Roof Joists

[helpme2012]

I've been asked to help out a relative with some wiring, and have discovered a possible problem.

The roof is a trussed construction and the joists (I'm not sure whether they're called roof joists or ceiling joists?) measure approximately 135mm x 35mm.

One of them has been drilled from below with a 19mm drill, approximately 80mm up through the joist (my relative thought he was drilling into a batten which was used purely to secure the plasterboard - most other rooms have these, but it turns out it was actually one of the joists within the loftspace).

My concern is this hole is about half the width of the joist and goes 2/3 of the way through it vertically, which will obviously weaken the joist significantly.

My questions:

1) How much of a structural aspect do the roof joists perform? I understand they are partially in place to stop the two sides of the roof "spreading" apart but what other structural part do they play?

2) Is this hole a massive concern? If so, what should I do about it? Can I attach some nail plates over the area to hold the joist together just in case the worst should happen? Or can I bolt another joist alongside it? If so, how long should this be and how should it be attached?

Thanks in advance

 

[DAZB]

A hole of that size in one joist is not going to bring the house down and the easiest solution would be to just shape an 80mm long section of broom handle to the correct diameter and, after giving a liberal coating of wood glue, just knock it home into the hole and the integrity of the joist is complete once again. If anything make it a tight fit but not too tight as you may split the joist instead.

 

[catlad]

Try using a 12mm bit next time.

 

[helpme2012]

A hole of that size in one joist is not going to bring the house down

Good to know my concern was more about the integrity of the joist if someone where to stand on it. I wouldn't want to entrust my own weight to a piece of wood only 13-14mm wide which is effectively all that's left of this joist

and the easiest solution would be to just shape an 80mm long section of broom handle to the correct diameter and, after giving a liberal coating of wood glue, just knock it home into the hole and the integrity of the joist is complete once again. If anything make it a tight fit but not too tight as you may split the joist instead.

Thanks for the tip. I'll probably do that. I might fasten another joist alongside the drilled one with a few coach bolts just for piece of mind as well. What would be the normal way of doing this?

 

[helpme2012]

Try using a 12mm bit next time.

thanks for the tip!

Personally I like to drill small pilot holes through ceilings and find out where the cables are going to come out, then I know if it's suitable before I mutilate the ceiling (or a joist!)

Sadly though a 19mm hole was required for some round trunking, so that's what was drilled!