Aluminum clad windows are windows with aluminium wrapped around the outside frame or sash that is exposed to the weather. Aluminium protects the outside of the window.
Aluminium "capping" has long been used on window installations and is proven to last a long time and serve as a good way to cover exposed wooden sills and unsightly joins between the old frame and the newly installed sashes.
More recently sashes have been developed that use a totally seperate aluminium frame that is "thermally broken" from the wood frame on the inside. The outer aluminium frame often has a small air gap between it and the wooden sash beyond.
Making a combination aluminium/wooden sash is just a logical extension of the idea of capping a window. The best aluminum clad windows come from Germany and many USA companies are now distributing them. There are also a number of excellent clad sashes made by Canadian manufacturers.
Aluminum Clad windows have some of the best insulating values in the industry, especially the german versions. This is not all due to the aluminum cladding though. German windows usually have triple glazing and multiple layers of weatherstripping. The build quality is also very high.
The benefits of windows with aluminum cladding are as follows:
There are also some disadvantages with combination aluminium-wooden sashes.
Overall, if you are considering wooden sashes for your home because of how nice they look, then having aluminium clad frames on the outside makes it possible for you to have the best of both worlds.
Some will argue that old wooden windows have often lasted for more than 100 years in older homes. But wooden sashes do require regular maintenance on the outside and the inside regardless of the quality of the wood or joinery.
In the past protection was always done with regular painting and caulking. The biggest threat to wooden sashes is water. On the outside it may make its way through worn or improper flashings until its gets into the wood sashes and rots them.
On the inside years of condensation can work its way into the mullions and warp and expand the joints. Keep the humidity under control and provide plenty of ventilation near frames that are exposed to very cold or very hot weather.
Aluminium cladding on the outside provides a practical alternative to wood on the outside.