Why double-glazing doesn’t solve your comfort issue – and can make it worse

See if any of this sounds true to you.

You live in a typical English home. It’s made of brick, it has timber-frame and single-glazed or double-glazed windows and woolly yellow insulation stuffed into the rafters in the loft. It was built after the first or second world war in post-boom Britain.

You spend £800 to £3000 a year heating your home. Despite this, it’s still cold on your feet at floor level when you wake up in the morning. It’s also cold when you stand right by the windows.

Sometimes it gets too hot in winter when the central heating works too hard and you have to take off your jumper because you start sweating and the air feels stuffy.

And it’s always cold in the bathroom in the mornings, mainly because of the little fan in the wall that your landlord made you put in, or that was there when you bought the house (Building Regulations is to blame for that).

Does any of this sound correct? If it does, do you want to solve it so you’re not paying thousands of pounds every year for heating that still makes you and your family feel uncomfortable?

Well, there are four things you need to do:

  1. Improve your ventilation – the gold standard being an MVHR system. More about the cost of an MVHR here.
  2. Make your home more airtight
  3. Install high-performing windows
  4. Change your heating set-up.

Today I’m discussing Number 3: Install high-performing windows. Let’s go back to basics.

The UK double-glazing industry

Double-glazing is a fantastic invention. It’s stronger than single glazing, more secure, it’s practically draught-proof (apart from the trickle vents built into the window – more on that later), it keeps out noise and it keeps in heat.

UK homes built in the post-war years and earlier, with all of their timber frame windows and cavity wall insulations, are naturally leaky and draughty. But that was actually a good thing, because it brought in fresh, cold, dry air through what building physics engineers call “unregulated ventilation“, and what we call “draughts“. High levels of ventilation were often needed to fuel the open fireplaces. 

Trickle Vents

With modern double-glazing your windows are effectively sealed shut. No more fresh air in your home through the old timber frames. Now, all of your fresh air comes through the window’s little trickle vents. But these trickle vents don’t do enough ventilation, particularly in winter.

Washing, cooking and breathing all create moist air in the home. In a double-glazed home, this moist, warm air gets stale, especially in winter when windows are shut tight. This has to be dealt with or it causes condensation, humidity and, as a consequence, health problems like asthma.

And, when damp air hits a cold surface it forms condensation – usually on your cold windows but often on other surfaces such as north-facing walls or any steel elements of the property that extend to the outside (aluminium windows or sliding door-frames, for example).

Condensation forms black mould, and black mould causes asthma and other respiratory problems.

According to the UK Building Regs, trickle vents in your double-glazing, combined with the little fans in your kitchen and bathroom, are enough to ventilate your home with fresh, dry air. But they aren’t enough to do it healthily.

We need fresh air all the time

Humans each need 30 cubic metres of fresh air per hour – all day, every day.

Traditional single-framed timber windows would give you a lot of that freshness because they were so cold and draughty.

Modern double-glazing doesn’t. It’s too airtight.

What’s the solution for double-glazed windows?

Double-glazed windows should be considered in harmony with a proper ventilation strategy that combines increasing airtightness with high-performing insulation. That involves considering:

Vapour-permeable (“breathable”) walls

A mechanical or passive ventilation system

Proper insulation

Installing double-glazed windows without considering condensation risks or ventilation issues will only create heartache and further problems with your home in the future. Always take a “whole-house” approach when you’re upgrading your home, and take proper advice from a building physics engineer before you decide to replace your old, leaky windows with modern double-glazing.

 

Patrick

2 Comments

  1. Hi
    I am a retired male who spends several hours a day word-processing in a smallish upstairs box room (2.4m x 3.8m) that faces south-west. It is centrally heated (20.5 Celsius) and efficiently double-glazed. For years now I have suffered from minor, but persistent respiratory problems, stuffy nose, sore throat etc. I also have chronic sinusitis, which I plan to do something about just as soon as Covid 19 finally abates. . . whenever that might be? Meanwhile, I have noticed that my respiratory problems have diminished considerably since using a humidifier. It seems that it counters the dry air I’m breathing, which may be due to running two PCs in the room? What is puzzling, though, is that I only really get the full benefits when the room’s humidity levels hover around the 70% mark. I mention this because it’s routinely cited that optimum humidity levels should be approximately 50%. This is far too low for me, which means either I’m an exception, or else I’m failing to understand something fundamental about humidity. I would therefore be interested in reading any responses you care to make on my behalf. Thanks for reading my comments.

    • Hi Graham, interesting perspective, thanks. The healthy range for humans is actually 40 – 60%, with 50% being the “target”. Although a little higher, 70% doesn’t make you too much of an outlier.

      I wonder if your symptoms are related to dust or Volatile Organic Compounds, ie, low ventilation. It could be that the humidifier is helping to move the air, or even catching the VOCs in its filter or within the water vapour, and this is why your symptoms are alleviating.

      Best wishes,

      Patrick

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