Fixig holes in joists close to joist ends

Joined
1 Aug 2022
Messages
31
Reaction score
0
Country
United Kingdom
I have pulled down the ceiling underneath my first floor bathroom and I have found out that two of the joists have a large very close to the end of the joist.

It does not seem like it is creating problems at the moment, however, I, upstairs I have tiles and I would hate to have cracks in them a few years from now due to sagging or movement. The ceiling is down so if there's something I can do to prevent this, I'd rather do it now before I put the new one up.

Do you think this is going to be a problem?

Joists are 17cm by 5 cm
Using this as a reference:

1672759862022.png

The big hole in joist number 3 is about 8cm in diameter and is at around 11cm from the wall
The one in joist 4 is about 6cm in diameter and is closer to the wall, maybe around 7cm
The joists end in the wall so there's no joist hanger.

I was thinking the following:
  1. sister joist number 3 with 1.8 structural plywood or a 4x2 cutting a section out to accomodate for the pipe
  2. place one noggin between joist 3 and joist 4
  3. place one noggin between joist 3 and joist 2
However.... with so little space between the whole in joist 4 and the wall... what's the best solution there?
 

Attachments

  • IMG_20230103_103251.jpg
    IMG_20230103_103251.jpg
    351.7 KB · Views: 130
  • IMG_20230103_103320.jpg
    IMG_20230103_103320.jpg
    238.5 KB · Views: 139
  • IMG_20230103_103327.jpg
    IMG_20230103_103327.jpg
    326.6 KB · Views: 131
  • IMG_20230103_103336.jpg
    IMG_20230103_103336.jpg
    348.9 KB · Views: 130
  • IMG_20230103_103344.jpg
    IMG_20230103_103344.jpg
    150.3 KB · Views: 131
Sponsored Links
I'm not a joiner/builder but I think you are ok with what is there. The bulk of the wood is below the holes and the pipes look like a loose fit so no pressure on them. My biggest concern would be putting a nail or screw through the floorboards and puncturing the higher-level pipe.
Is this the drain from your shower?
 
I'm not a joiner/builder but I think you are ok with what is there. The bulk of the wood is below the holes and the pipes look like a loose fit so no pressure on them. My biggest concern would be putting a nail or screw through the floorboards and puncturing the higher-level pipe.
Is this the drain from your shower?
yes, correct
 
TBH structural plywood isn't really that wonderful - it is meant to be laid on floors in roofs and walls, ideally as full sheets not narrow rips which don't confer much additional strength. If you really want to plate the joists I'd just sister the existing joists to something of the same cross section (e.g. C16 grade softwood) and pocket the ends into the wall. If that masonry wall where the pockets are is an external wall, or within 1m of an external wall, use treated timber

Why do you want noggins in a floor? Solid strutting, which should be near or identical cross section to the joists, is actually added to add stiffness to floors (i.e to remove bounciness) but doesn't increase strength (or load bearing capacity) very much. If you sister the affected joists their increased stiffness will probably make solid strutting superfluous
 
Last edited by a moderator:
Sponsored Links
I pu glued and screwed 18mm ply rips to our floor which was 2 by 7s notched half way in places, and added herringbone strutting across the full run in two places, and as a whole it helped a lot. Not sure which part was most helpful. It was a lot of work though, but the floors were up anyway.
Definitely worth it for me.
 
TBH structural plywood isn't really that wonderful - it is meant to be laid on floors in roofs and walls, ideally as full sheets not narrow rips which don't confer much additional strength. If you really want to plate the joists I'd just sister the existing joists to something of the same cross section (e.g. C16 grade softwood) and pocket the ends into the wall. If that masonry wall where the pockets are is an external wall, or within 1m of an external wall, use treated timber

Why do you want noggins in a floor? Solid strutting, which should be near or identical cross section to the joists, is actually added to add stiffness to floors (i.e to remove bounciness) but doesn't increase strength (or load bearing capacity) very much. If you sister the affected joists their increased stiffness will probably make solid strutting superfluous
So... do you think it would be worth doing it or it's fine to leave as is?
The 3rd joist has a much larger hole but in the 4th one the hole is very close to the end of the joist.
 
The bulk of the wood is below the holes
That's the problem; it's the top and bottom of a joist that carry the stress of the tension and compression the most, which is why you're supposed to follow specific rules for notching or holing them

One of those joists has the hole right at the top so it looks to effectively be a notch and it's way out of spec on depth, probably also on location. Muppets

It looks to be possible to drill holes of the correct size (max 42.5mm) in the correct location (centre line, between 0.25 and 0.4 of the span) and reroute the plumbing through them, then patch/sister over the old holes with glued and bolted timber
 
Last edited:
That's the problem; it's the top and bottom of a joist that carry the stress of the tension and compression the most, which is why you're supposed to follow specific rules for notching or holing them

One of those joists has the hole right at the top so it looks to effectively be a notch and it's way out of spec on depth, probably also on location. Muppets

It looks to be possible to drill holes of the correct size (max 42.5mm) in the correct location (centre line, between 0.25 and 0.4 of the span) and reroute the plumbing through them, then patch/sister over the old holes with glued and bolted timber
OK, no, moving the pipes is not an option and I cannot create a pocket either for the wood to sister the joist with. If I can do something, it has to be based on the current layout.

As I see it, my options are:
- partially sistering the joist with plywood or c16. In that case I will have to cut inserts into the wood used to sister to accomodate for the pipes
- use something like this to reinforce the joist without sistering it (maybe screw or nail 2 on each side, at top and bottom of the joist?) or something like this

Probably, given the situation, the second option would be more effective?
 
Last edited:
Whoever installed that waste wants there arse kicking.Apart from the obvious work on joists you need to get rid of that appalling flexi.
It's not if but when it will block, plus if you have the misfortune to get mice in they love chewing flexi wastes.
 
I have taken a few more measurements and here's the situation:

First problematic joist:
1672910422028.png

The notch is quite close to the wall but not so close that I can't fit anything in there.
I was thinking to sister with 2 notched c16, one at each side, and use screw Coach screws as close to the wall as possible. Length would probably be 1 meter or so.

Second problematic joist.
1672910778537.png


Here the whole is dangerously close to the wall and there's not much that I can no I suppose.
The only thing I can think of is screwing something like this at the bottom and on the sides to provide a bit more support.
I suppose that sistering would be useless as we are so close to the wall...

Any thoughts?

As I've said... unfortunately, I cannot re-route the pipes. I am trying to do my best to prevent this to become a problem in the future without making too many alterations
 

Attachments

  • 1672910395138.png
    1672910395138.png
    8.4 KB · Views: 33
The issue at the ends is shear (snapping), the "bending" takes place in the middle which is where the depth is required so it's unlikely to be an issue.
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top