Precautionary reinforcement of holes in joists

[DKenn]

Hello everyone...

 

I am about to buy a new bed and wardrobe which will add around 300Kg to the floor of a first-floor bedroom. Much of the weight will be distributed along the span of the joists, not against the joist ends.

 

My concern is that while the floor has no discernable sag/bow or bounce, the two rows of 30mm holes (for the central heating pipes) in each joist (150mmx50mm, 6x2) might weaken under the increased load. The two rows of holes in each joist are around 1.5m apart, running the entire length of the room. 

 

I propose reinforcing these holes (as a precautionary measure) using 600mm x 140mm strips of 18mm external plywood bolted with timber connectors over the holes (which will need drilling to allow the pipes through). The two bolts would be spaced approximately 200mm on each side of the pipe hole, leaving an overhang of around 100mm on each end of the plywood. So, each 600mm x 140mm strip of plywood would be as follows:

 

• 10mm of plywood, and then;
• carriage bolt and timber connector, and then;
• 200mm of plywood, and then;
• the hole for pipe, and then;
• 200mm of plywood, and then;
• carriage bolt and timber connector, and then;
• 10mm of plywood.

 

I have approximately 200mm of access above each hole to slide under the plywood and drill the holes (this is why the lengths of plywood are limited to approximately 600mm). I would prefer not to take up any more of the tongue and groove floorboards.

 

I have read everything I can find on reinforcing bouncing and slagging floors, but little is relevant to this situation. I would appreciate any constructive advice or support from the community.

 

PS. I hope this makes sense!

[SteamyTea]

Are you saying that you are going to drill more holes in the joist for the coach bolts?

 

Why not use an adhesive to attach the plywood?

 

 

[Big Jimbo]

16 minutes ago, SteamyTea said:

Why not use an adhesive to attach the plywood?

Much better idea.

[DKenn]

Thanks for the replies.

 

I have considered adhesive; however, I felt that the carriage bolt option allowed for a tiny amount of movement and reduce the risk of shearing that screws. I felt that one bolt per side of the patch might be less invasive that several screws.

 

I was planning to drill 10mm holes for M10 bolts.

[Big Jimbo]

If you start shearing screws, you have got a big problem. 18mm ply either side glued. Going nowhere.

 

[DKenn]

So, do you feel that glue would be enough without screws or bolts?

 

[JohnMo]

3 hours ago, DKenn said:

the two rows of 30mm holes (for the central heating pipes) in each joist (150mmx50mm, 6x2) might weaken under the increased load. The two rows of holes in each joist are around 1.5m apart, running the entire length of the room. 

Bit confused by this

 

Can you draw what you mean?

[saveasteading]

These are static loads so any deflection will be a one-off , not a bounce.

It follows that any pedestrian movement will be nearer to the walls, where strength is greater and bounce is less.

 

If these joists have been designed for domestic use then the weight of beds and wardrobes is included.

If the holes for pipes are through the centre of the joists then they have very little effect on strength.

 

On the other hand if the above don't apply please give more details.

[DKenn]

Hi JohnMo,

 

It's a bit rudimentary. But hopefully is helps.

 

 

[DKenn]

Hi saveasteading,

 

The weight will be static; however, much of the movement will be at the end of room and either side of the bed. The bed and wardrobe are going to be following the line of the two pipes - see diagram.

[Mr Punter]

No reinforcement needed.  Find something else to do.

[saveasteading]

And are the pipes half way up the joists? If so , no problem.

If cut through near the top or bottom that would be bad.

What depth of joist snd span?

[SteamyTea]

https://www.labc.co.uk/news/how-get-it-right-notches-holes-solid-timber-joists

[DKenn]

12 hours ago, saveasteading said:

And are the pipes half way up the joists? If so , no problem.

If cut through near the top or bottom that would be bad.

What depth of joist snd span?

The joists are 3.8m long and the joists are 150mm x 50mm.

 

The holes are largely centred.

 

The the two pipes/holes are 1.2m from the walls on either side of the room.

[saveasteading]

No problem then. Also, the floor boards add extra strength if well fixed....

but don't burst the pipes. You can fit these first to be sure.

 

[DKenn]

Judging by what has been said, it looks like I might be overthinking this. So I am going to check and reinforce any "loose" floorboards and leave it at that.

 

Just as an aside - can anyone see any any actual problem with my method of reinforcement with plywood fixed with timber connectors and carriage bolts?

[saveasteading]

4 minutes ago, DKenn said:

any actual problem with my method of reinforcement

Again overcomplicated. Screws instead of bolts. Simple rectangles of ply above and below the pipes. Both sides better than one side.

[SteamyTea]

4 minutes ago, saveasteading said:

Screws instead of bolts

And adhesive. A polyurethane adhesive will stick very well as long as the mating faces have been cleaned.

 

You could create some 30° Vs either side of the pipes from timber, 30° is the optimal angle as it spreads 50% of the forces, and can be alternated, like a W.

 

 

[saveasteading]

14 minutes ago, SteamyTea said:

30° is the optimal angle as it spreads 50% of the forces, and can be alternated, like a W.

I'm not understanding this. 

[SteamyTea]

14 minutes ago, saveasteading said:

I'm not understanding this. 

Have made a model of a lattice with Costa Coffee stiring sticks.

 

Edited February 17 by SteamyTea

[DKenn]

44 minutes ago, saveasteading said:

Again overcomplicated. Screws instead of bolts. Simple rectangles of ply above and below the pipes. Both sides better than one side.

I can't see how using two pieces of plywood is less complicated that using one?

 

Also, wouldn't the use of screws near to the top or bottom of the joist increase the likelihood of splitting?

[DKenn]

9 minutes ago, SteamyTea said:

Have made a model of a lattice with Costa Coffee stiring sticks.

 

Love the on the fly illustration!

[saveasteading]

5 minutes ago, DKenn said:

Two pieces of plywood is less complicated that using one?

With just one it needs to be somehow threaded over the pipe.

[saveasteading]

6 minutes ago, DKenn said:

wouldn't the use of screws near to the top or bottom of the joist increase the likelihood of splitting?

Yes. But a number of small screws is less impact than a bigger hole for a bolt.

[SteamyTea]

8 minutes ago, DKenn said:

wouldn't the use of screws near to the top or bottom of the joist increase the likelihood of splitting

Just (expletive deleted)ing glue it.