[mikeyouse]

Unfortunately, it doesn't take lead to attenuate WiFi signals. Many turn-of-the-century buildings used chickenwire under plaster on the interior walls. This makes a pretty effective Faraday cage:

http://www.wsj.com/articles/SB126221116097210861

My SF apartment is the same -- well under 1,000sqft, need an enterprise router and a substantial repeater to get signal on the end opposite from the cable modem.

[acdha]

It's not just old buildings, either – at a previous employer we learned that a lot of the interior walls had a similar mesh inside. You could put a Cisco AP set to the highest power levels on one side, move a laptop one foot away on the other side and barely be online. We solved that by adding extra APs, which wasn't a big deal since we had the budget and plenty of Ethernet drops but in a residential building - especially a rental - that'd have been an annoying amount to pay.

[stordoff]

My house, built <20 years ago (UK), has something similar. Currently at 4 APs (DD-WRT routers acting as APs, all hardwired to a central router), and still some rooms only get a patchy signal (fortunately we're more than 50ft on all sides from other building, so not too concerning about interference). 5GHz is even worse - for any practical use, it's pretty much limited to a single room per router.