Loft conversion windows – what are the rules?

General, Loft conversion

Loft conversions are one of the most popular options for homeowners who want extra space without the hassle of moving. In fact, according to The Nationwide, you can even improve the value of your home by as much as 20% by adding an extra room in the loft. At an investment of around £20,000 for the work, it is easy to see that this is a great choice for growing families… However, if you fail to stick to the building regulations rules for loft conversions, you might find that your lovely new room might be nothing more than an expensive storage space.Loft conversion windows - what are the rules?

Building regulations for windows

Since 2002 building regulations have applied to all replacement glazing and this means that certain standards need to be met with regards to insulation and ventilation requirements, allowing escape in a fire, avoiding privacy issues with neighbours and preventing any risk of falling from windows.

You can choose a contractor that is registered with your local authority to carry out loft conversion work to the right standards, or you can have any work done inspected by building control during the construction to ensure you are meeting the requirements.

Thermal loss

The thermal value of your windows is measured using a U-value – the value of which is set depending on the type of home and your local authority requirement. It is important that your new windows do not exceed this maximum u-value. Choosing double glazed units will almost always mean you are meeting the minimum requirements.Loft conversion windows - what are the rules?


Safety glazing (glass that does not easily shatter) needs to be used for any window that is below 800mm from floor level, less than 300mm from a door and up to 1500mm from the floor and within any glazed door. In a loft, windows are expected to be around 1.7m from the floor.


The amount of ventilation required for your loft conversion will depend on how it is being used. If it has a bathroom, it will need more. In most cases, an opening window is enough ventilation for most spaces. Trickle vents are also a great idea.

Fire safety

In addition to good fire doors, your loft conversion needs windows that allow a means of escape. Usually, only one window that opens to allow escape is needed in each room. In a loft, it is clear that getting from this window to the ground will be harder than in other rooms, so you need to understand how it will work. Is there a nearby flat roof that can be used? In rare cases, an escape ladder may be needed.


Any side window in a loft conversion needs to be made from obscured glass to ensure privacy for your neighbours and for you.

Loft conversion windows - what are the rules?The rules for windows in your loft are relatively simple and therefore planning permission is rarely needed. However, you do need to ask the advice of your local building control office. They can help you to ensure you create a loft conversion that is truly usable and will add the value you want to your home.

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