All You Need to Know About Pressure Washing, Roofs & Moss

Tis the season….for green. Green on your lawn. Green buds on your trees. Green bulbs ready to burst into color. And then there’s the green on your roof.

It’s also that time of year when a homeowner scratches his head, flips through the phonebook (or Google), wonders who to call for help and ends up giving it a try with the guy who left a small flyer stuck to his front door.

But how do you recognize a qualified professional who actually knows what your roof needs?

You see your neighbor lady down the street hiring a pressure washing company to clean her composition roof every single year. But just because her roof looks great from down below, how do you know if that’s the best course for the roof’s longevity?

And there’s your colleague - whose endurance brings him up to the top of his tile roof each spring to scrape off moss with a garden tool and brush – one tile at a time. And you’re not about to risk life and limb (and lose a whole weekend) to do that to yours.

So I’m here to save you a few hours of research in the world of Google, and perhaps save your roof.

This week I sat down with my favorite service provider, an industry leader in the Gig Harbor community for the last ten years. He jokingly says that he only knows what he’s talking about because he’s made all the mistakes. And in my book, that wisdom counts for something. Licensed, bonded and insured counts too; but the long list of 1000+ loyal clients waiting patiently for their appointments with him speaks more volume than anything.

He was gracious enough to chat late into the night with me on the joys of pressure washing, the invigorating smells of zinc, and the technicalities of psi vs gpm. This guy loves his job.

So today, you’re lucky enough to read some of his advice on how to clean your roof; and if you’d like more details I’d be more than happy to connect the two of you.

First of all, here are two important terms to understand:

Psi stands for pounds per square inch. It is a measurement of the pressure that is applied when breaking the bond between the grime (oil, dirt, paint, etc) and the surface to which it is stuck. So, when considering someone to hire, be wary of anyone who says they’ll use a high psi on your roof or he’ll cause serious damage.

GPM stands for gallons per minute, and this is really the key for efficiency in pressure washing. It is simply a reflection of how quickly the water comes out of the machine. 8 gallons per minute will clean an area twice as fast as 4 gallons per minute.  Many municipal water systems won’t allow for more than 4 or 5 gpm, and that is why you’ll often see expert pressure washers utilize a barrel of water hooked up between the machine and your hose spigot; it simply allows them to increase the gpm to align with the capacity of their machine. The great advantage of a high gpm capacity is that it provides high volume for a thorough clean, while still cleaning gently with a lower psi.

So, in summary, anyone who brags about their high psi, without giving credit to the role of gpm, might not be the best fit for your roof.

Now let’s talk about roof types.

Cedar Shakes have to be pressure washed periodically, but you must be cautious because an untrained person can cause serious damage, leakage and erosion on your roof.  Experts generally recommend pressure washing and oiling your cedar shakes every 5 years.  It is also recommended that oil be spread on newly cleaned cedar shakes for three reasons.

It acts as a natural water repellant, it conditions the wood so that it doesn’t split and cup, and it is fantastic at inhibiting new moss growth. Oiling a cedar shake can be quite expensive to do, however, the return on investment is very high when evaluating the life of your roof. If oiling is cost-prohibitive, then zinc (NOT bleach) can be utilized in between cleanings to reduce moss.

Tile Rooftops need to have their tiles lifted regularly so that the valleys can be cleaned underneath. Otherwise, these roofs will begin leaking – causing thousands in damage. Pressure washing tile roofs while using too much psi can remove their smooth finish. When this finish is removed, the rough surface of the tile will then allow for more moss to grow at a faster rate and the life of your roof will be shortened.

If you choose to proceed with pressure washing, hiring a qualified expert to clean your roof is of critical importance, because if done incorrectly, it can lead to water being forced into the underfelt and timbers where it can eventually touch insulation and electrical fixtures. Anyone caring for your tile roof should understand the intricacies.

Composition Roofs should only be power washed if you have to get rid of moss (if you’re putting the house on the market, for instance).  And here’s why: Every composition roof has what they call “Roof Sand,” which is actually ceramic shavings that have heat-deflecting properties. When you use a power washer or an air compressor, you remove precious roof sand that deflects the hot sun.

Ideally, roofs should be treated for moss on a preventative basis. Skip a year of treatment and suddenly overnight your roof will turn green again. But treat it with zinc (or a few other choice products) every 6 to 12 months and you’ll be consistently killing moss as it grows, thus prohibiting the overgrowth that is unsightly and damaging. The moss will slowly die off after treatment, and can then be cleared off using a backpack blower.

Word of warning

 Be cautious of businesses who only do roof pressure washing. If this is their sole source of income, be wary of their attempts to convince you that pressure washing is the best and only solution. They need your business, and if they tell you there’s another, cheaper, better way….they go out of business. Be a smart consumer, do your research, and make sure you can trust the source.

So, here’s the funny part. He offers these last pieces of advice as a summary: If the guy shows up with a pressure washer just like the one you saw on sale at the hardware store last week, hire someone else. If the guy tells you he can take the pressure washer up to the top of your roof and clean it from there, hire someone else. If the guy tells you his 4000 psi machine can clean your roof super fast and not do any damage, hire someone else.

And call me. I’ll set up a personal consultation so you can ask your own questions of the expert and get a no-obligation quote for your roof. It’s that simple.

Sarah Friesen is an experienced & trusted Home Manager who offers an array of Home Watch, Concierge & Organizational Services that bring Peace of Mind to local homeowners. You can reach her at sarah@gigharborhomemanagement.com or visit her website at www.GigHarborHomeManagement.com