Installing Pitched Rooflights

March 11, 2018

The first thing you need to know when installing your rooflight is how flat your roof is. To do this, you need to measure the slope in the roof which is known as its pitch.

Rooflights need to be installed at an angle to encourage rain water to run off instead of pooling.

If water pools, it can cause dirt to collect on the rooflight which could also cause staining. That’s why our rooflights have an Easy Clean glass coating to discourage dirt from sticking.

There is also the risk of the membrane being damaged if any pooled water freezes.

It is therefore best to install your rooflight at an angle of at least five degrees.

Measuring your roof pitch

When measuring your roof pitch there are three types of measurements to make:

  • Run – the horizontal distance between the peak of the roof and the wall.
  • Rise – the height of the peak above the wall.
  • Span – the distance between the walls. It may be helpful to measure this too.

Measuring from the rafters

When there’s no roofing material to cause an uneven surface, measuring from the rafters should give you an accurate measurement.

You can measure the roof pitch from the rafter in the attic, or from the overhang of a rafter in the roof, or even from a barge rafter at the side of the gable.

To do so, follow these steps:

  1. Position one end of the carpenter’s level against the underside of the rafter, and adjust it until the bubble is centred between the two lines.
  2. Find the 12-inch/30cm mark on the carpenter’s level. If yours doesn’t have markings, use a tape measure to mark on where 12-inches is.
  3. Measure the vertical distance from the carpenter’s level to the rafter. When you measure the distance from the 12-inch/30cm mark to the underside of the rafter, make sure your carpenter’s level stays in position.
  4. Work out your roof pitch, which is the ratio of the rise to the run.

Measuring from the roof surface

You can also measure your roof pitch on the roof surface but you’ll need to make sure it’s safe to walk on and be careful not to injure yourself.

Once you’re safely on the roof, you’ll need to measure as follows:

  1. Place your carpenter’s level against the roof and adjust it until the bubble is between the two lines. If your roof is particularly bumpy, then try laying a flat board down so that you can get an accurate reading.
  2. Measure the vertical distance from the roof to level by holding the 0-mark of the tape measure against the roof and extending upwards, so it’s perpendicular to the carpenter’s level. Once the tape measure has reached the 12-inch/30cm mark, write down the vertical distance measurement.
  3. Work out the pitch slope, which is the rise over the run.

If you don’t have a calculator to hand, you can use a roof pitch calculator online instead.

How to install a flat rooflight

If your flat roof has been built with a pitch greater or equal to five degrees then you can proceed with a standard installation.

This video shows you how to create the right angle and install your rooflight too.

If you have further questions, one of our experts will be happy to advise you. Just call us on 0116 214 7151.