Roof Ventilation - The Only Guide You Need to Read

Words: 1137 💻 Read time: 5 mins 📚 

Writer: Scott Beddoes 👨🏻‍💻

Roof ventilation is one of those problems you know you should sort out, but you ignore it until it's too late.

You know those things that always seem to stay at the bottom of your to-do list?

Roof ventilation is the definition of one of those things!

And if it stays at the bottom, you could be running the risk of condensation and damp.

So it's important that you get roof ventilation right.

This Roof Ventilation Guide will show you everything you need to know, in one neat place.

And, you'll find out how to choose the best option for you and your home.

What is the purpose of roof ventilation?

It’s simple. Roof ventilation is the movement of air in and out of your roof space. You can use natural or mechanical methods to create that airflow. 

How much roof ventilation does your home have? Well, that depends on many factors including the property's age, the type of roof on the property, and any roof vents that have been installed.

Bottom line: you need at least some roof ventilation to control the temperature in the loft or roof space.

Why is roof ventilation important?

But why is roof ventilation so important? 

You’re probably thinking there’s no harm in the temperature of the loft being too high or low.

What’s wrong with a little bit of condensation? Or a loft that’s slightly warmer?

Here’s the problem:

In winter, warm air from the rooms in your house rises through the ceilings and into the loft. This warm air condensates when it touches any cold surfaces (particularly inside the roof).

Condensation in the loft can cause black mould growth, wood rot, and damage to the roof structure. And it can even reduce the efficiency of your loft insulation.

During hot summers, a warm roof space can also be a problem.

The sun makes the loft hotter and hotter through a process called solar gain. This can make the bitumen under sarking smell, and can even damage the felt under sarking or felt shingles (if you have them).

So the key takeaway is this: good roof ventilation protects your home.

It protects the health of your home, the energy efficiency of your home, and most of all the VALUE of your home.

You don’t want to spend money on a new roof, and neither does a potential buyer (if you’re looking to sell that is).

How much roof ventilation do I need? (Roof ventilation requirements UK)

To meet UK roof ventilation requirements, you have to provide enough ventilation to avoid condensation in the roof space.

Ridge or high-level ventilation should be equivalent to a continuous opening of 5mm at the highest point of each roof slope.

For a roof pitch of 15° or more, you should provide ventilation equivalent to a 10mm slot running the full length of the eaves.

And for a mono-pitch roof, you need cross-ventilation, plus the equivalent of a continuous 5mm slot and some eaves ventilation.

Sound confusing? We made the basic drawings below to give you a better idea. 

We refer to the cold roof section in the ventilation segment of 7.2.15 by the National House Building Council (NHBC).

How to improve roof ventilation

If you want to improve roof ventilation, a combination of roof vents and extractor fans is your best option. 

We wrote a guide about the best types of roof vents. 

But I’ll save you a click: we recommend roof tile vents because they’re low cost, super easy to install, and can be used for roof ventilation or extraction for your bathroom fan.

Installing roof vents allows fresh air to be drawn in at low levels, circulated inside the roof space, and exhausted through vents at higher parts of the roof.

This gentle airflow minimizes stale air and condensation — keeping a healthy environment in your loft.