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What Size Roof Light Do I Need? Rooflight Sizing Guide


When it comes to roof lights, size does matter. You have already made the fantastic decision to install a roof light into your home but then stumble on the question of "what size roof light do I need?" Well, that's where we are here to help.


Roof windows increase the light in a room 3 times more than standard windows. As a result, they are becoming increasingly popular to open up a room and create a bigger space, particularly in living rooms. Therefore, ensuring you get the right size roof light for your home is essential.


Several factors can contribute to the size of your roof light, such as the size of the room, the roof's structure and position. These are all factors we will talk about in the blog.


Keep reading, find out the answer to what size roof light you need, and get in touch if you have any further questions about our roof lights.


How to choose the right sized roof light

Picking the right skylight size can sometimes be dictated by what you are working with. For example, you might really like the idea of a large roof lantern but only have room for a small fixed flat rooflight.


So the best thing to do is to be realistic and think about what would look best in the room. For example, if you are placing the skylight in the kitchen, consider where you would benefit from more light. Perhaps you need more light over your food prep area, dining room, or both.


These are the questions you need to ask yourself before choosing the size roof light you need. It is an investment, one that could add value to your home, so it is important to get it right and find something that is cost-effective and has the right energy efficiency. This is where our team can help you find the roof light for you.


What you need to consider when picking the size of your roof light

We will go into further detail throughout the blog, but we will highlight key things you need to consider before choosing the size roof light for your home.


Firstly, which way is the room facing? Is it south facing or north facing? South-facing roof lights will naturally get more sunlight, whereas the north will only get the sun in the morning. Therefore, north-facing rooms will probably benefit from a larger roof light.


At first, you might think South-facing rooms will need a larger roof light, but it is pretty impractical as it heats the room quicker.


Secondly, you need to think about practicality. Along with planning permission, you will need to consider privacy. For example, your plans might get rejected if the roof light exposes too much of the home. But, on the other hand, you also don't want it to compromise your privacy if your property is overlooked.


Finally, you need to look at the structure of your home. For example, if you have an older house, it might not have the structure to hold the roof light you desire. Therefore, understand your roof and what it can handle before deciding what size roof light you need. This helps to eliminate some options.


Additionally, if you are thinking ahead, you could consider the house value it will add. Adding features such as roof lights and lanterns are unique ways to add light and value. It could elevate your house spec in the future if you want to sell.


What is the difference between a skylight and a roof lantern?

So, there are slightly different types of roof lights you can go for. So before answering 'what size roof light do I need?', we need to work out what style you want.


The umbrella term for any glass structure added to the roof is a roof light. Typically, a roof lantern has dimensions and project above the roof. The clue is in the name, as they can be in the shape of a pyramid or lantern. The benefit of a roof lantern is that it adds height to the roof and lets the light in from all angles, leading to more light.


A skylight is more conventional than what you will see in most homes with roof lights. It is flat and usually on an angled part of the roof or flat on the top. Also, unlike most roof lanterns, skylights usually open and have good ventilation.


Both are excellent options and are available in different roof light sizes. But, again, it is down to what would suit your home best. If you have any queries about the roof lights we install, contact us.


Is the roof strong enough for a roof light or roof lantern?

So unlike standard roof lights, some roofs can't hold the weight of a roof lantern. When determining what size roof light you will need, it is best to consult a structural engineer.


They will take all the stress from assessing whether your roof can withstand a roof lantern. If you have a single-storey house or a flat roof, sometimes the structural design is not strong enough for a roof lantern.


A structural engineer will be able to prepare a report for your local planning authority and assess whether the roof can take it.


This is something to be considered in the cost, as if you want a large roof light and your roof needs strengthening, this will increase the price.


Where will the roof light be positioned?

So let's dive further into where your roof light should be positioned. This is just as crucial as deciding the roof light size you want. It can completely change the shape, light and feel of the room.


South Facing

The benefit of a south-facing room is the warm light beaming all day long. However, in the summer, it can be a nightmare.


For example, if you choose a roof light in your main living area, such as the kitchen, it can make the room too hot when you're cooking. If you don't have sufficient ventilation in the room, it may be too hot in summer, so this is something to consider.


Therefore, if you want a roof light south facing, we would consider this when choosing what size roof light you need.


North Facing

North-facing rooms usually get the least amount of light throughout the day. The light you get in these is more neutral rather than bright light.


Most people pick north-facing roof lights because the rooms are naturally darker and need brightening. It is suitable for an office room or studio as you won't get screen glare and will benefit from the extra light for reading. 


Customers tend to go for bigger size roof lights in north-facing rooms. In fact, we've seen a big trend for ridge roof lights in these circumstances.


East Facing

East-facing rooms tend to be the lightest in the morning. As a result, they create shadows throughout the day and get minimal light towards the end of the day.


