How to tell if your sill plate is rotting and what to do

The sill plate is the piece of lumber that sits on top of your foundation and carries the weight of the entire wall above it. When it rots, the wall above it loses its bearing. Most homeowners do not know they have a problem until they notice a door that will not close right or a floor that has developed a soft spot near an exterior wall. By then the rot has usually been going on for years.

Why sill plates rot in Vermont homes ¶

Older homes in central Vermont, particularly those built before the 1970s, often have sill plates that sit directly on a stone or concrete foundation with no capillary break between them. Moisture wicks up from the foundation into the wood. Add a basement that does not drain well or a grading situation that sends water toward the house, and you have a sill plate that is wet more often than it is dry.

Modern building practice calls for a sill seal gasket between the foundation and the pressure-treated sill plate. A lot of older homes have neither the gasket nor the pressure-treated lumber.

Signs you can check yourself ¶

Go to your basement and look at the sill plate where it with the foundation. Press on it with a screwdriver. Sound wood resists. Rotted wood gives, sometimes dramatically. Look for discoloration, a soft or spongy texture, or wood that crumbles when you press it.

Also look at the band joist, the vertical piece of framing that sits on top of the sill plate. Rot often travels from the sill plate up into the band joist, especially at corners.

• Doors or windows that have started sticking without an obvious cause
• Floors that feel soft or springy near an exterior wall
• Visible gaps between the sill plate and the foundation
• Discoloration or staining on the foundation wall below the sill
• A musty smell in the basement that is concentrated near one wall

What a proper repair looks like ¶

Replacing a sill plate means temporarily supporting the structure above it, removing the damaged wood, treating any adjacent framing that shows early signs of moisture damage, and installing a pressure-treated replacement with a sill seal gasket. The new sill plate gets anchored to the foundation with the appropriate hardware.

This is not a weekend project. The temporary support has to be set correctly or you risk racking the wall above. We have done this repair on a number of older homes in Washington County and the work typically takes one to two days depending on the length of the affected section and the condition of the adjacent framing.

If you are not sure whether your sill plate is in good shape, a quick look in the basement with a screwdriver will usually tell you. If you find something soft, it is worth getting someone out to look before the next winter adds more moisture to the situation.