Window Glass Replacement in St. Louis

Inside, outside or between the panes?

Where the water sits tells you what you have. Wipe both faces of the glass with a dry cloth:

• It wipes off on the room side. Room air met glass colder than the room, which the rating council's consumer guide names as the cause. That is mostly a humidity question, covered next.
• It wipes off outside. That is dew. One major window maker says it shows up mainly in spring and fall, when a cool night follows a warm day, and that it means the glass is insulating well enough to keep the outer pane cold. It burns off during the day.
• It will not wipe off from either side. The moisture is inside the sealed unit. The window industry's own description of a failed unit is permanent fogging, a milky-white film on the inner glass faces, caused by a broken hermetic seal; the gas fill can escape along with it.

One more pattern worth knowing: a band of condensation about an inch wide around the edge of the glass with the middle clear. The same maker traces that to metal parts at the glass edge carrying cold inward, not to a leak, and the rating council notes that warm-edge and non-metal spacers cut that edge condensation.

Room-side condensation is a humidity problem

Window makers are blunt about it: condensation on the inside of the glass means too much moisture in the house, and the glass is simply the coldest surface around. One maker's condensation guide puts a family of four's breathing at about half a pint of water an hour, cooking three meals at four or five pints a day and each shower at another half pint, more than 18 gallons a week in all.

The same guide prints maximum indoor humidity by outdoor temperature, based on University of Minnesota lab work with the house at 70 degrees:

Most fixes cost nothing: run the bath fan until the mirror clears and the kitchen fan while you cook, keep drapes open so warm air reaches the glass, turn the humidifier down as it gets colder, and make sure dryers and gas appliances vent outside. If the inner face of a storm window fogs, room air is leaking past the main sash into the gap (see storm windows). A newer window with a higher condensation resistance number on its label will sweat less, but it will not dry out a damp house.

A failed seal: new glass unit, new sash or new window

Once a seal has failed, nothing restores it in place. The fix is a new sealed unit, and it can go in three ways:

• A new insulated glass unit in the old sash. The glazing stops or clips come off, the old sealant is cut free, a unit built to the exact size goes in on fresh sealant, and the stops go back on. Frame, trim and wall stay untouched.
• A new sash from the window's maker, where the maker still sells one for that line. The glass arrives sealed into a new sash that drops into the old frame.
• A new window, when the frame or sash has failed as well, or when neither a unit nor a sash can be had for that model.

On a sound frame the first two are the right recommendation, and we would rather sell you a pane than a window you do not need. A replacement unit is built to order, so there is a gap between measuring and installing. Ask for the new unit to match its neighbors in glass coating, tint and grille pattern, or it will stand out on that wall for as long as you own the house.

The rules that still apply to a glass-only job

Glass replacement is lighter on paperwork than window replacement, with four things worth knowing:

• Energy code. New glass in an existing sash does not trigger the U-factor rule; a new sash and glass together do (window energy code).
• Permits. Unincorporated St. Louis County exempts glass-only work in an existing sash outright (county rules). University City is the one to check: its code calls for a permit to add, remove or change out any glazing in a building's thermal envelope, so ask the city before treating a glass swap as exempt there.
• Safety glass. New glass going into one of the code's hazardous locations, such as beside a door or over a tub, must be safety glazing carrying its permanent mark (IRC R308). The existing-building code says replacement glass has to meet the rules for new installations.
• Lead. EPA's definition of renovation names window repair. On a house built before 1978, scraping old paint or putty brings in the lead rule unless the job stays inside the minor-repair limits of 6 square feet of painted surface per room indoors or 20 square feet outside (lead paint rule).

Drafty windows: glass, sash or frame?

The National Park Service splits a window's heat loss two ways: conduction through the glass, and air leaking around the sash and frame. A new glass unit only touches the first. Before blaming the glass for a draft, the Park Service says to deal with the leaks: caulking, weatherstripping and failed glazing compound.

On a wood double-hung, its repair brief treats modern weatherstripping as part of any repair and warns that old felt holds moisture at the bottom rail. The alternatives it names are rolled vinyl, metal strips and plastic spring strips. It also recommends a sash lock on the meeting rail, which keeps the sashes pulled tight so the weatherstrip can work.

On a newer window, run the same checks before anything else: does the lock pull the sashes together, is the weatherstrip still in its groove and still springy, and does the sash sit evenly in the frame when closed? Each of those is a part or an adjustment. A draft that is still there with the window locked and the weatherstrip sound is coming from around the frame, where the gap between window and wall needs sealing. That is an installation question, not a glass one.

A sash that drops, creeps or will not stay open

A double-hung sash that slides down on its own, or takes two hands to lift, has a counterbalance problem, not a glass problem.

In an older wood window, each sash hangs on cords running over pulleys to weights hidden inside the wall. The Park Service calls replacing broken sash cords one of the most common items in repairing these windows. The weight pocket is often reached through a small door low on the side of the frame, and the cords can be renewed with rope or chain.

Newer double-hungs use spring balances in the jambs or header. This Old House's guide to replacing them notes that often only one side has failed, that both should be replaced together for even tension, and that the balances are rated to the weight of the sash, so the sash gets weighed before new ones are ordered. Either way, it is a parts job on a window that may have years left in it.

A sash that sticks is a different symptom: layers of paint, swollen wood, or a frame that has moved. Paint and swelling can be repaired. On a pre-1978 house, freeing a painted-shut sash disturbs paint, so the lead limits above come into play. A racked frame is the next section's problem.

When the frame is the real problem

Glass, balances and weatherstripping are parts. The frame is the window. The Park Service's repair brief singles out water as the leading cause of rot in wooden windows, and its checklist is short: water getting in around the edges of the frame, cracked or missing glazing putty that lets water soak the wood, and a sill that should slope down and away from the house so water drains off it.

Signs that a repair will not hold:

• Wood at the sill or the bottom rail that a screwdriver sinks into.
• A sash that rubs in the same spot because the frame has gone out of square.
• Water stains on the wall or floor below the window.
• On vinyl, corners that have split open.

The Park Service's own rule of thumb is a good one: if most of the work is routine maintenance and stabilization, repair; if a large number of new parts are needed, a good matching replacement may make more sense. That is where a new glass unit stops being the answer and window replacement starts, usually full-frame so the opening can be flashed. In a local historic district the bar for replacement is higher; see the historic district rules.

Common questions about window glass replacement in St. Louis

Where we work

Window glass replacement across greater St. Louis, from the city and St. Louis County out to St. Charles, Jefferson and Franklin Counties and across the river into the Metro East. Each city has its own page with the permit rule and code edition that apply there: