Row of cows at farm in Shropshire

'Mist' opportunities – when double-glazing fails

20/07/22'Mist' opportunities – when double-glazing fails

When our surveyors are carrying out appraisals and evaluations, there are some problems they encounter much more regularly than others. One of the most common defects spotted by our surveyors is problems with windows, especially the failure of double-glazed units.

Double glazing has been around for decades now and many houses that didn’t have it originally have had it retrofitted since. It has been used as the solution to many issues, from the deterioration of old timber frames (and their replacement with uPVC glazed units), to problems with noise, and environmental and energy efficiency. It’s not always suitable to replace old timber frames in this way – if the property is a period cottage, or is listed or in a conservation area, you may not be allowed to install uPVC. But in the main, double-glazing is a timely solution to a number of issues with old single-glazed buildings.

Replacement programme

However, many double-glazed units are showing their age and even relatively ‘modern’ examples, from the 1980s and ‘90s, are beginning to indicate they are failing. This can be due to several different factors – most of which will require attention and probably replacement. One of the most obvious signs to spot is when the seal around when the edge of the window unit fails or becomes ‘blown’. When this happens, moisture-laden air can enter into the space between the panes of glass. This is identified by tell-tale misting up of the glass on the inside faces of the sealed unit, and also the formation of crystals around the inside of the seal.

Once the seal on a unit has failed it cannot be repaired and the self-contained window unit – though not always the entire frame – needs to be replaced. This can also occur in Velux rooflights and other roofline or attic windows, but again replacement of the glazing is an option, without the wholesale replacement of the frame and mechanism. The process is comparatively straightforward – the beading will have to be removed and the unit substituted for a new one.

Weather or not?

Atmospheric moisture levels in certain weather conditions and external dirt can disguise evidence of some blown double-glazed units. But equally other weather conditions can highlight the presence of failed units. If condensation is forming inside double-glazed units, for example, on wet days or damp mornings, then this is usually a sign of a failed unit. The moisture will dry out as the temperature rises, but the problem will persist over time and need to be addressed. Cracked panes will also result in faults in the units too – this is another common problem with rooflights.

Under normal circumstances sealed double glazed units can be expected to last around 20 years before the seals begin to fail. However, this can occur quicker where windows are in exposed or vulnerable situations – in an open rural location, for example, rather than a more protected suburban environment. Failed sealed glazing units will become increasingly unsightly, with mould and other greenery such as moss and rot forming, and will eventually require replacement. It should also be considered that, where some sealed units within a window have failed, others may also fail in due course. It’s an ongoing problem, as building technology that was once ‘new’ eventually reaches is natural lifespan.

When it comes to building surveys, whether you are a first time buyer, or looking to move house, or an investor looking for an investment property, get in touch with us to find out how we can help you.

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