In mid-century modern homes, sliding glass doors are the definition of clean, modern living. They provide beautiful light for the home interior; offer an uninterrupted view to a captivating backyard or atrium; and when open, create a cooling breeze that prompts the family inside to breathe a sigh of relief.
Minimal and modern, single-pane aluminum-framed Arcadia-brand sliding glass doors represented the technology of the 1950s and early '60s and were part of the Eichlers' original well-planned design. Simple handles let homeowners open these doors with little effort, and cleaning was a breeze.
"With the floor-to-ceiling glass, it fit right in, basically making a glass wall that only minimally blocked the view to the exterior," says John Klopf, an Eichler-specialty architect based San Francisco. "It has as much connection to the outside as possible. When the door is open, there's nothing there."
Over time, things can go wrong with the original sliders: rollers and tracks wear to the point that the doors are difficult to operate; the locking mechanisms break down; safety becomes a concern, especially with breakage tied to earthquakes and accidents; or owners want improved energy efficiency and savings. Some may look to a new sliding door as part of a home addition or remodel.
"If you're adding a door, you'll want to think about why you are doing it," Klopf says. "Is there a view, an access you're trying to gain for more light or air circulation?" What's more, how will the door capture light, and will it bring about unwanted privacy issues?
As with any major replacement in a home of historical value, aesthetics are key. "It is important to retain the original Eichler look as much as possible when replacing the doors and windows," recommends Dave Stellman of glass door and window dealer Palo Alto Glass.
Most modernist homeowners seem to agree. They want to retain the sleek appearance of their exteriors and opt for anodized aluminum window frames. "More people today have the good idea that you replace aluminum doors with aluminum, particularly in an original Eichler," says general contractor Henry Calvert of Calvert Ventures in San Mateo. "People are really aware of the look and, in my experience, are staying true to it."
Although aluminum frames look good, their biggest disadvantages are condensation and high thermal conductance, or heat transfer. Simple aluminum frames let heat out in the winter and in during the summer.
Door and window manufacturers today offer thermally broken frames, which reduce conductivity by splitting the frame components into interior and exterior pieces joined together by a less conductive material, such as plastic. In cold climates, a non-thermally broken aluminum frame can easily become cold enough to condense moisture or frost on the inside surfaces of window frames.
Because mid-century modern homes have large expanses of glass, window condensation is more noticeable than in other types of homes. In cooler months, the original single-pane glass, which has an R-value (a measure of insulating capacity) of less than 1, results in cooler air next to the inside surface of the glass than the rest of the air in the room. Moisture condenses on the inside surface of the glass.
Today's double-pane 'low E' sliders have R-values ranging from R-2 to R-4 and can help reduce the amount of humidity inside the house. Double-pane doors also make for a quieter interior. Low E glass has a transparent coating applied to its surface that separates long wave (heat) energy and short wave (light) energy. The long wave is reflected back to the heat source, and the short wave is allowed to pass through its coating to brighten the home interior.
Thermally sealed sliders are sealed against moisture. The insulating glass is made up of two sheets of glass separated by a roll-formed metal spacer tube all the way around the glass, which contains moisture-absorbing material. The glass is completely sealed to create a moisture-free air space between the panes of glass.
Homeowners also replace doors, as well as windows, for safety. Tempered glass, or 'safety glass,' which breaks into small pieces when struck, has been used in cars since the 1920s, but was not required in 1950s-era houses. The Eichlers were built with glass that can potentially break into dangerous shards upon impact or during an earthquake.