View Full Version : shake roof/ green algae

Jerome W. Young
02-18-2008, 05:16 AM
This is a nice courtyard home in Florida. The home just just completed. The roof is about 1 year old and the north facing slope has this algae growing already. What can be done to remove this? What should be done to prevent it in the future... if possible. Any other concerns etc? The builder is telling my client that it will burn off this summer. I thought it might turn brown from the heat but likely not go away.

Jim Luttrall
02-18-2008, 09:32 AM

Check out this thread.

Jerome W. Young
02-18-2008, 02:17 PM

Found this helpful also.

Markus Keller
02-21-2008, 09:01 AM
Were the shingles installed on top of sleepers or right onto a plywood substrate? I don't know about Florida conditions, but up here (Chicago) shake installed directly onto a plywood substrate causes these problems and voids every manufacturer's warranty I've read through (6-7). Also looks like some curling is starting.

Jerome W. Young
02-21-2008, 11:30 AM
plywood with spray foam behind it. That is how it is installed down here. Doesnt mean its right but thats the way it is

Markus Keller
02-21-2008, 01:08 PM
Jerome, I have zero knowledge about this type of installation.It sounds very bizarre to me. Depending on chemical composition, absorption properties and exposure the insulation could be acting as a magnet for moisture. With the shake not being installed on sleepers the underside of the wood gets no air movement and can't properly breathe or dry.
I noticed on your photo that there is no gutter. This appears to be a very large roof not to have a gutter. Is this common in Florida? It also looks like this may be a semi-courtyard elevation? Is the north elevation along with several other factors such as fair amount of rain, non-permeable ground cover, 2 or more walls, and low wind creating a high moisture containment area? Just asking. I think 'Jerry Peck' is in Florida, try him on this site. He seems to know a lot. Good luck

Jerry Peck
02-21-2008, 01:23 PM
Spaced sheathing does not give the roof the structural diaphragm rigidity which is needed to resist high winds (aka 'hurricanes'), plus, flying debris will go right through those wood shakes and shingles, not to mention that when the wood shakes or shingles are lost to the wind that leaves the entire attic open to the wind, which then proceeds to destroy the house.

No, wood shakes or shingles *do not* perform as well on solid plywood as they do on ventilated spaced sheathing, but, given all relative conditions, when you loose your roof covering during a high wind event, *you do not* want to lose your roof sheathing, for both wind and water concerns.

Once the solid plywood is under the shingles, installing the foam under the roof sheathing really does very little to the life of the wood shakes or shingles, but (if designed properly) it enhances the performance of the house below.

Why would you use wood shakes or shingles in Florida? Because that's what 'Northerners' want on their house, they don't care about roof life ... until the roof gets a few years old and then they go 'Wait a minute, why is this roof doing this?' - 'Er, because ... they did not use "shakes" they used "shingles" and because wood shakes and shingles do not perform as well on solid sheathed roofs.' - 'Oh, then I will need to replace my roof sooner than I thought?' - 'Yep.' :D

Markus Keller
02-21-2008, 04:12 PM
Dear Jerry, from your other posts I knew you would know something about florida conditions. I did not give any thought to hurricane conditions since it is not something we generally deal with. Under those conditions, I agree with you.
As a point of information, in the Chicagoland area, generally wood shake/shingle is used in the suburbs, new construction and 700K+ price range, sometimes less but not usually.
I generally counsel my clients to stay away from wood roofing for the obvious reasons. I wish I had a camera ready to capture the horrified face of a new client when I tell them what the problems are and that they probably don't have a warranty on their newer wood roof. Even the richest, smartest clients get sick when they find out the LLC (builder) was dissolved soon after the project and the principles aren't personally liable.
Not to let you off too easy Jerry, how about giving Jerome some actual answers about his algae problem.
Those darn 'northeners' always sticking their noses into southern business.
Have fun.

Eric Barker
02-21-2008, 05:22 PM

Builder is wrong. Algae does not burn off - it would not grow in the first place in an area where sun shines. Shame on the builder for coming up with his explanation. Algae can be carefully power washed with an application of fungicide applied. Though I rarely see it, the use of copper or zinc strips will prevent algae growth - see attached.

Algae/moss significantly reduce a wood covering's life. The roots of such growth get down into the wood and aid in the retention of moisture.

As already mentioned, solid decking is always used around here and as a result wood roofs last no longer than asphalt shingle. One hurdle in the upper income neighborhoods is that some homeowner association will only allow shake roofs.

Richard Rushing
02-21-2008, 06:11 PM
Be berry, berry careful....

I would never tell a client that power washing a roof was something they could do. I'll let some other (think--"last one touching it") sole have the honor.


Jerry Peck
02-21-2008, 07:04 PM
I have never seen a power washed (pressure washed) wood shake or shingle roof survive in any decent condition, the pressure just eats the wood away ... just like the rain does, only much more so and much quicker (one close swipe of the wand and the spray nozzle raises the grain in that circular path, you will see that for a long time to come).

Jerry Peck
02-21-2008, 07:14 PM
Not to let you off too easy Jerry, how about giving Jerome some actual answers about his algae problem.

The only way to rid the roof of algae is to clean it off chemically with an algaecide (or bleach, but be careful with bleach).

Of course, though, being on the north side (which never gets much sun, if any direct sun) - the algae is just going to grow back.

Those darn 'northerners' always sticking their noses into southern business.


I was not referring to you or other HIs from 'up north', but to buyers who come down and expect wood to last like it did *up there* and thus 'demand' a wood shingle roof (thinking they will be getting a wood shake roof, except that they choose the 'lower cost' wood roof and end up with wood shingles).

Even where I am now, in Central Florida (on the east coast, but still considered Central Florida), we have sun all year. Just not as strong as South Florida has, and Jerome in almost down into South Florida.

Other areas, such as 'up north' in Rochester, NY, may only see the sun 6 months of the year, and that's if they are lucky. It's hazed over almost all winter.

Sun, and its UV rays, damage the wood almost as fast as it does asphalt shingles. Actually, maybe even faster. I've seen many an asphalt shingle roof outlast many a wood shingle roof in South Florida when I was down there.

Jon Randolph
02-21-2008, 07:51 PM
I have heard of using copper at the ridge to prevent it, but by the time it gets this sever, it is probably too late for that. Commercial algecide may be the only option. I don't know who to recommend for that.

Mike Schulz
02-24-2008, 05:58 PM
With that pitch you're going to need a bucket truck and Commercial algaecide in a plant pump sprayer.
I'm not sure but I bet you can get a chemical with the zinc or other algae resistant chemical to treat the wood annually or longer.