Ontario's Plain-English Guide to Custom Home Buildingπ 705-533-1633 | βοΈ 1-866-868-6606 | βοΈ info@icfhome.ca
Exterior Wall Moisture Inspection: What a Qualified Inspection Does, Pin and Pinless Meters, Probe Tests, Infrared, What the Readings Mean, What It Costs and When It Is Worth Paying For
Exterior Finishes
A Moisture Inspection Is Two Pins in the Sheathing and a Number, Not a Beep Through the Siding
Before you pay to strip a wall, before you buy a 1990s stucco house, and before you believe anyone who found “hidden moisture” from the driveway, there is a test. It is not complicated. A qualified inspector pushes two insulated pins through the cladding into the sheathing at the places water gets in, reads the moisture content of the wood, seals the holes and writes the numbers on a drawing of the house. It costs $400 to $900 for a siding house and up to about $2,500 for a stucco or EIFS house with thirty probe points, and it is the difference between a $7,500 repair and a $90,000 sales contract. Here is what it does, what the numbers mean and when to buy one.
The tools and what each can and cannot tell you
| Tool | What it reads | Good for | Useless for |
|---|---|---|---|
| Pinless (capacitance) meter | A radio-frequency field about 3/4 in. deep, reading everything in it as one number | Screening a drywall surface inside for a wet area, comparing one spot with another | Reading through siding. It sees the vinyl, the air gap, a metal flashing or a foil-faced foam and beeps on all of them. The door-to-door tool. |
| Pin meter, short pins | Electrical resistance between two pins, calibrated to wood moisture content | Drywall, baseboard, exposed wood, the sheathing once a panel is off | Anything it cannot touch |
| Pin meter with insulated probe pins, 3 in. | The same, but only at the tips, so it reads the sheathing through the cladding | The real test. Through vinyl, fibre cement, stucco or EIFS into the sheathing at the suspect spots, holes sealed after | Masonry; brick needs a different approach |
| Infrared camera | Surface temperature, which wet areas change by evaporating | Finding where to probe on a big wall, inside after a rain or with the heat on | Proving anything on its own. It shows cold, not wet; a draft reads the same as a leak. |
| Hose test | Where the water comes in when you put it where the rain does | Pinning a window leak to the window, the flashing or the wall, one at a time, from the bottom up | Walls where the damage is from inside air leakage; no amount of hose finds condensation |
| A pry bar | The sheathing itself | Three courses of vinyl off under the worst reading settles every argument in twenty minutes | Stucco and stone, where opening a spot is a repair |
What the numbers mean
Moisture meters read wood as a percentage of its dry weight. Framing and sheathing in a heated Ontario house sit at 8 to 12% in winter and up to about 15% in a humid August. Those are dry. 15 to 19% is damp: something is adding water, slowly, and the spot is worth a second visit after a storm. 20% and up is wet, and the wood will not get there from humidity alone; there is a leak. Above 28%, fibre saturation, the wood has been wet long enough that rot fungi can live in it, and OSB at that number is usually already soft. Health Canada’s line on mould is the same as mine: find the water, stop it, then deal with what grew.
Two things about the number. It is a point reading, so an inspection that takes four readings on a 2,400 sq ft wall has told you about four square inches. The suspect spots, below window corners, at roof-wall corners, at the bottom plate, at a ledger, are where the readings go, and a good report has twenty to forty of them on a drawing. And a reading on a cold wet day in April is not a reading on a dry day in August; the report should say the weather and the date, because the fellow who tests after three days of rain and announces the wall is wet has discovered rain.
What a qualified inspection actually does, in order
- Inside first. Every stain, every soft spot, every musty closet on an outside wall, with a pinless screen and a pin reading, marked on a sketch. The inspector asks when it appeared and what the weather was; April stains are condensation until proven otherwise.
- The outside walk, from the ground. Kick-outs present or missing, head flashings, sill condition, caulk instead of metal, siding at grade, downspouts, the deck ledger, the roof-wall junctions. On a stucco house, the cracks, the terminations at windows and the bottom of the wall. Most of the diagnosis is this walk; the flashing details page is the list.
- Infrared, if the weather allows, to find the wet areas on the big walls so the probes go where they count.
- Probe readings through the cladding at every suspect spot, both corners below every window on the weather walls, the roof corners, the bottom of the wall, twenty to forty locations, each one numbered on the drawing with its reading. Holes about 3/16 in., sealed with colour-matched sealant.
