@Izzy_R 

Deco M5 uses 5GHz for WiFi backhaul, can't turn that off when WiFi backhaul is in use. See signal source in Deco app for Satellite Deco connected to Main Deco by WiFi.

@Alexandre. Heya, thanks for the quick reply.

I've done some quick reading, and the backhaul is the system in which the Deco nodes communicate with each other yes?

I assume this would mean that the only way of disabling this background 5Ghz broadcast would be to connect them via ethernet cables as there would be no option for 2.4Ghz backhaul?

That will not be a fun task...

@Izzy_R 

Have conversation with your housemate to find what is she actually concerned about: 5G or 5GHz?

Cellular networks offer 5G for cell phones, where "G" stays for "Generation." 5G just means it is "Fifth Generation" cellular network. 

WiFi networks offer 2.4GHz and 5GHz bands for wireless home devices. Here, "GHz" means frequency spectrum.

If you find that your housemate reads articles about cellular operators 5G networks, with little googling you should be able to present the case that these networks are totally different from WiFi 5GHz, despite similarity in naming convention.

If not, finding modern WiFi mesh system that doesn't use 5GHz for wireless backhaul (or allows to turn it off) might be a challenge. You are correct, backhaul is what mesh nodes use to communicate with each other.

@Alexandre. 

Thanks for confirming about the backhaul.

I'm aware of the difference between 5G cellular and 5Ghz wifi, but she is unwilling to change her stance on this. Unfortunately, she's rather taken on conspiracy theories and believes the evidence of 5Ghz wifi harm is being suppressed. She also believes certain semi-precious stones placed on the router will help absorb some of the harmful radiation, so we're really not starting from a terribly scientific background.

It's a shame as the system itself works beautifully, and trying to run wires through a two story house to create an ethernet backhaul really defeats it's purpose. 

@Izzy_R 

I am afraid I may have more bad news for you: it is possible Deco mesh continues broadcasting on WiFi 5GHz backhaul channel, even if Deco units all use Ethernet backhaul.

You should test that before drilling holes for Ethernet cables through your house.

If Deco does turn off backhaul WiFi broadcasting when using Ethernet backhaul, or you could find mesh from different brand that does that, you have other options to consider before wiring your house with Ethernet.

Options that available are 1) powerline adapters and 2) Ethernet over TV cable adapters. Deco mesh (or other brand mesh) could use them as Ethernet backhaul.

I am not big fan of powerline adapters, but perhaps your household has just right electric wiring to provide adequate data transfer speed. Mine does not, I tried. 

If you have TV cables going to different floors of your house, check Ethernet over TV cable adapters. They go under MOCA name. Whatever I could find are surprisingly expensive, and you'll need at least two, but it is an option.

The idea is the same as with powerline adapters, but you might get much better speeds over TV cable than over electric wiring. Also, speeds could be more consistent.