Does double glazing keep your home cool in summer?

Most people think of double glazing as a winter upgrade. New windows go in before the cold arrives, the heating bills drop, job done. But the same physics that keeps warmth in through January works in reverse through July, and in a hot North London summer that matters more than people expect.

The short answer: yes, double glazing helps keep your home cooler in summer. Here’s how, and what to specify if overheating is your main problem.

How it works

A double glazed unit is two panes of glass with a sealed gap between them, usually filled with argon gas. Heat moves through that gap slowly in either direction. In winter, the warmth from your radiators stays inside. In summer, the heat radiating off a sun-baked street takes far longer to get in.

Single glazed windows do almost nothing to stop this. If you live in an older terrace or a conversion flat with original single glazing, the glass itself heats up and radiates warmth into the room all afternoon. Upgrading to double glazing cuts that transfer significantly, which is why rooms with new windows feel noticeably less stuffy by evening.

Solar control glass for south and west facing rooms

Standard double glazing slows heat transfer, but rooms that get direct sun through large panes can still overheat. That’s a solar gain problem, and there’s a glass for it.

Solar control glass has a coating that reflects a portion of the sun’s heat back out while still letting daylight through. It’s worth specifying for south or west facing rooms, big bay windows, and anywhere with a lot of glass, like patio doors or a conservatory. If your windows are otherwise sound, a solar control film can be retrofitted to the existing glass instead of replacing the full unit.

If you’re not sure which of your rooms face south, our post on south facing windows explains how to tell and why it matters.

Ventilation without leaving the house open

The natural response to a hot night is an open window, and the natural worry in London is what an open window invites. Modern uPVC and aluminium windows deal with this in two ways.

First, night vent locking. Most of the windows we install can be locked in a slightly open position, wide enough to let warm air out overnight, too narrow for anyone to get through. You get airflow and a locked window at the same time.

Second, trickle vents. These are the slim vents fitted above the frame that keep air moving through the room with the window fully shut. Building regulations have required them on most replacement windows in England since 2022, and in summer they earn their keep by letting humid air escape rather than letting it build up indoors. That constant background airflow also helps hay fever sufferers, since stale humid air is exactly where pollen lingers.

Protecting your furnishings from sun damage

UV light fades sofas, curtains, wooden floors and photographs, and summer is when it does most of its work. Closing the curtains all day defeats the point of having sunlight at all. Modern glazing coatings filter a good portion of UV before it enters the room, so you keep the light and lose most of the fading. It won’t stop it entirely, but the difference over a few summers is visible.

Thinking about new windows before winter?

Summer is genuinely the better season to do it. Installation is quicker and more comfortable with the weather on your side, lead times are shorter than the autumn rush, and you get the cooling benefit immediately rather than waiting for it.

We’ve been installing double glazing across North London since 2012, FENSA registered, with a 10 year manufacturer warranty on our products. If you want a price, get an instant online quote or call us on 020 8800 1838.