Need the 411 on cleaning roofs

Haven’t done any of this & don’t want to “de - grit” a roof.

Going to get Shingle Shield & a pressure washer.

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IIRC, max PSI from a hose is 60 to 65 PSI & this stuff calls for 85 PSI. I guess this means to make sure the nozzle is backed off sufficiently enough to prevent grit loss, right? I’m estimating the roof @ around 10 years, 4:12, no ridge vent - has 1 turbine, 1 static ‘turtle’.

Once the roof is cleaned (mix w/ water, heavily water down drip line, bug sprayer to apply, wait 30 min. per section, clean with pressurized water), we’ll be going back on with zinc strips & I need to find out from the customer if he wants a ridge vent or the solar powered units we discussed.

So, give me your insight to roof cleaning.

PS: Geaux Tigers!!!

I normally strongly recommend against power washing a roof.

It can be done by someone who knows what they are doing.
I think you will be fine.

Depending upon how bad it is the roofs life is shortened by moss/algae growth, and it will shortened by granule loss from power washing.
6 of this a 1/2 dozen of that.

Why don’t you try the zinc strips first? Then rinse?

I would never pressure wash a shingle roof, but I’m just a salesman. I probably recommend a new roof.


James, please pardon my upturned nose but that is precisely why IMO “just a sales person” isn’t always the best candidate (although if I had a sales person who I could rely on, then maybe… just maybe I’d be doing more work, so what do I know).

This is a 10 year old roof.

That means zinc won’t do anything other than prevent FUTURE staining & algae blooms / mossy buildup. You have to clean it FIRST to get down to the base shingle minus algae growth / buildup, & THEN add the zinc to prohibit any future blooms.

The 10 year old roof also means the grit content is a bit degraded & more prone to being damaged than a freshly laid roof.

A benefit to me is that the roof is only a 4:12 for a large portion & 1:12 to the rest… that means we won’t be placing a lot of pressure on the shingles as it’s walked. Of course I won’t be pointing the wand up slope…

As to power washing it, IMO the best thing I can do is to make sure the right nozzle is selected & keeping the tip @ least 18" away from the roof deck (maybe a bit further… will have to be really careful here, obviously).

If anyone has any suggestions as to the proper distance from the roof, I’d like to hear from them.

I’m with the don’t do it crowd. Pressure washing a shingle roof is not a good idea. Check with the shingle manufacturer before doing any pressure washing to make sure your aren’t voiding the remaining warranty.

Donl, I’d agree if someone intended to put the wand tip really close to the shingles, however I am going to back it off & only get in there enough to get some cleaning action.

I know there HAS to be someone else on here who does roof cleaning… they just might not have clicked in or added their .02 cents.

With 100+ views, there has GOT to be a viewer who has done this before.

Where’s my usual suspects? Marshal? Axiom? RooferJ? Bushhog (btw, where has he been these past few weeks anyhow?)…

Well Ranch I gave you my opinion.
If somebody asks about power washing their roof I strongly recommend against it.

You on the other hand are an experienced roofer.
You know the dangers/pitfalls.
You know the precautions that you need to take.
If you do this YOU should be the one doing it, personally…
It is kind of like giving a torch to an employee with minimal experience…

If it is a Timberline roof, it is going to lose a lot of granules no matter what you do…
Have you ever noticed how many loose granules are in a Timberline package?
They don’t stick too well to begin with.
Power washing the roof is going to take some of the life out of it.
How much depends upon how bad the existing moss/algae is.

This is definitely not something you want to actively sell to the general public.

Axiom, I DO appreciate your opinion, that’s why I’m engaging you in a discussion about it.

I also know there are a LOT of people that do it. This particular house is a 3T, no idea on the mfg, & he’s trying to extend the life a bit.

There is a heavy tree canopy & IMO, the subsequent algae from condensation not burning off is causing more blooms than would result from a safe & proper cleaning.

It will be me & one of my guys from the crew doing the work. I will NOT let them fly solo on this as I’m the one holding the liability should any part of it go wrong while on the roof or months downline.

I was, however, hoping a fellow roofer out there who DOES do this would have chimed in by now… alas, no luck. Yet. :slight_smile:

A good stiff broom and a regular garden hose should do the trick.

I think that you already know that power washing is going to shorten the life of the roof.
Can’t really get around that one.
Have you told your customer this?
It will of course look much better during the remainder of its shortened service life.

Moss and algae tend to get embedded in the granules.
If you scrape some off with your finger I am confident that you will see that granules will come off also.
They will come off if you broom it also, just not as bad.

