I have done a couple projects were IT type spaces required some buffering to similar issues. Mass walls (thick block w/ cores filled, ICF, precast, etc) go a long ways at reducing it. However the roof and floor also has to be of similar construction. The saferooms I have done we had to put stand alone routers in those spaces if they wanted WIFI due to the single unable to pass through the thick walls from the rest of the building. There are also drywall products we have used that help reduce. Quietrock sound gyp has a series (forget the model number) but it has a thin layer of metal inside the gyp that was intended to block sound. Turns out it is great at blocking various air wave singals, WIFI, etc as well.

"Mass walls (thick block w/ cores filled, ICF, precast, etc) go a long ways at reducing it."

this wil not due much at all to reduce EMF (Elctro magnetic Fields).

To reduce field str4ngth you need layers of a very good metallic conductor, and concrete is not it.

It can help with RF (radio frequency) fields, but a single layer of foil faced thermal insulation would be as effective (and possibly more depending on frequency) than concrete.

The latest hysteria is magnetic fields anyway since no one has proved that anything but relatively strong fields are harmful.

Even cell phones are not confirmed by any means.

Correlation is not causation.

"shielding wall paint"
Better have a very low resistance, like metal foil.

Lighting bulbs from the EMF in your floor seems like a possible danger sign.

The first lawsuit I ever worked on as a lawyer was a suit against a power company, who we represented, claiming EMF's caused harm to the plaintiffs (it was a class action). At the time, almost 20 years ago, there was almost no good science showing any harm. I don't know if the science has changed (switched law firms to one that didn't represent power companies!) . . . interesting concept though.

Wi-Fi can be considered "a major reducible source of EMF" only if you choose to ignore the much larger source of EMF in a home: radio & TV transmissions, electrical wiring, electrical appliances, etc. And while electrical fields are easily screened, magnetic fields penetrate most substances so many screening methods don't work well.

Cellular phones operate in the low energy radio frequency part of the electromagnetic spectrum and are non-ionizing radiation so they cannot break the molecular bonds of cells nor can they effectively penetrate the skin (the depth of penetration is limited by the radio energy being transferred to water in the skin, turning that energy into heat so at very high levels of exposure, RF causes warming of tissues like an infra-red heat lamp would).

However, there are reasons to shield spaces other than for health, most notably security; many people don't like to share their EMF.

Health Effects of Non-Ionizing Radiation

Interesting unsourced chart. Just glancing at the first entry, though, I wonder about its accuracy. UVA rays, for instance, are connected with a lot more than pigmentation. They are associated with cancer, according to the Centres of Disease Control.

The risks of EMF are not in question by even the most mainstream of authorities.

For instance:

The Swiss government summarizes exposure and risks.

WHO last year concluded that cell phone use is "possibly carcinogenic".

It seems prudent to me and no inconvenience to limit cellphone exposure by using a Bluetooth, not use my IPad2 and laptop on my lap, use a wired router and wired landline phones and get rid of my last remaining tube type TVs. (But I'm still keeping my tinfoil hat.)

The reasons the computer expert wanted hard wiring are: hard wiring has much greater bandwidth, and hard wiring is more secure.

Chart is from Wikipedia and credited to:
Kwan-Hoong Ng (20 - 22 October 2003). "Non-Ionizing Radiations Sources, Biological Effects, Emissions and Exposures". Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN ICNIR2003 Electromagnetic Fields and Our Health.

I should have noted that the article says that UVA radiation is non-ionizing but it "produces free radicals that induce cellular damage, which can be carcinogenic."

The original question was about reducing EMF exposure in a building which is an issue for building designers to consider.

The exposure from small radio broadcasting devices held against your head is a different matter only indirectly related to building design.

Since these devices operate at greater power when the signal strength is poor, a more RF transparent building envelope might be desirable but that could be in conflict with the issue of reducing interior EMF exposure and security.

But one thing is for certain: RF shielding of buildings does not address the effect of EMF's inside the building especially those that are used in close proximity to people and rely on signals from outside the building like computers and cell phones.

Also, it is virtually impossible to completely shield a house from EMF (in either direction) and aluminum foil is not effective. The most common material used for architectural shielding is nickel alloy sheets/meshes and special paints.

"magnetic fields penetrate most substances so many screening methods don't work well. "

Not really correct.

A static magnetic field (not time varying) is indeed very hard to shield.

