What Is Considered Low Pressure for Roof Cleaning?

By Mark Cave May 29, 2025

What Is Considered Low Pressure for Roof

In the UK exterior cleaning industry, there’s often confusion about what counts as “low pressure” when cleaning roofs especially when using standard jet washers. Many professionals claim to be “softwashing” with a pressure washer turned down low, but in reality, most machines can’t reach the truly gentle levels that roof tile manufacturers recommend.

🔧 Typical Pressure Washer Output in the UK

Most commercial jet washers in the UK operate at high pressures by default. Below are some typical values:

Maximum Pressure: 150–250 bar (2,175–3,625 PSI)
Common Mid-Range Pressure: 110–160 bar (1,600–2,300 PSI)

Pressure washers such as the Interpump WS202, widely used in exterior cleaning, operate up to:

200 bar / 2,900 PSI (at 21 LPM)

With a standard pressure regulator (unloader valve), these machines can usually be turned down to:

Minimum Adjustable Pressure: Around 30 bar / 435 PSI (best case with good TRV setup)

Even at their lowest regulated setting, this is still far too aggressive for delicate roof tiles.

🏠 What Do Roof Tile Manufacturers Recommend?

UK roof tile manufacturers such as Marley, Redland (BMI), and Sandtoft are crystal clear:

“Use only low pressure no more than 4–5 bar (60–70 PSI) and avoid high-powered jet washing entirely.” Roof Tile Association (RTA)

This means standard pressure washers simply cannot reach the safe pressure levels required for cleaning roofs without damaging tiles, seals, or coatings.

💡 Can Jet Washers Be Used for True Softwashing?

While some pressure washers claim variable pressure, they almost never go as low as the industry’s safe range of:

4–5 bar (60–70 PSI)

At best, turning a jet washer “down low” means 25–30 bar (350–450 PSI) — still several times too strong. This level of pressure can erode tile coatings, strip protective granules, and force water under tiles.

✅ Use a Softwash Pump

If you want to comply with roof manufacturer guidance and perform true softwashing, you’ll need a pump designed to operate at low, safe pressures:

Softwash pumps operate at 40–100 PSI (2.5–7 bar)
Safe for all roof tile types when combined with correct chemicals and dwell time

Softwashing systems such as diaphragm pumps or booster pumps, often paired with Dosatron injectors, allow you to apply a cleaning solution at gentle, controlled flow rates — removing grime and organic matter safely.

🚫 Don't Be Fooled by "Low Pressure Jet Washing"

Some contractors claim they’re “softwashing” when they are simply pressure washing with the power turned down. Unless you're operating below 5 bar (70 PSI), you are not softwashing.

Proper low-pressure cleaning requires the right setup and most importantly, following manufacturer guidance and safe working methods.

🔍 Final Thoughts

If you want to clean roofs without damaging them and stay within warranty safe practices it’s vital to understand pressure limits:

💧 Standard jet washers: too powerful, even on “low” settings
🧼 True softwashing: 60–70 PSI with chemical application, rinse, and dwell time
🛡️ Roof tile manufacturers do not recommend jet washing

If you want to comply with best practices and avoid voiding roof warranties, invest in softwash equipment that’s built for purpose not just a pressure washer dialled down.

Need help choosing the right softwash system?
Visit SoftWash UK for expert advice, training, and CPD-certified courses on safe roof cleaning techniques.

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Soft Wash Calculator App

Now you can say I've got an app for that!

Available NOW Click Here To Download

Softwashing calculator is an indispensable tool for juggling complicated chemical mixes. It helps reduce wastage and keeps operating costs down by giving accurate proportions

If you are having difficulty getting your head around the maths, trying to work out what percentage of softwash you need, how much chemical, surfactant and water to add, then this is the App for you.

The Soft Wash Calculator App allows you to work out your soft wash recipe by telling you exactly how much chemical, how much water and how much surfactant to add to get the desired soft wash recipe.
It doesn't stop there!.
- It can also remix your leftover softwash to a new stronger or weaker recipe.
- all controls in one place for see at a glance operation
- ease of input via pre-loaded dials. no more calculator style typing
- instantly responds to changes of complex combinations
- works in both Litres and US Gallons
- tested for Protan and Deutan colourblind users
- links to SoftwashingUK website

Take this scenario
You started with a 1% soft wash recipe of 50 gal (or litres) for a deck clean and you’re left with 13 gallons.

You get a call from a prospective customer to clean their roof. Past experience tells you a 4% soft wash recipe is needed, but what about your leftover mix at 1%?.

Do you waste time and effort driving back to base to transfer into a standby tank?
You could consider the 13 gal as just water, top up the tank and start again.
But that’s throwing away the value of the mix and raising your overhead.

Soft Wash Calculator App to the rescue.

You get to the new job and it requires 100 gal / litres.
Switch into remix mode , confirming the 13 gal already in the tank
Move the dials to your new recipe and the app immediately updates the different amounts to add in front of your eyes including the correct amount of extra surfactant.

You now have a 100 gal / litres tank of 4% soft wash recipe ready for your roof clean job!

Not forgetting you’ve saved money too, all without stress and uncertainty . Don’t underestimate what confident calmness has on your customer putting out referrals.

The same applies if you have a 4% recipe left in your tank and you need to dilute it down to 2%. Again the app will tell you how.

Softwashing calculator will also work for any chemical recipe. For instance you can use it for Sodium Hypochlorite, Bleach, Biocide , TFR traffic film remover and degreaser. Even the mathematically-challenged rocket scientist can top up their booster tanks to new fuel mixes after launch delays caused by changing weather conditions.

Using this app you will know exactly what chemical strength to put on any surface giving you the confidence and the knowledge of a professional soft washer and you’ll save money as well.

So if you have little knowledge of how to mix a soft wash recipe then this app is for you.
If you have little knowledge of how to remix a soft wash recipe then this app is for you.
If you want to save money when mixing a soft wash recipe then this app is for you.

This app is also backward compatible to devices running iOS7. We've done this so you can re-purpose an old iPhone 4 or iPod Touch 5 for what could be hazardous work environments. Just toss one in your cleaning van's toolkit.

Once you learn the methods and procedures of how to apply the soft wash to the different surfaces that need cleaning you’ll be unstoppable!

The app also has a guide to what percentage for what surface. And if you are the lucky owner of a Clever Injector it will remind you the correct setting for the job.
However you should always consider and risk assess what soft wash recipe you need to clean the surface.

** A major iOS code-base change may require a re-purchase. The appiverse at the time will confirm our promise that we won't do so unless the necessity is apparent.

01733 736191 Voicemail