Roof underlayment is specified as part of a roof assembly, not as an isolated upgrade. The roof covering, measured slope, deck, climate designation, flashing sequence, exposure schedule, and written product instructions all affect the answer. This guide compares four named examples—Tarco asphalt-saturated organic felt, Owens Corning ProArmor synthetic underlayment, GCP GRACE ICE & WATER SHIELD, and Malarkey 406 Secure Start HT—so their published limits are not mistakenly turned into claims about every product in a category.
A homeowner’s useful role is to make the specification traceable. Ask for the exact covering and underlayment models, the adopted code edition, current installation documents, and a detail for each eave, valley, wall, and penetration. Roof access, deck acceptance, installation, and technical interpretation belong to qualified parties. The result should be one compatible drainage assembly whose requirements can be checked before it is concealed.
Quick answer for choosing roof underlayment
Begin with the selected roof covering and the rules that apply at the address. The official 2021 International Residential Code Chapter 9 is a useful example of how an adopted code organizes roofing requirements: Section R905 addresses roof-covering applications, underlayment and ice barriers, while the tables distinguish covering types and attachment conditions. A jurisdiction may adopt another edition or amendments, so the contractor must identify the locally controlling text rather than treating the 2021 IRC as universal law.
For an asphalt-shingle project, one documented option is Owens Corning ProArmor. The ProArmor product page and installation documents identify it as a mechanically fastened synthetic underlayment for asphalt-shingle roofs and give product-specific slope, lap, fastener, exposure, deck, and application instructions. That evidence supports ProArmor only; it does not establish that every synthetic sheet has the same approval or installation pattern.
Where the assembly requires a bonded ice-barrier membrane, use the current instructions for the exact model. The retrievable GRACE ICE & WATER SHIELD data sheet describes that named product as a fully adhered roofing underlayment and publishes its accepted deck surfaces, minimum application temperature, primer conditions, side and end laps, temporary-exposure limit, vapor permeance, and listed roof-covering contexts. Those fields support GRACE ICE & WATER SHIELD only. A covering manufacturer may impose a narrower requirement, and a different bonded membrane may use another adhesive, facer, temperature range, or lap detail.
Asphalt felt remains a possible specification when the covering instructions, adopted requirements, planned exposure, and project conditions permit the exact product. Tile requires its own approved assembly; it should not inherit a shingle specification by analogy. The quick decision is therefore: select the covering first, resolve code and climate provisions, compare only products documented for that assembly, and record every boundary before tear-off.
Decision inputs that change the specification
Slope affects which covering and underlayment instructions apply. Do not estimate it from a photograph or call a plane “low slope” without a measurement. For example, the ProArmor instructions use different coverage and lap provisions from 2:12 to below 4:12 than at 4:12 and above. That is a product-specific rule, not permission to install any shingle or any underlayment at those slopes. The selected shingle instructions and locally adopted requirements must agree.
The deck must satisfy the instructions for every layer attached to it. Record the actual substrate and whether moisture, frost, gaps, coatings, debris, or old material affects installation. For GRACE ICE & WATER SHIELD, the current data sheet calls for a clean, dry, continuous structural deck. It separately directs installers to remove dust, dirt, loose nails, old roofing materials, and protrusions and to repair voids, damaged areas, or unsupported areas; its listed substrates and primer conditions remain additional product-specific checks. ProArmor has its own deck requirements. Neither document accepts decayed sheathing, establishes structural capacity, or permits concealment of an unresolved deck defect.
Climate must be translated into project facts. Ask whether the local climatic table triggers an ice barrier, what wind provisions apply, what application temperatures are expected, and whether wind-driven rain, wildfire classification, or coastal exposure changes the approved assembly. The IRC source illustrates that an ice-barrier rule depends on the locally completed climatic criteria. A contractor should cite the jurisdiction’s adopted edition and amendment, not merely say that the house is “in a cold area.”
