Thermal Rating: How To Get A Warm & Cosy House Extension

Thermal rating - how to warm your house extension

If you have ever owned a house with a conservatory on the back of it you will know you have that 15-day sweet spot that makes it a habitable room, the rest of the year you experience this see-saw effect of being too hot or being too cold.

It’s a common theme with customers that they want to extend their home but they want it to be a usable space all year round. Given the historical data we tend to experience more cooler days than warm. So a new extension must be warm and cosy!

Thermal Rating & House Extensions

This is where thermal rating comes into play. The lower the thermal rating the more efficient the space is. Current building regulations insist that a newly built extension should have U value of 0.28w/mk. Well that seems a nice low number right? Sure its low, it’s also like the minimum requirement, just good enough to pass.

The main thing to consider when you heat up your new room, whether it is radiators, underfloor heating or another source is how well you retain that heat? This is where efficiency comes in. If you can retain more of your heat longer you spend less on energy consumption.  

Brick has a great thermal mass, its stores the heat really well. It’s also a great conductor. This means it allows the heat to pass though it easily. Similar to a hot sandy beach, almost impossible to walk on in the middle of the day, but as soon as the sun sets the heat dissipates quickly.

How Warm Is A LIGNA Extension?

Timber by contrast is the opposite, it doesn’t store the heat but it also does not conduct the heat as well. This means the heat you have in the room stays in the room for longer. As part of the construction process of a timber building all joints are sealed with a barrier tape. This also further ensures heat stays in your room for longer. The flip side benefit is that if it’s harder for heat to pass through it will keep the room cooler in the warmer months. A LIGNA extension has a u value of 0.14w/mk this makes it twice as efficient as a brick extension.

A practical example of this, during this lockdown period I choose to walk past the show extension. We haven’t had any heating on since lockdown began 5 weeks ago. Taking a picture through the window, the thermostat read an ambient room temperature of 21.4 degrees.

What does this mean for you? You get to save money on your heating bills. The extension you are creating will potentially be a room you spend a lot of time in. You will always want to feel comfortable in that room and you won’t want to spend a small fortune heating it. The smaller the u-value of your build, the more efficient your space is. The added feel good factor, the less energy you use to heat your space also reduces our Global carbon emissions.

It all counts WIN WIN!!


A LIGNA Home Extension boasts a modern, grand design style single storey rear extension completed in 3 weeks.  A choice of flat, sloped and pitched roof designs. External finishes include wood, grey aluminium, white render and brick.

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