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How to Insulate French Patio Doors

If you’re looking for a way to bring your home out into your patio, and vice versa, then the traditional French door has a great deal to offer. They make a fantastic addition to the modern home and garden, neatly bridging the two and creating a single, cohesive space. They were first developed to allow French aristocrats to look out onto their estates, and to allow natural light to permeate the interior. Both virtues also apply to the modern French door, too.

French Doors are a traditional and relatively affordable alternative to more modern sorts of patio door, like folding and sliding varieties. Flanked by a pair of sidelights, they can create just as great a visual impact, but without the associated price-tag. 

Double Glazed External French Doors

One of the purported drawbacks of a set of French doors is that they aren’t very energy-efficient. This stems from the fact that they’re made largely from glass, which conducts heat more capably than solid wood does. 

But glazing technology has advanced considerably over the past few decades. What might once have been considered an energy-efficient external door in the 1990s is surely, by modern standards, antiquated. This is thanks to a steady accumulation of complementary technologies, including double-glazed glass packed with inert gas, metal-oxide coatings which reflect energy back into the home, and ‘engineered’ cores which provide structure and resist the warping that allows draughts to creep in. As such, double-glazed French doors tend to more energy efficient than standard sorts of glazing. 

As well as offering greater energy efficiency, double-glazed external French Doors will also tend to provide superior security and safety, since the glass will be more difficult to break. Moreover, since there are two panes to contend with, there’s a far greater chance of forensic evidence being created in the event of a break-in.

Finally, double-glazed French doors tend to last longer than their rivals. They offer superior insulation, and so will future-proof a property for longer. To get the best out of yours, however, you’ll need to perform regular maintenance. This is especially so in the case of timber doors, which must be sanded and re-finished in order to protect them from warping and rot.

Are Patio Doors Energy-Efficient?

Energy-efficiency is crucial to the modern home, and by extension the doors which surround it. This is so for several reasons. To begin with, building regulations demand that external doors be able to contain a given amount of heat. If your French doors open out onto a sufficiently robust conservatory, this consideration might not be so crucial; but for most of us, it is.

Another important consequence of having an energy-efficient home, however, is that it’ll save money directly. The less heat escapes from your property, the less energy you’ll need to spend generating heat to replace it, and the less money you’ll need to spend on energy.

Finally, it’s worth considering the environmental cost of using all of that extra energy. The laws of thermodynamics dictate that the extra energy has to come from somewhere, and for the most part the slack will be picked up by burning fossil fuels, which contribute to man-made climate change.

So how is energy efficiency measured?  Among the most popular means of measurement is the U-value. This describes how effective a material is as an insulator.  The lower the value is, the less heat is able to pass through a given area of material in a given amount of time. It’s typically measured in watts per metre squared. A double-glazed window will have a U-value of just under three.

This measure of efficiency, while accurate, tends not to be terribly useful for homeowners. The figure advertised tends to only account for one part of the door (the glass) and only in a specific area (typically the dead centre). It’s therefore worth considering the colour-coded energy ratings offered by the British Fenestration Council, which vary from A++ right down to E (the lowest legally available).

Wooden French doors tend to be more efficient than their uPVC equivalents, because the material is far denser. Heat therefore has a far more difficult time passing from one side of the material to the other. 

How to Insulate External French Doors

If you’re the owner of an old set of external French doors which aren’t quite as energy-efficient as they ought to be, you’ll have two options. You can either attempt to restore a little bit of energy efficiency, or you can replace the entire set.  The former option is well worth exploring, as with just a little bit of money and effort, you’ll be able to vastly improve the energy-retaining performance of the door. Let’s examine just how this might be done.

Around the edges of your door, you’ll find strips of weather-stripping, designed to compress when the door is closed, and form a tight seal that’ll keep draughts at bay when the door is closed. These tend to come in the form of either brushes or lengths of rubber. To replace yours, it’s best to first remove the old ones and take them down to your local hardware shop.  That way you’ll be able to easily find a like-for-like replacement.

If your draught is coming through the bottom of your door, then you’ll be able to improve matters with the help of a draught-excluder. These long, cushion-like devices are built to sit on the floor and form a barrier. If the draught is between the two doors, however, your options will be extremely limited – short of stuffing a layer of felt or rubber in between the doors during the winter, or hanging a plastic sheet over the entire door, there will be little you can do.

One further source of energy-inefficiency occurs when the gas leaks from between the double-glazing. This is typically evidenced by condensation forming in between the two panels during winter; if moisture can get in, then the gas will almost certainly already have gotten out. It’s impossible to repair this wear-and-tear, and so it should usually be taken as a sign that the door is nearing the end of its life.

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