Roofing underlayment is the secondary water-shedding layer installed over roof decking and beneath the finished roof covering. For roofing contractors, choosing the right system starts with more than picking a roll: roof slope. Covering material, local requirements, manufacturer instructions, and expected exposure all shape the plan. A consistent review process helps you set clear expectations, coordinate the work, and protect the quality of the full roofing assembly.
Talk with The Attic Depot team
What does roofing underlayment do?
Underlayment is a layer between the roof deck and the outer roof covering. It provides a secondary line of water shedding below shingles or another approved covering. It can help protect the deck during the roofing process and in situations where water gets beneath the outer layer. It is not a substitute for correctly installed flashing, a suitable roof covering, or sound roof details.
Think of the roof as a system. The deck provides the base. Underlayment covers the deck. The roof covering sheds most rain and weather. Valleys, penetrations, eaves, ridges, and transitions need details that work with the selected materials. A mismatch at any one layer can undermine the rest, so use the roof-covering manufacturer's instructions and the applicable local requirements as your project references.
Underlayment also matters during scheduling. Roof sections may be exposed while a crew works, but permitted exposure time depends on the chosen product and conditions. Confirm that information before staging the job, and plan the sequence so installed materials are protected as specified.
What are the main roofing underlayment types?
Three common categories are asphalt-saturated felt, non-bitumen synthetic underlayment, and self-adhered modified-bitumen products, which may use rubberized asphalt. The Asphalt Roofing Manufacturers Association's underlayment bulletin discusses product types, specifications, and features. The InterNACHI overview of underlayment types also describes these broad categories. Product names alone do not tell you whether a specific roll fits a specific roof assembly; check its technical data and intended applications.
| Type | General description | Questions to check |
|---|---|---|
| Asphalt-saturated felt | Traditional roll underlayment made with a felt base saturated with asphalt. | What grade is specified? Is it suitable for this roof and covering? What fastening and exposure instructions apply? |
| Synthetic, non-bitumen | A manufactured sheet underlayment made from synthetic materials. | Is it approved for the assembly? What are the fastening pattern, overlap, surface, and exposure instructions? |
| Self-adhered modified bitumen | A peel-and-stick sheet product with an adhesive layer; formulations and intended uses vary. | Where is it intended to be used? Does the deck need preparation or a primer? What temperature and installation limits apply? |
This is a comparison of broad product families, not a ranking. Performance, handling, approved uses, and installation steps vary by product. Read the current product instructions rather than assuming that two rolls in the same category install the same way.
How can you compare product instructions before ordering?
Compare the documents for the exact products you are considering, not just the category names on a distributor page. Start with the stated applications and any limits on compatible roof coverings or substrates. Then look for the practical details your crew will need: permitted installation conditions, fastening or adhesion method, overlap requirements, exposure period, and storage or handling directions. If a detail is not clear, ask the manufacturer or supplier before the crew is on the roof.
It also helps to make a one-page job note for the selected product. Include the product name, the approved assembly, key installation details, the source of the instructions, and any project-specific requirements. This is a working reference for the crew, not a replacement for the full documentation. Keep the current product instructions available so installers can check a detail directly when needed.
When evaluating alternatives, compare like with like. Two products may both be described as synthetic, for example, but their approvals, application details, and exposure limits may differ. Likewise, self-adhered products can have distinct substrate preparation and application directions. Choose based on the requirements and documents for the actual project rather than the broad material description alone.
How should you choose underlayment for a roof?
Start with the project's required assembly, then compare products that are appropriate for it. A practical review can be completed before materials are ordered:
- Identify the roof covering and deck. Record the covering type and deck material. Confirm that the proposed underlayment is approved for both and that all layers are compatible.
- Review slope and roof geometry. Slope, valleys, eaves, dormers, and penetrations affect water movement and detailing. Check the covering manufacturer's guidance for underlayment requirements and any special roof areas.
- Check applicable requirements. Confirm the requirements adopted for the project location, including any local amendments or project specifications. Do not rely on a generic online summary when the authority having jurisdiction or current product instructions provide the controlling detail.
- Match the product to exposure and schedule. Check how long the underlayment may remain exposed and the conditions that affect that limit. Align the installation sequence and covering delivery with the product's instructions.
- Read installation details before mobilizing. Verify the fastening or adhesion method, overlaps, end laps, substrate preparation, and temperature limits. Make sure the crew has the right tools and the current instructions at the jobsite.
Use those checks to narrow choices, not to improvise a roof detail. For a field question, consult the manufacturer's current documentation or technical support. When a job includes broader attic-performance work, The Attic Depot's contractor product range and dealer support overview can help you explore complementary services without confusing their role with roofing underlayment.
What installation details deserve the most attention?
Many callbacks begin with a small detail that was treated as routine. Build a repeatable check into the crew's workflow:
- Deck condition: Inspect the substrate and resolve issues that could prevent the specified fastening or adhesion. Follow product directions for preparation; do not cover a condition that needs attention.
- Placement and laps: Lay out courses and overlaps according to the product instructions and roof design. Keep sheets aligned and avoid wrinkles, fishmouths, or open seams where water could travel beneath the material.
