Why moss grows on lower mainland roofs
Moss grows where moisture lingers, especially on shaded roof slopes with tree debris and limited sunlight. Lower Mainland rain supports growth, but roof orientation and maintenance explain why neighbouring roofs can look different. Site measurements and observed condition should take priority over a general rule of thumb.
Shade slows drying
North-facing slopes, overhanging branches and nearby buildings reduce sun and airflow. Damp organic debris then provides a place for growth to establish.
Rough surfaces hold spores
Aged shingles and cedar can retain more moisture than smooth surfaces. Moss may lift shingle edges and conceal wear, but it is not the only cause of deterioration.
Removal must protect the roof
Pressure washing can strip granules or force water under materials. Condition should be assessed before using a gentle, material-compatible treatment.
Details worth checking
- Clear loose debris
- Keep gutters draining
- Trim vegetation where safe and permitted
- Use roof-compatible treatment
- Avoid aggressive pressure
- Recheck shaded slopes
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