- Open one spot where it is allowed. On siding, three courses off under the worst reading and a photograph of the sheathing. On stucco or EIFS the probe is the opening, which is why those inspections cost more and need more holes.
- A written report: the drawing, the readings, the weather, the photographs, the probable entry points and a scope of what to open and repair. Not a siding quote. If the same company does the inspection and sells the wall, you have not had an inspection.
What it costs, and who does it
A moisture inspection of a siding house with probes at a dozen or so locations and a report: about $400 to $900, depending on the house and whether infrared is included. A stucco or EIFS inspection with twenty to forty probe points, which is what a 1990s EIFS house needs before anyone buys it: $1,200 to $2,500. Those are market figures, not mine; I do not sell inspections, and the person who does should not be selling siding either.
Who: a home inspector with building-envelope training and the insulated-pin meter to prove it, a building science or envelope consultant, or for EIFS a certified EIFS inspector, which is a real designation with a course behind it. Ask what meter they use and whether they probe. If the answer is a pinless meter on the outside of the siding, you are talking to a salesman with an instrument. The door-to-door page covers that conversation.
What the readings cost to act on: sheathing replacement $6.50 a square foot, framing repair $400 to $900 per opening, a wall of vinyl off and back on at $2.00 and $9.50, flashing kits $85 an opening. Water behind siding works the common repair through to $7,526 before HST, and the whole-house case to about $41,000. A $700 inspection that turns a $90,000 pitch into a $7,526 repair is the best money on this site.
The four times to pay for one
Before buying a stucco or EIFS house built from about 1988 to 2005. Face-sealed EIFS with no drainage was the standard then and the walls are the problem, not the look. A general home inspection does not probe; a $2,000 EIFS inspection on a $900,000 house is a rounding error that can move the price by $50,000. Moisture behind stucco is the page for what they find.
When there is a stain inside and no obvious cause. Window leaks, flashing leaks and condensation all make the same brown mark, and the repairs are different. The window leak page and the wall flashing leak page cover the two commonest, and the probe decides between them.
After anyone tells you there is hidden damage, especially if they found it from the driveway and have a contract in the truck.
Before a re-side, to set the scope. If the siding is coming off anyway, a probe inspection tells you how much sheathing and framing to put in the contract as unit rates, so the “rot found” line on day three is $6.50 a square foot you agreed to and not a change order written on the hood of a truck. The cladding inspection checklist is what to look at once it is open.
Questions people ask
How much does a moisture inspection of exterior walls cost?
About $400 to $900 for a siding house with a dozen probe points and a report; $1,200 to $2,500 for a stucco or EIFS house with twenty to forty probes. Infrared adds a little. Free is the price of an inspection that ends in a siding contract.
What moisture reading is bad in a wall?
Wood sheathing and framing at 8 to 15% is normal for an Ontario house. 15 to 19% is damp and worth a second look after rain. 20% and over means water is getting in. Over 28% the wood has been wet long enough to rot, and OSB at that level is usually soft already.
Can you test for moisture without removing siding?
Yes, with a pin meter fitted with insulated 3 in. probe pins pushed through the siding into the sheathing. The holes are about 3/16 in. and are sealed after. A pinless meter on the outside of siding does not test the sheathing, whatever it beeps.
Who does moisture inspections in Ontario?
Home inspectors with building-envelope training and the right meter, building science consultants, and certified EIFS inspectors for stucco and EIFS houses. Ask whether they probe and what they use. Avoid anyone who also sells the repair.
Is infrared enough to find water behind siding?
No. Infrared shows surface temperature differences, which wet areas cause and so do drafts, studs and shadows. It is a good way to decide where to probe. The probe is the test.
Turn the readings into a number
Once the report says which wall and how much sheathing, the exterior cladding cost calculator prices the tearoff, the rot, the wrap, the flashing and the new siding for that scope. If you already have a quote that came with its own “inspection”, the $99 review reads it against what a real one would have found.
Sources and further reading
- Addressing moisture and mould in your home: Health Canada: what to do when the sheathing under the siding turns out wet.
- Canada Mortgage and Housing Corporation: the Canadian wall-assembly and moisture research behind rainscreens and the second plane of protection.
- Dryvit: EIFS and acrylic finish systems: what a drained EIFS assembly is, the base coat, mesh and finish, and the details at openings.
