Mold inspection and indoor air help in Boston, MA
We do not keep an office in Boston. Every job starts with a free call. For large and complex properties in the Boston area we travel to you; for smaller jobs we tell you exactly what to ask for and point you to a local inspector we are comfortable recommending.
What the Boston climate does to a house
Measured at NOAA's Boston weather station.
- At the NOAA Boston station, mornings average 72 percent relative humidity across the year, and afternoons 57 percent.
- The dampest mornings come in September, averaging 78 percent. Afternoons are driest in April, at 55 percent.
- A normal year brings 43.77 inches of precipitation over about 127 days, with the most in March (4.32 inches).
- No month averages 80 percent morning humidity, which is why mold here almost always traces back to a water event rather than damp air.
| Month | Morning RH | Afternoon RH | Precip. (in) | Days with precip. | Mean temp (°F) |
|---|---|---|---|---|---|
| January | 69% | 58% | 3.36 | 12 | 29.0 |
| February | 68% | 56% | 3.25 | 10 | 31.7 |
| March | 68% | 56% | 4.32 | 12 | 38.3 |
| April | 67% | 55% | 3.74 | 11 | 48.1 |
| May | 70% | 58% | 3.49 | 12 | 57.9 |
| June | 72% | 58% | 3.68 | 11 | 67.7 |
| July | 72% | 56% | 3.43 | 9 | 73.4 |
| August | 76% | 58% | 3.35 | 9 | 72.1 |
| September | 78% | 59% | 3.44 | 9 | 64.9 |
| October | 76% | 57% | 3.94 | 9 | 54.0 |
| November | 74% | 58% | 3.99 | 11 | 44.7 |
| December | 70% | 58% | 3.78 | 11 | 34.7 |
Source: NOAA National Centers for Environmental Information, Comparative Climatic Data: average relative humidity (period of record through 2018), normal precipitation, mean temperature and cooling degree days (1981 to 2010 normals), and mean days with 0.01 inch or more of precipitation, 90 degrees or more, and 32 degrees or less. Last updated September 24, 2026.
Where moisture hides in Boston homes
Winter condensation in the attic
Warm, moist indoor air leaking into a cold attic condenses on the roof sheathing. The result is frost in January and dark staining on the underside of the roof by spring. Here about 97 days a year drop to 32°F or below.
Humid summers in basements
Basements stay cool, so humid summer air that reaches them hits the dew point. Musty basements and mold on stored items are the classic sign. Summer mornings here average 73 percent humidity.
Snowmelt and spring rain
Water that pools against the foundation during the thaw finds cracks and gaps and wicks into finished basements. A normal year brings 43.77 inches of precipitation.
Tight houses with little fresh air
Homes sealed up for winter trap cooking and shower moisture. Windows run with condensation and the corners of exterior walls grow mold. Winter afternoons here average 57 percent humidity outdoors.
Common questions from Boston
Large, custom or multi-property situations: see Keystone.
Mold or air problem in Boston?
Start with a free 15 minute call. We will tell you what you need, whether that is a local inspector, a virtual consultation or an on-site investigation.