Why cedar shake and carpenter ants converge in Metro Vancouver
Metro Vancouver's housing stock has a significant concentration of pre-1995 homes with cedar shake roofing — a material that was the default residential roofing in BC before asphalt architectural shingles became dominant. Cedar shake performs well for 25-30 years but deteriorates progressively. In the Pacific Northwest climate, aging shake accumulates moss, which retains moisture against the shake and underlying felt. The shake itself becomes increasingly moisture-absorbent as it ages, eventually maintaining 20-30%+ moisture content through most of the rainfall season (October-April). The roofing deck boards below the shake reach comparable moisture levels. This is Camponotus modoc's ideal nesting substrate.
The attic pathway
Carpenter ants entering through deteriorated shake roofing rarely establish in the shake itself — they move down into the attic framing, which may be drier but offers the structural volume for galleries. The typical progression: moisture elevation in ridge board and top plates, followed by carpenter ant scouts entering through gaps at ridge or eave, colony establishing in top plate or rafter near the ridge, workers foraging down through wall cavities toward interior, frass appearing at ceiling-wall junction or on top of attic insulation.
How to assess your shake roof for moisture and ant risk
- From the ground with binoculars: look for green moss growth, lifted or cupped shakes, and dark discolouration at the ridge. Any of these indicate moisture retention.
- From inside the attic: look for dark staining or soft spots on the decking from below. Take a moisture reading on the decking near the ridge — above 19% indicates elevated risk.
- Frass on insulation: check attic insulation surface near the ridge and near eaves in late spring. Fresh frass indicates active colony.
- Soft probe test: in accessible attic areas, probe top plates and ridge board with a screwdriver. Soft or crumbling wood indicates decay.
The replacement vs treatment decision
If your cedar shake roof is 25+ years old with visible moss and moisture damage, the decision tree is: treat carpenter ants now AND plan roof replacement within 1-2 years. Treating ants in a roof that will maintain 25%+ moisture content through every rain season means annual recurrence — the treatment is fighting the structural conditions. Roof replacement that brings the attic framing to below 15% moisture content eliminates the carpenter ant habitat. In our experience, the homeowners who resolve carpenter ants permanently are those who treat the ants and replace the roof. Those who only treat the ants average re-treatment every 18-24 months.
Moss treatment as preventive
For shake roofs that are not yet at replacement age, professional moss treatment significantly reduces moisture retention. Zinc strip installation at the ridge (zinc runoff inhibits moss growth) combined with biocide application and physical removal can extend shake life by 5-10 years and materially reduce moisture content in the underlying decking. This should be evaluated alongside any carpenter ant treatment on a property with cedar shake roofing.