Drilling through a Metal Web Joist

[wozza]

Hi All,

 

I have a narrow room that has metal web joists at 400mm centres - they span 2300mm - the floor is covered with Egger protect (glued with D4) - so the floor is very solid, the joist supplier calculated that 600mm centres would be fine but I wanted 400mm to ensure that it was solid.

 

When constructing the floor, the builder doubled up with an extra joist to support the non load bearing stud wall above, this seemed a bit overkill to me at the time, but he said we always double up the joists when putting a stud wall above (he had never used Metal webs before and was very set in his ways)

 

I need to get 15mm hot and cold water supplies into the stud wall from below for a shower.

 

I am aware that you must not drill / cut etc any part of a metal web joist.

 

My original idea was to place the stud wall sole plate over the edge of one of the joists so the majority of it is over the joist, then drill up through the floor and through the sole plate without touching the top chord of the metal web joist. My new idea is, that as I have an extra reduced centre metal web joist, could I drill through the top chord of the extra Metal web joist as shown below

 

Your thoughts?

 

 

 

 

 

 

 

Edited February 22, 2020 by wozza

[ProDave]

I would drill the joist but then never admit to doing it.  You are after all just drilling the "spare" one.

[Russell griffiths]

Try and keep your two holes as far apart as you can so they don’t act together. 

I don’t think 15mm is going to hurt, try and do the hole in the centre not on the edge. 

[JFDIY]

It'll be fine, the wall and sole plate above it will also brace it.

[Hilldes]

I could do with doing a similar thing - but I have only single post joists at 400mm centres (don't have a 'spare' ?). The top and bottom chords of the posis are quite wide due to span - 145mm. Scenario is there is a stud wall running directly on top and parallel to a posi joist, need to drill a couple of 15mm holes to get services into the stud wall. I've googled and looked at NHBC, but can't locate any guidance specific to metal web/posi joists. The most direct in terms of advice is here (Professional Electrician), which states that no drilling is permitted anywhere.

 

Can anyone share any official guidance that can be used if required with Building Control and Warranty provider please? 

[saveasteading]

A 15dia hole isn't much worse than a knot. keep it central and the forces will swerve around it. 

As you need more than one hole, keep them well apart. I think the rule of thumb is something like 40 diameters, so 600

 

I would expect an Engineer could prove it, esp as the joists are overdesigned, one redundant even, but best not go there.

wall bridging 2 joists is better.

if you have  a choice, a hole like this is best as far from central span as you can, ie towards the supports.

[Hilldes]

Thanks @saveasteading for the guidance. As you suggest, I'm not keen to get a structural engineer involved (from my experience charge high fees and deliver little of value). I'll try the timber frame company - they may have some specific guidance or maybe can pass me to the joist manufacturer.

[markc]

Drilling a couple of 15mm holes (not next to each other) in the top cord won’t be detrimental. If you want to be sure and have access then put a few extra screws in either of the holes to distribute the load into flooring and or bottom of stud wall.

[PeterW]

Ok so I would use a series of5x100 screws at 300 centres all the way down the sole of the stud wall through the floor and into the top chord. I’d then make sure the two 15mm holes are staggered at least 300mm and on opposite sides of the flange.  That will be bomb proof. 

[Hilldes]

12 hours ago, PeterW said:

Ok so I would use a series of5x100 screws at 300 centres all the way down the sole of the stud wall through the floor and into the top chord. I’d then make sure the two 15mm holes are staggered at least 300mm and on opposite sides of the flange.  That will be bomb proof. 

 

Thanks PeterW and @markc . I've also been in touch with timber frame supplier (MBC) who will put me in touch with their joist designer - just to be sure I can reference if queried.

[saveasteading]

16 hours ago, Hilldes said:

I'm not keen to get a structural engineer involved (from my experience charge high fees and deliver little of value).

V disappointed at your comment here. 

You have had good advice from many knowledgeable people here, for what is a relatively simple solution (and which your free advisors all understand).

These people may or not be Engineers.

An SE would not have made you put in over-specified joists, and you haven't minded paying for that. 

 

No more from me on this case.