Why Does Exterior Paint Peel on the North Side of Minnesota Homes?

Walk around almost any older house in Wright County in April and you will find the same thing: three sides look fine and the north side is blistered, flaking, or bare down to grey wood along the bottom courses and under the windows. Homeowners often assume the painter used bad paint on that wall. Usually the paint is the same. The wall is different, and it is different in ways that are specific to how a Minnesota house behaves in winter.

Why does the north side of my house keep peeling?

Because the north wall gets wet from both directions and dries slower than any other wall on the house. In winter, moisture from inside the house migrates out through the wall and freezes or condenses behind the paint. In the warm months, the north side sits in shade, so rain, dew and snowmelt stay on the siding longer. Paint that is repeatedly pushed from behind and soaked from in front loses its grip. Then ice dams, overflowing gutters and dried-out caulk add liquid water on top of it.

None of that is fixed by a better can of paint. It is fixed by drying the wall, removing everything that has let go, and sealing the paths the water is using.

Moisture drive: the house pushes water out in winter

Here is the part most national painting articles skip, because it does not happen in Georgia. In a Minnesota January, the air inside your house might be 70°F and holding moisture from cooking, showers, plants and breathing. Outside it is zero. Water vapor moves from warm and humid toward cold and dry, and in winter that means outward, through the drywall, the insulation, the sheathing and finally the siding.

In a house with a good vapor retarder on the warm side of the wall, most of that moisture stops at the drywall. In a lot of homes built before the 1980s, and in plenty built later with a torn or missing poly layer, it does not. The vapor reaches the cold sheathing and siding and condenses, or freezes, right behind the paint film. It sits there all winter. In March and April, the sun starts warming the wall from the outside, that moisture turns back into vapor, and it pushes the paint off from behind. That is what the spring blisters are. Pop one and it is often damp inside.

Every wall gets this to some degree. The north wall gets it worst because it is the coldest wall, so it condenses the most vapor, and it never gets the winter sun that dries the others out on a mild afternoon.

Bathroom and kitchen exhaust make it worse. A bathroom fan that vents into the soffit instead of through the roof, or a dryer duct that leaks in a wall cavity, dumps concentrated moisture right where it does the most damage. If one wall peels badly under a bathroom window, that is the first thing we look for.

Shade and slow drying

The second mechanism is simpler. The north side of a house in Minnesota gets almost no direct sun from October through March and only early-morning and late-evening light in summer. It stays cooler and it stays damp. Dew that burns off a south wall by nine sits on the north wall until noon. After a rain, the north side may still be wet the next morning.

Wood siding that stays damp expands. When it finally dries, it shrinks. Paint that went on when the board was one size is being stretched and squeezed every cycle, and eventually it cracks at the board edges and along the grain, which lets in more water, which makes the next cycle worse. Mildew also likes a shaded, damp wall, and a mildewed surface holds moisture against the paint.

Mature trees make it worse still. A north wall behind a row of spruce is in permanent shade with poor airflow, and it can be the one wall on the house that needs repainting twice as often as the rest.

Ice dams and gutter overflow

Now add liquid water. In a snowy winter, heat escaping through the roof melts the underside of the snowpack, the water runs down to the cold eave, and it refreezes into a ridge of ice. Water pools behind that ridge. Some of it gets under the shingles and into the house, which is the ice dam damage people know about. The rest runs over the edge, down the fascia, and behind or down the face of the siding, where it freezes into a sheet at night and thaws every afternoon.

Dams build higher on north eaves, because there is no sun to melt them from above. So the north wall gets weeks of daily wetting from ice melt at exactly the spots, under the eaves and at the corners, where paint is thinnest and joints are most exposed.

Gutters that fill with ice do the same thing in slow motion. Once a gutter is a solid block, every bit of meltwater goes over the edge. By spring the siding below an iced-up north gutter has had more water on it than a whole summer of rain.

If the house has a recurring ice dam, we will tell you, because a paint job will not outlast it. Air sealing and insulation in the attic are the real fix, and the paint holds far longer once that is done.

Failed caulk and open joints

Caulk ages faster than anything else on the outside of a house. The joints where siding meets window trim, where trim meets corner boards, and where two boards butt end to end all rely on caulk to keep water from getting behind the surface. Minnesota’s freeze-thaw swings pull those joints open and shut every day in spring and fall, and after a decade or so the caulk hardens, cracks, and pulls away from one side.

An open joint on a north wall is a water inlet. Rain and ice melt run in behind the siding, soak the back of the board and the end grain, and come back out through the paint as peeling that starts at the joint and spreads. If you see paint failing in a line down from a window corner, that corner joint is almost certainly open.

The prep that fixes it

A repaint that lasts on a north wall is mostly prep, and it is the reason our exterior estimates in Rockford and Monticello often show more hours on the north elevation than on any other side. Here is what it involves.

• Scrape every bit of loose paint, then scrape a little past the edge of it. If the film lifts with a putty knife, it is not sound.
• Sand the scraped edges so the transition from bare wood to old paint is feathered, not a step.
• Let the wood dry. We do not prime bare wood until it has had time to dry through. On a shaded wall in spring that can mean a few dry days, not a few hours.
• Wash off mildew and chalk with a mildew-killing cleaner and let that dry as well.
• Cut out failed caulk and recaulk with a quality exterior sealant, including the butt joints and around windows.
• Prime all bare wood with an exterior primer that seals the end grain. Skipping this on bare cedar or hardboard is how a fresh coat fails in two years.
• Repair or replace boards that are rotted at the bottom edge, and hardboard that has swelled at the ends.
• Then paint, two coats, in the afternoon when the north wall is finally warm and dry.

We sequence the north wall last in a spring job and paint it in the warm part of the day. On a fall job, we make sure it is done before the overnight lows get close to the dew point, for the reasons covered in our post on the best time to paint a house exterior in Minnesota.

What paint alone will not fix

A few things are outside a painter’s toolbox, and we would rather say so than repaint a wall we know will peel again:

• A bathroom or dryer exhaust venting into a wall or soffit needs to be rerouted outside.
• Chronic ice dams need attic air sealing and insulation.
• A missing vapor retarder in an older wall is not something to fix from outside, but running the bathroom fan properly and keeping indoor winter humidity moderate helps a lot.
• Hardboard siding that has swelled and gone soft at the bottom edge needs replacement, and painting it only delays that.

Once those are handled, a properly prepped north wall holds paint about as long as the rest of the house. Our exterior siding painting page covers the full process by siding type.

If the north side of your house is starting to let go, send a couple of photos of the worst spots through our contact page and we will tell you what we think is causing it.