Secondary Glazing FAQs

Secondary glazing is a separate, slim window fitted on the inside of your existing window, usually within the window reveal. It adds a second layer of glass and an insulating air gap without replacing or altering the original window, so it suits period and listed properties as well as modern homes and commercial buildings.

Yes. A well-fitted secondary unit reduces draughts, cuts heat loss through the window and helps block outside noise. How well it works depends on the glass you choose, the size of the air gap between the two windows and how well the unit is sealed and fitted.

Yes. Secondary glazing is one of the most effective ways to reduce outside noise through windows, because the wide air gap separates the two panes. Historic England notes it is even better than double glazing at reducing noise. Acoustic laminated glass and a larger gap improve it further. See our acoustic secondary glazing guide.

For heat loss, Historic England’s research found secondary glazing can be as effective as double glazing, particularly with low-emissivity (Low-E) glass. For noise, it is often better, because the gap between the panes is much wider. It also lets you keep your original windows, which matters for character and for listed buildings.

For many homes it is a cost-effective way to make rooms warmer, quieter and less draughty without the cost and disruption of replacing windows. It is especially worthwhile for period and listed properties, for single-glazed or draughty windows, and for rooms affected by traffic or street noise. See our secondary glazing cost guide.

It often reduces condensation on the room side, because the inner pane stays warmer and the seals cut down the cold draughts that cause it. Condensation can still form between the two windows if warm, moist room air gets into the cavity, so good seals on the secondary unit and sensible room ventilation both help.

Yes, provided there is enough depth in the window reveal for the secondary frame. Adding secondary glazing behind existing double glazing is a common way to improve noise reduction in busy locations.

Historic England’s advice is that secondary glazing that is carefully and reversibly installed does not generally need listed building consent, unless it would damage historic features, affect shutters or need fixings into stone or brick. Practice varies between councils, so always check with your local planning authority. See our guide to secondary glazing for listed buildings.

Secondary glazing is fitted inside the building and does not change the outside appearance, so it does not normally need planning permission, including in conservation areas. Listed buildings are covered by separate listed building rules.

It depends on the window and how you use it. Horizontal sliders suit wider windows. Vertical sliders suit sash windows. Hinged / casement units give full access to the window behind. Lift-out panels suit windows you rarely open, and fixed panels suit windows that never open. Keep an opening unit on any window needed for ventilation or as a means of escape.

Yes. Vertical sliding secondary glazing can be lined up with the meeting rail of the sash, so it follows the lines of the original window while cutting draughts and noise. Read our guide to secondary glazing for sash windows.

Yes. Choose supply only (DIY) and your units are made to your measurements and delivered for you to fit. You will need to measure accurately and be comfortable with a drill and spirit level. Every supply-only order includes the made-to-measure secondary glazing unit(s), fixings and fitting instructions.

Measure the width at the top, middle and bottom and the height at the left, middle and right, in millimetres, and note the smallest figures. Then check the diagonals and the reveal depth. Our how to measure for secondary glazing guide explains each step.

Yes. Secondary glazing is reversible: it can be taken out in the future and the fixing holes filled. Lift-out panels are designed to be removed easily, for example seasonally.

The price depends on the size of each window, the opening style, the glass and whether you choose supply only or supply & fit. You can get an instant guide price including VAT online for our aluminium range. See our secondary glazing cost guide.

The online guide price is an instant indication, including VAT, based on the sizes and options you enter. Your price is then confirmed in a formal quote, and nothing is made until you have approved it.

We supply and fit UK-wide. Delivery to UK mainland addresses is free on orders of £500 or more (inc VAT). For orders under £500, delivery to UK mainland addresses costs £60 (inc VAT). We also deliver to the Scottish Highlands, islands and offshore locations, at an extra site-specific cost that we quote separately; the free delivery and £60 delivery charge above apply to UK mainland addresses only.

Delivery and fitting lead times vary by product and location, and are confirmed on your quote.

We give a 10-year manufacturer’s warranty on the secondary glazing units we supply. On supply & fit orders, we also give a 1-year warranty on our installation work. These warranties are in addition to your statutory rights and do not affect them.

There is no online payment. When you are happy with your guide price, request a formal quote. We confirm your price and send you an invoice, and you pay in full, by the payment method shown on your invoice, before your order goes into manufacture. We do not take deposits.