Mold inspection and indoor air help in Boise, ID
We do not keep an office in Boise. Every job starts with a free call. For large and complex properties in the Boise 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 Boise climate does to a house
Measured at NOAA's Boise weather station.
- At the NOAA Boise station, mornings average 64 percent relative humidity across the year, and afternoons 42 percent.
- The dampest mornings come in January, averaging 79 percent. Afternoons are driest in July, at 20 percent.
- A normal year brings 11.73 inches of precipitation over about 90 days, with the most in December (1.55 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.
- Even in the afternoon, average humidity stays above 60 percent in 2 of 12 months. Indoors, 60 percent is the line where mold starts to find it easy.
| Month | Morning RH | Afternoon RH | Precip. (in) | Days with precip. | Mean temp (°F) |
|---|---|---|---|---|---|
| January | 79% | 70% | 1.24 | 12 | 31.3 |
| February | 76% | 58% | 0.99 | 10 | 36.5 |
| March | 69% | 43% | 1.39 | 10 | 44.5 |
| April | 65% | 36% | 1.23 | 8 | 50.8 |
| May | 63% | 33% | 1.39 | 8 | 59.1 |
| June | 60% | 28% | 0.69 | 6 | 67.5 |
| July | 49% | 20% | 0.33 | 2 | 75.8 |
| August | 47% | 22% | 0.24 | 2 | 74.7 |
| September | 53% | 28% | 0.58 | 4 | 64.9 |
| October | 62% | 38% | 0.75 | 6 | 52.8 |
| November | 73% | 59% | 1.35 | 10 | 40.0 |
| December | 79% | 70% | 1.55 | 12 | 30.7 |
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 27, 2026.
Where moisture hides in Boise homes
Plumbing leaks nobody sees
In a dry climate, mold is almost always a water event, not humidity. Slow leaks under sinks, behind dishwashers and in slab plumbing can run for months before anyone notices. Afternoons here average just 42 percent humidity, so damp air is rarely the cause.
Short, violent storm seasons
When the rain does come it comes hard. Roofs, parapets and flat-roof drains that sit dry most of the year fail all at once. Only about 90 days a year bring measurable precipitation, most of it in December.
Evaporative coolers
Swamp coolers cool by adding water to the air. Poorly maintained ones add humidity and their own microbial growth to the house. 48 days a year reach 90°F or more, which is when coolers run hardest.
Pools, spas and irrigation
Water features and landscape irrigation next to the foundation keep one side of a house damp in an otherwise dry place. A normal year brings only 11.73 inches of rain, so irrigation water often outweighs rainfall at the foundation.
Common questions from Boise
Large, custom or multi-property situations: see Keystone.
Mold or air problem in Boise?
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.