Black streaks, moss and lichen: what is growing on your Austin roof

You looked up at the roof, noticed something dark on it, and now you are trying to work out whether that is a problem or just what the roof looks like now. Fair question. There are three different things that commonly grow on a Central Texas roof, homeowners tend to call all of them black streaks, and they are not equally serious. One is mostly a looks problem. One is a maintenance problem. One genuinely damages the roof, and it is the one people worry about least, because it is the least dramatic to look at.

The dark vertical streaks are algae, and they are by far the most common of the three around Austin. They run in streaks rather than patches because the growth spreads downhill with the rainwater, and they take hold worst on whichever slope stays damp the longest. If you want the detail on what algae is doing to the shingle and why a roof has to be washed at almost no pressure, that is on our roof washing page. The point worth making here is a different one. In its early years, algae is mostly a curb appeal problem. It looks terrible and it is doing very little. That is good news, because it means the streaks are the least urgent of the three things on this list even though they are the most visible.

Moss is the green growth with actual thickness to it, the small cushions and tufts that sit up off the surface. Around Austin you find it wherever the roof stays shaded and damp, under a live oak that has grown out over the house, in the valleys where leaf debris collects, along the slope that never gets full sun. Moss is a maintenance problem rather than a cosmetic one. It behaves like a sponge, holding water against the shingle long after the roof should have dried out, and as it thickens it works under the shingle edges and lifts them. A lifted shingle is a way in for water. Moss is worth handling on a normal timeline rather than as an emergency, but it should not be left for years.

Lichen is the one to actually care about, and it is the one almost nobody asks about. It looks like flat crusty patches, grey green or a pale sage, spread across the shingle like something was spilled and left to dry. It has no height to it, which is exactly why people ignore it. Algae sits on the surface. Moss sits on top and grabs the edges. Lichen puts anchors down into the shingle mat itself, so it is not resting on your roof, it is attached to it. That is what makes it stubborn, and it is why pulling old lichen off aggressively can take granules with it. Lichen is the growth that can reach the point where cleaning is no longer the answer.

You can work out which one you have from the ground, with a phone camera zoomed in and no ladder involved. Algae runs downward in streaks and follows the water. Moss is three dimensional, it stands up off the roof far enough to cast its own small shadow, and it is a true green. Lichen is flat, irregular in shape rather than streaked, closer to grey than green, and it looks welded on rather than laid on. A rough rule: if you can still see the shape of the shingles clearly through it, it is algae. If it has bulk, it is moss. If it looks like a stain that will not wash off, look closer, because it is probably lichen.

Here is the part that decides what you do next. A roof wash runs $300 to $700, with the pitch of the roof, its height and how far the growth has got deciding where in that range you land. Replacing a roof years earlier than you should have because growth was left to work on it is not a bigger version of that number, it is a different order of magnitude. Washing is cheap by comparison, and it is cheap precisely because it is preventive.

One thing we will not tell you is that a wash undoes what has already happened. It does not. Cleaning kills and clears the growth and stops it doing any further work, but a shingle that has already lost granules under an old lichen patch does not get them back. That is the whole argument for dealing with it sooner. You are not buying back the years, you are stopping the meter.

And if you send us a photo and the honest answer is that your roof is fine and can wait another season, that is what we will tell you. We would rather clean your roof at the right time than talk you into cleaning it twice.

Call or text (254) 319-3275, or send a few photos through the quote form and we will tell you what you are looking at and what it would cost. Free quote, no obligation, and we offer a discount for seniors and elderly homeowners.