PROJECT GUIDE / ROOFING
What goes underneath your shingles, and why does it matter?
Shingles get most of the attention when you choose a roof. The layers beneath them deserve a place in the conversation, too. Here is what underlayment does and how to understand the materials listed in your proposal.
What is roof underlayment?
Underlayment is a protective layer installed between the roof covering and the roof deck. It provides secondary protection against water that gets past the outer roofing. Once the roof is finished, you generally cannot see it from outside.
Shingles
The visible roof covering that sheds rain.
Underlayment
A secondary protective layer over the deck.
Roof decking
The structural surface the roofing is installed over.
This is a simplified overview, not an installation drawing. Flashing, edge details, fasteners, ventilation and the specified products all play a part in the complete roof system.
Felt, synthetic and ice-and-water barrier: what is the difference?
Asphalt-saturated felt
A traditional underlayment made with an asphalt-saturated base. It provides a water-shedding layer beneath the roof covering. Its suitability depends on the product and the roof assembly.
Synthetic underlayment
A manufactured sheet, commonly made with polymers such as polypropylene. Many synthetic products are lighter and more tear-resistant than traditional felt, but performance varies. The product name and instructions matter more than the word “synthetic.”
Self-adhered ice-and-water barrier
An adhesive-backed membrane used for added water protection in specified areas. It may be used at roof edges, valleys or around penetrations, depending on the roof design, product instructions and applicable requirements. It has a different role from a typical water-shedding field underlayment.
These are not simply three interchangeable price levels. A roof may use more than one type in different locations.
Is synthetic underlayment waterproof?
Do not assume it is. Water-resistant and waterproof are different claims. For example, GAF identifies its FeltBuster synthetic underlayment as water-resistant, not waterproof. Check the specifications for the exact product being proposed.
Likewise, an exposure limit describes a product's permitted conditions before the finished covering is installed. It does not mean the unfinished roof can be treated as a completed roof for that period regardless of weather or installation details.
Ask how your home will be protected while work is underway and what happens if the weather interrupts installation. That is more useful than comparing advertised exposure periods alone.
What matters for a Western Washington roof?
When you are planning work in Lakewood, Tacoma or the surrounding areas we serve, ask how the specified materials and installation plan address your particular roof and weather exposure.
- Roof covering and slope: Is the underlayment suitable for this roof material and pitch?
- Vulnerable details: Where are additional membranes or flashing needed, and how will they connect?
- Existing conditions: What happens if the deck needs repair before the new layers go down?
- Workday protection: How much roof will be opened at once, and how will it be protected if conditions change?
There is no single “best” roll for every home. Ask for an explanation tied to the roof being built, rather than a blanket upgrade recommendation.
Does metal roofing need different underlayment?
It can. Underlayment for a metal roof must be compatible with the panel system and its installation requirements. Temperature resistance is one consideration: products intended for high-temperature conditions may be needed beneath metal roofing.
“High temperature” and “ice-and-water barrier” describe different characteristics. Do not assume any self-adhered membrane is suitable for every metal roof. Ask which product is specified and whether the panel manufacturer permits that assembly.
What should your proposal say?
“New underlayment” leaves room for questions. Before agreeing to a roof project, ask for enough detail to understand what is being installed:
- The manufacturer and product name for the main underlayment.
- The product and locations for any additional leak barrier.
- How flashing, roof edges and openings are included in the scope.
- How decking repairs or other concealed conditions will be handled.
- Which written product and workmanship coverage applies to the agreed work.
You do not need to become a roofer to compare proposals. You need a clear description and a contractor who can explain why those choices fit your home. See our roof proposal checklist for the wider scope.
Will better underlayment fix an existing leak?
It depends on what is causing the leak. Underlayment is one part of the roof, so choosing a different product is not a diagnosis or a substitute for addressing a failed detail.
If you are dealing with a current problem, begin with an inspection rather than a material upgrade. Our repair-versus-replacement guide explains the questions to ask before deciding on the work.
Bring the whole roof into the conversation
If you are comparing roofing options, ask John to walk you through what goes above the deck, what happens at the edges and openings, and what is included in the proposal.
Start with a free initial roof inspection or a conversation about your project. You do not need to arrive with a material list already chosen.
John will follow up to discuss your request and coordinate the next step. Submitting a request does not book an appointment.
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