Exposure time is a maximum boundary under stated conditions, not a target schedule or a substitute roof. The exact product document controls how long the sheet may remain uncovered and how it must be fastened during that period. Record the planned interval between dry-in and covering, the forecast threshold for tear-off, the maximum area opened at once, and the response if the schedule slips. Before covering a sheet that experienced wind, heat, or rain, the responsible installer should evaluate it using the manufacturer’s repair or replacement criteria.
Covering temperature and chemistry also require exact matches. Dark metal or architectural metal can create a different service environment from asphalt shingles, but appearance alone does not select a high-temperature membrane. Obtain the metal manufacturer’s underlayment requirements and compare its approved products with the membrane’s published service temperature, substrate, facer, ventilation or separation instructions, and metal restrictions. For tile, use the tile manufacturer’s approved underlayment and fastening system, considering the roof’s project-specific wind and climate conditions.
Inspect the deck and map every water path
Planning can begin without climbing. From the ground, identify roof planes, eaves, rakes, valleys, dormers, sidewalls, chimneys, skylights, plumbing vents, mechanical curbs, pitch changes, gutters, and places where runoff from an upper plane reaches a lower one. From a safely floored attic area, if available, note staining, active moisture, daylight, corrosion at fasteners, damaged sheathing, and condensation patterns. These are observations, not a diagnosis: water may travel before it becomes visible.
Have the roofer create a roof plan with measured slope for each plane and a reference for every transition. The plan should show the sequence of underlayment, eave or valley membrane, flashing, and roof covering. The U.S. Department of Energy Building Science Education page on sealing roof penetrations supports the bounded principle that flashing or self-sealing membrane should integrate with roof underlayment in drainage order. It does not select a brand, approve a proprietary detail, or diagnose concealed moisture.
Deck inspection belongs after tear-off and before new sheets hide the surface. The contract should define how the crew will identify damaged panels or boards, who decides whether structural review is needed, how replacements are priced and approved, and what photographic record will be retained. “Replace bad wood as needed” does not establish acceptance criteria or authorization. Widespread decay, sagging, fire damage, unusual movement, or uncertain framing should stop routine underlayment work until an appropriately qualified person evaluates the condition.
For each penetration, specify an exact published detail. Record whether the sequence uses a boot, curb, flange, cricket, step flashing, counterflashing, sealant, membrane patch, or combination, and which layer drains over the next. The same discipline applies at valleys and roof-to-wall intersections. A neat hole and a bead of roof cement do not demonstrate that drainage continuity has been restored.
Underlayment installation mistakes to prevent
The first mistake is mixing category names with specifications. “Synthetic,” “felt,” and “high temperature” describe broad families, not interchangeable performance. A proposal should name manufacturer, model, applicable standard or approval, roll orientation, fasteners, lap dimensions, application-temperature range, exposure limit, deck requirements, and accepted coverings. If the delivered label differs, work should pause until the substitution is reviewed against every dependent document.
The second mistake is reversing drainage order or trusting printed guide lines without measuring. Courses, end laps, valleys, penetrations, and transitions between two products must follow the selected instructions. Fishmouths, wrinkles, damaged edges, unsupported laps, and poorly placed fasteners need the manufacturer’s repair method before concealment. Adding sealant where it is not specified can interfere with adhesion or drainage rather than correct the detail.
The third mistake is treating low vapor permeance as a universal upgrade. The current GCP data sheet publishes a maximum vapor-permeance value for GRACE ICE & WATER SHIELD, calls the installed membrane an air and vapor barrier, and directs full-roof applications to use properly designed and installed insulation and ventilation. That is a design boundary, not proof that full coverage suits every building. Unvented assemblies, persistent condensation, damp decks, or an uncertain drying path require project-specific evaluation by an appropriate design or building-science professional.
Other common failures are application to a wet or contaminated substrate, incorrect or uncapped fasteners, insufficient laps, missed primer where the named product requires it, and leaving a sheet exposed beyond its documented conditions. These are checked against the exact installation document, not a generic online diagram. Homeowners should not climb onto exposed underlayment to conduct that inspection.
