How to tell if double glazing has failed?

Two of the key requirements for buying a home these days are safety and a guarantee of warmth that doesn't dissipate quickly when the heating is switched on.

With the intricacies of the manufacture of today's double-glazed (and even triple-glazed) windows and doors, it is certainly something that a homeowner should expect from their products. It also makes sense from a financial standpoint given that the Energy Performance Rating (EPC) should be significantly improved making the home more saleable. But it is also eminently sensible from the position of keeping the heating costs down at a time when fuel bills are seemingly exponentially increasing every year.

Double glazing, or insulated glazing, is generally manufactured and installed as a sealed unit. The sealed space between the two panes of glass is filled with a gas which reduces the heat energy conducted through the unit, which is what protects the home from internal heat loss and the encroaching coldness outside.

From a security standpoint, for anyone trying to break in, they will find there is a struggle to do so compared with standard door and window fitments, and probably they would raise the alarm in any attempt. If they are unsuccessful, they are very unlikely to keep trying and they'll simply move on to somewhere where it is simpler to gain access.

But what about the problems you might find with your double-glazed doors and windows?

First of all, it's worth pointing out that any failure of a double-glazed door or window is rarely serious. You won't find that they are the cause of a house collapsing by any means, but if they are faulty, it'll be a constant source of frustration.

Moisture - One of the most common problems that homeowners have identified with their glazing is condensation. Condensation occurs on the side where the heat is greater than that on the other. The best parallel is the cold glass mirror in your bathroom when you have a hot bath or shower - the hot steam condenses against the cold surface.

Because the window unit is sealed and contains the gas that limits the heat transfer to the outside, there should be no condensation. But, if that seal is broken, the modulating gas can escape, water and air can enter the space, which then transmit more heat through the unit, and quickly reduce its efficiency. As a result, it allows the differing heat on either side of the pane to create condensation.

Of course, where failure of this nature has occurred, the double-glazed unit will cease to function effectively as insulation. This will result in excess heat loss, and higher utility bills for the owner. 

Irrespective of the visual problems, this lack of insulation can quickly make replacement of the double glazing a more cost-effective option that it may first appear.

Black mould - this is a worry for any homeowner, but especially where there are children or vulnerable adults living there since the effect of the spores from the mould can be especially detrimental to their health.

Usually, the evidence of black mould is a symptom of poor air circulation and where there is greater moisture, which is why it is more prevalent in bathrooms and kitchens. But it can sprout anywhere where there is relative dampness and no process to deal with the excess moisture.

If there are damaged sealed units in the double-glazing, condensation may form and therefore be a source for the mould to grow quickly.

Again, this is a symptom of the failure of the seal in the window or door. While replacements of the specific panes might be appropriate, in many cases, it makes greater financial sense to replace the entire window or door.

Draughts - this something that should not be happening with a double-glazed system and will certainly have an impact on fuel bills in the colder months. 

You should try to identify the source of the draught, which might be because of a broken sealed unit or a cracked window-pane, which in both cases will probably need replacement. 

Or it could even be a failed seal around the window or door itself so that when it is closed, the rubber seal fails to make full contact all round with the frame. This should be a relatively cheap and easy problem to resolve.

The other possibility is that it might be down to poor workmanship on behalf of the company that fitted the units originally. If that is the case, check whether your warranty is still running on the fitments and call the company back in to rectify the problem.

If you have no option but to replace any items of double-glazing not covered by a warranty, it is worth checking the provisions of your buildings insurance to see if that covers any remedial works.

Difficulty opening and closing windows/doors - if this has always been the case, you should refer to the firm that fitted them in the first place, especially if the products are still within their warranty period.

And, assuming it's not a simple matter of a lost key (for which you can bring in a locksmith or the fitting company if it is covered under any existing warranty), if the problem with opening or closing the window or door has only just occurred, it might be indicative of a more serious problem, such as subsidence.

If you suspect there is a structural problem, look for any other evidence such as cracks appearing in the walls, usually at a diagonal leading to the corners of the double-glazing fitments. If you are at all concerned, you should get an expert in to inspect the problem to identify the cause.

Noise - one of the main benefits pushed in advertising double-glazing products after savings on fuel bills is the reduction in noise. If you live in a particularly busy area, such as facing on to a well-used main road or under the flight path into an airport, things can get pretty noisy, so anything that can effectively reduce that noise pollution coming into the home has to be a considerable benefit.

However, if you notice that there is an increase in the noise you're experiencing, this might be an effect created by the sealed unit being defective. Again, if this is still under warranty, it is worth contacting the company who fitted the doors and windows to rectify the problem.

We are all trying to tighten our belts, and there will be a considerable focus on how energy-efficient your home is. There may have already been an EPC assessment completed on your home, and you can find out what yours is by trying out a calculator such as the one provided by the Mortgage Advice Bureau.

If you don't agree with the calculation, or simply need to renew your EPC evaluation (they expire after ten years).

Are you looking to buy a new home but are worried about the state of the double-glazing and its effectiveness? Then you'll need a conscientious and focused chartered surveyor to carry out the necessary checks in a detailed survey.

That's where it is really worth contacting Surveyor Local! 

Call  to get your no-obligation survey quote started, or to discuss your concerns with the acquisition of your planned property.

Or you can get a quick quote, using Surveyor Local's easy-to-use quote generator. Simply input your name, postcode, email address, phone number and an approximate value of the property (usually the agreed price), and we'll give you an instant quote for the work (with an email copy). 

We'll do the rest once you confirm your acceptance of the quote.