Dry Summer, Wet Basement: A Fall Moisture Plan for Maine Homes
Maine went into this weekend with every county in at least moderate drought. WGME’s September 17 drought update put the Midcoast from Casco Bay to Penobscot Bay back in extreme drought, with Portland at 8.65 inches of rain for June through August against a normal of just over 11, and Wiscasset finishing its fifth driest summer since 1998. The National Weather Service in Gray said in its September 10 drought statement that drought now touches 90 percent of Maine residents and is expected to persist into fall. The same week, frost advisories went up for Oxford, Penobscot and Aroostook counties.
The question we are getting is “my basement was bone dry all summer, do I still need to do anything before winter.” Yes, and a dry year is the easiest year to get the plan right, because you are starting from a clean baseline.
Why a dry summer does not mean a dry fall
First, the soil around the foundation shrinks. On the clay and silt lots we see around Gorham, Windham and the Midcoast, that pulls the backfill away from the wall and opens a gap at the top of the foundation. When the fall rain comes, that gap is where it goes, straight down the concrete to the footing. Baked ground sheds water instead of soaking it up.
Second, the sump pump has not run since May. A float switch that sat still for four months is the most common failure we find on a fall assessment.
Third, heating season changes the moisture picture entirely. Once the heat runs, cold surfaces below grade become the place water vapor lands. That is why a basement that was fine in July grows a bloom on the north wall in November. EPA’s moisture guide is the standard we work from: keep indoor humidity below 60 percent, ideally between 30 and 50, and dry anything that gets wet within 24 to 48 hours.
The plan, in the order we do it
Outside first, before the leaves drop. Walk the foundation. Look for the gap between backfill and wall. Fill it and regrade so the first six feet fall away from the house. Extend every downspout past that. In a dry year the gutters fill with dust and seed and nobody notices until the first real storm overtops them at the foundation.
Test the pump with a bucket. Pour water into the pit until the float lifts. If it does not start, or starts and hums, fix it while the ground is still dry. Check that the discharge line leaves the house and does not dump beside the wall.
Put a meter in the basement and read it for a week. A humidity meter costs 10 to 50 dollars and it decides everything else. Under 50 percent in late September with the dehumidifier off, you are ahead. Over 60, it stays on until the basement drops into the 50s, where most portable units ice their coils and stop doing useful work, usually late October in southern Maine. Then empty it, clean the filter and bucket, and store it dry. A bucket left half full over winter is a mold source of its own.
Pull storage off the walls and the floor. Cardboard against a foundation wall is the most common thing we find fruiting on a fall visit. Plastic totes on a shelf, four inches off the wall, is the fix.
Find the cold spots. The rim joist, the corner behind the oil tank, the wall behind the bulkhead door. That is where condensation forms once the heat is on, and air movement on the surface does more there than a dehumidifier.
What this has to do with an abatement plan
If you already have a remediation scope in hand, or you are about to get one, read it for the moisture section before you read it for the price. Cleaning mold off a wall that is still getting wet is money spent twice. A scope that does not say what the water source was and what was done about it is not finished. Our cost page shows how much of a typical job is moisture correction versus removal.
Our own process runs the same way. A free assessment starts with the moisture meter and the exterior, not the wall with the stain on it. If the answer is a regrade and a downspout extension, we say so and you do the work yourself. If the growth is past surface cleaning, the remediation includes the source fix or it is not worth doing.
Landlords: this is your walkthrough month
If you own rental units, the shoulder season between the last dry week and the first heating bill is the walkthrough to do. Photograph the basement, the bathroom ceilings and the closets on exterior walls with a date stamp, read the humidity in each unit, and put it in the file. Maine’s habitability rules now name mold specifically, which we covered in our post for landlords. A dated set of dry photos from September tells you in December whether a complaint is a new leak or a humidity problem.
What to do if the rain never comes
The Climate Prediction Center outlook in the WGME piece calls for near or below normal precipitation through the end of the month. Maine Emergency Management Agency tracks the weekly monitor and the seasonal outlook on its drought conditions page. If it stays dry, the outside work still matters, because droughts usually end with a storm, not a drizzle. The inside work matters more, because heating season is coming either way, and condensation does not need rain to start.
We serve Gorham and the greater Portland area and the rest of the state. If you want a second set of eyes on the basement before the heat goes on, call 207-464-8202.