If this is what your customer wants there is nothing wrong with doing it provided that you inform them of the consequences.
Put it in writing that they requested it and that they were informed of the consequences.
They may just want the roof to look good for a few more years before getting a new one, nothing wrong with that.
But if they think this procedure is going to extend the life of their roof, they are mistaken and should be so informed.

There is/was a landscaping company in my area that sells this “service”.
From what I gather they sell this as an improvement.
In my mind this approach closely resembles fraud, ignorance at the very least.
I saw them doing it a couple of times last year.
The homeowners don’t seem to connect the power washing of a few years ago to the need to replace their roof sooner than expected.
Until it is explained to them, then you can see by the look on their face that they just had an epiphany.

Full disclosure is the key here.
If they still want this done after you explain this to them, have them sign the disclaimer and go ahead.
Or they will just have somebody else do it, or worse, do it themselves.

Keep in mind that if any of your local roofing brethren see you doing this you are going to be thought of as an idiot.
Or there may be a potential customer in the area that knows this should not be done, you probably won’t get a call from that one when the time for a new roof arrives.

Do you have a picture of this algae?
How bad is it?

I have a large weeping willow tree in my front yard.
As a result 1/2 of the backside of my house has this problem.
It is very bad, this is more of a blue/green lichen and it does not come off.
I tried to broom it once but it is part of the shingle now.
The shingles are fine, they have been like this as long as I have lived here.
It is in the back so nobody ever sees it.

Go to the Power Washing Institute or Power Wash Network and visit the roof cleaning boards. All the info you need is available. They use a mixture of bleach, TSP, and borax, diluted with water and applied with pumps at very low PSI. Pressure similar to what comes out your garden hose. Never pressure wash a roof.

Did you do it Ranch?

Certainteed recommends the following:

  1. Mix a solution of 1 part chlorine bleach, 3 parts water, and a pinch of trisodium phosphate(known as tsp).

2.apply this solution GENTLY to the surface of the roofing.

  1. Avoid scrubbing as well as other physical contact with the roof because the friction may loosen and remove granules that coat the surface of the asphalt shingles.

  2. Finally rinse the bleach from the roof by GENTLY spraying the surface with water.

CAUTION: high-pressure washing systems for algea removal should be used only by reliable professionals because incorrect application can result in removing and shortening the life of the roofing system.

I got this info straight from the Certainteed Shingle Applicators Manual Eight Edition.

I noticed that I’m a little late on this conversation, but I was once a sketptic of roof cleaning. After doing the first one, I am sold on how great an old roof looks once it is cleaned. Any roofer with common sense can use a pressure washer to clean a roof. We know what too much pressure is. I started out with trying Bleach, water and tsp mixtures and found that they just didn’t work for me. Bleach is funny about leaving a white residue on the granules. I am trying to get that diamond cut back to reflecting again. I have been using Shingle Shield, following the directions to the “T” and have had fantastic results. I modified a Simpson BD series 2700 psi down to about 700. I think SS calls for 350psi? Just back off, change your tips and you will be fine. I also include doing any caulking, painting and fish mouth repairs with my cleanings. One of the best examples was a church on IH 59 just outside of Houston. Tree fell on one slope. We replaced the slope and cleaned the rest of the 10yr old black stained roof. You cannot tell which is the new shingle and which is the old. Oh yeah, It was golden cedar, sentinal…

In closing, I feel that if you have a 10yr old roof with staining, you have nothing to lose by cleaning it, but everything to gain. Not only does it give life back to the shingle, it alos brings back the new appearance. We paint our homes, mow our grass, why not clean your roof? I have a 12/12, 1.5 story home with a 40yr Sablewood. I clean my roof at least once a year with shingle shield. I bought a 25 gallon tank with a 2hp pump, sprayer. We mount it to a 4 wheeler and it will spray right at about 35 to 40 feet. You can spray your solution from the ground. Let it sit and just hose it off with your homes hose bib pressure. A little preventative maintenance goes a long way. I guess you know where I stand on this.

If you did pressure wash it, what would you charge a square?


Rooferama do you have any pics you can post I’d like to see how well it does?

Sorry for not posting on this thread recently; for some reason, my notebook (the one I use up in the living room end of the house) woudln’t let me log in & I wasn’t able to get the time to go in the office due to time issues.

We’ve got two little kids (both under 3) & when I’m in the living room preventing nuclear war, I surf & post from the notebook. Time in the office is 99% estimates & work.


