Water, Water Everywhere

IAQ IQ, Fall 2025
©2025 Jeffrey C. May

Properties located near large bodies of water can present issues and conditions that may not plague properties located inland and that may be of concern to both indoor air quality professionals and home inspectors alike.

Window- and door-cap flashings: Properties near large bodies of water can be particularly susceptible to wind-blown rain. If window- and door-cap flashings are sloped toward rather than away from the cladding, the rain can flow toward rather than away from the building. Water trapped on top of the flashing travels to the ends where by capillary action, the water can flow through small cracks in the cladding, potentially causing decay to the framing and sheathing. If the decay is serious enough, musty odors can spread indoors, and structural work may be needed.

Gutters and downspouts: Gutters should be maintained free of debris, and downspouts should direct roof water away from a foundation. This is always true for any home, but for homes that are not consistently occupied, that face large bodies of water, and that potentially face wind-blown rain, a clean and efficient gutter system is of utmost importance.

Mechanical systems: I’ve looked at a number of vacation homes near or on the shores of large bodies of water. I often find air quality problems stemming from how the mechanical systems are used or not used when the occupants aren’t present.

1. Unless the water main is shut off, leakage can occur when no one is in the house. That is why I recommend that the water main be shut off until someone is occupying a vacation home.
2. Another practical step would be to install floor/water alarms at the bases of a hot water tank/heater and a washing machine (such alarms can be battery operated or attached to a central alarm system, if present).

Controlling the relative humidity (RH):

1. If the homes aren’t consistently air conditioned in the humid season (in New England, generally between mid-April and mid-November), conditions of high relative humidity (RH) can develop that can lead to mold growth. The same is true if the below-grade spaces aren’t being air conditioned or dehumidified adequately. (One cannot necessarily depend on the A/C system to dehumidify adequately; if necessary, a dehumidifier should also be used.)
2. The RH in below grade spaces should be kept under 50% in crawlspaces and unfinished basements, and under 60% in finished basements.
3. The RH should be measured separately from a dehumidifier by placing thermo-hygrometers on or near the floor in exterior corners; some such devices can be “remote read.”
4. When occupants are away from the house (whether for a few days or for a longer period of time) in the heating season, the heat should not be turned down below 60^oF above grade or in a finished below-grade space.

The Exterior: Plantings should be trimmed to leave at least a foot clearance around the house. This will allow someone to keep an eye out for water ponding as well as pest activity next to the foundation wall. There should be no openings at the exterior as well as between an attached garage and the interior that would allow pest entry. When home occupants are away, the pests can play!

Checking the property: When away from the property, an owner of a vacation home should arrange to have someone check the house inside and out at least once a week, as well as after a heavy rain. Such work might be a potential source of income for a home inspector, who could check the following on such visits:

1. Is the gutter system working as intended?
2. Are there any signs of leakage inside – leakage from pipes, a washing machine, a refrigerator, etc.?
3. In the heating system, is the thermostat above grade and in a below-grade finished space set no lower than 60^oF?
4. In the cooling season, is the air conditioning running? Setting the thermostat to 75^oF might suffice to help control the RH above grade; if not a dehumidifier can be installed that drains to the exterior or into a sink or sump.
5. Are unfinished, below-grade spaces being adequately air conditioned or dehumidified?
6. Are there signs of pest activity in the house (including below-grade) or in an attached garage?

All wishes for a pleasant Thanksgiving.

Jeff May