Roof Window Guide - What to Buy & How to Install A Roof Window

Benefits of Roof Windows

There are many benefits of adding roof windows to your home: 

  • Increases the amount of natural light in the room

Natural light is shown to be beneficial in a large number of ways, including increasing productivity by up to 40%, increasing serotonin levels and also improving sleep and concentration levels Also, a roof window can provide a better quality of light than a standard window as it offers continual light over the course of a day - a roof windows can let in up to twice as much light than a conventional vertical window due to the angle and positioning of the window, and also spreads light more evenly into the room which helps to reduce harsh shadows. A study found that 30% all buildings provide an unhealthy indoor climate with too little daylight. 

  • Improves the Energy Efficiency of your home

A study found that up to 1/3rd of a buildings electrical energy consumption was through lighting alone – by increasing the amount of natural light through well-placed roof windows, you can reduce the need for artificial lighting and offset this energy usage.

  • Increases the livable space in your home

A roof window can bring natural light into areas of the home where a standard window is unable to be installed, for example in attics, hallways and other rooms which do not have outside wall. By bringing in additional natural light into rooms you may not have considered being a useable space, it increases the areas within the home you have to work with – and makes the most of every inch of your house.

  • Overcome building restrictions

For some homes, building restrictions may limit the amount and style of front-facing windows you can have in your property, and a roof window may be a great (or the only) option for introducing additional natural light into the house.

  • Improve sound insulation

Sound insulation is incredibly important. Unwanted noise can lead to stress and fatigue, and it can interfere with the enjoyment of daily life. Installing roof windows that have glazing with superior acoustic insulating properties can keep out sound pollution such as busy roads or low-flying aircraft when deployed in conjunction with other noise-reducing strategies.

  • Add to your home’s value

Energy efficiency, sound insulation and an increase in natural light are all very attractive to prospective buyers – a study by Origin Global showed that 26 per cent of people picked natural light as the 'must-have' feature for a family home. Research done by Nationwide Building society found that a loft conversion can increase the value of a house by up to 20% A home with more natural light, improved ventilation and acoustic insulation, superior thermal comfort and that maximises its livable space is likely to prove very attractive to home buyers. As roof windows can help in providing all of these things, they can be a sound investment in your home.

Types of Roof Window

There are a few different types of roof window, which are generally a combination of finish and appearance and how they open. There are quite a few things to think about when buying a roof window, so we’ve listed out our most common questions – the first of which is;

What’s the difference between a roof window and a skylight?

The main difference is that roof windows are designed to meet building regulations and skylights do not – you may also find that skylight is sometimes used interchangeably with the term ‘rooflight’ too, but these are generic terms. Generally, skylights or rooflights should only used in uninhabited spaces, such as hallways and outbuildings as they usually have not been safety tested. A roof window will be CE marked under EN 14351-1:2006 product standards, which means manufacturers do performance tests to show that their roof windows reach these standards. These tests cover items such as acoustic performance, air leakage, draft proofing and performance under heavy rain, which are reported on within a Declaration of Performance. This means you can be sure you’re getting a safe and high-quality product.

Conservation Roof Window

A conservation roof window is designed to accommodate the renovation of traditional and period style buildings within conservation areas. They are finished in black on the exterior to mimic the look of cast iron roof lights that were popular in Victorian buildings, with a slim black glazing bar running vertically along the centre of the glass. Conservation windows also have a lower profile so they sit recessed into the roof. The Keylite Conservation Roof Window retains the standard pine frame and sash inside, whilst retaining the traditional conservation look on the outside and is designed to complement both renovation & new build projects. While traditional in its external appearance, a Keylite Conservation Roof Window benefits from all the fantastic Keylite features which come as standard, including great thermal efficiency, low maintenance and ventilation control.

Fire Escape Roof Window

A fire roof window opens to 45° to be in compliance with building regulations and safety standards. This type of roof window generally has the opening handle located at the bottom so it is easily accessible, opens outwards on a top hung pivot and creates an unobstructed area for safe exit in the event of an emergency. A fire roof window also must have a minimum measurement of 450mm x 750mm, which will give you the required unobstructed opening area of 0.33m² with the windowsill being no more than 1.1m above the floor, so people are able to climb out with ease in the event of a fire. See: Do I need a fire escape window? (link to planning permission section? Or add this here)

Opening Types

Roof windows also have different opening types, typically Top Hung (TH) and Center Pivot (CP) – we often get asked what are the differences and benefits of each type of opening

Top Hung (TH): A top hung roof window is hinged at the top and opens fully outwards

Keylite Top Hung Fire Escape Window

Centre Pivot (CP): A centre pivot window has the hinge in the middle

Keylite Center Hung Roof Window

Which type of Roof Window is best?

There are a few factors which go into picking the right type of roof window for your projects and they come in a wide range of sizes and types, so choosing the right roof window for your project is critical depending on the space you have available and the effect you want.

Top Hung vs Center Pivot

Benefits of Top Hung roof windows:

  • Opens outwards – doesn’t encroach on valuable floor space
  • Great for low pitched roofs 

Benefits of Center Pivot roof windows: 

  • Easier to clean 

What is Roof Flashing?

You also need to check you have the right type of roof flashing to go with your roof window. Having the right roof flashing is essential for a good finish.

What size roof window do I need?

