Do Not Pressure Wash Your Roof Before the Inspector Sees It

A pressure washer is a quick way to make a roof look newer before anyone has checked it. It is also a quick way to make the roof harder to read. If a washing crew has been on your roof this year, or you are thinking about booking one, hold off until the inspection is done. The problem is not that washing always causes harm. The problem is that the inspector needs to see the shingles as they are, and a high-pressure stream changes them.

Inspection

Asphalt shingles carry a layer of mineral granules on the top side. The granules shade the asphalt mat from the sun and carry much of the weathering protection. A stream of water at high pressure can knock granules loose, and it can do that unevenly, so one slope may lose more than the next. What the inspector sees afterward is a bald patch that looks like wear. It may be hard to tell apart from storm marks, or from a shingle that was already aging. Once the granules are gone, the record of that slope's condition is harder to read.

Water also goes places it does not belong. A nozzle aimed up under the lower edge of a shingle can push water past a sealant strip that is already weak. It can get under laps near the valleys, around the pipe boots, and along the chimney flashing. Much of that water drains away on a dry day. Some of it stays in the underlayment, and in St. Louis that matters in winter. Water that sits in a joint can freeze, and the freeze can push the joint apart. An inspector who arrives after a wash may find wet decking or stains and have no reliable way to say whether they came from the wash or from the roof itself.

The wash also changes the roof's appearance in a way that matters later. Dark streaks from algae are common on local roofs and usually come from the shingle surface, not from a leak. A wash removes them, which is usually the reason people book it. But the same wash can expose areas that were lighter and less protected, so the surface looks uniform while the condition underneath has changed. An inspector who has to tell those two things apart needs the roof as it was on the day of the visit.

The inspector also checks things a washing crew does not look at. A wash does not lift the tabs on the north slope, read the valley metal, or check the nail line at the ridge. If you have already had a wash, tell the inspector the date and the method, and photograph the gutters and downspouts before anything else is moved. A dated photo is useful even when the roof looks fine.

Timing around the season

St. Louis roofs go through freeze and thaw cycles all winter and take hail in the spring and early summer. An inspection in the fall, after the leaves are down and before the first hard freeze, gives the inspector a clean read of the shingles. A wash in the same window may be fine for the roof itself, but only once the inspection report is written and in your hands.

Spring is when hail season arrives, and a roof washed in spring leaves the inspector less to compare against once the storms have passed. If you expect to have the roof checked again after a hailstorm, keep the first report and the photos from the walk. Those photos are the baseline that the next visit will be compared against. Without them, the second visit starts from whatever the roof looks like that day, and the washing becomes one more thing nobody can account for.

What it costs

A wash and an inspection are not priced the same way, and the cheaper one is often the one that gets booked first. A wash is a line on a crew's schedule. An inspection is the step that tells you whether the roof should be washed, repaired, or replaced. If the wash goes first and the inspection then finds a worn valley or a cracked pipe boot, the repair costs the same as it would have before. What changes is that you no longer have a clean record of how the roof looked before anyone touched it.

There is also a cost to the roof itself. Granules that come off in a wash do not grow back, and a slope that has lost them ages faster from that point on. That shows up in the years after the wash, not on the day it is done. You are not paying for the wash today. You are deciding how much service life the roof has left, and the inspector's notes are the only written baseline you will have for that decision.

To book the inspection, call (314) 220-2333 before you book any washing crew. Ask the office what the visit includes, including whether you receive a written report and photos, and get the answer in writing before the appointment. If a washing company offers a discount for bundling the wash with roof work, ask what the discount is taken off. A number that only makes sense after the wash is not a number you can compare against another bid.

What to ask

Ask any washing company these questions before they start. Ask your roofer the same ones if the wash is part of their proposal:

1. What pressure and nozzle will you use, and will the wand be held above the surface or aimed up under the shingle edges?
2. Will you spray the gutters and fascia from the roof, and where will the runoff go?
3. Will you wash any slope that the inspector has not yet walked?
4. Can you give me a dated before and after photo of each slope, sent to me as original files?
5. Does your written estimate say who pays if granules are lost or tabs come loose during the wash?
6. Can the wash wait until the inspection report is in my hands?

Soft washing is a different method from high-pressure washing. It applies a cleaning solution at low pressure, with the aim of removing algae without driving water into the shingles. Some crews do this carefully. The better question is not whether a crew says it uses a soft wash. Ask whether they can show you the pressure setting on the day, and whether they will stop if they see granules coming off in the runoff.

Ask your roofer what they plan to do about washing before any roof work starts. If the wash is part of the scope, it should appear on the written proposal as a line of its own, and the inspection should come first. If you still want the streaks removed and the wash is not part of the roof job, a separate crew can do it on a day you choose, after the report is in your hands. Put the wash date on the calendar next to the inspection date so the order is never in doubt.