Was The Roof a Lightning Rod

Is your house on a hill? If so, it might be a good idea to install a lightning rod.

Lightning will follow the most conductive path, and it seems that your table was part of that path. If it went straight through the roof insulation and not along it, I suspect the roof insulating foil did not have much effect.

Hopefully your insurance will fix the roof. On the bright side, you have a fascinating story to tell guests and the evidence in the concrete floor!

You didn't mention if the house has a properly grounded lightning rod in place. If not, now would be a good time to add one. Lightning can strike the same place again.

Electricity normally follows the path of least resistance, but static electricity and lightning seek the greatest potential difference. The air is changed to a plasma state during the strike, creating a path. Anything in the way doesn't matter. It often seems to have a mind of it's own.

There was a discussion about lightning on this forum recently, and a lot of good answers can be found.

"There was a discussion about lightning on this forum recently, and a lot of good answers can be found."

It can be found under:

Recent Active Threads

http://cr4.globalspec.com/thread/94918/Proof-That-Lightning-is-Totally-Unpredictable

Lightning is unpredictable, and can strike randomly....How long has the cabin been there? Has it been struck before? It's like winning the lottery, once you've been struck you say,"that will probably never happen again", and it probably won't, but it could strike again at any time....I had a friend, had a restaurant, had been there for 30 years, never been struck with lightning, got struck one day and it burned to the ground....rebuilt it over the course of 6 mos....2 weeks after grand opening, same thing happened.....

http://www.kuefler-lightning.com/design-layout-details.htm

Overall the best answer is that you can not predict lightning.

I used to work for a company that produced electrostatic field measurement equipment. Two of the more dominant things to understand are:

1) The house, trees (hills, other things) compress the atmospheric electric field. The field intensity will increase over the house and the tree as shown below.

The closer the lines the greater the intensity of the electric field. Thus, the cloud is more likely to spark to ground at the house or tree.

2) Corona is a "leakage" of charge. Corona happens far more often than you would think. Trees, houses, blades of grass, etc. can all have corona "leak" from their sharp points. As this charge floats around it can create a very significant "path of less resistance" and that path can float around. Thus, not only could the sharp point of the house have attracted the lightning but the tree could have created corona charge and that charge could have been blown to the side a bit to make your house a tempting target.

Good conductors (metal buildings and towers) will compress fields and leak charge faster than poor conductors. But, with static fields poor conductors will do a lot more than you would think that they do. ... Back to the "can't predict" way of thinking.

Also, smoke puts a lot of charge in the air. This charge isn't exactly "lightning dangerous" but if lightning is in the mood to come down then a little extra free charge might help it decide which way to go.

Basically, I don't know. But the two topics above affect lightning.

By the way, nice picture. Thanks for sharing.

I wonder if the two layers of double foil faced foam created a capacitance significant enough to have an effect.

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I also suspect the aluminum table in the basement was not a primary path for the current. It seems like the table legs would have been noticeably damaged/deformed had the table been the primary path.

By definition no the foil on the insulation is not a lighting rod. If it was it would have hit it first before going thru the shingles, tar paper and plywood.

I would have a look at the foil. If the lighting strikes path to ground was thru it under what appears to be the undamaged roof. It may have destroyed the foil and melted some of the foam insulation it was adhered to.

Buy a kite.