Compare named felt, synthetic, bonded, and high-temperature products
Tarco’s Asphalt Saturated Organic Felts data sheet covers its No. 15 and No. 30 products. It identifies the applicable ASTM classifications, roll dimensions, approved roof-covering contexts, storage precautions, deck preparation, fastening, laps, and weather limitations. Those facts support a decision about these Tarco felts. They do not prove that all modern “15-pound” or “30-pound” felt has identical mass, thickness, exposure behavior, or installation requirements.
Owens Corning ProArmor is the mechanically fastened synthetic example. Its current manufacturer material identifies the intended asphalt-shingle context and publishes the fastener and lap scheme, including special low-slope coverage. A large roll and printed fastening pattern can aid installation, but neither feature proves that the deck is acceptable or that another roof covering approves the product. Compare its current instruction revision with the chosen shingle documentation and local approval before purchase.
GRACE ICE & WATER SHIELD is the bonded-membrane example. Its current GCP data sheet identifies a rubberized-asphalt layer with a release film and gives product-specific substrate, primer, minimum-temperature, lap, exposure, and vapor-permeance requirements. The full bond may be relevant where the selected assembly calls for this type of ice or water barrier, while also making surface preparation and eventual removal practical considerations. The document does not transfer those properties to every product sold as “self-adhered.”
Malarkey’s 406 Secure Start HT technical data sheet is the high-temperature example. It identifies the product as a self-adhering underlayment, gives thickness and ASTM D1970 information, and states intended roof-covering contexts and published limits. Use those claims only for this model. A different membrane with “HT” in its name may have a different adhesive, facer, service temperature, exposure allowance, metal compatibility, or installation procedure.
A tile assembly needs tile-specific documents. The Tile Roofing Industry Alliance’s retrievable Concrete and Clay Roof Tile Installation Manual, dated March 2024 and revised May 2025, presents concrete-and-clay tile practices based on IBC and IRC provisions and states limits for moderate-climate applications. Its roof-slope provisions, deck and underlayment tables, flashing details, and fastening criteria must be read within those limits. High-wind provisions appear inside Appendix B of the manual; cold-and-snow projects are directed to the separate Concrete and Clay Tile Roof Design Criteria Manual for Cold and Snow Regions. Use the applicable material alongside the selected tile’s approval, manufacturer instructions, and locally adopted requirements. Neither document authorizes reuse of an asphalt-shingle underlayment schedule.
These underlayment system examples show how comparison should work: write one row per exact product, then compare allowed covering, slope, deck, application temperature, primer, fastening or rolling, laps, exposure, vapor permeance if published, service temperature if relevant, approvals, and warranty conditions. Blank cells become questions for the manufacturer or responsible professional; they are not invitations to infer a favorable answer.
One set of underlayment selection steps
- Define the assembly. Record covering manufacturer and model, deck type, measured slopes, insulation and ventilation design, local climate criteria, and every transition.
- Collect governing documents. Obtain the locally adopted code provisions, permit instructions, covering installation manual, underlayment data and installation sheets, flashing details, and warranty conditions. Record revision dates.
- Map water-control details. Assign a published sequence to eaves, rakes, valleys, walls, chimneys, skylights, vents, curbs, and pitch changes. Resolve boundaries where different membranes meet.
- Compare exact products. Complete the documented comparison fields rather than ranking categories. Request written manufacturer clarification for conflicts or missing compatibility information.
- Set deck acceptance and weather rules. Define inspection, repair authorization, surface preparation, moisture or adhesion evaluation, primer decision, storage, open-roof limit, temporary protection, and stop-work thresholds.
- Coordinate installation. Confirm course direction, fasteners, laps, rolling or pressure, wrinkle and damage repair, exposure schedule, and inspection hold points with the crew before tear-off.
- Inspect by stage. The designated qualified supervisor verifies the exposed deck, vulnerable membranes, field underlayment, flashings, and penetrations before the next layer conceals them.
