How do you calculate the roof area for a project?

When undertaking work on a roof, accurate measurements are important. Roof projects may include tiling, installing insulation, ventilation, and even installing guttering. To calculate the roof area of a property with a classic gable roof*, all you need are two key dimensions.

You will firstly need the measurement for the length of your roof (i.e. the length of the wall of your property on which the bottom of the roof sits). Next, you will need the ‘roof slope height‘. Note: this measurement is different to the height of the roof which is taken at the apex of the roof where the two sides meet.

When you multiply the length of your property by the roof slope height of your roof, this will calculate the roof area of one side of a gable roof in metres squared.

If you have these dimensions, the pitch of the roof won’t matter. Most owners will have access to the information as upon purchasing a property there will be building plans. However, if access isn’t available to these plans, the local council should be able to provide this.

How to calculate the roof area using the roof length and roof slope height

calculate the roof area for a roofing project

Roof Width (m) x Roof Slope Height (m) = Half Roof Area in m²

For our example (image right) we’ve used a perfectly square house with 76m² floor space, a 45° pitch and a 2.35m roof height. The roof slope height is 6.98m.  Please note if you are working out how many roof tiles you need, this calculation assumes there is no chimney or other section of the roof which is not covered by tiles. 

The length of the roof is 8.7m for this square house as 8.7m x 8.7m is 76m² (total floor space).

The roof slope height is 6.98m. So, for our example:

8.7m x 6.98m = 60.73m²

Because this is only one half of the roof, we will need to double this number to find the entire roof area.

60.73 x 2 = 121.45m²

With the above information, it is possible to work out how much insulation you may need, how many roof vents you’ll need to install and also how many roof tiles to purchase. If you’re unsure on any of the above or your roof is not the classic ‘gable’ roof, please consult a professional installer so you can make informed decisions.  Alternatively, contact our helpline on 01752 692 760 and we will be able to help you with your calculation.

*A classic gable roof is where 2 roof sections meet in the middle in an inverted ‘V’ shape