Underlayment is the secondary water‑resistive layer beneath shingles; manufacturers and industry guides recommend using synthetic (non‑self‑adhering) underlayment as the field layer and self‑adhering ice & water membrane in critical detail zones (eaves, valleys, flashings, and penetrations) as standard practice for asphalt roofs[3][4][5].
Self‑adhering polymer‑modified bituminous membranes ("ice & water" products) are specified by the ASTM D1970 standard for ice‑dam protection and many manufacturer products are supplied to meet D1970 criteria[1]. The International Residential Code requires an ice‑barrier membrane in areas with documented ice‑dam history and specifies a minimum 24‑inch horizontal extension inside the exterior wall line from the lowest roof edge, though local code adoptions can change triggers or extents[12].
Manufacturers design ruberized asphalt, self‑adhering membranes (for example, Grace Ice & Water Shield) to seal around fasteners and resist leakage from ice dams and wind‑driven rain; these products may include a film or top sheet to protect the adhesive and help resist damage during installation[2][10].
Common failure modes to watch for
UV degradation and weather exposure beyond allowable exposure windows can embrittle or tear underlayments and degrade some adhesives[3][4][10][5].
Improper fastening (wrong spacing or fastener type) can allow leakage or separation; fastening patterns are specified in manufacturer instructions[4][10].
Poor adhesion from wet or contaminated decking, or installing over incompatible substrates, can cause early peeling of self‑adhering membranes[2][10][11].
Incompatible layering or incorrect installation sequence (for example, peel‑and‑stick over some synthetic underlayments) can create wrinkling, buckling, or other field failures reported in trade discussions[11][2][10].
Recognizing failure: exterior and attic signs
Exterior signs include lifted shingle edges, blistering or wrinkling in valleys or eaves, seams peeling at rakes/edges, and gaps or missing continuous membrane at eaves[5][7].
Interior and attic signs include water staining on ceilings or sheathing, drips from eaves during melt events, wet or rotted sheathing, and repeated icicle/ice‑dam recurrence as an indirect sign that detail protection or attic heat control is inadequate[5][6].
Safe inspection basics
Roof inspection and repair are fall‑hazard tasks; consumer guides and manufacturer literature recommend hiring licensed roofers for work above one story or when homeowners are inexperienced[7]. A safe attic inspection includes checking roof sheathing from the inside for wet, soft, or delaminated decking and looking for evidence of underlayment wrinkling where the membrane was installed beneath shingles[5].
If you find soft or rotted sheathing you will typically need to remove shingles and underlayment to access and inspect the decking properly; see the separate step‑by‑step guidance on inspecting and repairing roof decking for more on when to patch versus replace sheathing[5] — and consult our Inspecting and Repairing Roof Decking (Sheathing) Rot After a Leak article for detailed decking repair workflow where applicable.
Repair workflow: from small patch to full replacement
Remove shingles in the affected area to expose the underlayment and assess damage; this is required to see fastener holes, adhesion failures, and the condition of the decking beneath[5][7].
Strip and remove failed underlayment and any debris; inspect and replace damaged sheathing as required[5].
Install appropriate underlayment: use self‑adhering ice & water membrane only in recommended detail zones (eaves, valleys, roof‑to‑wall flashings, penetrations) per ASTM D1970 guidance and manufacturer instructions; use synthetic underlayment in the field per the product's fastening and overlap schedules[1][2][4][10].
Reinstall shingles following the roof covering manufacturer's instructions and the underlayment overlap/fastening guidance in the underlayment product data sheet[2][4][10].
For small, local failures some manufacturers and guides note temporary patches (self‑adhering patches or roofing cement with patch material) are used by owners, but reliable long‑term repairs typically require stripping to decking and following full installation instructions[5][7].
Installation details that determine success
Manufacturers' technical data sheets and installation guides specify surface preparation, allowable UV exposure limits, lap widths, and fastening type/spacing — and these product‑specific limits must be followed. Different products list different maximum allowable exposure times, so do not assume all membranes have the same UV exposure tolerance[2][3][4][10].
Field discussions and manufacturer literature emphasize that installation sequence, substrate preparation, and adherence to both the underlayment's and the roof covering manufacturer's instructions determine long‑term performance; installing peel‑and‑stick membranes beyond their tested/detail use can cause compatibility and installation issues[10][11][4].
When to call a pro (and temporary measures while you wait)
Because of fall hazards and the technical needs of proper substrate prep, adhesive performance, and shingle reinstatement, hire a licensed roofer for work above one story or if you are inexperienced[7]. For active ice‑dam events temporary measures include clearing gutters/downspouts and using professional ice‑dam removal (steam) or approved heat‑cable approaches as temporary mitigations; long‑term fixes require addressing attic insulation, ventilation, and underlayment details[6].
Costs and next steps
Underlayment replacement costs vary by material (felt, synthetic, self‑adhering) and project factors; consult local cost‑estimating sources and contractors for quotes that reflect your roof size and labor conditions[8][9].
Before starting repairs, gather the product technical data sheets for any underlayment you plan to install and follow those instructions for surface prep, allowable exposure, and fastening. If the failure shows repeated ice dams, pair underlayment repairs with an attic insulation and ventilation audit to address the underlying cause of ice dams[6][10].