Not all basements leak, but many will leak will during a winter rain, like today's.
Frozen Ground + Rain = Wet Basement (potentially...)
In summer, water finds a way into your basement when an accumulation of rain exceeds the amount of rain the ground can absorb. The ground surrounding our homes acts like a sponge, soaking up rain and runoff. In winter, the ground acts like asphalt. Gravity pulls runoff into any and all low spots until full. Unfortunately, basements are often the destination as they provide the only thawed ground to be found on this the arctic tundra (Brunswick).
Laws of thermodynamics dictate that heat moves from hot to cold. Your warm basement will lose the most heat via the exterior concrete walls. Concrete is a terrible insulator. A 60° basement is like Jamaica to a 10° winter day. During an average southern or central Maine winter, the ground surrounding an average basement will not freeze for 4-6 inches due to this escaping heat.
This is the exterior of my home with a traditional basement. Note the visible stones and leaves that are not covered by snow (get off my case about not cleaning up last fall...). The ground below them is not frozen, either. This is the path water will take if it accumulates in this spot.
This is the exterior of my garage foundation. This foundation does not have a heat source as its on a slab. Snow has settled against the siding and the ground is frozen solid, resisting water from getting to the foundation. No heat, no thaw. No thaw, no water intrusion.
Its important to note that we don't heat the basement. The basement doesn't have its own thermostat and we don't use space heaters. However, our furnace, water heater, and pluming supply lines in the basement naturally radiate heat to keep this space at 58°-60° during winter months. After inspecting thousands of Maine homes, I can tell you that this is the most common setup. You and your clients likely have something similar.
How about a solution?
Two schools of thought: Offense and Defense
Offense: Possibly too late for this year, but get ready for next
Insulate the Basement: Insulating the foundation walls will minimize heat loss and also minimize the thaw that occurs outside your foundation.
On-Call Ready Sump Pump: While you may not need one in summer, having one ready in winter to collect any water may be helpful if you've experienced winter water intrusion in the home. If it happened once, expect it to happen again.
Insulate the Attic: What? Why? If your attic has improved insulation, icicles and roof dripping will decline to minimize accumulated snow/ice along the drip-edge of your home. Remember, this acts as a barrier to trap water close to your foundation instead of spilling it over your yard.
Eat a Donut: Can't hurt, right?
Defense: The water is coming in and you need to deal with it.
Sump Pumps: If you have a sump pit and use a sump pump in summer, keep it on-the-ready all year. Test it today (right now!) to confirm it will run when needed. I often find these unplugged or plugged in but no longer operable.
Keep Items off of the Basement Floor: Don't keep anything porous (cardboard, wood, fabric) in direct contact with the floor. You could lose valuables if the basement gets wet. Many use pallets to set boxes and belongings on.
Watch: Defend as needed when you find a problem, typically a few hours into a rain event. Identify any issue-prone areas of the basement and seal as-needed. (Be careful of attempting to seal cracks or the foundation floor/wall connection. This typically just shifts the entrance point. Be aware and react as-needed.)
Good luck and pass this around to your friends and neighbors.
Thanks for reading,
Matt and Matt
Square One Home Inspections