Everyone says low pressure
Read any five companies in this market and all five will tell you they use low pressure on roofs. It's the most repeated phrase in the industry. What almost none of them do is put a number next to it, and without a number the phrase means whatever the person saying it wants it to mean. Fifteen hundred PSI is low compared to four thousand. It's also more than enough to do damage to a roof.
So here it is: the roof never sees more than 70 PSI.
What 70 PSI actually feels like
It's roughly what comes out of a garden hose. If you've ever rinsed a car or watered a bed by hand, you already know exactly how much force that is, which is to say not much. It comes from a battery-powered pump, not a gas engine, so there's no loud machine running in the driveway for hours while the work happens.
Put that next to the other end of the range and the gap is the whole story. Concrete, sidewalks, curbing and pavers get 3000 to 4000 PSI. That's the correct number for those surfaces, and it's roughly fifty times what the roof gets.
The fear this actually answers
The real worry isn't a number on a spec sheet. It's a cracked tile you can't see from the ground, that turns into a leak in two years, that nobody wants to take responsibility for by then. That's a completely reasonable thing to be afraid of, and it's why people hesitate on this job more than almost any other exterior work.
Here's the part that answers it properly: the roof isn't cleaned by force at all. Not at low force, not at any force. The cleaning solution breaks down the growth at the source. The water's only job is to rinse what's already dead off the surface. There is nothing in that process applying enough force to crack a tile, strip a granule, or drive water anywhere it shouldn't go, because force isn't the mechanism doing the work.
That's a different claim from "we're careful" or "we use low pressure." Careful still implies something forceful is happening that requires care. This is a method where the forceful part was never there to begin with.
Nobody walks on the roof either
Worth saying separately, because on tile especially it's the bigger risk of the two. Plenty of tile damage in this region comes from the weight of a person moving around up there, not from anything sprayed on it. A roofer will tell you the same thing, usually more bluntly.
Both the solution and the rinse reach the roof from the ground. There's no reason for anyone to be on it, which removes that risk entirely rather than managing it.
Shingle
Asphalt shingle is protected by the granules embedded in its surface. Those granules take the sun and the weather so the material underneath doesn't have to. Real pressure strips them off, and they don't grow back. A shingle roof that's been pressure washed can look dramatically better the same afternoon and be measurably worse off for it.
At 70 PSI there simply isn't enough force to move a granule, which is the entire reason the number is that low.
Tile
Tile handles weather fine. It's been doing it on these roofs for decades. What it doesn't handle is concentrated force or the weight of someone standing on it, and a cracked tile is often invisible from the ground until water finds it.
Since nothing about a soft wash involves force or foot traffic on the roof, tile ends up being one of the surfaces this method suits best, not one that requires extra caution.
Metal
Metal is the most forgiving of the three, and it's the one people worry about least, usually correctly. It still has a coating on it that isn't worth testing against high pressure, and the growth that lands on it responds to the same treatment as everything else. The legacy approach of writing metal up as its own special case was always a bit beside the point. Same method, same low-pressure rinse.
So where does 4000 PSI belong?
On the ground, on hard surfaces built to take it. Concrete, sidewalks, curbing and pavers all need real pressure, because the growth on them works down into the texture and the joints rather than sitting on top the way it does on a smooth surface. Low pressure would leave most of it behind.
That's not a contradiction with the roof number. It's the same principle applied honestly: the pressure gets matched to the surface, which is why there are several different numbers instead of one setting used on everything. A company running the same pressure across a whole property is either underdoing the driveway or overdoing the roof.
What to ask anyone quoting your roof
Ask for the number. Not "do you use low pressure," which everyone answers yes to, but what PSI actually goes on the roof and whether anyone will be walking on it. The answers to those two questions tell you more about how a job will go than any amount of description.
Common questions
Isn't higher pressure just going to clean it better?
On a roof, no. Force knocks the surface layer of growth off and leaves the rest alive to come back, so the result looks good briefly and doesn't hold. Treating it properly lasts longer and costs the roof nothing.
Can 70 PSI really get a badly streaked roof clean?
Yes, because the rinse isn't the part doing the cleaning. By the time the water touches the roof, the growth has already been dealt with. The rinse is just removing what's left.
What pressure goes on my house exterior, then?
Exterior soft wash, meaning soffit, fascia, pool cage screens and home exteriors, runs 900 to 1200 PSI. Higher than the roof, well below concrete, because that's what those surfaces call for.
Get the number for your roof
Text a photo from the street and you'll get pricing back the same way, with a straight answer about what goes on your specific roof. No appointment, nobody in your driveway to give you a number.