- Close out the record. Reconcile delivered labels with the approved schedule, save location-based photographs and changes, obtain required inspections, and retain final instructions and warranty documents.
Before tear-off, useful underlayment planning questions expose unresolved authority: Which adopted provision controls the ice barrier? Which exact covering accepts the proposed sheet? What happens if the deck is damp? Who can approve a substitution? Which published detail governs each penetration? Which stage must remain visible for inspection? Any unanswered question becomes a hold point assigned to the contractor, code official, manufacturer, or design professional who controls that decision.
Product instructions and job records
Build a document register rather than a folder of unidentified downloads. For each file, record manufacturer, product, document title, revision or access date, source URL, and the decisions it controls. Highlight only explicit requirements: approved substrate and covering, slope, preparation, application temperature, primer, roll direction, fastener type and spacing, side and end laps, valley and penetration treatment, repair method, exposure, and storage. Marketing comparisons should not replace current technical instructions.
The contract and product schedule should use the same names as delivered labels. Photograph full labels, including model and lot information where visible, before installation. Also keep the roof plan, deck-repair allowance, weather plan, permit record, inspection hold points, manufacturer correspondence, daily condition notes, change orders, and final warranty materials. Records make concealed choices traceable; they do not themselves prove correct installation.
Professional roofing help is appropriate for roof access, slope measurement, deck evaluation, assembly selection, flashing design, installation, and interpretation of conflicts among documents. Structural damage may require an engineer or other qualified structural professional. An uncertain vapor and drying strategy may require a building-science or design professional. The code official interprets the locally adopted provisions, while each manufacturer controls statements about its product.
Document conditions, approvals, and changes
Use location-specific descriptions. “North garage plane at the valley” is more useful than “bad area.” For deck repairs, record the observed condition, dimensions, photograph, proposed response, responsible reviewer, price and schedule effect, approval, and completion evidence. For a product change, compare every affected field—not just price—and attach written confirmation where covering, membrane, sealant, flashing, or metal compatibility is in question.
A photograph log should include an overview and close views of exposed deck repairs, eave terminations, valleys, end laps, field fastening, walls, chimneys, skylights, vents, curbs, pitch changes, and repaired sheet damage. A ruler placed safely by the crew can document scale. Photographs may show that a detail was visible at a moment; they cannot certify hidden bond, structural capacity, moisture condition, or compliance outside the frame.
When weather or access prevents a required check, record the limitation and keep the hold point open. Do not convert “not observed” into “acceptable.” When an installer follows a manufacturer-approved deviation, retain who authorized it, the exact written response, its date, the affected location, and the completed condition.
Roofing work safety and professional boundaries
The OSHA activity sheet on roof inspection, tarping, and repair describes worker exposure to falls, ladders or scaffolds, slippery or deteriorated surfaces, electrical hazards, power tools, falling objects, and changing site conditions. It also discusses fall protection, controlled access, equipment inspection, electrical precautions, and personal protective equipment. OSHA explicitly frames the sheet as guidance that cannot cover every hazard; it does not certify a contractor or teach a homeowner to walk a roof.
A homeowner can review documents, observe from the ground, move possessions from a designated debris area when safe, keep children and pets away, and discuss photographs with the supervisor. A homeowner should not climb a ladder to measure laps, walk on felt or synthetic sheet, lift bonded membrane, approach a skylight, step onto uncertain attic decking, or inspect during rain, wind, frost, or extreme heat. Exposed underlayment can be slippery, and covered openings or weak decking may not be visible.
The contractor is responsible for the site-specific work plan, trained workers, access control, fall protection, ladder and tool safety, electrical precautions, material handling, weather response, and protection from falling debris. Stop work and use the appropriate emergency or utility response for contact with energized conductors, fire, structural movement, or another immediate hazard. These boundaries are part of roof underlayment safety even though they do not select the material.