It require large amounts of iron, nickel, and other ferromagnetic material and can never be made completely zero.

A time varying magnetic field (what mist EMI is) is shielded effectively by a layer of metal, and the lower the resistance and thicker the metal the better.
The varying magnetic field induces eddy current in the metal that cancel the applied field. Any conductor works for this, with the lower the resistivity of the conductor the better the cancellation.

The chart above is old, and uses the known effect of tissue heating.
There is circumstantial evidence that we may be more sensitive than the simple heating model indicates (especially the brain).
Cell phones do not produce enough heating effect to cause problems, but there may be other mechanisms that have not been identified lately.

The danger of higher power fields (time varying electric or magnetic) has never been in dispute.

What IS in dispute is the level of exposure that may crate danger.

There are 'keep out' zones on naval vessels near radar and communications antennas, and even on planes sitting on the ground.
You can feel your skin start to 'crawl' from the high power fields if you get closer than you should be.

I have even worked in labs with RF power warning systems.
Sort of like a smoke detector for excessive RF energy.

The issue is identifying some mechanism related to lower power RF beside direct heating, or establishing specific tissue sensitivity (like brain sensitivity) as being lower than other tissue.

Since you cannot prove a negative, we cannot prove anything has zero effect.
All we can do is identify limits that produce no observable effect, and try and identify mechanisms for the RF effects observed.

You have to keep in mind that we are exposed to the static (more or less no real fast time variation) field of the earth itself.
Simply moving around in this field induces currents in our bodies since under the dry epidermis we are pretty good conductors, and ANY conductor moving in a magnetic field has current induced.

We know that wavelength of the RF matters, but not all that well how our bodies respond to excitation beyond direct heating effects.

So what is your recommendation for reducing EMF in a house?

Hi,

The best way to reduce EMF is to use a Faraday cage. This is a cage of conducting material that has a connection to earth. It is named after the British scientist Michael Faraday who invented it in 1836.

Faraday cages are often used in laboratories where you need to test radio equipment. The volume inside the cage has no radio signals or EMF radiation. All the signals are taken to ground. The effectiveness of the cage is related to the material conductivity. So thick slabs of copper are best but very expensive. Often cages are constructed of copper mesh. So long as the holes are much smaller than the wavelength of the EMF radiation you are trying to block.

A cheap way of making a cage is by using cooking foil. You need to have this foil on the ceiling, floor and walls. Then earth the foil to a good earth.

Note slow moving EMF radiation, for example the earths magnetic field are difficult to block.

The other good piece of news is that the intensity of the radiation falls off with relation to the inverse square law. So if you can move away from the sources by say three feet or so you will already have decreased your exposure substantially.

Warmest regards, Mike.

So what is your recommendation for reducing EMF in a house?

EMF from what source?

Source in the house?

Source from outside the house?

Power line fields?

Stray power currents?

Radio frequency fields?

What are you worried about?

You have to identify the threat before anyone can make a recommendation on reducing it.
Different techniques are needed for different types of fields.

The original post raised the issue of WI-FI possibly being a major reducible source of EMF.

Hi,

I think the reduction of EMF comes down to cost and how much it bothers you. If you really want to be serious about EMF shielding then you can look at Tempest.

Tempest is a NATO military defence standard. The standard is for blocking EMF signals for military inteligence. So NSA, CIA and GCHQ (Cheltnam MI6) buildings are designed to this specification. Typically the whole building and rooms are "Faraday" cages. There are double sets of doors and windows with "conductive" glass. (Glass with fine wire meshes). This can get expensive. Even at this level Tempest is graded at three levels. Each level having different associated costs and protection.

Warmest regards, Mike.

"There are double sets of doors and windows with "conductive" glass. (Glass with fine wire meshes)."

Or evaporated metal on the glass, creating a semi-transparent mirror appearance.

Long wavelengths can still penetrate.
They simply excite the whole surface and re-radiate energy.

Even in a purpose built screen room, it can be very difficult to contain wavelengths long in relation to the size of the enclosure.
The entire Faraday cage becomes a radiation element (despite solid grounding).

Solidly grounded metal shielding is still the method for reducing EMI from the exterior.
It can actually increase EMI on the interior since the energy is now trapped.

Metal shielding costs money, and every opening must be treated to continue the shield.

Holes in a shield, or even inadequately bonded seas form antennas.
And the antennas formed operate in both directions, in to out and out to in.