It's 35 degrees out and we're shingling.

Yes. At 35°F, asphalt shingles are brittle and sealant strips won't activate. You are installing a "cold weather roof." Follow these steps or expect blow-offs and cracked shingles.

1. Hand-Seal Every Shingle (Critical) Factory sealant strips will not activate until sustained temps hit ~70°F. You must hand-seal with asphalt plastic cement (ASTM D4586 Type I or II).

• 3-Tab: Two 1" diameter spots under each tab, 1"–2" from edges.
• Architectural/Laminate: Four spots (two per layer) or a continuous 3/8" bead 1" above bottom edge.
• Code: IRC R905.2.8.2 / IBC 1507.2.9 – "Fasteners shall be applied... and sealed per manufacturer's instructions for cold weather."

2. Prevent Cracking

• Store bundles flat, warm, and off the ground. Bring only what you’ll install in 1–2 hours. Keep the rest in a heated box/trailer (>50°F).
• Do not bend shingles over hips/ridges/valleys. Pre-bend them in a warm area or use pre-formed ridge cap/hip shingles rated for cold install.
• Cut shingles on a warm surface (not frozen roof deck). Use a hook blade; utility knives shatter cold shingles.

3. Nailing Adjustments

• Gun pressure down. Cold wood is harder; standard pressure drives heads through the mat. Test on scrap decking. Heads must be flush, not countersunk.
• Hand-nail hips, ridges, valleys, rakes, and eaves for control.
• Use 1¼" min. ring-shank (IRC R905.2.6).

4. Underlayment & Deck

• Deck must be dry and ice-free. Sweep frost/moisture before laying paper.
• Use synthetic underlayment (less wrinkling/tearing than #15 felt in cold). Cap-nail edges.

5. Ventilation/Attic Heat

• If attic is warm, deck may be damp. Verify dew point. Vent bath fans outside, not into soffit.

Bottom Line: If you can’t hand-seal and keep shingles warm, stop and wait for warmer weather. Manufacturer warranties void if cold-weather instructions ignored.

At 35°F (2°C), shingling requires special precautions to ensure proper adhesion and long-term performance. Here’s what you need to do differently:

1. Use Cold-Weather Shingles or Modified Asphalt: Standard asphalt shingles become brittle below 40°F. Use shingles rated for cold-weather installation (often labeled “cold-weather” or “low-temperature” by manufacturers like GAF, Owens Corning, or CertainTeed). These have modified asphalt that remains flexible.

2. Warm the Shingles Before Installation: Store shingles in a heated area (above 50°F) for at least 24 hours before use. Cold shingles crack easily when bent or nailed. Never install frozen shingles.

3. Hand-Seal the Tabs: At temperatures below 40°F, the factory-applied adhesive strip may not activate properly. Manually apply a dab of roofing cement (about the size of a quarter) under each shingle tab — especially on the windward edges and eaves — to prevent uplift. Follow manufacturer specs; some require two spots per shingle.

4. Adjust Nailing: Use corrosion-resistant nails (galvanized or stainless steel). Drive nails straight and flush — do not overdrive. Cold shingles are more prone to cracking if nailed too tightly. Use a nail gun with adjustable depth or hammer carefully.

5. Avoid Ice and Moisture: Ensure the roof deck is dry and free of frost, ice, or snow. Installing over moisture traps water and leads to premature failure or mold. Wait for a dry, sunny day if possible.

6. Follow Manufacturer Guidelines: Check the shingle manufacturer’s cold-weather installation instructions (e.g., GAF’s “Cold Weather Application” bulletin). Some warranties are void if installed below recommended temps without proper procedures.

7. Safety First: Cold increases slip risk. Wear insulated, non-slip boots. Watch for black ice on ladders and roofs. Take breaks to avoid hypothermia.

Bottom Line: You can shingle at 35°F, but only with proper prep, warm shingles, hand-sealing, and careful nailing. If unsure, consult the shingle maker’s tech sheet or a licensed roofer — improper installation voids warranties and leads to leaks. When in doubt, wait for warmer weather.

(Reference: IRC R905.2.1, manufacturer cold-weather specs)