Lightning protection for metal roofed residential housing in the UK?

Are we discussing grounding (or earthing) in the context of main equipotential bonding for extraneous conductive parts, or is this primarily related to lightning strikes? My perspective is that the necessity for grounding a metal roof isn’t solely determined by its material composition; rather, it depends on factors such as location and height. Ultimately, the presence of a lightning protection system (LPS) for the entire building is crucial. In my opinion, a metal roof alone doesn’t inherently attract lightning strikes more than a non-metal roof.

The current roof (shingles over plywood) is obviously not electrically connected to the ground in any manner. So the current construction practice is just to remove the defective shingles, replace defective plywood and then add metal sheeting. No electrical (grounding) wire is connected to the new metal sheeting. 

I have also recently discovered that apparently solar panels are not allowed to be mounted on a metal roof, based on home insurance rules.

Peter Brooks

Palm Bay 

The current roof (shingles over plywood) is obviously not electrically connected to the ground in any manner.

Keep in mind that the lightning stroke has passed through several hundred metres of air and is quite happy to discharge through dry masonry and timber structures as well as metallic ones. A conductive roof covering might be thought to do the equivalent of shortening the path by a few mm or at most a few metres.

   - Andy.

To a good first approximation the lightning behaves like a constant current source, where the voltage drop across the object will keep rising towards infinity, until the current does actually flow and discharge the strike-  or at least more accurately the open circuit voltage is several tens of megavolts and will quite happily breakthrough materials often thought of as insulating....

The 50m rolling sphere model for estimating protection zones, is based on an assumption of a maximum voltage of circa 50 megavolts, in turn based on the convenient if a bit flaky rule of thumb that air breaks over at a stess field of about 1 million volts per metre.

In turn this tells us that when the thunder  cloud is 5km up, then the lightning has made a hundred (or more) 50m long (or shorter) zig-zags of successive breakdown before reaching us. - rather like a string of unequal capacitors in series all failing one after the other as each in turn suffers a greater over-voltage.

In turns of your tin can roof, the best you can do apart from erect a higher point near by, is to make it the LPS, and design it to survive the I2C associated with the strike current. This sets a minimum metal thickness that will not get a hole blown in it and requires electrodes and low inductance wiring that tie it firmly to the ground beneath. In effect all the steps in designing a LPS

Mike

To a good first approximation the lightning behaves like a constant current source, where the voltage drop across the object will keep rising towards infinity, until the current does actually flow and discharge the strike-  or at least more accurately the open circuit voltage is several tens of megavolts and will quite happily breakthrough materials often thought of as insulating....

The 50m rolling sphere model for estimating protection zones, is based on an assumption of a maximum voltage of circa 50 megavolts, in turn based on the convenient if a bit flaky rule of thumb that air breaks over at a stess field of about 1 million volts per metre.

In turn this tells us that when the thunder  cloud is 5km up, then the lightning has made a hundred (or more) 50m long (or shorter) zig-zags of successive breakdown before reaching us. - rather like a string of unequal capacitors in series all failing one after the other as each in turn suffers a greater over-voltage.

In turns of your tin can roof, the best you can do apart from erect a higher point near by, is to make it the LPS, and design it to survive the I2C associated with the strike current. This sets a minimum metal thickness that will not get a hole blown in it and requires electrodes and low inductance wiring that tie it firmly to the ground beneath. In effect all the steps in designing a LPS

Mike