A few years ago I had a window and brick work removed and a patio door fitted. It was a standard window with brick wall below it. When I tap the wall either side of patio door level with we're the old window was it's solid, but when I tap wall either side level with were bricks we're removed, down to floor it sounds hollow. Also, the skirting board directly next to patio is often damp to touch. I'm assuming that when wall was cut out that any insulation in cavity came out and wasn't refilled. So, I was wandering if I could drill a small hole just above skirting into cavity and then spray in expanding foam to insulate the bottom section of wall.