Drilling joist Query

[veedee]

I'd like to drill and feed a cable through a joist

It looks like there was a chimney breast in this area and someone made good the area with a few short joists

The span for all the joists are approx 4m

But the span of the short joists are about 1.3m

What i want to know is whether rules/calculation for drilling these short joists still apply

ie

130x 0.25
130 x 0.4

Max hole size = height of joist x 0.25

 

[sparkwright]

Have the short joists been sistered to the old joists, or do they run the other way, or what?

The span of a joist is goes from the ends where the actual support is. So if that's the case with the new joists, then typically you should apply that formula.

Probably not the case if the new joist has been bolted onto the side of an old joist.

More detail required to give a correct answer.

However, anything seems to go in an old house.

 

[big-all]

if you think off it logically assuming they fully affixed and the same thickness and height as the main joists because the span is 1/3rd off the 4m you have at least 2/3rds redundancy as in you could remove 2/3rds the timber without compromising strength over that span so would just put what you want where you want kepping in mind end and floor fixings