The distance between the rafters in the roof construction typically determines the size of the window, with the most popular ‘standard’ size for roof windows being 900x600mm, which is due to most roof rafters having 600mm centres. Other common sizes are 980 x 980mm roof windows and 900x1200mm, which is designed for double-rafter spaces. Don’t think you are tied to a window the same measurement as your rafters, however, as you can get the rafters cut and trimmers installed if you would like a larger window installing, but this does require structural work which will take time and cost a little extra. It is definitely worth checking the size and placement of the existing rafter space and aiming to position the window to fit into this as it will reduce the amount of work needed to install. You can get < a href="/building/roof-windows">Keylite roof windows in ten different size options that go up to 1340mm x 1450mm so you’ll definitely find a window suitable for your project. It’s not just the rafter size that needs to be taken into account - you also need to take into account the function of the room, their layout and the positioning of the room first in order to pick the best roof window for the room.

Where Is The Best Place to Position the Roof Window?

Firstly, you need to think about what kind of room the window will be going in, as different room types will require different amounts of light – a hallway will have different natural light needs compared with a living room for example. You should also consider the shape and volume of the room when choosing the number and position of the windows – odd-shaped corners may miss out on natural light if a window isn’t positioned correctly, however you may need to come to a compromise if you’re limited on the possible locations for the roof window. Another aspect to think about is which direction the room and roof is facing, as this changes the light level and intensity which also changes during the day here in the UK;

  • South Facing: Consistent sunlight throughout the day
  • North Facing: Dim lighting
  • West Facing: Sunshine in the afternoon
  • East Facing: Sunshine in the morning

What is the optimum level of daylight for a room?

There have been many guidelines and pieces of research to find out how much light is optimum for n a room. The current British Standard BS8206 measures this using ‘Average Daylight Factor’ (ADF) which is defined as the ratio of average indoor to outdoor illuminance, and they recommend an ADF values of between 1% and 2.5%, however, they state that most people now prefer daylight levels that are around twice that amount. This is difficult to measure if you’ve not got the correct tools to calculate this. Most guidance from window manufacturers propose a minimum glazed area equivalent to roughly 10% of the floor area as a general rule of thumb and also state that people prefer an increased level of light achieved with a 20% coverage of the floor area. A rough calculation using the 20% coverage figure that you can to use to decide the amount of window space needed is by calculating the room size in meters squared and dividing this by 5.

Window Space Needed = Room Size in m2 / 5

Don’t forget to include previous If you already have a window in the room, you can take off the window area to get the figure you want to hit the 20% figure. Again, you may need to take into account which direction the room is facing – the amount of light that gets through may not be as bright depending on the sun during the day, so you may want a larger window to counteract that.

Do I need Planning Permission to install a roof window?

There are two aspects of ‘permission’ which you may need to adhere to – namely Planning Permission and Building Regulations Approval, and you may one or both types depending on the type of work being carried out. You usually do not need planning permission to insert roof windows. House owners have ‘permitted development rights’ which means you can perform certain types of work without needing to apply for planning permission – which, under Section C, permits roof windows being installed if certain limits and conditions are met, which are;

  • Any alteration to the roof must project no more than 150 millimetres from the existing roof plane.
  • No alteration to be higher than the highest part of the roof.
  • Side facing windows to be obscure-glazed; any opening to be 1.7m above the floor.

Some of these permitted development rights may be different however if the local authority has issued an 'Article 4' direction, which are made when the character of an area of acknowledged importance would be threatened - common (but not specific to) conservation areas. This will mean that you have to submit a planning application for work which may not normally need one. Do check beforehand whether you will need planning permission for your project - you can get more advice from the Government's Planning Portal website and you can also check the specifics for your Local Authority Even if planning permission for a new roof window is not required, you may still need to abide by building regulations.

What's the difference between Planning Permission and Buildings Regulations?

Planning Permission is required when you’re building something new or making a major change to the building such as building an extension – however some work which you may think could come under this umbrella may be a permitted development which does not require an application for planning permission Buildings Regulations cannot be ignored - by law, any building or structural modification work must comply with building controls which stipulate minimum standards for design and safety. You may need buildings regulation approval under the Building Regulations 2010 which covers the construction and extension of buildings. You can find further information on Building Regulations for roof windows and you can always check with a building control body if you’re unsure if you need approval. Also, you do not need to get approval yourself if you use someone registered with a competent person scheme. You can search for a competent roofer from the government backed Competent Roofer scheme website. Approval under the Building Regulations will generally be needed for the installation of a new roof window, as generally a roof window installation requires adjustments to the roof structure in order to install the roof window.

Other items that are stipulated in the Building Regulations are ensuring the roof will be able to carry the weight of the new window, and if the roof is not able to do so it will need to be strengthened prior to installation. The new roof window must also have sufficient insulation against heat loss with effective energy performance.

Note: Planning laws in Scotland & Wales generally are different to the rest of the UK – in Scotland planning permission is often needed for any roof window installation. It’s always best to contact your local authority to determine the best way forward.

How to Fit A Roof Window

There are two parts to fitting a roof window – installing the window itself and then installing the roof flashing. Modern roof windows can be installed very easily – this video shows a Keylite window being installed in under two minutes.

What is Roof Flashing?

You also need to check you have the right type roof flashing to go with your roof window. Having the right roof flashing is essential to create a watertight seal and maximise heat insulation, and it also creates a professional finish on the exterior