What WiFi signal attenuation through concrete wall?

[johnos999]

I'm getting a surprisingly strong WiFi (2.4GHz) signal coming from my next door neighbors
house, despite having a solid concrete block [laid flat] wall between us. (This is a semi-detached
house.) What level of signal attenuation should be expected through such a wall?

 

[Nigel Goodwin]

How long is a piece of string? - however, are they 'concrete blocks' or 'breeze blocks', very different things - and breeze blocks are much more transparent to RF. Breeze blocks are what are commonly used for internal walls.

 

[alec_t]

Does the concrete have steel reinforcing in it, or not? That would make a big difference to the RF attenuation.

 

[johnos999]

Hi, Thanks for the replies.
The blocks are the standard 4-inch masonry blocks commonly used for building houses in the UK and Ireland (see pic). They measure 4 x 8 x 17 inches approx. and are solid (meaning no internal air cavity) and do not contain any metal. They are made from small stones bonded together with cement.
The wall I am referring to is the wall between the two adjoining houses in a demi-detached block, not internal walls within one house.
My living room and my neighbours living room are separated by just this wall.
What I am seeing is that the WiFi signal strength in my living room from the neighbours WiFi is roughly the same as from my own WiFi router, located in the same room! I was expecting a much lower level from the neighbours WiFi, given the wall construction method.

 

[rjenkinsgb]

If the wall is dry, as an interior wall generally is, the blocks will be quite a good insulator so there will be very little attenuation.

[A damp wall (or material) would attenuate more, as the moist material would absorb more of the RF energy].

 

[crutschow]

According to some Google sources, a 4" concrete wall should attenuate a 2.4GHz signal by at least 16dB.

Do you have an idea as to how much loss you are actually seeing?

You might try something like this to get an approximate dB level change:
From How-to Geek:
How to check Wi-Fi signal strength in dB?
For a more precise measurement, use apps like AirPort Utility on an iPhone, Wi-Fi Analyzer on Android, or WifiInfoView on Windows and look for a dBm measurement (sometimes labeled as the RSSI). dBm ratings range between -30 (strongest) and -90 (weakest).

 

[johnos999]

I used Netspot on a laptop to measure the WiFi signal strength. The laptop was positioned about 8 feet from the WiFi router. I am reading about -45dBm from my own router but about -47dBm from my neighbours WiFi. So only about 2dBm difference. I was expecting much more attenuation than this, as the block wall is at least 8-inches thick. I believe both routers are the same type, being supplied by the same TV and Broadband provider (SKY TV). Also the house is two-story, so the wall is quite high.

 

[rjenkinsgb]

According to some Google sources, a 4" concrete wall should attenuate a 2.4GHz signal by at least 16dB.

I cannot find anything that distinguishes damp (or exterior) walls from dry internal walls.

Also, the building blocks are likely "Aerated concrete", a low density material rather than literal solid concrete - eg.

H+H Celcon Standard Grade Aerated Block 3.6N – 440mm x 215mm x 100mm - A1 Building Supplies

Celcon Blocks are BBA Certified, are fire resistant and have been classified 0 surface spread of flame and non-combustible to Class A1, Celcon Standard Aerated blocks are extremely versatile and can be used below DPC as infill for Beam and Block flooring systems and above the ground in walling...

a1building.co.uk

 

[johnos999]

Yes, the 440 x 215 x 100mm Aerated blocks you mention look like the type used in the wall construction alright. The size is the same too. Despite not being made of solid concrete, I was expecting more than 2dBm of attenuation through an 8-inch wall made of this material.
The nearest figure I have seen browsing the internet is 11dB attenuation for an 8-inch concrete block with hollow cavities inside at 2GHz. I would expect more than this for 8-inches of block with no internal cavity at 2.4GHz. So I'm still puzzled.

 

[crutschow]

Perhaps his router is very close to the wall.

 

[rjenkinsgb]

The nearest figure I have seen browsing the internet is 11dB attenuation for an 8-inch concrete block with hollow cavities inside at 2GHz. I would expect more than this for 8-inches of block with no internal cavity at 2.4GHz. So I'm still puzzled.

I suspect it is down to moisture content, and the blocks being aerated (~1/3rd the density of solid concrete).

Most building walls will have a slight moisture content, but as yours is not exposed to outdoor weather at either side, it can be absolutely dry with very low moisture content??

Internal dividing walls between semi-detached houses in the UK such as you show in the plan are often only single-brick thickness - one block.

So something like equivalent to 33mm of very dry concrete?

 

[johnos999]

Internal dividing walls between semi-detached houses in the UK such as you show in the plan are often only single-brick thickness - one block.

So something like equivalent to 33mm of very dry concrete?

Sorry, but this is just daft. If a wall was made of brick only 33mm (1.3 inches) thick, you could probably put your boot through it! As I already mentioned this is a two-story semi-detached house, so the dividing wall between the two houses is quite high (at least 16 feet at its lowest point - higher at the roof apex) and quite thick (8-inches or more). The masonry blocks (not bricks) are laid on the flat, accounting for the 8-inch wall thickness. I can see the wall construction in the attic, where the wall is not plastered.

It would be great if somebody else living in a semi-detached house could measure their own and their next-door neighbours WiFi signal strength and post it here. Some people may be concerned about long term exposure to WiFi signals, not realizing how much their neighbours are contributing.

 

[rjenkinsgb]

Well, I've owned a detached for 25 years now so have way of testing anything - but I do know for a fact that the brick-built Semi I had previously had a single brick wall between the two sides - I accidentally knocked a brick out of place while chiselling out for a socket backing box.... Luckily I was on good terms with the old couple next door!

Quick google - these are standard strength aerated concrete blocks; at 100mm & up, they are rated for "Load-bearing single-leaf walls" - so fact not daft.

https://www.mgnbm.co.uk/amfile/file/download/file/1732/product/8867/

(There is also a high strength version with twice the load rating).

It does mention thickness & sound attenuation - I'd guess that's part of the building regs, so now thicker walls between semis?

If your blocks are flat, then, as they are around 1/3rd the density of solid concrete, the attenuation (not structural strength) should be equivalent to ~66mm dry concrete.