Roof power/w

I just thought i would open a discussion in regards of roof power washing.

Power washing moss and dirt etc, off roof slates.

I have noticed alot of roofs that could do with such work carried out and am thinking of giving this service a go.

So if anyone has any thoughts or info, or if they carry out such a service i would love to hear from them on this thread… i think i was on someones website from this forum a few months ago and saw they offered suh a service, PM’D them but got no reply, so i know such a service does exist.

p.s there is for the most part pitched/gabled rooves where i am based, so would be mainly concentrating on them.

Topics covered could be:

-access to pitched or gabled rooves (how you actually go about power washing on a roof, what ladders to use in assisting the job, ropes and so on)

-safety concerns?

-marketing of such a service (what benefit does such a service have for the customer, i.e is such a service carried out just to improve apperance of roof or can i market the service by saying that it improves lifetime of the roof slates?)

-what p/w system do you use?

-how long does/would such a job take per sq foot. is it a messy job


-is there a viable market for such a service?

-is it just power washing to be xarried out on the roof, or can we treat roof slates to prevent future growth…chemicals

-also do you just clean down surface of roof, or do you power wash into the nooks and crannys between slates to remove slime?

  • anything i should look out for/investigate further?

-websites/ pictures…before/after?

Anyway as i said only thinking of trying this out, don’t have a clue what i am talking about so any help/advice is appreciated.



You don’t need to use a pressure washer. Infact, a pressure washer will harm the roof. You only need a roof cleaning solution and a means of applying it on the roof with low pressure.

The most common roof cleaning solution is 12.5% sodium hypochlorite at a concentration of 30% mixed with water. There are other chemicals to aid in cleaning or to prevent the moss and algea from coming back, but the 12.5 and water are the main ingredients.

Sodium Hypochlorite can kill plants. It’s a very dangerous chemical if not used properly and safely. You will need to pre-wet all plants, keep them wet, and then do a final rinse.

I can post more later, but my battery is going dead…

Hey Rob,

Like Micah said, a good mix, ( I use 12.5 % Sodium HypoChlorite, water, and a good soap like Dawn for the surfactant). We spray down all , surrounding vegetation and landscaping super super good, and we’ll put a hose left running next to the downspout, where the water coming out of the gutter will be constantly diluted.

We then spray down the roof, starting from the bottom and going up, let it dwell far a while, and if you use a Pressure Washer, you’ll need a limiter valve tip to bring the pressure down to maybe 300 psi, so as not to knock the grit off, and basically rinse off.

Here are some pics of a few roofs we did. Any questions ask away.


Ok thats great.

Thanks to both of you

So tell me if i have this right?

You spray down shrubs and plants in the garden? Is that what you are saying?
Is this so that if the chemicals hit the plants they wil be diluted?

Then do you spray on the chemicals to the roof with a spraying apparatus (non mechanised)?

If the roof is very dirty how do you go about scraping off muck and moss and thick algea or does this just come off with the solution?do you scrape before initial treatment with chems.

After you have sprayed the roof with the chemical, what happens?, are the chemicals rinsed off or is the roof just left like that?

Also how do you guys go about getting around on the roof? do you use roof ladders…how would you go about this on a very steep roof(as most are around here)?

thanks guys appreciate the help.

J.Racenstein Co. has a stain remover named BioWash (page 60 in 2008 catalog) removes bacteria,fungi,algae,lichens, and mosses. Safe on landscape plantings and grass. I have never used it, but seems like a safer alternative to some of the other products. Maybe worth checking out and finding a local distributer. Has anyone used BioWash if yes, on what surfaces and what was the result?

Rob, take a look HERE and get reay to spend some time reading there. It’s a lot of info and easy to understand once you get the general idea of how it works.

Rob, if your serious about roof cleaning, you’ll want to look into one of these…

I’ve demo’d the Bobcat, and it’s the best thing I’ve seen for roof cleaning (really, any kind of low pressure cleaning). Very quiet, can even be ran upside down.

I have used 12v sureflow pumps to apply the chemical. The problem is sodium hypochlorite, often times just referred to as 12.5%, is very corrosive and will eat through those pumps in no time. You need a special kind of pump, like a 12v Delevan, or the Bobcat, to last.

The problem with using a pressure washer is many people will assume you’re using full pressure. Even though they can be used safely, many people don’t know this and won’t let you touch their roof with a pressure washer, at least around here. In my opinion, a 12v pump or the bobcat are much easier ways of doing it too.

The First and most important thing you need to do is get insurance, Good Luck.

Cheers guys, as i said i am only looking into it at the moment.

I will have a good look at those websites and articles.

I am pretty excited with the prospect of offering such a service.

selling roof cleaning is not easy. And removing what you said was on the roof’s you see is a process that many will not pay for.

Wow that link is particularily helpful/relavent.


Yep Rob.

Just keep in mind that the guys that do this everyday usually have a helper… It’s more a two man job because you really need somebody on the ground watering plants.

Will bear that in mind Micha. Thanks for all the advice.

Early days yet anyway, will see where my research takes me

there is great info to learn there. If you have any questions pm me.

Get yourself a copy of Kevin’s book.

Actually it can be very easy to sell. Showing them before and afters of past jobs helps build confidence. Showing the equipment that you’ll use, the amount of pressure that you use also builds confidence. Explaining that it will add life to their roof builds a call to action. Many people don’t know that the algea is actually eating their roof.

I have done some power washing of roofs and I must say do not do it with a power washer. If you do, use a hot water machine and use a flat surface cleaner up there. However, the much more efficient and safe method is the one described with bleach and a low pressure system. Make sure to keep plants and all vegetation completely wet because bleach has a way of clinging to whatever it touches (as far as vegetation) if the surface is dry on contact. By keeping a wet layer, it helps the chlorine not attact to the surface so damage doesn’t result a few hours after the job.

A pressure washer and a flat surface cleaner will destroy a roof. You’ll remove the granules from the roof and have to end up replacing it. If you use the chemical mix and ‘no pressure’ it runs off the roof like melted butter, even the moss.

where i am from it is not an easy sell. you would think with all the roofs that need to be cleaned around here it would be easy. to stay in business you have to maintain a certain price range for different sized jobs. people who have had it on there roof for a number of years are reluctant, but people who have just witnessed the growth within a few years are quicker to want cleaned due to the fact of not being used to seeing it.
also i would not recommend using a surface cleaner or a power washer, these will remove granules from tile.

if your using a chem to water mix that is removing moss “making it slip off like butter” it is too strong. moss and lichen should not fall right off.