We did the cleaning. Used two quart bottles of Shingle Shield - I had bought it about 1+ years ago to try on my in-law’s house, but never did the job because I was unsure about the water pressure situation. Their roof is really REALLY badly stained due to a large canopy of Oaks on all sides but North, so the condensation never gets burned off.

Back to the paid job. This was a 16sq 4:12 / 8 sq .5:12 or less, really more of a ‘true flat’.

@ First, I had the mixture off because on the bottle it says “@ 1:1 ratio, this mixture becomes inert” but I didn’t spot the “inert” part & our 1st sprayer full was too thick a mix, I think.

I will also get a larger sprayer for the next roof because the one we used needed constant re-pressurization since it only held a smaller quantity of product.

We rented a pressure washer from ‘Big Orange Box’ - the smaller of their gas powered units, & did the 24 hour rental because I figured I’d clean off my porch & sidewalk while I was @ it. The job took over 4 hours, anyhow, so that was a good thing (their rental program for it was 4 hours or 24 hours).

I also got a 2nd jet hose (goes between the sprayer & the unit) so I wouldn’t have to worry about repositioning from the ground. It really was a 2 man job because the hose is so heavy, it pulled on the spray operator & would get in the way a lot.

The roof came out very good & the only area that didn’t look factory new was one that had a LOT of deep, impregnated algae due to a low hanging tree directly over this part of the roof.

We never got the spray tip closer than around 18" to the shingles & there was a small amount of water that leaked in around a shallow curbed skylight.

We also had some rotten fascia, drip edge & one 2x4’d rafter tip to fix, so I can’t break this part out exclusively. The total price for all the structural repairs as well as the cleaning was $ 1,600.00 - no shingle work was required & there weren’t any fish mouths to worry about.

I’d say the total time onsite for the cleaning (not including a fuel run & to / from the rental) was around 4 hours or so.

I took some before photos & think I might have some after pics. I did take a photo on the roof with the customer; he was very satisfied with the results (that’s him on the L - the R photo is a job we finished last Wednesday).

Right now, I’m dealing with the flu & am having a hard time thinking straight what with my head feeling like it’s in a vise.

I’m guessing I will ask for 400.00 labor, 40.00 per gallon of cleaner, 75.00 for the rental & 20.00 per square for a 6:12, 30.00 per square for a 7:12, 40.00 / sq for 8:12… I think I’ll try out my inlaw’s roof next. They are a 6:12 & that will give me a feel for how dificult the added pitch is.

One last item - I seem to have got a nasty case of “sprayer’s elbow” from the constant back & forth motion of the wand. Ouch.

Ranchhand, sorry about that flu. Hey that roof looks good. I have found that for a simple roof, we charge by the sq. ft instead of charging shingle language. 20 to 25 cents a foot sounds a lot better. I figure about 15 minutes per square. I can generally clean a 2000 sq ft home in about 6 hrs if I hump it and don’t mess around. It’s all about common sense and it looks like you’ve got it. Keep making customers happy.

Rooferama, forgot to say that for THIS house I charged $ 400.00 & would probably base it off the same figure moving forward.

Seems like our figures were about the same.

Do you have any pointers for working steeper roofs? @ What point do you say “Nope, this one just can’t be safely done?” or do you just use spray hosed pressure from further away? I guess if you had a bucket lift you could get to steep 2 story houses, but then trees might interfere, etc.

The one thing I do want to avoid is a streaky looking roof.

BTW, since you’re also in Conroe - can you tell me what NCAA team you lean towards?

It’s interesting that I didn’t know what to charge when I started doing it. I just had to figure it out, but once I did one, I knew pretty much what my time and material was worth.

You can buy a sweeper at some of the box stores. It comes in several lengths, with 2 or three tips. It has wheels on it and does a pretty good job. I’m really not interested in the steep cleanings. We have the roofer in a bucket fall protection in the office, but I don’t think I’m ready to clean anything that I have to be strapped to. Shingle Shield can get a little slippery. For now, I’ll have to let those go.

I married an Aggie, but spent my time at Houston Community College and Sam Houston State. I happen to be a tried and true Longhorn fan.

You need to sign up for & a recent offshoot, - not only are they good sites for Longhorn football info, but a great networking location.

I am a regular on “Horn Depot” & am the “resident authority” for roofing over there. I won’t mind the added roofer because we havea LOT of people in H-Town who ask for roofing work & I don’t know where to point them.

On HF, I have almost 5,000 posts & the Shag has only been up & running since late November; I’m nearing 800.