Warm Roof Velux Extension

How to choose the right type of Windows for your Extension

Choosing the right type of window for your project can make a big difference to the comfort of your home, your energy bills and your ongoing maintenance costs. We asked the experts at VELFAC, makers of modern aluminium/wood windows, to explain the wide world of window options.

Windows today come is all shapes and sizes – and also a range of materials.

Timber and PVCu are common choices, but metal frames are another option for domestic projects. There are also composite systems that use external aluminium and internal wood, a construction that already popular in roof windows such as VELUX.

To help you decide on the right windows for your project, here’s a quick guide to the different window materials currently available.


Advantages: Many homeowners replace their wooden windows with PVCu alternatives as these require far less maintenance, and offer good insulation and improved security often at an affordable price. PVCu can also be specified in a range of solid colours, not just white, and also in wood-grain effects.

Disadvantages: PVCu systems can also suffer from thick sight lines which impact on the appearance of the window, cutting down natural light and reducing acoustic insulation. White and pale coloured frames can discolour in sunlight, and although ongoing maintenance is limited, the expected lifetime of a PVCu window can be relatively short.

Bishop Window


Advantages: Metal windows (usually aluminium or steel) are also very low maintenance and offer a long performance lifetime. Design versatility is a hallmark of metal-framed window systems, making them an option for traditional and contemporary homes, and they are also very secure.

Disadvantages: Metal frames are more commonly used in business projects, and as a result can look ‘cold and commercial’ in a domestic environment.

Insulation is an issue – good performance can be achieved, but at a cost. As with wood and PVCu, sight lines can also be quite thick – slim frame options do exist, but again, they can be expensive.

Guardian Solstice

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