How to Install Roof Vents

Roof Care & Maintenance
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How to Install Roof Vents

Whether you’re constructing a new build or gearing up to tackle condensation in your own home, adequate roof ventilation is a must. There are a few things to consider before you begin installing roof vents. Firstly, you need to determine how many roof vents you need, what type of vents are best for your property and most importantly how to install them correctly.

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How Many Roof Vents Do I Need?

The bad news is, there isn’t a concrete answer to the question how many vents you should install in your roof. The amount of ventilation and by extension number of vents you’ll need can vary massively, even for houses on the same street. It can change based on the shape of your house, its size, location, positioning, how many people live there and what exactly you’re planning on using your roof space for. Approved document F of the Building Regulations provides some insight into what you may require, but this can prove inaccessible to non-professionals. We’d recommend consulting our experienced customer service team, as they’ll be able to advise you on the best roof vents for you and their ideal locations. That being said, if you’d like to calculate how many roof vents you need yourself, here are two questions you’ll need to answer:

How Much Continuous Airflow Do You Need?

This is the key figure in determining how many vents you’ll need in your roof. For example, a normal roof with a pitch over 15 degrees (find out how to calculate your roof pitch) will require free airflow equivalent to a continuous 10mm opening (10,000mm² per metre run), so if your roof is 5000mm long you’ll need 50,000mm² of airflow.

How Much Ventilation Do Different Vents Provide?

Once you know your airflow requirement you will need a series of roof vents to meet this. When pick out your vents this number should always be kept in mind. Using the example above if you require 50,000mm² and each vent provides 10,000mm² then you will need 5 vents.

Regardless of the approach you’d like to take, it’s always best to err on the side of caution. If you install the wrong number of vents in your roof it’s far easier to add more than to remove ones that are already installed.

Once you’ve got a clear idea of the ventilation your roof requires and how many roof vents you need, you can start looking into the types of roof vent that are available. One thing to remember is always to take care when working in loft spaces.

Types of Roof Vents

The first thing to know is that there are three main types of roof vent. These are: tile or slate vents, ridge vents and eaves vents (also known as soffit vents). This isn’t a matter of choosing one over the others, as most good ventilation systems will make use of multiple types of roof vent to ensure a strong circulation of clean air.

Tile/Slate Vents

Tile vents are some of the most discreet yet effective roof ventilation solutions out there. Designed to blend seamlessly into a tiled or slated roof, these vents come in a wide range of profiles and finishes and can even be connected to exhaust vents. The key thing to remember is to order the correct tile vent to match your roof tiles.

The best place to install tile or slate vents is just above your loft insulation, as the air here is able to draw out most of the moisture from the insulation without allowing heat to escape. To ensure that the placement of your vents is correct, you can poke a wire through your undersarking from inside your roof space to act as a marker. Once your marker is in place, simply cut an appropriately-sized hole in your undersarking where the rear of the vent will be laid and replace an existing roof tile with the vent.

One way to do this is to cut an “X” shape in the undersarking and fold back the four flaps created. By bailing the top flaps into a rafter, you can create a small gutter which will deal with any future run-off water that may make it through your tiles. If you’re installing tile or slate vents, it’s important to install them on both the front and rear sides of your roof to allow for complete air circulation. If your home is susceptible to condensation, we’d recommend installing tile or slate vents at varying heights for more thorough air circulation.

It can be difficult to say how many tile vents your home will require. In general however, two vents on the front of your roof and two at the rear should be a good starting point, perhaps also in conjunction with some ridge or lap vents.

Ridge Vents

Ridge vents are designed to be installed at the apex of a pitched roof. Some ridge vents are designed to be attached to gas appliances to allow for direct ventilation, however they can also be used in tandem with eave or tile vents to effectively release moist and warm air from your roof space.

Ridge vents can be installed by securing them to your roof ridge above suitably cut roofing felt or undersarking. These vents provide an impressive level of ventilation, but can almost never be used as a singular vent, but rather as an exit for rising air. Be aware that it is possible to install too many ridge vents however, particularly when it is very windy. This is because for homes with many ridge vents partnered with large eaves vents (a common occurrence in new builds), too much air can enter your loft space, potentially blowing your insulation about at the edges and causing damage.

As opposed to traditional wet fixed ridge vents, Timloc have manufactured a highly convenient dry fix ventilated ridge kit, designed to be easy to install whilst still providing an impressive 5000mm²/m of ventilation. This is an ideal solution for DIYers looking for a low maintenance roof ventilation solution.

Eave Vents

Eave vents are designed for low-level ventilation and are a common feature in new build properties. Eave vents are found along a home’s soffits, and it’s important to remember to give these a spring clean every now and then to clear away dirt, dust or debris.

If you do need to fit eave vents, there are a few options available. Firstly, are continuous eave cents, which run the entire length of the soffit. These are a great choice but require a fair amount of work to install. Fitting continuous eave vents may require scaffolding, removing tiles, laths and undersarking – so are not ideal for existing properties. Conversely, circular soffit vents are the perfect choice for DIY retrofitting or refurbishment, as they are quick and easy to install. Simply drill a hole large enough to house your vent through the underside of your soffit boards and push it in to fit. One health and safety concern here is to ensure that you do not have asbestos soffits. If this is the case, do not drill or cut into them under any circumstances. If your home does feature soffit boards made from asbestos, we’d highly recommend having them replaced by a professional with high-quality UPVC soffits.

The number of eave or soffit vents you’ll need will depend upon your desired airflow and local building requirements. However, taking Manthorpe’s Circular Soffit Vent as an example, to achieve 10,000mm2/m of free airflow, they should be fitted at 200mm centres.

A third option, useful for retrofits or when replacing fascia boards, are over fascia vents. These provide highly discreet ventilation, along with features designed to repel unwanted visitors such as birds and insects. These vents are made from small units that clip together and are nailed over the top of your fascia boards. Installing these roof vents is difficult, but highly effective when done right.

Lap Vents

A bonus fourth type of roof vent. Lap vents such as Manthorpe’s Felt Lap Vent are by far the easiest to install out of all the types of vents mentioned above. They can be easily slipped in between a horizontal overlap of your undersarking. This creates an air pathway which can help combat condensation build up. Initially, it is recommended that one vent be placed into the laps in every other rafter bay as close to the eaves as possible, but more can be installed in extreme circumstances. It should be noted that these vents alone will never provide adequate roof ventilation and should always be partnered with the options listed above to create and suitable amount of ventilation.

How Much Do Roof Vents Cost?

Creating a high-standard roof ventilation system is a vital factor in the longevity of your roof and many structural components within your home. Whilst this will require an initial investment of time and money, installing adequate roof vents into your property will pay dividends in years to come. With the question of cost in mind, we’ve listed some of our most popular products below to give you a general idea of how much high-quality roof vents will cost.

Roof Vent

Total Cost

Corovent – Ridge Vent with Extension Sleeve x 4


Timloc Roll Out Dry Fix Ventilated Ridge Kit – 300x6000mm


Timloc Roll Out Dry Fix Ventilated Hip Kit – 300x6000mm


Manthorpe Double Pantile roof Vent (Pack of 4)


Manthorpe Circular Soffit Vent (Pack of 50)


Manthorpe Felt Lap Vent (Pack of 50)



Now you should be equipped with enough information to accurately calculate how many roof vents you need, select the products that are right for your property and get started on installing your roof vents. There’s no understating the importance of roof ventilation, particularly for homes that may suffer from condensation, damp or mould – all of which are highly hazardous to human health. Who knows, perhaps you may make your loft such a pleasant space to be in that in future you’ll consider undertaking a full loft conversion.

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