East-facing rooms are great for kitchens as they are bright in the morning when it is not as hot. Then throughout the day, they still allow light into the room without it beaming through. So when considering roof light size, you could opt for a larger size in an east-facing room.


West facing

Unlike east-facing, west-facing rooms get most of the light throughout the late afternoon. Creating long shadows and warm sunshine.


If you want natural light for as long as possible, placing a roof light on the west side will provide that. But, again, to avoid the room heating up too much, we suggest considering that when picking your roof light size.


What type of glass do you need for your roof light?

Another factor you should consider is the type of glass you use for your roof light. This can be impacted by the size roof light you chose and where it is positioned on the roof. Let me explain.


You want to ensure you are choosing the glass that has the good thermal performance to ensure you are letting out as little heat as possible. Not only that but to stop noise pollution from the outside.


You might be thinking, what has this got to do with the size of the roof light? Well, the bigger your roof light, the more heat it could let out and the more noise it could let in. So picking a high-quality glass for your size roof light is essential.


There is also the cleaning aspect of the glass. If you have a large roof light, it will take longer to clean. The better quality your glass is, the easier it will be to clean as it will be more durable.


We offer bespoke roof light products for clients wanting special glass to fit their home's unique requirements and structure. Bespoke products allow you to have larger roof lights in west-facing rooms without worrying about overheating.


To learn more about this offering, get in touch.


Do you need planning permission?

If you have read our blog about whether you need planning permission for roof lights, you will already know the answer to this question. But let's touch on it here briefly.


So, typically you do not need planning permission for roof lights or skylights. However, this is under the rule that it does not project more than 150mm from the existing roof plane or higher than the highest part of the roof.


You will only need planning permission if your home comes under Article 4. Article 4 states that if your home is listed or in a conservation area, then it will need planning permission. For obvious reasons, it will change your home's structure, affecting its history or the surrounding area.


Additionally, you will need planning permission if you are building a new extension. Usually, when building an extension, you will have a contractor who will be able to advise you in line with building regulations guidelines.


However, roof lanterns are a bit different. This is because they project above the house and could affect your neighbours. This might not be the case, but we would advise contacting your local planning authority to ensure it is okay.


As a rule of thumb, we would always check the planning portal to ensure your size roof light can be installed.


Skylight Vs Roof lantern cost

There is not an exact cost we can give you for Skylight Vs Roof light because it solely depends on the size of the roof light you pick. Other factors include glass quality, electronic mechanisms and whether the roof needs more reconstruction.


Typically roof light prices can go from £3,000 and upwards, but this will always depend upon your unique requirements and location. Naturally, a roof lantern tends to be more expensive due to its dimensions. With more dimension comes more structural reconstruction, which adds to the price.


It all depends on the size of roof light you end up going for. 


What features do you want your roof light to include?

The size of your roof light can affect the other features you might want. This could be opening, remote controlled, ventilations and blinds.


For example, a basic flat roof light may not be able to open (unless you go for our opening range) and doesn't usually come with a blind option. Therefore, if you would like a roof light to open and offer ventilation, you will need to take this into consideration when picking your size.


Similarly, suppose you are looking at placing your roof light really high on the roof. In that case, you will need remote-controlled windows, rather than a manual option, to open it up. Again, rooflights are ideal for creating natural ventilation in the room.


You need to consider this when choosing the size of your roof light. 


Conclusion: "What size roof light do I need?"

When looking at roof lights, size does matter. Once you have answered these important questions, picking the roof light's size will be easy.

  • What direction is the roof light going to face?
  • Where do you want the roof light to be positioned?
  • Do you want added features such as opening and remote controls?
  • Do you need planning permission?
  • Do you want a skylight or roof lantern?


For example, if it is the kitchen, where in the kitchen do you want the light the most? This will help determine how big the space is and what size roof light you will need.


Similarly, if you want a roof lantern, can your roof structure support that? Once you have answered that question, you will have a clear idea of what size roof light you will need.


Or, you might want your roof light in a darker room. Therefore you might want to maximise the light as much as possible so you can opt for a larger roof light.


For a general rule, if you are installing a roof light in a ground floor extension or a loft conversion, a roof light that takes up 15-20% of the floor space will be optimal. This optimises the light that will come through into the room and combats any heat issues.


Please get in touch with us if you have any questions. We can give you a quote today for your roof light. Contact us through our website, and we would be happy to assist.


Roof light Sizing FAQ's

Below we have added some of the most frequently asked questions we get about sizing a rooflight.

How do I choose a roof light?

To choose the right roof light, you must consider your personal preference, the size of the room and the structure of your building. The bigger the window, the more light it will let in. You need to ensure it is balanced with other items in your space. Sometimes too big means too much light and heat, so assess your room & roof first.


How big should my skylight be?

Size does matter in the case of a skylight. By rule of thumb, we would say that the window should be 20% of the total room floor size. Therefore, you need to consider where you want the most light in the room and place the skylight near that area.

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