How many soffit vents do I need?

This is a difficult question to answer when ventilating older roof spaces, and I’ve seen many people try to take the one size fits all approach over the years, sometimes they are right, sometimes they are wrong.

The short answer is that every building is different, not only by shape and size but by geographical location and positioning, even in the same street. This makes a one size fits all approach hard to achieve. For example.

House one – A standard semi-detached home. This is located five hundred meters down the road from house two (see below) and placed in a row of other semi-detached houses. It has continuous soffit vents all round, and two roof vents front and back. And it has great ventilation in nearly all weather.

House two – Another semi-detached house identical in every way to house one. This house though is an end semi-detached house and is located five hundred meters up the road placed on a slight hill. The wind channels through the estate, up the road and blows violently into the vents and soffit vents. So much that it often blows back the insulation in very strong winds, this causes heat loss from the insulation near the edges of the roof in winter, creating mould and black stains.

Do you see the issue?

So, if you are unsure call an experienced architect or roofer to evaluate. Personally, I would suggest being cautious. A little extra ventilation is easier to add later than it is to remove. You do not want to end up with your roof void being too cold, warm air can hold more moisture than cold air and this will evaporate moisture from your insulation better, reducing the heating bills.

Do you need the same amount of soffit vents for a bungalow

The issues are the same for a bungalow roofline as a semi detached house. The Lancashire extreme weather can also affect the decision if you live in a rural exposed location.

Which material do you recommend for soffits

Redline has many years experience replaciing fascia and soffits in Lancashire and recommend uPVC as an ideal material for your roofline as it is more durable in the harsher Northwest weather. UPVC is relatively inexpensive compared to timber, and wood is prone to rot and insect damage, and so requires much more maintenance and upkeep, particularly if you live in a more rural Lancashire area having to withstand high rainfall levels. UPVC would also be used on bungalows and other residential properties manufactured in many colours that can be matched to your house exterior.