The efficiency of a window doesn’t only depend 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 gas filled panes and corner are also important elements of its energy efficiency, durability and cost.

Good performing windows demand high-quality frames and sashes.

Important Details Related With Frame And Sash

A window is a whole. Its glass is particularly important, but the frame and sashes and the materials they are made from, or details like argon gas filling, warm edge spaces (to reduce thermal bridging at the edges of the window), thermal breaks (for high conductive materials like aluminum) and insulated frames (the hollow sections of the frame and sash can be filled with foam insulation to increase the energy efficiency of the window) are also crucial.


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 they aren’t efficient in cold climates.

Simple aluminum windows are a very bad option, even in moderate climates, due to the highly conductivity of aluminum (a cause of high energy losses).

Only aluminum frames with thermal breaks (that is, with their external and internal frames separated by a good insulating material) can rate high, and constitute a good option in moderate climates.

Use the Energy Star UR-value and other equivalent ratings (the ER number, in the case of Canada) to assess the effectiveness of thermal breaks.

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.

Hollow sections of the frame and sash can be filled with foam insulation to increase the energy efficiency of the window. Prefer this type of frames.

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.

There is however a huge drawback concerning vinyl (PVC): vinyl is often named the ‘poison plastic’ and has potential harmful impacts during its product life and its manufacturing, and we all should avoid it.

Besides, large vinyl windows need to be reinforced to allow a better strength, and 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 durability 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 nature doesn’t necessarily mean high-efficiency. The final performance depends on multiple manufacturing details.

The Best Frames And Sashes

We advise fiberglass window frames and sashes. They allow an excellent combination in terms of durability, cost, insulating value, strength and aesthetics…

But the material isn’t all. Other details, involving the manufacturing of the window are also important. It’s possible to have an excellent with different materials.

Just avoid aluminum frames in cold climates, even if they have thermal breaks. Also avoid vinyl window frames for environmental reasons. And pay attention to the window labeling: that’s the easiest way to measure its energy-efficiency. Look for Energy Star, NFRC or equivalent ratings (ER, in the case of Canada).

Selecting Frames And Sashes

When choosing window (or skylights or patio doors…) frames and sashes, you may 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 (skylights and patio doors) requiring additional reinforcement, inquire about the impact of the reinforcement material on the thermal performance.

– the sealing methods used involving the interface between the glass unit and the sash (to prevent water from entering).

– insulated frames: the hollow sections of the frame and sash 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.



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