Sun Angle Decides What a Roof Inspection Can See

A roof inspection is mostly a matter of seeing. The inspector needs to see whether each tab lies flat, whether granules have washed into the gutters, whether a flashing has lifted at its top edge, and whether a crack runs through the rubber of a vent boot. None of those things show well in every light. The angle of the sun on the day of the visit can make a sound roof look worn, and a worn roof look sound. For a St. Louis homeowner waiting on an appointment, the time of day is a small question that affects what the photos can prove.

Why low sun shows more than high sun

When the sun sits low, usually in the first hour after it rises or the last hour before it sets, every raised edge throws a shadow. A shingle tab that has lifted a quarter inch from the course below will show a dark line along its underside. A nail head that has backed out of the mat will catch the light. Granules that have worn off the surface reveal the asphalt beneath as a flatter, darker patch. Those details are the evidence an inspector photographs. On a slope facing the same direction as the low sun, the shadows are longest and the relief is clearest.

Low light also reveals texture. Blistering and cupping look like faint bumps at noon and like clear ridges at a low angle. The inspector can photograph them from one side and note the change in the report.

What noon glare hides

Around midday the sun sits nearly overhead, and most shadows shrink to nothing. Lifted tabs look flat. Granule loss can look bright, because bare asphalt reflects light differently from the granules around it. On a dark shingle in July, the surface can be hot enough that a careful inspector will move slowly and may not walk the steepest slope at all. Noon is not a bad time to walk a roof, but it is a poor time to judge a slope from the ground through a camera lens.

Glare also hides the difference between a fresh repair and an old one. A patch sealed last spring and a patch that has been lifting since winter can look the same at the wrong angle.

Which slope gets which light

A house has at least two sun-facing sides, and in St. Louis the south and west slopes take the most heat across the year. The north slope gets the least direct sun, so its shingles stay cooler and its shadows stay longer. A reading taken on the east slope in the morning may look different from one taken on the west slope in the afternoon, even on the same day. A thorough inspection covers every slope, and the photos should say which light each one was taken in.

This matters for the freeze thaw cycle too. Shingles on the north side of a house may hold frost for days after the south side has thawed. A slope that stays wet longer can show different wear from a dry one, so the inspector should note the time and sun position in the report rather than assuming every slope was seen the same way.

Trees and neighboring roofs cast their own shadows

Mature trees on a St. Louis lot can block the morning sun from one slope for most of the day. A shaded slope can look cleaner in photos because the light is soft, and it can also hide algae, moss and early granule loss that would show clearly in sun. Neighboring two-story houses can do the same thing to a lower roof. If a slope was mostly in shade, the report should say so, so that a clean photo is not read as a clean roof.

What to ask before the inspection day

You do not need to know the sun's position to ask about it. A few plain questions will tell you whether the visit is set up to see the roof properly.

• Which time of day is the inspection scheduled for, and which slopes will be photographed in that light?
• If a slope is in shade for most of the visit, will the inspector come back for it or note the limit in writing?
• Will the photos be taken from the same position on each slope so you can compare them later?
• Will the written report list the time and the orientation of each photo?

You can put these questions to Keys Roofing at (314) 220-2333. The answers belong in the written scope, next to the photos and measurements, so you have them when you review the findings. The inspection does not decide whether you need a repair or a new roof. It gives you a record of what was seen and in what light, and you can use that record with your own judgment and with any other contractor you call.

Reading the photos you get back

When the photos arrive, look at where the shadows fall. A lifted tab should show a shadow along one edge in a photo taken in low sun. If a slope looks flat and bright, check whether it was photographed at midday. A photo taken in shade is not proof that the slope is sound, and a flat photo taken at noon is not proof that it is damaged. Ask for the time stamp on each image and set the photos side by side by time of day.

Keep the photos with your roof log. If the same slope is inspected again in a year, a photo taken in the same light will show change more clearly than one taken at a different hour. You do not have to be a roofer to compare two images. You only need the time and the slope for each one.

Scheduling around the light

In practice, a morning visit tends to show the east and north slopes with the most relief, and an afternoon visit shows the west and south slopes. The inspector sets the visit window, and that is reasonable. What you can do is ask for the time, ask which slopes will be photographed in that light, and keep the answers in writing. The sun does not change what the roof is, but it changes how much of the roof the photos can show.