window frames and sashes

The efficiency of a window doesn't depend only on its glass. Frames and sashes (the glass element fits into the sash, and the frame holds the sash) and details like thermal breaks or argon filled panes and spacers are also important elements for the energy efficiency of a windows and its lifespan.

Good performing windows demand high-quality frames and sashes, conveniently insulated.

Important details related with frame and sash

A window is a whole. Its glass is particularly important. Details related with the glass panes are also very important: details like krypton- and argon-filling, warm edge spaces (to reduce thermal bridging at the edges of the window)...

But the frame and sashes and the materials they are made from and their insulation (the hollow sections of the frame and sash should be filled with foam insulation to increase the energy efficiency of the window) can also be crucial.

Materials

Window frames and sashes can be manufactured from a variety of materials – aluminum, fiberglass, vinyl (PVC), wood, or a combination of these materials -, which has implications in the thermal efficiency, durability, environmental impact and costs of the windows…

Aluminum frames

Aluminum windows are durable and offer low maintenance and low costs. But simple aluminum windows can be a wrong option in cold or even in moderate climates, due to the highly conductivity of aluminum (a cause of high energy loss).

Only aluminum frames with thermal breaks - that is, with their external and internal frames separated by a good insulating material - can rate high.

Use the Energy Star UR-value and other equivalent ratings (see Window Rating) to assess the effectiveness of thermal breaks, in the case of aluminum frames and sashes.

Fiberglass frames and sashes

Fiberglass frames and sashes are very energy efficient, and offer good structural strength, high durability and minimal or no maintenance costs.

The hollow sections of the frame and sash can and should be filled with foam insulation to increase the energy efficiency of the window.

Vinyl frames and sashes

Extruded vinyl frames (PVC) are good or even excellent in terms of energy efficiency, and demand low or no maintenance costs; vinyl frames can also be filled with foam insulation to provide a better energy efficiency. Thermally welded corners also improve the performance of vinyl frames and sashes, preventing air and water leakage.

But vinyl windows have also some disadvantages. Vinyl isn't an environmentally-friendly material, and large vinyl windows need to be reinforced to allow a better strength, which can diminish it's energy efficiency (some reinforcing materials aren’t good in terms of energy efficiency...).

Wood frames and sashes

Solid wood frames have a good insulating value, and a good structural strength…

The disadvantage? The impact of the weather on them… and their possible short lifespan and high maintenance costs.

High performing wood frames and sashes demand factory-applied cladding and finishes, and well-sealed corners and gaskets. They tend to be expensive.

Composite windows

Some window frames and sashes combine two or more materials (aluminum, fiberglass, wood…) in order to get the best features of each material. But a composite window doesn’t necessarily mean high-efficiency. The final performance depends on multiple manufacturing details.

the best frames and sashes

There are excellent fiberglass, vinyl and composite window frames and sashes. These are often considered the best options in what concerns the frame and sash materials. These materials provide durability, cost-competitiveness, insulating value, strength and good aesthetics…

But... the material may mean little. The glass panes, and the options and details associated to them, are at the core of the window efficiency. And there is several other details, involving the manufacturing of the window, that are also important. It's possible to have an excellent or a poor window with the same materials.

Pay special attention to aluminum frames and sashes in cold climates, even if they have thermal breaks. They may not be enough.

And pay special attention to the information in the label performance of the window: that's the easiest way to measure the energy-efficiency and quality of a window. See, on this issue: Window Rating

Selecting frames and sashes

When choosing window frames and sashes, check or inquire about:

- Tight-fitting sealed joints (they prevent air and water leakage).

- In the case of aluminum (and other materials requiring thermal breaks), ensure that the exterior and interior surfaces of the frame are separated by an adequate insulating material.

- In the case of large windows (and skylights and patio doors), additional reinforcement is crucial (also pay attention to the impact of the reinforcement material on the thermal performance).

- the sealing of the glass units to the sash (to prevent water from entering).

- insulated frames: the hollow sections of frames and sashes should be filled with foam insulation to increase the energy efficiency of the window.

- warm edge spaces: they are particularly important to reduce thermal bridging at the edges of the window.