that seals around the nails
$50 to $120 per roofing square material only, before labor. A square is 100 sq ft of roof surface.
Rubberized asphalt membrane with an adhesive back that bonds to the deck and seals around every fastener driven through it. That single property is why it belongs in valleys, at eaves, on low slopes and around chimneys and skylights.
The catch. Five to ten times the price of synthetic, and it needs a clean dry deck to bond to. Nobody sheets a whole roof in it on a house, and a quote that claims to is either confused or charging for it twice.
Want a quote that names the underlayment?
Ours specifies the product and the rating, not the word “underlayment”. Book a free inspection and we will write it out.
What we specify
Synthetic in the field, membrane where water sits
A 50-year rated synthetic across the whole roof, with self-adhering leak barrier in the valleys, along the eaves, on any low-slope section, and around every chimney, skylight and wall. That combination is what a manufacturer system warranty expects.
The reason it is split rather than all one product is cost against benefit. Membrane is five to ten times the price of synthetic, and the property you are paying for, sealing around fasteners, only matters where water actually collects.
Note that the ice barrier requirement most calculators assume does not apply here. North Carolina ties it to places where the January average is 25 degrees or lower, which is nowhere near the Triangle. Our leak barrier calculator works out the rolls for the places that do want it.
If a quote says only “underlayment” with no product, weight or warranty class, assume the cheapest felt. That is the default when nobody specifies otherwise, and it is a few hundred dollars across a whole roof.
Questions
Underlayment questions
What is the best roofing underlayment?
A 50-year rated synthetic across the field of the roof, with self-adhering leak barrier in the valleys, at the eaves and around every penetration. That combination is what a manufacturer system warranty expects and it is what we specify as standard.
Is synthetic underlayment better than felt?
Yes, on every measure that matters. It is four to five times lighter, five to ten times more tear resistant, it does not absorb water and it does not wrinkle. A 25-year synthetic costs about what No. 30 felt costs.
How much does roofing underlayment cost?
Material only, roughly $5 to $22 a square for felt, $15 to $25 for synthetic, and $50 to $120 for self-adhering leak barrier. On a 30 square roof the gap between the cheapest felt and a good synthetic is a few hundred dollars.
Do I need ice and water shield in North Carolina?
Not as an ice barrier. State code ties that requirement to places where the January average is 25 degrees or lower, which is nowhere near the Triangle. You still want leak barrier in valleys and at penetrations, and our leak barrier calculator works out the rolls.
Can underlayment be left exposed?
Only for the period the manufacturer states, which for synthetics is usually measured in weeks and for felt in days. A roof dried in and then left for a month is a roof where the underlayment is already past its rating.
Does underlayment stop leaks?
It sheds water that gets past the shingles, which is not the same thing. Nails driven through it leave open holes. Only self-adhering membrane seals around its own fasteners, which is why it goes in the places water actually collects.
Is underlayment included in a roofing quote?
It should be, by name and rating. A quote that says underlayment with no product, weight or warranty class is a quote you cannot compare to anything, and the cheapest felt is the default when nobody specifies otherwise.
Keep reading
Related guides and calculators
Underlayment is one layer of a system. These cover the rest of it.
Squares and bundles from your footprint and pitch.
Free on-site inspection
Get a quote that names every layer
We get on the roof, photograph what is actually there, and hand you a written report with a price. No charge, and no obligation to book the work with us. If the roof has years left in it, that is what the report will say.
