Windows

Failed seals show up as fog or condensation between the panes, which means the insulating gas has gone and the window is now doing roughly the job of a single sheet of glass. Frames that have rotted or racked out of square let air through no matter how good the glass is.

We replace windows on Minnesota homes and make sure the opening is properly flashed and sealed, because a good window installed badly still leaks.

What this covers

• Full window replacement
• Failed seal and fogged glass
• Rotted or damaged frames
• Proper flashing and air sealing

What a failed seal actually costs you

An insulated glass unit is two panes held apart by a spacer, the perimeter sealed and the cavity filled with argon or krypton. The gas slows heat transfer better than air. It is invisible, and it is why the window performs the way the sticker said.

Seals fail slowly. The gas leaks out over years, room air works in, and moisture comes with it. Trapped between the panes, that moisture condenses whenever the outer pane gets cold. That is the fog. By the time you see it, the gas has been gone a long while.

A fogged unit is not much better than a single pane. The air between the panes convects freely and the low-e coating is often etched by the trapped moisture. The window still keeps rain out. It has mostly stopped keeping heat in.

A failed seal is not an emergency. Nothing is rotting, nothing is leaking into the wall. If it fogged in May, run it through the summer and deal with it before cold sets in. But seals do not reseal.

On many windows the glass unit can be replaced without replacing the whole window. If the frame is sound and the hardware works, that is a smaller job. On older or off-brand units the glass may not be available, but ask before you price out a replacement.

Reading condensation: inside, between, outside

Where the water sits tells you what is wrong, and homeowners mix the three locations up constantly.

Cold outdoor air holds little moisture, so when it comes indoors and warms, indoor humidity drops. If your windows sweat at ten degrees outside, you are making more moisture than the house sheds.

Common sources are showers without a working bath fan, a humidifier set too high, cooking without a range hood that vents outdoors, and a damp basement. Bath fans are the usual culprit. Run them during the shower and twenty minutes after. New windows tighten a house, so humidity that used to leak out now finds the glass.

If your only complaint is wipeable interior fog on sound windows, replacing them is the expensive way to solve a moisture problem. Get the humidity down first and see what is left. Heavy condensation that soaks the sill is worth looking at, because standing water on a wood sash will eventually rot it.

• Between the panes, where you cannot wipe it off: the seal has failed. This is the only one of the three that means the window itself is broken.
• On the inside surface, where you can wipe it off: the glass is colder than the dew point of the air in your house. That is a humidity problem, not a window problem.
• On the outside surface in the morning: the glass is colder than the outdoor air because so little heat is escaping through it. The window is working well.

Frames: rot, racking, and material by material

Frames are what usually put a window past saving. Wood absorbs water and rots. Any frame can rack, meaning the rectangle has gone out of square, usually from settling or bad shimming at install. A racked frame will not seal no matter how good the sash is.

Wood rots from the bottom. The sill and the bottom few inches of jamb take the water, so press there with a screwdriver. If the tip sinks in under light pressure, the wood is gone. Soft spots the size of a quarter can sometimes be cut out and filled. Soft along the whole sill means the frame is finished.

Vinyl does not rot, but it expands and contracts hard, and Minnesota swings from ninety above to twenty below. That movement works the welded corners loose, so check frame corners for hairline separations. Older vinyl also gets brittle and chalky on south and west exposures.

Aluminum conducts cold straight through: frost on the metal on a cold morning, water running onto the sill. Fiberglass and composite move about as much as the glass does, which is why their seals last, but bad flashing still defeats them.

One honest note on rot. If it is in the framing around the window rather than the window frame, and especially if it runs into sheathing or a header, that is a different conversation. Small areas of rotted framing we can address as part of the opening. Structural questions about a header or bearing wall belong with a structural engineer, and we will tell you when we think you are looking at one.

Insert versus full-frame replacement

An insert, or pocket window, sets a new window inside the existing frame. The old frame stays, trim usually stays, and the siding is untouched. Full-frame means the entire old window comes out, down to the rough opening. Trim comes off, siding at the perimeter is disturbed, it takes longer and costs more, and it is sometimes the only thing that makes sense.

If the existing frame is sound, square, and dry, an insert is a good use of your money. If the frame is rotted, racked, or you have reason to think water has been reaching the wall, an insert hides the problem behind a new window. You will not know what you sealed in until it comes back out.

The tradeoff with an insert is glass area. A frame inside a frame costs a couple of inches overall. On a big picture window nobody notices. On a small bathroom window it shows. We will tell you what you lose before you decide.

Full-frame also lets us see the opening. With the old window out we can check the sheathing, the sill, and whether the original flashing existed at all. On older houses that inspection is often worth as much as the window, because it tells you whether the wall is dry.

Why a good window installed badly still leaks

The window is a manufactured product and performs as built. The opening is job-site work, and that is where the difference gets decided.

Water enters walls at the top and sides of openings and drains down, so flashing has to shingle: the sill pan goes in first, jamb flashing laps over the pan, and head flashing laps over the jambs and tucks under the water-resistive barrier above. Reverse the order and you have built a funnel into the wall.

The sill pan matters most. It is a waterproof tray under the window with the back edge turned up, so water that gets past the window is caught and drained back outside. Plenty of older Twin Cities windows were installed with nothing under the sill but a bead of caulk. Caulk is a seal, not a drainage plan, and it does not last thirty years.

Air sealing is a separate job from water. The gap between frame and rough opening gets low-expansion foam or backer rod and sealant. Too much pressure from expanding foam bows the frame and the sash stops closing right. Fiberglass insulation stuffed in the gap, common for years, stops almost no air.

We replace windows on Minnesota homes and flash and seal the opening as part of that work. If you are getting bids, ask each contractor what goes under the sill. The answer tells you a great deal about the rest of the job.