The downstairs of my house has thick walls and (tin?)foil insulation in it. Combined with odd corners and lack of line of sight it's a wireless-killer par excellence. In the end, getting fed up with lack of wireless signal, I cabled from the router in the garage, out on the outside of the house (couldn't get under the floors), with external pvc clad cat 6 (6 for future proofing) and brought it in through the walls for a port in every room. Cat 6 has a plastic wire separator in the middle and it makes it very unflexible and unaccomodating to lay and plug. Network is now fab but my hearty recommendation is do *not* do this until and unless you need to :)