Buying a house with double glazing – misted units, ventilation, condensation

When buying a house with double glazing you might think great, no draughts, lower heat loss, etc.  However, double glazed units can fail and require replacement, particularly older units.

Double glazed windows have now been in use for several decades.  Early double glazing was often in either a timber frame or a metal frame, sometimes with insulation within the frame members.  Some of the older units had narrow sealed units which were not as effective against heat loss as more modern units.  Today, the vast majority of double glazed windows, whether replacement windows or used in new housing, have PVCu frames.

Double glazing is virtually essential for a modern dwelling to enable it to meet the requirements of Building Regulations in respect of heat loss.   The sealed air gap (filled with air or another insulating gas) between the two panes of glass reduces heat loss from the dwelling and prevents condensation on the glass itself.

When buying a house with double glazing it is important to check for the following:


Failed double glazed units

The sealed double glazed unit can fail either due to a defect in manufacture, damage or deterioration over time.  This can be identified by misting/fogging, ie, condensation occurring between the two panes of glass which form the double glazed unit.  The amount of misting can vary from day to day depending on weather conditions.   Once a sealed double glazed unit has failed it cannot be repaired.  It may be possible to replace the unit only, or it may be necessary to replace the whole window.  If only one or a small number of units have failed then other units of the same age may fail in the not too distant future.

If you are buying a house with double glazing and note one or more failed double glazed units, ask the vendor when the windows were installed and check whether there is a warranty to cover failure.  If there is a valid warranty, check whether this can be transferred into your name.

If the whole window requires replacement then contact a FENSA contractor to obtain a quotation and replace to ensure that the work is carried out in accordance with Building Regulations.


Insufficient ventilation

The purpose of double glazing is to reduce heat loss, reduce the risk of condensation on the glazing and help to maintain a comfortable temperature within the home.  However, as homes have become better insulated they sometimes suffer condensation due to a lack of ventilation.  It is important to provide adequate ventilation to a dwelling to allow excess moisture to escape and reduce the risk of dampness, condensation and mould.  Condensation isn’t simply water running down a window, it can also occur within furnishings resulting in dampness, a musty smell and possibly mould spores within the fabric.

Ideally, windows should have a combination of large opening casements and smaller top hung opening vent lights.  Windows should have locks so that they can be locked in an open position without reducing security, enabling windows to be left slightly open at night to prevent a build-up of moisture.  If there is mould on window frames and around window openings then this is a sign of inadequate ventilation.

If you are buying a house with double glazing, check whether trickle vents are provided.  Trickle vents allow background ventilation and can help to avoid a build-up of moisture and the risk of condensation.



  1. Check the configuration of opening windows.
  2. Check whether windows can be locked in an open position.
  3. Check whether there are trickle vents (usually found in the head of the window frame).
  4. Check the working order of window handles.
  5. Check whether there is any misting or fogging within the double glazed units.
  6. Check that any replacement windows have been installed by a FENSA contractor (if replaced since April 2002).
  7. Check whether there is a warranty for any replacement double glazed windows or doors and whether this can be transferred into your name

See also buying a refurbished house. 

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1960s houses: common defects – asbestos, condensation, wall ties, pitch fibre pipes

1960s houses are now around 50 to 60 years old.  Construction methods have improved since that time particularly with regard to thermal insulation and safety.

This article deals with just some of the defects commonly found in traditionally built houses built during the 1960s (some can also be found in houses of other decades).


Asbestos Containing Materials (ACMs) in 1960s houses

Asbestos containing materials (ACMs) were commonly used in buildings in the 1960s.  Common uses include:

  1. Textured coatings to walls and ceilings, including Artex. Some may have had an additional coating (or coatings) applied over the years.  In any one property there may be different finishes which may have been applied at different times.  It is possible that some may contain asbestos while others may not.
  2. Asbestos cement products including soffits, verge boards, corrugated roofs to garages, flue pipes, water tanks, cladding to walls/panels, gutters and downpipes, pipes, man-made slates.  Asbestos cement products at eaves level are sometimes hidden by new PVCu fascias and soffits.
  3. Vinyl floor tiles particularly to solid ground floors, often hidden below carpets or sheet flooring.
  4. Asbestos insulating board (AIB), loose fill insulation, lagging, sprayed coatings.

If any asbestos containing materials are damaged, or if any planned works, eg, drilling, sanding, cutting, are likely to disturb any ACMs then have sample/s tested for asbestos content and obtain advice from an asbestos contractor.    Most higher risk works must be carried out by a licensed contractor while other works may be undertaken by a non-licensed contractor.



High heat loss and condensation

1960s houses have walls which typically allow high heat loss compared to properties built to meet the requirements of current Building Regulations.  High heat loss not only results in higher heating bills, it leads to colder surfaces and often results in condensation.  Condensation isn’t just water running down windows.  Condensation can occur within the structure and on furnishings and it can lead to mould on affected surfaces.  In some instances, condensation can be reduced or avoided by increasing the level of heating and ventilation, but where surfaces are cold, eg, window reveals, corners of rooms, walls behind furniture and where cold bridging occurs, it can be difficult to eliminate completely.

High heat loss (and condensation) can be reduced by increasing insulation.  One popular method is to install cavity wall insulation.  However, not all properties are suitable for cavity wall insulation.  If you plan to buy a house with cavity wall insulation then check the property has been assessed by a CIGA registered installer to ensure it is suitable for cavity wall insulation.  Some properties may suffer rain penetration if they are not suitable for cavity wall insulation.   Following installation, the installer will apply for, and issue, a guarantee.  The CIGA guarantee can be passed on to subsequent owners of the property.  (Similarly, if you plan to install cavity wall insulation in your property then contact a CIGA registered installer to check the property is suitable first).


Lack of safety glass

Some 1960s houses have large windows and glazed doors which incorporate low level glazing.  These houses predate the requirement under Building Regulations for glass in critical locations, eg, at low level, to be safety glass.  Full height or low level glazing which is not safety glass will break easily and this presents a danger to occupants, particularly children.  The glass can easily be upgraded by replacing with safety glass or by applying an adhesive safety film.


Wall tie corrosion

The inner and outer leafs of cavity walls are usually tied with wall ties.  Houses constructed in the 1960s were often built using galvanised steel wall ties.  The steel corrodes over time and can cause cracking and/or bowing.  While wall tie corrosion is more common in older properties this is becoming more common as housing of this era ages.  If there are any signs of wall tie corrosion the condition of the ties should be checked to see if additional wall ties need to be installed.


Pitch fibre pipes

Pitch fibre pipes were widely used in the 1960s.  They have a tendency to deform under the load of ground, walls, traffic, etc.  This can lead to blockage of the drains or settlement of any structures above the drain runs.  If you plan to buy a property with pitch fibre drains and suspect there may be a problem then it is a good idea to arrange a CCTV survey to check their condition and establish whether they require lining or replacing.

See also How much does a survey cost?  and  What should I do after having a survey?

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