Hot and Cold Shingles for the Trades That Walk Roofs

Why this matters

The HVAC tech servicing a rooftop vent, the solar crew mounting standoffs, the gutter crew, the chimney sweep and the antenna installer all walk asphalt roofs they did not install and do not warranty. The roofer who did will look at scuffed granules, a cracked tab or a lifted shingle line after your visit and say, correctly, that the damage arrived with you. Asphalt shingles behave differently at the two ends of the year: soft and easy to mark when hot, brittle and easy to crack when cold. Choosing the hour you go up, and how you move once you are there, decides whether you leave the roof the way you found it.

This card is about what the roof surface does. The crew's own limits on a hot or cold roof (heat stress, footing, when to stop) belong to Heat and Cold Weather Work Limits on a Roof, and fall protection applies on every one of these visits regardless of the weather: under 29 CFR 1926.501 for construction work and under 29 CFR 1910.28 for general-industry service work, with the trigger height and the system set by whichever applies to the work you are doing.

What an asphalt shingle is made of

A shingle is a fiberglass mat saturated and coated with asphalt, with ceramic-coated mineral granules pressed into the top surface and a strip of factory sealant across it. The granules shield the asphalt from ultraviolet light; once they are gone, that area of the shingle ages fast. The sealant strip is a heat-activated adhesive: it bonds the shingle above to the one below after the roof has seen enough sun to soften it. Laminated (architectural) shingles add a second layer bonded to the first, which makes them thicker and stiffer.

Asphalt is the variable. It softens as it warms and stiffens as it cools, and both ends of that range cause damage of a different kind.

The hot roof

On a sunny summer afternoon, the surface of a dark shingle runs far above the air temperature, often well over 140 F. The asphalt under the granules softens, and three things happen under a work boot.

• Granules scuff loose. Turning on the ball of your foot, dragging a hose or a ladder across the surface, or sliding a toolbag scrubs granules off. A scuff path is visible from the ground on a dark roof and permanent.
• Footprints set. A soft shingle takes the shape of a boot tread and keeps it, especially on the tabs near the downslope edge.
• Tabs and edges deform. Stepping on the exposed edge of a tab, or kneeling with a knee on a single tab, can push it out of shape or pull it from its sealant.

Hot roofs are also slick in their own way: a softened surface with loose granules on top can roll under a boot on a steep slope.

How to move on a hot roof, if you must: step flat, put weight on the field of the shingle rather than on tab edges, do not pivot on the ball of the foot, keep traffic to one path, set tools and materials on a moving blanket or a padded mat rather than directly on the shingles, and stay off hips, ridges and valleys, where shingles are bent over a change of plane and the material is thinnest.

The better answer is the clock. The same roof at 8 am on a summer morning, before the sun has loaded the surface, is firm and quiet underfoot. Once dew is off, early morning is the best window of the summer day for walking an asphalt roof. Late afternoon after the sun has moved off a slope is the second window for that slope.

The cold roof

As the shingle cools, the asphalt stiffens and the mat becomes less forgiving.

• Bending cracks it. Lifting a tab to get at a nail, slide in flashing or check the course below is ordinary work in warm weather. In the cold, the same lift can crack the tab across its width, often at the line where it bonds to the sealant strip. Many shingle makers' instructions flag extra care around 40 F and below; your shingle's installation instructions say where theirs sits.
• The sealant bond is brittle. Breaking a sealed tab loose in the cold snaps the sealant rather than peeling it, and often tears the shingle with it. The tab will not re-seal itself until warm sun comes back, and it may not seal well even then if the sealant is fouled with dust.
• New shingles may not be sealed yet. A roof installed in late fall may go through its first winter without its sealant strips ever activating, because they need sun-warmed shingles to bond. Those tabs are loose under your hand and in the wind. That is normal for the season, which is why many manufacturers call for hand-sealing in cold-weather installs; it is not your defect to fix and not one to make worse.
• Ridge caps are the most fragile. A cap shingle is bent over the ridge at install and is under stress already. Stepping on a ridge in the cold is the fastest way to crack one.

The safety condition that comes with the cold roof (frost, ice, snow) is a separate question, covered in Snow and Frost on a Roof Before Anyone Climbs It. A roof dry enough to walk can still be too cold to bend.

