Temperatures hit the roof but a well-insulated one can help to keep you cool

In this heatwave, we are working on site where a room-in-roof has been constructed and
insulated at rafter level using rigid PIR fitted and our Insulfix Track. The site is ongoing, and
we were surprised at how popular the new room was with all the contractors. The reason?
Well, it’s so much cooler than outside!

We set up some temperature probes and the temperature inside the well-insulated room-
in-roof was 22.4°C, that’s nearly 10°C lower than the outside temperature of 32.3°C. The
tightly fitted insulation boards between the Track create an airtight barrier making it as
difficult as possible for the heat from the outside to get through to the room-in-roof.
We always hear the story that insulation works both ways – keeping you warm in the winter
and cool in the summer and our experience backs that up, but why then is overheating on
the increase and how can well fitted rafter level insulation help make a difference? Let’s try
to dig a little deeper to find out more.

One of the main causes of overheating is solar gain – where sun coming through the
windows heats up the rooms and, if the house is insulated, that heat will hang around. This
is why insulation often gets blamed for overheating, but it is not the root cause. Limiting
solar gain with shading and by closing shutters, blinds or curtains will help, as will ensuring
there is adequate ventilation for the warm air to escape by opening windows and vents to
get a through draft of cooler air. Of course, when the air is hot outside, opening the
windows must be done with caution as it will allow potentially hotter in the house and if
there is no wind blowing that will also make life trickier.

That’s solar gain, but what about thermal gain from your roof? If your loft is insulated at
ceiling level with fluffy insulation and you have ventured up during a hot day, you will
probably feel like someone has built a sauna up there without telling you. The heat from the
roof tiles heats up the air in the loft. If the air outside is hot, the ventilation in your loft
won’t make much of a difference unless there is a cool wind blowing. This means that there
is a bank of hot air in your loft space, and it will gradually heat up the ceilings of the rooms
below the roof. If the ceilings themselves are not airtight as this will allow the heat to enter
the rooms more rapidly.

If your loft is insulated at rafter level, this creates a habitable space where temperature,
humidity and indoor air quality can be controlled. In this situation, the insulation is
positioned close to the tiles outside and during hot weather, will be exposed to high
temperatures. The heat from the sunshine on the tiles will look to travel through the
insulation to warm up the cooler air in the loft. If the insulation is doing its job, then it will
slow that process down and help to keep your loft space cool – exactly in the way we are
seeing on site now. However, the insulation won’t be so effective if thermal bypass is taking
place. Thermal bypass is where gaps allow warm air to escape past the insulation in the
winter, making your room colder and your fuel bills higher. In the summer those same gaps

will allow the warm outside air to creep past the insulation and gradually heat up your
house.

So, if you are thinking about insulating your roof at rafter level – making sure that the
insulation you use properly fitted and tightly locked in position will not only help warm you
up in the winter it will also keep you cooler in the summer.
Independent testing showed that with traditional friction-fitted insulation the thermal
performance of a test rig roof was 179% worse than expected. Using Insulfix Track to fit the
same insulation between rafters increased the airtightness of the roof and gave the
expected U-value and thermal performance. Now that’s pretty cool. If you would like to find
out more please contact us today.