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Fixing common problems with double glazing

Fixing common problems with double glazing

This is our run down on the most common problems that we get approached about and what you can do about them:

Condensation on the inside surface of the window:


It’s a common misconception that energy efficient double or triple-glazed windows will eliminate condensation from your home. In fact in certain circumstances they can even make it worse.

In sealing-up our homes more and more effectively, we’re making them warmer and more energy efficient but we’re also giving moisture nowhere to go.

There is a limit to how much water vapour the air can hold. The rule is that the warmer the air, the more vapour it can accommodate, which is why on colder days, condensation is more likely to form. This will happen if moisture in the air  makes contact with a cooler surface, for example outside wall or window. When this happens, the vapour in the air will become more concentrated, forming droplets – condensation.

Condensation on windows is really about inadequate ventilation and our own behaviours, for example not opening windows after showers or cooking with the lids off pans.


Trickle vents are a halfway house. They can be left open to provide continuous background ventilation, ensuring circulation of air and avoiding build-up of condensation without allowing the heat in your home to escape.

There are three types of trickle vent to choose from – through frame, over frame and glazed-in. Glazed-in ventilation sits at the very top of the double or triple-glazed unit, while over-frame routes ventilation over the top of the frame into the property.

The most common form of window ventilation is a through-frame trickle vent. This routes fresh-air through the top of the window frame and can be adjusted through a simple open and closing mechanism to provide as much ventilation as required.

The good news is that in many cases these can be retro-fitted to your existing windows. The other advantage of through frame trickle vents is that they can be left fully open without impacting on home security, maintaining air flow and reducing the build-up of condensation, regardless of whether you’re at home or not.

I have condensation on the outside of my windows


The same principles that cause condensation to form on the inside of windows in cold weather can also apply outside. This is normally only a problem in autumn through to spring when the outer pane of the glass can drop to a lower temperature than the air around it and water droplets form.

This isn’t really a problem in the summer when the glass is warmer or winter when the air temperature is lower – just in that midway point as the seasons change.​


Condensation on the outside of your windows is a short-term problem and will go in a couple of weeks as the weather changes. It only effects top performing energy efficient double and triple-glazed windows, so if you have condensation on the outside of your windows, think of it as a sign that they’re doing their job and keeping your home warm inside.

I have black mould growing around my window frames


We’re back to adequate ventilation! Black mould and mildew is in most cases caused by inadequate ventilation, particularly in those areas of the home, where air moisture content is high, for example kitchens and bathrooms.

It’s a problem which effects just as many new homes as it does old ones. Housebuilders are tasked with improving the energy efficiency of new homes. The problem is, not enough focus is put on ventilation –  a problem which becomes more acute when it’s cold.​


As per our answer to condensation, if you don’t already have them, trickle vents can help but most importantly remember to open windows and let moisture filled air out of your home.

My windows are misted on the inside


This is a definite problem. Energy efficient Double glazing and triple glazed windows work by creating a barrier or multiple barriers between the warm air inside your home and the cooler air outside it. The voids between them are filled with inert gasses which make them even more efficient acting almost like an ‘invisible’ loft insulation.

If your insulated glazed units are misted, it means that moisture has entered them from the air outside but more importantly that the gas will have ‘leaked’ out and while completely harmless, your windows won’t be working properly and your heating bills could rocket.


There’s good news. Glass units are very easy to replace. Contact your local window fitting company and they can arrange a replacement. It involves no fuss, no mess and can be replaced within minutes.

My windows catch on the bottom when I open and close them​


The opening window sash can catch on the top of the frame as it passes over it, if hinges have ‘dropped’ or the glass unit hasn’t been fitted inside the window or door sash correctly.

You’ll know if it’s the latter straight away. Hinges, can however, deteriorate over time and with use and the problem can build up over a longer period.

There’s a common misconception that windows are ‘no maintenance’ rather than ‘low maintenance’. As with any mechanical joint if hinges aren’t maintained and oiled, they can become damaged and fail.


If you have just had new windows fitted they can settle. Minor adjustment of the hinges and re-packing/fitting of the glazed unit inside the window and door sash will generally solve this.

