Why do some roofs get moss and others do not?
Short answer. Some roofs get moss and others do not because of small differences in shade, slope direction, tree cover, roof pitch, shingle age and debris. Two neighboring houses can get the same spores and rain, but the one with a north facing slope under oaks stays wet for hours longer, and that is where moss wins.
Side by side: what tips the balance
- Orientation: a house whose main slope faces north gets far less direct sun than one facing south. The south facing roof dries by midmorning.
- Tree canopy: overhanging limbs shade the roof, drip on it after rain, and drop leaves and needles that hold water.
- Pitch: steeper roofs shed water and debris faster. Low slope porches and additions are more prone.
- Shingle age and type: new shingles with intact granules and tight laps resist moss better than weathered ones. Wood shake roofs are especially prone.
- Gutters and valleys: clogged gutters back water up under the lowest courses, and packed valleys stay wet.
- Metal near the ridge: roofs with copper or zinc flashing, chimney caps or strips higher up shed small amounts of metal that discourage growth below.
Why it matters in North Georgia
Many North Georgia lots keep mature hardwoods and pines close to the house, and the mountain counties add fog and cooler, shadier slopes. Two identical homes on the same street can behave very differently depending on which one has the big oak on the north side.
Making your roof the one without moss
- Thin or cut back limbs over the roof to let in sun and air.
- Clear valleys, the uphill side of chimneys and gutters each fall and spring.
- Address moss early with a gentle, roof safe treatment.
- When you replace the roof, choose shingles with algae resistant granules and consider zinc or copper strips.