The middle of the range is the working window

For any work that bends shingles, the best conditions sit between the two ends: the shingle warm enough to flex, the surface not yet soft. In practice that is a mild morning in spring or fall, or a summer morning before the sun has loaded the slope. A handheld infrared thermometer pointed at the shingle surface tells you what the roof is doing far better than the forecast high, which is an air temperature and says little about a slope in direct sun. Read a surface in the sun and one in shade, because the two can differ by tens of degrees on the same roof.

Read the roof before you put weight on it

Two minutes at the top of the ladder, before you step off it, tells you what the roof was like before you arrived. That record is what protects you when the roofer later inspects your work.

• Photograph each slope you will cross from the eave, plus close-ups of anything already wrong: bare spots, cracked tabs, lifted or missing caps, old footprint paths from the last trade.
• Look in the gutter at the ladder. A heavy band of granules in a gutter on a young roof is a sign of wear already under way, and it is worth a photo before your own traffic adds to it.
• Press a tab with a gloved hand near the ladder. A tab that lifts freely with no resistance is unsealed. On a roof that should be sealed, that is a sign of wind or earlier traffic; on a late-fall install, it is the season. Either way, you now know the tabs on this roof will move under a foot or a hose.
• Note the shingle type. Three-tab shingles are thinner and crack more easily when cold than laminated ones; a laminated roof is more forgiving but heavier to lift at a tab.

Worked example: flashing solar standoffs on two dates

A solar crew is installing standoffs with flashings on a 6/12 laminated-shingle roof. Each flashing slides under the course above the mount point, which means lifting the shingle above and breaking its sealant bond at every mount, then re-sealing after. The array has 24 mounts. The crew is offered two dates.

Date one, mid-January. The forecast says 36 F at 10 am rising to 41 F at 2 pm, clear. At 10 am on the south slope, the crew lead's infrared thermometer reads the shingle surface at 48 F in the sun and 33 F in the shade of a dormer. Twelve of the 24 mounts are in the dormer's shade until noon.

What will happen: on the sunny mounts, lifting a tab at 48 F is borderline and depends on the shingle. On the shaded mounts at 33 F, lifting the tab above each mount is likely to crack it or tear the sealant. The crew lead tries one tab on a sunny mount with a flat bar slid under the sealant line and feels the sealant snap rather than release, with a short crack started at the edge of the tab. That is the shingle answering the question. At least 12 of the 24 mounts are wrong for today, and the sunny ones are marginal.

Date two, the following Thursday, a mild spell. Forecast 52 F at 9 am rising to 61 F, partly cloudy. At 9 am the surface reads 58 F in the sun and 50 F in the shade. Tabs lift with the sealant releasing in a slow peel and the shingle bending without a crease. The crew works the shaded mounts first, while the sun is loading the open slope, and the sunny mounts last. By 1 pm the sunny surface reads 96 F: soft enough that the crew stops kneeling directly on shingles and moves to a kneeling pad.

The re-seal. Every tab whose sealant was broken gets re-sealed at the end of the day with dabs of asphalt roofing cement placed as the shingle maker's instructions describe, because the factory strip is now broken and the crew cannot count on it re-bonding. The crew lead counts: 24 mounts, 24 tabs lifted, 24 re-sealed, and photographs a sample of them with a reference to the mount number.

The ticket. The surface readings at the start of each work block, the shingle type, the number of tabs lifted and re-sealed, and photographs of the roof before access, so that the condition of the roof before the visit is on record if a roofer later questions it.

When you cannot pick the date

• A leak call or an emergency does not wait for a mild morning. Walk as little as possible, stay on one path, do not lift tabs you do not have to, and note on the ticket any tab or cap you had to disturb and how you left it. Temporary protection, not shingle work, is the cold-day job.
• A tab cracks anyway. Do not try to glue a cracked tab back together and leave it. A cracked tab is a shingle replacement for a roofer, and the honest move is to photograph it, tell the customer, and refer it.
• A roof is under a roofing warranty. Some manufacturer warranties exclude damage from other trades. That is a reason to document the roof before you go up, not a reason to avoid it.

References

• Asphalt shingle manufacturers' installation instructions for cold-weather handling, sealing and hand-sealing
• 29 CFR 1926.501 (construction) and 29 CFR 1910.28 (general industry), fall protection
• See related: Heat and Cold Weather Work Limits on a Roof
• See related: Snow and Frost on a Roof Before Anyone Climbs It
• See related: Weather as a Work Condition: The Rule for Every Trade