If hinges have worn, either because they haven’t been properly maintained, there’s an underlying fault or simply through use, they can be replaced.

In this case, it is, however worth considering the cost and the overall condition of your windows or doors and if they warrant repair or if replacement could be more cost effective in the long-run.

Can I replace a broken double glazed window handle?


Occasionally older window handles will fail to close or lock, creating a serious threat to the security of your home. This is usually caused by poor quality handles, the handle being forced, or the main gearing being ‘dry’ due to a lack of lubrication. This will add extra strain when operating the handle.


Although  it can be an indicator that your windows may be becoming a little past their use by date, most handles can be replaced. What we would say is that if your windows are still using single cockspur-type handles, replacement should be considered. This is now a very old technology and there performance won’t come close to today’s high security windows and doors which us multi-point locking to firmly anchor the opening sash to the frame, making it almost impossible to lever them apart. Handle fittings are nearly standard throughout the industry, the only thing that usually varies is the spindle length, so if you order handles with a longer spindle then a hack-saw is required to shorten them.

Can I replace the rubber gasket seal around my windows?


Again this one comes down to wear and literally ‘tear’. Window and door gasket will deteriorate over time, which can mean that your windows and doors start to let in draughts and weather sealing also becomes a problem.


The fix on timber and aluminium windows and doors is  more straight forward than on PVC-U windows because of the way that they are made.

In aluminium and timber window manufacturer the gaskets are applied separately. PVC-U windows by contrast use a highly sophisticated co-extrusion process (when at least they have done for the last 10-15 years) This moulds the gasket directly into the window frame as bar length is made. This means that it delivers a far better level of performance because draughts can’t slip in behind, over or between the gasket, frame or sash, it’s literally sealed. The downside is that if it fails it can be very difficult and time consuming to replace.

In most cases this failure will only occur in older windows so consult a specialist to see if it’s worth replacing the seals or if you could save more in the long-run by replacing windows.

My white PVC-U windows have become discoloured


Some older PVC-U window formulations can become unstable over time and this can lead to discolouration ad the surface of frames reacts with sunlight  and pollution in the air. You should also only ever clean window frames with a specialist cleaner as harsh or abrasive cleaners can also lead to surface damage. While structural integrity of the window will remain unaffected, any discolouration or degradation of surface finish can appear unsightly.


While there are a number of PVC-U paints on the market, we would suggest their use with caution. If the surface of your PVC-U window has become damaged, discoloured or yellowed, it’s an indication that it’s no longer up to scratch and on that basis, forms a less than ideal foundation for paint.

Regardless of the condition of the surface of your windows you should also always make sure that you use a suitable primer. As said, unless you have scoured your PVC-U windows with an abrasive chemical cleaner, it’s highly unlikely that windows manufactured in the last 10-years will discolour, so if they have it’s probably because they’re older and if your budget allows, replacement should be considered.

My conservatory is too hot or too cold


Ok we’re going to go out on the big one and say it! If your conservatory is too hot or too cold it’s the product of a legacy of bad design and old technology in conservatories at an industry-wide level.

Manufacturers of older conservatories paid little consideration to how people were actually going to use them or consideration to the fact that glass magnifies the heat from the sun and the more of it that you have, the more likely it is you’re your home is going to become uncomfortably warm. To some this is a bonus, especially on a cold crisp sunny winters day. The solar gain is appreciated.


The world today has thankfully moved on. Intelligent design and solar control glass means that today’s conservatories and glazed extensions deliver highly flexible year round living space. That may be little solace if you have an older conservatory but there are still things you can do.

Solar control glazing prevents excessive temperature build-up in summer months increased affordability, means that solar control glass is now far more accessible to home owners including as a retrofit product supplied into older conservatories.

There are also a number of solid-roof solutions which can fitted as replacement conservatory roofs breathing new life into otherwise unloved spaces at a very affordable price point. These include modern tiled/glass roof options like the conservatory UltraRoof380 

Please don’t hesitate to get in touch to find out more by calling 01264 359355 or emailing email sales@kjmgroup.co.uk

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