Underlayment is the layer installed on top of the roof deck and underneath your shingles or metal panels. It's the second line of defence against water — if wind lifts a shingle or rain is driven sideways, the underlayment is what keeps the deck dry.
01
Felt Underlayment
Felt (often called tar paper) is the traditional option: a paper or fibreglass mat saturated with asphalt. It usually comes in two weights, #15 and #30, with #30 being thicker and tougher.
Pros
Lower material cost and a long track record.
Cons
Heavier, tears more easily when walked on, can wrinkle when it absorbs moisture, and shouldn't be left exposed for long before the shingles go on.
02
Synthetic Underlayment
Synthetic underlayment is made from woven or spun polymers. It has become the standard on most new roofs.
Pros
Lighter, much stronger against tearing, more water-resistant, lies flat, and can usually tolerate UV exposure for longer if weather delays the job. Many versions have a textured surface that's safer to walk on.
Cons
Higher material cost than felt, and quality varies between brands — it should be matched to the shingle manufacturer's system.
03
Which Is Better for Texas Roofs?
With Houston-area heat, humidity and sudden storms, synthetic is usually the better choice: it holds up to wind and handling, doesn't wrinkle in the heat, and protects the deck if a storm pops up mid-install.
Felt can still make sense on a tight budget or for certain repairs. Either way, the key is that the underlayment suits the roofing system and the manufacturer's installation requirements.
04
Don't Forget Ice-and-Water Shield
Self-adhering membrane (ice-and-water shield) is often added in valleys, around chimneys, skylights and vents, and along eaves — the places water is most likely to find its way in. It's worth asking about on any replacement.
