Mega Guide to Roof Ventilation
The roof is arguably the most vital part of a safe, comfortable home. Roofs offer protection from storms, direct sunlight, falling debris and more – but they can only perform at their best when properly maintained. Roof ventilation is likely not at the forefront of most homeowner’s minds, but it’s a simple way to keep your roof space happy and healthy long-term.
Why Ventilate a Roof?
There are many reasons why having a proper roof ventilation system is advantageous, which can be separated into three main categories:
Protecting your Roof
Perhaps the most pressing reason of all, a lack of proper air flow in your loft space can lead to serious long-term damage. Day-to-day life produces a lot of warm, moist air. Daily activities such as cooking, showering, and washing clothes all contribute, and this air can become trapped in your roof space if there’s nowhere to go. Once the moisture in the air touches a cold surface on the inside of your roof, it will form condensation. If that wasn’t bad enough, condensation can form the perfect breeding group for damp, rot and mould. All of these are hazardous not only to human health but can also cause massive structural damage to your home if left unabated.
In order to avoid nightmare issues such as these, if you spot signs of condensation or damp such as dark, wet patches, these need to be addressed immediately. Thereafter, fitting proper roof ventilation is a wise course of action to prevent the problem from recurring in future.
Converting your Roof Space
If you’ve decided to convert your loft or attic into a true living space, it would behoove you to add some extra ventilation. During the warm summer months, loft spaces without adequate ventilation can quickly become uncomfortably and stuffy. Installing roof vents will help to alleviate this by increasing the flow of clean air.
What’s more, if you want to prevent issues such as condensation mentioned above, it’s best to add more ventilation as part of a loft conversion. This is because adding a new living space often affects your airflow requirements, most commonly increasing to 25,000mm2/m.
New Build Air Leakage Requirements
Specific regulations have been put in place for new build homes to ensure that they are sufficiently airtight. Building regulation standards, specifically Part L1A sets out a required airtightness of 5m³/h/m²@50pa. Roughly translated into clear English, this means that no more than 5 cubic metres of air can escape per hour from every square metre of the building envelope, with an internal air pressure of 50 Pascals. However, to accommodate this level of airtightness, you’ll need a substantial level of control over your roof ventilation. A lot of new builds incorporate controlled mechanical ventilation such as MVHR (Mechanical Ventilation with Heat Recovery) systems. These can be used to ventilate a whole property, but additional traditional measures such as roof vents may still be required, if only to prevent issues already raised above.
Extra Benefits of Roof Ventilation
Roof ventilation is a very sensible investment for a number of reasons, not just limited to structural longevity mentioned above. Installing roof vents can even save homeowners money long-term by reducing the need for and cost of air conditioning in summer.
In winter, roof ventilation can help to extend the lifespan of your roof by preventing ice damming. This is when accumulated warm air heats the underside of your roof, melting away any slow above. This water then runs down your roof, refreezing towards the colder edges at the bottom. This new “ice dam” will prevent any more water from running off your roof space, potentially causing pooling and serious damage to your roofing material. Soffit vents are especially useful here as they can drive cold air into your roof, more on how to install these below.
Any ultimate guide would not be complete without mentioning health and safety. The below should be taken into account before beginning any work on your roof.
First and foremost, you should ensure that you have safe access to your roof surface. This can be done in a number of ways, including scaffolding, however for installing roof vents a ladder should be sufficient. Be sure to use a ladder with rubber feet for added grip, and get a friend to keep the ladder secure at the bottom. Remember to never reach out further than necessary when working atop a ladder, as this is one of the most common causes of serious accidents.
Never put your full weight onto a surface you don’t believe can support you. This is especially true when working inside your roof space. As you can imagine, replacing a hole in your ceiling can be very costly. All roofs should be treated as fragile until a qualified professional has confirmed that they are not.
If you are concerned about any aspect of your installation, a professional should be consulted. For more information on working safely whilst at height, refer to the government guidance by clicking here.
Getting to Work
Now that you’ve determined your ventilation needs and taken health and safety into account, it’s time to think about how exactly you’re going to ventilate your roof.
Pitched roofs can generally be split into “Cold Roofs”, where insulation has been placed horizontally across the ceiling level, and “Warm Roofs”, where it has been fitted above, between or below your roof rafters. Cold roofs are far more common in Britain, and will almost certainly require extra ventilation. This is because the void above the insulation layer will be cold and often filled with moist air. To solve this issue and avoid wind tunnelling, install vents at both high and low levels in your roof.
Warm roofs generally have a far lower risk of problems such as condensation, particularly if they feature a vapour control layer. However, it can be difficult to seal every last joint or gap. If you notice condensation beginning to form despite your warm roof construction, we’d also recommend installing vents at varying heights.
Flat roofs can also be separated into both cold and warm roof constructions. In cold roofs, the insulation is generally installed between or under the roof joists, whereas warm roofs have the insulation layer above the joists. Regardless of which construction you have proper ventilation can be achieved with the use of a vapour control layer installed below the insulation in conjunction with soffit vents.
Understanding Wind Tunnelling
If you’ve looked into roof ventilation before, you may have come across the term “wind tunnelling”. In essence, this is when air flows through one vent and directly out of another. This normally occurs when two vents have been installed at the same level on opposite sides of a pitched roof.
Wind tunnelling isn’t always a bad thing. If you just want a strong supply of clean air, there’s not too much to worry about. However, if you’ve been dealing with condensation, then you should install your roof vents at different levels to avoid this.
Understanding Vapour Control Layers
In very simple terms, vapour control layers are designed to prevent the passage of moist air into your roof space. Most often fitted on the inner face of a property, these layers are a common feature in roof ventilation systems today. In fact, some forms of insulation such as multifoil insulation come with vapour control layers built in. Previously, vapour control barriers were favoured due to their complete blockage of moisture. However, this can cause issues particularly in summer months, as moist air has nowhere to go and simply condensates and wreaks havoc in the roof space.
The importance of a proper vapour control layer cannot be understated. No matter how well ventilated your roof is, the temperature difference between the insulated inside and the outdoors can always lead to condensation. When ventilating your roof, regardless of whether for a new build or existing property, it’s important to ensure you install one.
Installing Roof Vents
Now it’s time to fit ventilation into your roof space. However, there are a few questions you’ll need to ask yourself. What kind of vents do you need? How many will be needed? And of course, how much will this all cost? For answers to these questions and more, check out our guide on how to install roof vents.