A Metal Faraday Cage Garage – Will It Protect From EMP?


I was asked if this would be effective as a ‘Faraday cage garage’. “I have a very big workshop/Garage and it is 95% metal. Would it protect in the event of an EMP attack?”

The question was from way back during 2012, which inspired this original post. I just read through the article comments. Good stuff in there. It’s a good topic. One which we do not have definitive absolute answers to.

I’m re-posting this and will add more to the original content below (I’ve learned more about the topic since back then).

To get you started, you might want to read this article:
Nuclear EMP Components E1, E2, E3, and what they mean…

Faraday Bags for EMP
(view on amzn)

Faraday Cage Garage

Will a metal building protect from EMP?

An enclosed metal structure will certainly provide some amount of protection (attenuation) in the event of an EMP (electromagnetic pulse). However…

There is one potentially very big caveat though… that is, there can be no big ‘leaks’ in the structure. A 95% enclosure will still allow electro-magnetic radiation to get in, provided that the opening(s) is larger than the wavelength of the electromagnetic radiation. More on that in a second…

An ideal Faraday cage would be an enclosed metal ‘box’. ALL (6) sides, including the floor. Conductive mesh screen will work too.

Maybe you have a metal garage or shop building. And you’re wondering if it’s EMP proof. A sort of faraday cage garage. A metal roof. Metal walls.

But… do you have windows? Those are big openings! Is the door made of metal? And, what about the floor? Will an EMP get through the floor? This is all debatable.

Any of these could be the Achilles heel for EMP protection.


Electromagnetic radiation from an EMP, if strong enough, will be conducting through the top surfaces of the ground and may find its way in through the ‘open’ floor (in the sense of ‘electrically’ open). A well constructed and grounded floor ‘may’ suffice though – poured concrete with re-bar that is well grounded for example.

The E1 pulse of an EMP will do the most damage to electronics. It happens faster than the blink of an eye. The pulse may rise to its peak value (up to, possibly 50KV per square meter) in about 5 nanoseconds (0.000000005)! To put that in perspective, ‘the blink of an eye’ takes about 300 milliseconds (0.300000000).

Research papers indicate that it’s the very high frequencies (up to around 1 – 2 GHz) that are of most concern regarding electronics damage from EMP.

“The electric field strength of an EMP remains fairly constant in the 10 kHz to 1 MHz band and it decreases by a factor of 100 in the 1 to 100 MHz band and continues to decrease at a faster rate for frequencies greater than 100 MHz”.

Excerpt from QST August 1986, “EMP and the Radio Amateur” and condensed from NCS TIB 85-10

I mention this because it has to do with mesh size (‘holes’, gaps, openings in the structure) as it relates to frequency / wavelength. Obviously a solid metal enclosure is not issue. But it’s good to generally understand what you might ‘get away with’ with regards to openings.

It appears that EMP field strength decreases by at least an order of magnitude for each decade of frequency above 1 MHz.

So with all that said, the frequency wavelength up around 2 GHz is somewhere around 5 inches or thereabouts.

That means a gap that size will allow that frequency right on through. Not good…

However the smaller the gap, the more it will attenuate that frequency. Long story short, without getting into all the math… For EMP protection, it appears any typical conductive screening (e.g. aluminum window screen) should do a good job of attenuating. There’s more to it, but that’s the general concept.

[ Read: Thoughts Regarding Faraday Cage Techniques For An EMP ]

EMP Shield

So, what about that metal Faraday cage garage? If I had a metal building with a metal roof and no windows, setting on concrete with rebar, I would feel pretty good about EMP protection to an extent. Hopefully we never have to find out.

As a side note, I do have a 40 foot metal shipping container on the property. However those things have wood floors. So maybe it will help with EMP (somewhat), or, maybe not.

Better yet, in either case, keep a homemade Faraday cage (galvanized can with lid – with interior lined with non-conductive material) inside the metal building or shipping container (sort of double protection?)…

[ Read: How To Decide What To Keep In A Faraday Cage ]