Retro Fitting Windows

Most retrofits consider changes to interiors such as kitchens, floors doors paints etc.

At the back of peoples mind the need to energy retrofit is a nagging thought but the lure of spending the money on other items can be persuasive.

If you are embarking on a retrofit project first write down the priorities you wish to achieve.

I will always say get the energy retrofit right and all the others will take care of themselves.

There are a few areas that require careful consideration when retrofitting.

Windows: If you are considering replacing windows you have a great opportunity to save energy and increase the comfort of your home.It is important to understand the differences in what makes one window superior to another.

The U value of a window consists of two distinct areas. The U value of glass differs from the frame.

The effective U value of the window is the combination of both. Allied to this is the comfort criterion.

This states that the interior surface temperature of a window should not be more than 3°C than the winter design day.

In Europe this is -10°C.

The effective U value should be not greater than 0.8w/m2K.The above U value is the Passive standard.

Achieving this standard requires that the windows are triple glazed and e coated and either krypton or argon filled.

The benchmark of window U values is the effective frame U value.

Glass.When looking at the type of window you buy you will have to think about the type of glass you use.

The coatings and fillings help the glass to trap solar heat and prevent heat loss.

They include.

1. Glass (Pilkington K Glass) which is installed in the inner pane of a double glazes unit.

It allows heat in to the room but reflects heat in the room.

2. Low emmissity glass: Low E glass coatings work by reflecting or absorbing IR light (heat energy).

The thickness of the Low E coating and the position in the window dictate how the window will perform.

3. Argon or Kryton fillings reduce heat loss by conduction as they have low thermal conductivity.

Window Frames

Window frames come in various materials such as Timber,Pvc,Aluminium,steel or hybrids such as as Timber/Pvc or Timber/Aluminium.

Whatever choice you make the overriding factor is the U value of the frame.

The frames should have thermal breaks or warm edge incorporated in the frame design .

All in all the most important feature will be the U value.

And any window can be both architectural and meet the low U values you require.

The final factor is price.

The use of triple glazing is expensive but coming down in cost.When deciding take the comfort and energy savings into account.If your budget cannot stretch to triple glazing get the best double glazing you can afford.And finally don’t forget to get the test certificates for your windows.

Installing Windows

Before you install new windows make sure they are treated to minimise thermal bridging.

Thermal bridging is the loss of heat through materials which are connected from inside to outside.

The materials such as blocks or timber form a pathway to allow heat to flow.

In older window opes this is a common problem.

Putting new windows in to this type of opening just negates all the benefits of the new window.

So before you install the windows make sure you treat the window opes in the following ways.

Install cavity closers so you break the thermal bridge. Cavity closers such as CAVALOK BUILDING PRODUCTS can substantially reduce the effects of thermal bridging.

Consider changing concrete sills to reduce thermal bridging.

Old concrete cills are a major source of thermal bridging.

The use of pressed cills can eliminate thermal bridging at that point. Contact Passive Homes Ltd for a free consultation.


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