Calgary mold and algae removal for north-side walls, shaded fences and roof streaks
Plant-safe biocide soft-wash kills algae and surface mold at the cell wall, not just rinsing off the colour. North and east-facing walls, basement walkout shade zones, shaded fence panels, asphalt roof streaks. Pre-wet beds, brief pets-and-kids window, rinse for plant-safe dilution. 12-18 month protection. Most Calgary jobs land between $200 and $700.
Surface rinse leaves the organism alive — soft-wash kills at the cell wall
Most homeowner mold-and-algae attempts fail because they treat the symptom (visible colour) without killing the cause (the living organism on the surface). A hose rinse takes the green tint off for a week; the algae cells underneath rebuild visible growth within days. The right approach is sodium hypochlorite plus surfactant at the proper concentration — the biocide kills the algae cells, the surfactant lifts the dead matter, and the rinse takes everything down. Result lasts 12-18 months on a typical Calgary wall because the surface starts essentially sterile.
Calgary mold and algae concentrate in specific zones: north-facing walls (most common), east-facing walls (second most), basement walkout shade zones (heavy when the walkout faces north), shaded fence panels under trees, asphalt roof shingles with low-angle sun exposure. Each gets the same chemistry at different dwell times. Pair mold-and-algae removal with house washing for the full envelope reset, with roof cleaning for the asphalt-shingle streaks or with fence cleaning for shaded perimeter panels.
Recent work
How a Calgary mold-and-algae removal runs
Four steps from environmental check to dry surface
Identify and pre-wet
Walk the property, confirm whether the growth is algae or true mold, note the environmental cause (drip line, shaded zone, branch overhang), pre-wet plant beds and brief you on pets-and-kids containment window.
Apply biocide soft-wash
Sodium hypochlorite plus surfactant mix at substrate-matched concentration, bottom-up application so it does not streak, 5-15 minute dwell so the chemistry kills the organism (not just rinsing the colour).
Rinse and dilute
Top-down low-pressure rinse, plant beds re-rinsed for dilution to plant-safe levels, runoff direction confirmed toward the lawn rather than the storm gutter so the lawn dilution helps the soil chemistry.
Walkaround and environmental note
Walkaround with the homeowner to confirm the wall is uniform-clean, environmental cause flagged for any follow-up trade work (gutter adjustment, branch trim), invoice matches the quote.
Calgary's dry climate is hard on algae but Calgary's specific microclimates concentrate growth in ways that catch homeowners off-guard. North and east-facing walls stay cool and damp under the eaves for hours each morning, even on dry summer days — that condensation cycle feeds the algae despite the overall dry climate. Basement walkout shade zones (especially north-facing walkouts) collect leaf debris and moisture in the corners where the foundation meets the slab. Fence panels under mature trees in the inner-city neighbourhoods (Mount Royal, Bridgeland, Briar Hill) grow algae year-round because the canopy never lets the wood dry.
Annual maintenance washes prevent visible accumulation between visits. Biennial works for shaded zones with slower growth. Pair mold-and-algae removal with soft washing as the master chemistry method, with roof cleaning for asphalt-shingle streaks or with sealing services for the post-clean penetrating sealer that slows future regrowth.
Written quotesPricing
Annual + as-neededCadence
Hartford mold algae removalStandard
Pair mold-and-algae removal with
Other services that pair with the biocide pass
Mold and algae removal is often part of a larger envelope wash. Pair with house, roof or fence for full-property reset.
Five questions that come up on most mold-and-algae quotes.
Algae is the green and black surface growth on north and east walls — most Calgary 'mold' is actually algae. True mold (the fungal growth that causes interior health issues) is rare on exterior surfaces in Calgary's dry climate. Both come off with the same soft-wash sodium hypochlorite mix, but identifying which one you have at the visit matters because true mold on the interior side of an exterior wall usually means moisture infiltration that needs a building envelope check, not just a wash.
The wash treats the surface — kills the existing growth and resets the visible appearance. The root cause is usually environmental: a north or east-facing wall that stays cool and damp under the eaves, a downspout that drips against the foundation, a tree branch overhanging the roof that blocks sun. We flag the environmental cause at the visit and recommend a contractor for the structural fix if needed (eavestrough adjustment, branch trim, grading).
12-18 months on a typical Calgary north-facing wall after a proper soft-wash. The soft-wash chemistry kills the algae at the cell wall, not just rinsing off the colour — regrowth takes months to a year because the wall is essentially sterile after the treatment. If the environmental conditions stay the same (still north-facing, still damp), it will come back; annual or biennial maintenance washes prevent visible accumulation between visits.
Black streaks on north-facing walls are almost always gloeocapsa magma (the same cyanobacteria behind black roof streaks) or black mold algae. Both lift with the soft-wash chemistry. True toxic black mold (Stachybotrys) on exterior walls is rare in Calgary because the climate is too dry for it to thrive outside; if you suspect Stachybotrys (visible interior growth, musty smell, recent water damage), an environmental remediation specialist is the right call, not an exterior wash.
Yes, with the prep we do. We pre-wet plant beds, brief you on keeping pets and kids indoors during the application window (usually 2-3 hours), and rinse the surrounding area after the wash so the dilution reaches yard-safe levels. The mix at the wall is at the upper end of plant-safe; the rinse takes everything down through dilution. Pets and kids can be back in the yard as soon as the dry walkaround is done.
Calgary mold and algae removal reviews
What homeowners say after the targeted wash
★★★★★4.9· 75 reviews on Google
★★★★★
North wall of our Mount Royal infill had thick green algae the previous wash company couldn't move. Hartford used the proper soft-wash chemistry plus dwell, the wall came back to original colour. Two summers later and it still looks clean.
Homeowner
Calgary · Mount Royal
★★★★★
Basement walkout in shade most of the year. Crew identified an eavestrough drip that was making the problem worse, recommended an eavestrough contractor before the wash. Did the job right after the fix and it has held.
Homeowner
Calgary · Strathcona Park
★★★★★
Cedar fence under a big elm tree, growing green-black streaks. They walked me through the difference between mold and algae, used the right biocide and the cedar came back to natural colour. Annual contract booked.
Acreage Owner
Calgary · Bridlewood
★★★★★
Asphalt shingle roof with the classic north-slope black streaks. Soft-wash plus dwell killed the gloeocapsa magma at the cell wall. Roof looks like it did at install, no granule loss in the gutter.
Homeowner
Calgary · Mount Pleasant
From the blog
Mold vs algae identification, biocide chemistry and prevention notes
Free written estimate
Get your Calgary mold and algae removal quote in writing
Tell us where the growth is (north wall, basement walkout, fence, roof), how long it has been there and any environmental conditions you have noticed (drip line, shade, overhanging tree). A Hartford estimator follows up within one business day with a written quote.
