Really, anyone who's lived in a sufficiently old house knows you can run your own Wi-Fi in a Faraday cage. Just probably not between rooms.

Underfloor foil insulation works pretty well as a cage. It also adds a nice electrocution risk when installing and is banned in my area for this reason.

Metal lath under the plaster. Ripping that out was a mess.

Houses finished with stucco tend to do this as a side effect, since stucco is applied onto a fine metal grid screwed to framing.