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I need to drill a vertical hole through a floor joist to accommodate a central heating pipe to supply a new c.h. radiator. The problem is that this hole would be next to a redundant hole. I would like to add strength to this weakened region of joist - any suggestions ?
The joist is at the perimeter of a ground floor room therefore one vertical side is inaccessible. Rubble is 600mm/24" below.

Hope I can find a solution before the plumber arrives!

Many Thanks.