Asphalt shingles are designed to be very resilient to heat exposure, but as they age they lose some of this resilience and become more prone to damage. It's a good idea to inspect older shingled roofs following a heat wave so any damage can be addressed quickly before the roof springs a leak. 

1. Sun Faded Shingles

Dark shingles are more prone to fading than lighter-colored ones, mainly because they absorb heat instead of reflecting it away. Fading itself doesn't mean that the roof is damaged, although faded roofs can be less attractive. The main concern is that visible fading can indicate that heat is drying out the asphalt shingles, which will make them more prone to cracks and leaks. A roofer should assess faded shingles to make sure they are still in otherwise good condition.

2. Cracks and Splits

Although sun fading can indicate a higher risk of cracking and splitting, sometimes shingles will crack even if they don't appear fading. The main cause of these cracks and splits on the shingle is heat drying out the oils present in the asphalt. Often, these cracks become more noticeable right after a very hot period. Cracked or split shingles will need to be replaced. 

3. Blistered Flashing Seals

The metal flashing around chimneys and other rooftop penetrations is usually sealed in place with some type of adhesive. On newer roofs, the sealant is usually made of flexible polymers combined with roofing tar. The problem is on older roofs where only tar may have been used as a sealant. Tar alone can dry out when exposed to extreme heat, which will cause it to blister and peel away. Resealing the flashing may be necessary.

4. Buckled Shingles

Buckling shingles are more often caused by ongoing moisture exposure, but sometimes heat can be the cause. If there are no leaks that have allowed moisture under the shingles, and the shingles still have a strong waterproof coating, then the issue may be rapid temperature changes. When nighttime temperatures are very cool, but daytime temperatures are quite hot, thermal shock to the shingles may cause them to buckle. Replacement is usually necessary.

5. Popped Nails

Thermal shock can also cause problems with roofing nails. During the cold winter months the shingles contract, gripping the nails tightly. When a heat wave comes on suddenly, the shingles expand and the nails loosen a bit. This is becomes a problem when more cold follows the heat, as the now looser nails can be pushed up out of the shingle if it contract quickly.

Contact a roof repair contractor if you suspect heat has damaged your asphalt shingles.