Most of this site is about things you can do yourself, because most damp problems genuinely are. This page is about the other set — the situations where continuing on your own costs more than stopping.
It is also about who to call, because the wrong specialist produces the wrong diagnosis. A damp proofing company sells damp proofing.
Call someone about mold when
- The affected area is larger than about 10 square feet — the EPA threshold where DIY cleanup stops being sensible
- It is inside the HVAC system — ducts, the evaporator coil or the drain pan. Growth there distributes spores through the whole house
- It followed sewage or flood water rather than clean water
- Anyone in the house is immunocompromised, has significant asthma or is undergoing treatment that suppresses immunity
- You can smell it clearly but cannot find it after checking the obvious places — it is inside a cavity
- Cleaning it has already failed twice and you do not know why
Call someone about the structure when
- A damp patch has a defined edge and worsens after rain, and you cannot find the exterior defect from the ground
- A wall shows a level tide mark with salt deposits and lowering the ground level did not help
- The water meter moves with everything turned off
- There is standing water in a crawl space or basement after rain
- Floor boards are cupping, or a floor feels soft underfoot
- You are considering work costing four figures or more on any diagnosis you are not certain of
Who to call for what
| Situation | Who | Watch for |
|---|---|---|
| Mold over 10 sq ft, or in ducts | Mold remediation contractor | Ask about containment and what gets removed vs cleaned |
| Suspected rising or penetrating damp | Independent damp surveyor | Not one employed by a company that sells the treatment |
| Clammy house with plenty of cooling | HVAC contractor | Ask about run time and latent capacity, not tonnage |
| Crawl space or basement water | Waterproofing or drainage contractor | Get exterior drainage assessed before internal tanking |
| Attic frost, ice dams, roof sheathing | Insulation and air-sealing contractor | Air sealing should come before added insulation |
| Cupped or damaged wood floor | Flooring specialist | Do not let anyone sand it while it is still wet |
| Persistent allergy or respiratory symptoms | Doctor, then an allergy test | Identify the trigger before rebuilding the house |
How to be a good client
Bring the evidence. Dated photographs of the patch over several weeks, your hygrometer readings, whether it changes with rain, and what you have already tried are worth more than any description.
Pay for the diagnosis separately from the work wherever the sums are significant. A free survey from a firm that sells the cure is a sales visit, and the damp proofing industry is the clearest example of that on this site.
Get the cause named, not just the treatment. A quote that says what will be installed without saying what is wrong is not a diagnosis — and if the answer is condensation, the correct treatment may cost nothing at all.
Finally, be willing to hear that it is condensation. It is the most common cause by a wide margin, it is the cheapest to fix, and it is the one an honest surveyor will tell you about for free.
Choosing someone, and what to ask them
Deciding that you need help is the easy half. The harder half is picking someone whose interests are aligned with a correct diagnosis rather than a particular treatment.
The single most useful rule is to separate diagnosis from treatment. A free damp survey from a company that installs damp-proof courses is a sales visit, and the industry has a long record of diagnosing the condition it sells the cure for. An independent building surveyor with no product to sell charges a few hundred dollars and regularly saves several thousand by finding a blocked gutter. If a survey is free, ask yourself what it is being paid for.
Ask what evidence the diagnosis rests on. A conclusion should reference the pattern of the damage, its behavior over time and weather, surface and air measurements, and what is happening outside the building — not a single reading from a handheld resistance meter. Those meters respond to salts, foil-backed board and metal fixings as strongly as they do to water, and they routinely read high on a dry wall that had a problem years ago.
For mold work, the questions are about containment and about the cause. How will the area be isolated so that disturbing the growth does not distribute spores through the rest of the house? What is being removed rather than cleaned? And — the one that separates a remediator from a cleaner — what is the moisture source, and what is being done about it? Remediation without a moisture fix is a receipt for the same job next year.
For heating and cooling work, ask whether the replacement equipment has been sized by an actual load calculation for your building rather than by a rule of thumb or by matching the old unit. Oversizing is the most common cause of a house that is cold and humid at the same time, and the moment of replacement is the only cheap opportunity to correct it.
Get the findings in writing, with photographs, measurements and dates, and get more than one opinion whenever the recommended work runs into four figures. A second opinion on a $4,000 quote costs a few hundred dollars and changes the recommendation often enough to be worth it as a matter of routine rather than as a sign of distrust.
Common questions
How much mold can I clean myself?
Up to roughly 10 square feet, per EPA guidance, on non-porous surfaces or sound drywall. Above that, in HVAC ducts, or after contaminated water, bring in a remediation contractor.
How do I choose a damp surveyor?
Pick one who sells the diagnosis rather than the cure, and pay for it separately. Ask them to name the cause before quoting a treatment — if the answer is condensation, the fix may cost nothing.
Who do I call about condensation?
Usually nobody. Condensation is the most common cause of household damp and the cheapest to fix — ventilation, habits and warming cold surfaces. Call someone when the pattern says penetrating damp, rising damp or a leak instead.
How much should an independent damp survey cost?
Typically a few hundred dollars for a residential property, depending on size and location, and it should produce a written report with photographs, measurements and a reasoned diagnosis rather than a quotation. If the person carrying it out also sells the remedy, you are not getting an independent survey regardless of what it costs.
Will my insurance cover damp or mold damage?
It depends entirely on the cause, which is another reason diagnosis matters. Sudden events — a burst pipe, a storm-damaged roof — are commonly covered. Gradual deterioration, condensation and maintenance failures such as blocked gutters generally are not, on the grounds that they were preventable. Document the timeline and the evidence from the start, because the distinction between sudden and gradual is exactly what a claim turns on.
Sources
- US EPA — Mold and moisture guidance — the 30–50% range and the 10 sq ft remediation threshold
- ASHRAE Standard 55 — Thermal environmental conditions for human occupancy — indoor comfort and humidity limits
- US DOE 10 CFR 430 — Dehumidifier test procedure — the 2019 move to 65 °F rating conditions