Being on your roof during our hot Houston summer may cause damage to the roof, but it may hurt you too.
I go up on roofs. I have to, since it is part of the home inspection process. There are a few outs that I could take if I wanted. The state has in its rules that I am only required to have a ladder which reaches the roof of a one story home. I also do not need to go on a roof if I deem it unsafe. I know from experience that a report from a person looking at the roof from the ground or from a ladder does not carry as much weight as a report from a person who goes up on the roof. Although I have been going up on roofs this summer, there is a good reason as to why I should not: the heat.
I burned my hand by touching a roof. I generally take precautions, but I did not heed my own protocols once. Lesson learned. Your outside temperature may be in the 90s, but your roof surface could be 135F or higher. If you have a breaker on your air conditioning compressor that is on the roof, you may find your AC shutting down. Breakers on these units trip when the temperature is above 135F. This is not common on a residential structures, but commercial buildings face this problem often. To deal with this surface temperature, I wear gloves. I like mechanics gloves, since these give me flexibility when examining parts of the roof during an inspection. Other precautions that I take is to plan my ascent. This sounds like mountain climbing, but you need to think about the pitch of the roof, how you will be getting on, and how you will be getting off. I walk around the building looking for a safe spot. If there is a valley between two roof planes, I find this to be a good spot. Any flat or lower pitched area is also good. When the pitch is at a steeper angle, coming down can be problematic (great for the life of the roof though). You need to be able to step on and off the ladder easily. If possible, using a bungee cord to hold the ladder to the home is wise.
How can walking on a hot roof damage the surface? This applies to any roof covering that uses a composite material. Composite shingles use asphalt as a base. The asphalt melts with the heat. A misplaced step can damage the shingle. There are a few factors that come into play, but you could tear or break the shingle. The bigger problem is what you may be carrying up on the roof. With the shingle being softer due to the heat, a falling tool is likely to cause damage than a step. If the shingles were not well installed, you are more likely to have a damage occur.
A note about ladder placement. If the home has a gutter, try to find where there is a fastener. You can see the head on the face of the gutter, but you can also see the nail going into the fascia in the gap between it and the gutter. Place the legs of the ladder to straddle this fastener. This causes less damage to the gutter with better support for the ladder. If there is no gutter, you can place it anywhere, but control your ladder. Letting it fall against the roof edge can damage the shingles or the bit of flashing that helps the rain fall away from the fascia. Also, have a good ladder that is the proper size. The ladder should go beyond the edge of the roof. If you are concerned about storage, I use collapsible ladders for work.
Be safe. Plan out the steps for climbing up on the roof. Even a low pitched roof can present dangers, but I am seeing many homes with higher pitched roofs, which is good for the home, but bad for safety. Just realize that bare skin on a hot asphalt roof can lead to injury.