Verify the assembly before concealment
Acceptance should compare observable work with the approved documents at defined stages. Before underlayment, verify the recorded deck type, authorized repairs, surface preparation, and unresolved structural conditions. At eaves and valleys, verify the exact membrane label, location, width or extent, lap direction, termination, and integration with edge metal or flashing according to the chosen detail. For field sheets, verify roll orientation, side and end laps, fastener type and pattern, wrinkles, tears, and repairs against the named instructions.
At penetrations and walls, compare the visible sequence with the selected published drawing. The question is not whether the sealant bead looks tidy; it is whether each layer returns water to the exterior and whether the products touching one another are approved for that use. Record deviations before shingles, panels, or tile hide them. A final roof-surface photograph cannot reconstruct every concealed layer.
Verification must not create a new hazard or defect. Do not spray water uphill, flood a valley, lift installed covering, puncture a membrane with a meter, or walk the surface. If controlled testing is justified, the responsible professional should define the method, safe conditions, boundaries, acceptance criteria, and restoration. A single dry moisture reading does not certify an entire concealed deck; an old stain does not prove an active roof leak.
Closeout requires reconciliation. The approved schedule, delivered labels, installation record, permit inspection where required, and warranty submission should describe the same assembly. List exclusions and unverified concealed conditions honestly. Acceptance evidence supports a decision; it is not a warranty beyond what the responsible parties and documents actually provide.
Maintain the finished roof and its drainage details
Roof assembly maintenance concerns the covering and its interfaces because the underlayment is normally concealed. Follow the covering and flashing manufacturers’ maintenance and inspection instructions, together with installer warranty terms and site-specific professional advice. Do not expose underlayment for routine checking. Keep records of later work so a future roofer knows which membrane and details are below the surface.
After severe wind, hail, falling limbs, fire exposure, or visible displacement, ask a qualified roofer to define an inspection appropriate to the covering and event. This is conditional advice, not a claim that every storm requires the same service. From the ground, note displaced covering, damaged flashing, loose edge components, blocked drainage, or debris. From a safely accessible floored attic, note new staining or active dripping without leaving the walkway.
New solar mounts, satellite equipment, HVAC curbs, vents, or plumbing penetrations can interrupt the assembly. Before that work, give the contractor the roof record and require a detail accepted by the covering and underlayment manufacturers where applicable. Document the location and sequence before concealment. An exposed fastener and a bead of sealant should not be assumed equivalent to a designed penetration detail.
Indoor discoloration, musty odors, damp insulation, frost at fasteners, or recurring condensation can have roof, plumbing, air-leakage, ventilation, or humidity causes. Diagnose the source before ordering a surface patch. Where a low-permeance membrane and unusual insulation or moisture condition are involved, have an appropriate building professional evaluate the whole drying strategy.
Roof underlayment checklist: stop-work gates
This roof underlayment checklist is not a second installation sequence. It identifies conditions that prevent the approved sequence from continuing:
- Product gate: stop when a delivered label, instruction revision, approval, or warranty condition differs from the accepted product schedule. Resume only after every affected document has been reconciled in writing.
- Deck gate: stop at decay, movement, widespread damage, an unapproved substrate, contamination, frost, or moisture outside the selected product’s limits. Record who has authority to accept the repair and surface condition.
- Weather gate: do not open more roof than the crew can protect within the forecast and the product’s application and exposure limits. A missed dry-in window requires a documented response, not concealment.
- Detail gate: keep eaves, valleys, walls, penetrations, product transitions, and repaired membrane damage visible until the designated supervisor has compared them with the location-specific approved detail.
- Change gate: reject verbal substitutions and improvised deviations. Require the responsible manufacturer, contractor, code official, or designer—as applicable—to authorize the exact change before dependent work covers it.
These gates turn uncertainty into a named decision instead of allowing the roof covering to conceal it. Choosing among roof underlayment types remains an assembly decision: once a gate is cleared, the project returns to the single selection and installation sequence above, and the final record states what changed, who approved it, and what evidence remains.