Drilling an oversized joist

[Adrian80]

Hi guys,
(Not sure if this is best in building or elecs)

was wondering if people had any thoughts.

I have some fully suported timber joists with a short maximum span of 1.8m.

Trada tables say the recomended size is 39x120.

I have 44x180mm timber n place.

My feeling is that the top 60mm of the joist is redundant.
i want to chop some notches for a 40mm waste, therefore do i treat the new centre of the joist as 60mm from the base for drilling holes, or do i go for the original 90mm for the base.

What do people think?

A

(apologies for double post)

 

[^woody^]

Go for it

Untitled

• ^woody^
• 16 Jun 2008
• 7

 

[ajstoneservices]

PMSL

 

[Adrian80]

NOW THATS A NOTCH!

 

[AronSearle]

If you know about timber, slope of grain, the knot's cross section ratio particularly in relation to the tension and compression edges, it is possible to visually "grade" the beam and access whether over notching in the desired position is suitable.

If you don't know what I mean, then don't even consider it and stick to the rules, the number of times i've seen plumbers b44ger up joists.

The best one I have seen is a plumber knotching and drilling into an I-joist flange, right where it said in big capital letters "DO NOT NOTCH OR DRILL HERE".

 

[^woody^]

That's what we need, techno babble.

If you want to notch outside the published recommendations, then you can do so but then need to reinforce the joist. You do this by screwing some ply, a metal plate or another timber across the side of the joist.

Use a 300mm metal splice plate, or 9mm ply. One side should do for this small span and just one joist. If using ply, gluing as well as screwing is good

 

[noseall]

That's what we need, techno babble.

 

[RonnyRaygun]

Hi guys,
My feeling is that the top 60mm of the joist is redundant.
What do people think?

You're right that the section won't be overstressed with a notch up to 60mm, especially if the notch is near the end of the member.

However, guidance has recommendations that notches are not more than a quarter of the way along the joist, and not more than an eighth of the depth.

It wouldn't be a huge job to reinforce it anyway.[/youtube]