Measuring the gap between roof tile and panel: Ø12, Ø15 or Ø20?

Everything in this shop comes down to one measurement: the gap between your roof tile and the underside of your solar panel. Once you know it, you immediately know which diameter you need. If you don't, there's a good chance you'll order a brush that is too thin, and then you're still stuck with birds.

What exactly you measure

You measure the vertical gap between the highest point of the roof tile and the underside of the panel, at the narrowest point of the row. Not at the widest point, because a bird looks for exactly the spot where it can get underneath most easily, and it will find it.

A tiled roof is never flat. The tiles have a wavy profile, and the mounting system the panels rest on has a fixed height. As a result, the gap varies by a few centimetres along the length of the row. So measure at three or four spots and go with the largest measurement.

How to do it safely

• Don't stand on the roof if you have no experience with it. From a ladder at the roof edge you can easily measure the bottom row, and that is usually the row that counts.
• Use a folding rule or tape measure and hold it upright between tile and panel, not at an angle.
• If you can't measure, take a photo with a tape measure or a credit card next to it. A bank card is 8.5 cm wide and gives you a usable estimate.

From measurement to diameter

The diameter is the thickness of the brush when it lies loose. You choose the first size that is larger than your gap, so the brush wedges in lightly and holds itself in place. That means no fixings are needed, and that is exactly the idea.

• Ø12 cm for a tight gap of up to about twelve centimetres.
• Ø15 cm for an average gap. If you measure 13 cm, for example, this is the first size that covers it.
• Ø20 cm for a wide gap or a high mounting system. This size can also be used as a gutter guard.

If you are right on the boundary, choose the larger size. A brush that is slightly too thick compresses and stays put. A brush that is too thin leaves a gap at the bottom, and that is all a bird needs. If in doubt, the rule of thumb is: too thick works, too thin doesn't.

And then the metres

Once the diameter is settled, the question is how many metres you need. Measure the sides of your panel array that are open. Usually that is the bottom edge plus the two sides; the top often already sits against the ridge and is then closed. Add up those metres and round up. A little too long is not a problem: if a roll is longer than the side, you bend the end over. Do not shorten the brush, because that damages it.

Don't know the number of metres, but do know the number of panels? Then the size finder works it out for you. By default it assumes a width of 1.70 m per panel, the long side of a standard panel mounted in landscape, and you can adjust that figure if your panels are laid differently. The size finder then works out the cheapest combination of rolls by itself, because with different lengths side by side that's impossible to do in your head.

Measure again before you order

The two most common mistakes: measuring at the widest point instead of the narrowest, and forgetting the sides of the panel array. Both cost you a second order. Five extra minutes on the ladder saves you that.