WiFi is very capricious. In my kitchen I get Excellent signal strength, in the sitting room 3m away (and the same distance from the antennae) I get Low or Very low, in the bog (sad I know), which is maybe 3m the other way on the same circumference from the router I get Very low or no connection.
The biggest difference, and this is rarely mentioned, is the WiFi adapter. I have three ones I play with.
The worst is the 3com PCMCIA with a pop out aerial, then an ActionTec which sticks out of the side of the PCMCIA slot, and the best is a USB one, because I can move it on the end of a USB extension cable to get the best signal.
I use a Draytek with high-gain antennae. It is a 1929 typical suburban brick house, but the bog is in an extension made of brieze block.