Using our high performance windows and doors as part of your new build or refurbishment project can significantly improve the energy efficiency of your home. When selecting new windows you should consider the durability and performance of the whole unit.  Frame materials, glazing features, gas fills and spacer bars all affect the performance of windows and doors.

Improving the thermal resistance of a window frame will contribute considerably to the window’s overall energy efficiency (its U-value). The U-value is the rate at which a window or door conducts non-solar heat flow, the lower the value the more energy efficient the unit. 

Frame Material

The low thermal conductivity of wood means that our timber windows are excellent insulators. Although Aluminium cladding does not contribute to thermal performance in its own right, it can allow for the use of deeper glass units, which provide further performance benefits. In addition, because the cladding protects the external timber, the whole window is more durable than the all-timber option. 


Whilst all aluminium frames are strong and light, aluminium is a very poor insulating material. In fact, as a raw material, aluminium is over 1000 times better as a heat conductor than wood (or 1000 times worse as an insulator). Obviously aluminium windows are not typically made of solid metal, but even with multi-chambered extrusions and thermal break layers Aluminium is still a poor relation where thermal performance is concerned. 


The right type of glazing really matters. Key factors here are the glass types used, the spacer bars and the gas filling.

Glass types

Our double and triple glazed units are produced with one or two panes of low-emissivity (low-E) glass respectively. This heat reflective glass reduces heat loss from the building. It allows the warming infra-red rays into your home but reflects back into the room heat that would otherwise be lost to outside. 

Gas Filling

All of our units are argon filled. This is an inert, non-toxic, clear, odour-less gas used in between each glass layer to minimise heat transfer between the interior and exterior of the window. Argon is 60% better as an insulator than air.

Spacer Bars

The spacer bars (the structural edges between the panes of glass in a unit) are a potential heat loss area. Our warm edge spacer bars are made from a low conductivity plastic and have superior insulation properties. They also keep the glass at the optimum distance apart, accommodate thermal expansion, and prevent moisture and gas leaks.


Both our inward and outward opening units have excellent seals and gaskets, giving low air leakage rates.

These five factors – frame material, glass type, gas filling, warm edge spacer bars and the seal used all add up to provide high-performance, thermally-efficient windows and doors.

A thermal conductivity image of a Norrsken triple glazed window