The foil test
This takes two or three days and costs almost nothing. Do it on the wall that looks wettest.
Dry a patch of wall
Wipe a section of the concrete or block about the size of a sheet of paper and let it air out for an hour, or use a hair dryer on low.
Tape a square of foil to it
Use plain aluminum foil or a piece of clear plastic and seal all four edges with duct tape so no room air gets behind it.
Wait 48 to 72 hours
Leave the room as it normally is. Don't run a dehumidifier harder than usual during the test, or the result will be skewed.
Check both sides
Peel it back. Moisture on the room side of the foil means the air is condensing on a cool surface. Moisture on the wall side, under the foil, means water is moving through the concrete from outside. Both sides wet means both are happening.
Why Englewood basements sweat in summer
Colorado air is dry most of the year, which surprises people when a basement wall turns damp in July or August. The reason is temperature. Soil a few feet down stays cool all summer, so the foundation wall stays cool too. When warm, humid air from a summer storm or from an open window drifts downstairs, it hits that cool concrete and drops its moisture, the same way a cold glass beads up on a patio table.
Older Englewood houses add their own factors. Many basements were finished decades after the house was built, often with paneling or drywall set close to bare concrete and no insulation behind it. A clothes dryer venting poorly, a humidifier on the furnace left running into summer, or a basement shower without an exhaust fan all push the indoor humidity up. The result can be damp carpet edges, musty smells and mildew spots that look like a leak but have nothing to do with groundwater.
How the two problems usually differ
| Condensation | Seepage |
|---|---|
| Worst on humid summer days, regardless of rain | Follows rain, snowmelt or heavy lawn watering |
| Spread evenly over the wall surface, often on cold water pipes too | Concentrated low on the wall, at cracks or the floor joint |
| Disappears when a dehumidifier runs | Leaves white mineral deposits as it dries |
| Foil test: wet on the room side | Foil test: wet on the wall side |
| Fix is humidity control, air movement and insulation done correctly | Fix starts outside with gutters, downspouts, grading and window wells |
When it is both
Plenty of basements have a little of each: a damp corner below a downspout and a general summer clamminess. Deal with the outside water first, because a wall that is soaking from behind will never dry no matter how much air you move. Then bring the humidity down and watch the readings for a full season before deciding whether walls that were finished over bare concrete need to be opened.
General information for Englewood, not a quote or professional advice. In an emergency, call 911.