- Edges and transitions: Follow the roof-system details at eaves, rakes, valleys, ridges, sidewalls, and penetrations. Coordinate underlayment with flashing and the covering rather than treating each as a separate task.
- Fasteners or adhesion: Use the specified fastener type and pattern, or follow the self-adhered product's substrate and application directions. Unapproved substitutions can change how the layer performs.
- Weather and exposure: Check conditions against the product limits, and cover completed sections within the stated exposure period. If the schedule changes, reassess protection instead of assuming the installed layer can remain uncovered indefinitely.
- Documentation: Keep a record of the product used and the applicable instructions. Photos of concealed details can help with project records and later questions.
These are review points, not a universal installation specification. The exact sequence and detail depend on the product and roof assembly. If instructions differ between components, pause and resolve the conflict with the relevant manufacturer or project authority before covering the work.
How can underlayment fit into your roofing business?
Underlayment is part of the core roofing scope, but the roof project can also surface customer questions about ventilation, heat, insulation, and attic access. Use the inspection and customer conversation to identify needs that fall within your business's existing services. A clear explanation of the roof assembly gives customers a better picture of what is being installed and why details matter.
Contractors who want to broaden their attic-efficiency offering can explore adjacent services separately from the underlayment specification. For example, The Attic Depot offers solar attic fans, attic stairway insulators, radiant barriers, and roof rejuvenation products. Each addresses a different need; none should be presented as a replacement for correctly selected and installed underlayment. Relevant options include solar attic fans for contractors, DraftMaster attic stairway insulators, RadiantX radiant barrier, and Shingle Serum roof rejuvenation.
Adding a service works best when it fits your customers and workflow. Consider what your crews already inspect, what questions customers regularly ask, and what training would make a new offering comfortable to explain. The Attic Depot's dealer program supports contractors with product education, installation education, sales tools, marketing resources, technical support, and ongoing dealer support. Enrollment is free, with no contracts and no order minimums. The company sells through its dealer network rather than directly to homeowners, so it does not compete with its dealers for their customers.
For roofing businesses exploring a broader attic service mix, start with a focused trial: choose one relevant customer need. Learn the product's purpose and instructions, prepare a simple explanation, and gather feedback from the first jobs. Keep the roof covering, underlayment, ventilation, insulation, and other attic products distinct in your recommendations. That clarity helps customers understand the value of each part of the project.
How do you explain underlayment choices to a customer?
Keep the discussion tied to the home and the work being done. Explain that the underlayment is a secondary layer below the roof covering. Describe why the selected product fits the planned assembly, and clarify how the crew will handle key transitions. Avoid promising that any single underlayment makes a roof leak-proof or eliminates the need for proper flashing and workmanship.
If the customer asks why the bid specifies one product rather than another, focus on the applicable project requirements, product instructions, and planned installation. Do not turn the conversation into a contest over labels such as "premium" or "best." Those words mean little without a clear project requirement behind them. A brief comparison of product type, approved use, exposure limits, and installation steps is more useful.
Good customer communication also separates the known facts from decisions that need confirmation. If the plans, local requirements, and product documentation do not align, explain that you are checking the detail before proceeding. That is a straightforward quality step, not a reason to overload the customer with technical terminology.
What should contractors check before the job starts?
- Confirm the roof covering, deck, slope, and project documents.
- Verify local requirements and the current underlayment instructions.
- Make sure the selected product is intended for the assembly and expected exposure.
- Review laps, fastening or adhesion, substrate preparation, and transitions with the crew.
- Coordinate delivery and installation so the underlayment is protected as directed.
- Record the product information and document important concealed details.
Use the same review on each applicable project, then adjust for the actual product and roof design. A short pre-install conversation can catch missing materials, unclear details, or schedule conflicts before they turn into rework.
A repeatable pre-install checklist also gives the office and field teams the same reference point. Record the selected product, roof conditions, required details, and open questions before materials arrive. That simple record supports cleaner scheduling, clearer customer conversations, and a better handoff when several crews or trades touch the same project.
Become a Dealer and explore contractor support
Frequently asked questions
Is roofing underlayment waterproof?
Underlayment is a secondary water-shedding layer, but its water resistance and approved use depend on the specific product and installation. It does not replace the roof covering, flashing, or properly detailed roof assembly.
Which underlayment is best for every roof?
There is no single type that fits every roof. Choose based on the roof covering and deck, project requirements, product instructions, exposure, and details such as slope and transitions.
Can underlayment remain exposed while work is delayed?
Exposure limits vary by product and conditions. Check the current instructions and protect the work within the stated limits; do not assume an underlayment can stay uncovered until the next phase.
Does underlayment replace flashing?
No. Underlayment and flashing have related but distinct roles in a roof assembly. Follow the relevant system details at edges, valleys, walls, and penetrations.
Build a dependable roof-system conversation
When you select underlayment for the specific roof system, follow its instructions, and coordinate the details with the rest of the assembly. You give your crew a clearer plan and your customer a more confident explanation. Keep the product choice grounded in project facts, and use each roofing job as an opportunity to identify other services that genuinely fit your business and customers.
