We are rewiring and when we got to the oldest part of the house we discovered that the walls of all the lower floor rooms rest on four main support beams that run in sort of a plus shape. So basically this rules out wiring on one wall of every downstairs room unless it is safe to drill into the beams.

What I have read on DIY forums is you can drill through horizontally but never vertically which is what we would need to access the inside of the walls. Then I got to thinking that these folks are all talking about 2x6 or 2x8 beams where of course a vertical hole would take out half the board. But my supports are 10x10 solid cedar beams.

Now I am taking into consideration that two stories of 12 foot plaster walls sit on these but it seems that one or two 1/2 inch holes in each beam would be okay. Anyone know?