Illustration for Algae on the Inspection Report

Here’s how to read the note, what to check, and how to put a number on it before closing. This is general information, not real-estate or legal advice.

What the inspector is telling you

A home inspection is a visual check for defects, not a cleaning estimate. One large home inspectors’ association sets standards of practice. They have the inspector look at the roof covering and the exterior wall covering. They also say the inspector isn’t required to determine “the presence of mold, mildew or fungus.”

The same standards define a material defect. It is an issue that may significantly hurt the home’s value or pose an unreasonable risk to people. Green streaks rarely meet that bar. On an inspectors’ forum, one inspector said he always points out roof algae anyway. He calls it mainly a cosmetic issue, but he doesn’t want the buyer surprised later.

State rules can go further. If you’re buying around Memphis, Tennessee’s home inspector rules say inspectors aren’t required to report on cosmetic damage. They define it as superficial blemishes that don’t interfere with how a component works. Growth is common there. Memphis averages about 83°F in July and about 55 inches of rain a year (NOAA normals).

So ask the inspector one plain question: “Is this cosmetic, or is it a defect?”

Green siding or a streaked roof

Siding. On a home inspectors’ forum, one inspector described another who called north-side mildew on vinyl siding a danger. The other inspectors pushed back. They called it common shade growth and suggested a cleaning. The EPA says molds outdoors are part of the natural environment. It’s mold growing indoors that should be avoided.

Roof. Dark streaks on shingles are usually algae. The asphalt roofing makers’ trade group says people can mistake the brown-to-black color for soot, dirt, moss or tree droppings. One shingle maker says studies show algae growth isn’t harmful to the building envelope. Moss is different. The trade group tells owners to ask the shingle maker about its effects. Thick moss is also what insurers tend to flag, as our guide to insurers flagging roof moss from aerial photos explains.

One tip for buyers: ask the seller for the roof’s paperwork. One maker’s algae-resistant shingles carry a limited algae warranty for the first 10 or 15 years, depending on the product. The maker says it will pay the reasonable cost to clean or replace affected shingles.

Signs of a moisture problem

Cleaning removes the growth. It doesn’t fix water that keeps feeding it. The same inspectors’ standards have inspectors check vegetation, drainage and grading where they may let moisture into the structure. Tennessee’s rules require inspectors to report signs of water getting into the building.

Look harder, and ask the inspector, if you see any of these:

  • growth only under one gutter, downspout or roof valley
  • soft, swollen or rotting trim or siding near the growth
  • staining or a musty smell on the inside of the same wall
  • shrubs or mulch packed against the siding, or sprinklers hitting it

Runoff stains have their own causes, covered in our guide to stains from an overflowing gutter or a new roof. If moisture is the issue, fix the gutter, grading or leak first. The wash comes second.

What cleaning costs

These are published prices from washing companies, not quotes for your house.

Job Published price Company (area)
House wash $0.20 per sq ft, $300 minimum visit KC Splash (Kansas City)
House wash, 1,500–2,500 sq ft Starting around $275–$350 JT’s Power Washing Pros (Kansas City)
House wash Most homes $350–$500 Gleaming Gutters (Charlotte)
Roof soft wash $0.25–$0.30 per sq ft of roof KC Splash (Kansas City)
Roof cleaning Starts at $599; most roofs $600–$1,000 Gleaming Gutters (Charlotte)

At the per-foot rate in the table, a roof with 2,000 square feet of shingle surface works out to $500 to $600. Heavy buildup can cost more. One company names the extent of algae or moss as a pricing factor. Our house washing cost guide breaks down siding prices by size and stories. And is roof cleaning worth it covers the roof method shingle makers describe.

Credit, repair or neither

The CFPB says you may want to negotiate with the seller. You can ask them to fix worn or damaged items or give you a credit for the cost. It also says the seller may or may not agree, depending on your contract and local market conditions. Talk it through with your agent.

Two practical points if cleaning ends up in the deal:

  1. Get a written quote first. It turns “the siding is dirty” into a dollar figure. Our questions to ask a house washing company help you get a quote you can compare.
  2. Know what a cleaned roof looks like. Dead algae can take weeks to weather off, as our roof soft wash results guide explains. The CFPB says the final walk-through is when to confirm agreed repairs were made. Ask for the invoice there rather than judging by the streaks.

Selling instead of buying? See washing a house before you list it. Here’s how we check our numbers.

Sources

Based on 12 sources · How we price