Hi guys I am trying to measure where I can drill from the loft so that I can feed a co-ax cable down the space between the plasterboard and the blockwork. I have a reference point in the loft as the coax from the outside aerial enters the loft from the gable end. I know the bricks are 100mm deep. What I need to know is what depth is the cavity and the blockwork. If I can find the total measurement of bricks + cavity + blockwork, I can roughly get a distance from the total width to where the aerial cable enters the house on the outside. Then when in the loft, I can measure back from the cable entry. This hopefully will give me a point to drill. Hoping to then feed a coax cable down the hole between the plasterboard and the blockwork. I had a look in the loft and the plasterboard ceiling butts up to a header plate (approx 4" wide). Will this be somewhere close to the point I need to drill? I am trying to cause as little damage as possible to the bedroom. Any suggestions? Thanks.