structural considerations for a bath

[conny]

Instead of having 4 pressure points, (i.e. the bath feet), lay a sheet of 12mm chipboard/MDF over the area underneath the bath.
This will have the effect of spreading the load over a larger area and reducing the flexibility of the supporting joists.

 

[conny]

Instead of having 4 pressure points, (i.e. the bath feet), lay a sheet of 12mm chipboard/MDF over the area underneath the bath.
This will have the effect of spreading the load over a larger area and reducing the flexibility of the supporting joists.

 

[Leofric]

Instead of having 4 pressure points, (i.e. the bath feet), lay a sheet of 12mm chipboard/MDF over the area underneath the bath.
This will have the effect of spreading the load over a larger area and reducing the flexibility of the supporting joists.

Yes, or a length of say plywood board under each foot to spread the load on to joists. Builders sometimes use offcuts from skirting boards under the bath feet . I added a rectangle of plwood under the central foot on my bath.

 

[tony1851]

If it’s OK for two people to stand close next to each other on the floor,
and it’s OK for them to lie next to each other in a bed on the floor,
then it’s OK for them to share a bath.

(Both morally and structurally.)

Don't forget the weight of the water.

 

[psychonaut]

forget weight of water - i wont! i haven't! i already included it!

lay ply - i am going to make a step, a big frame for the bath to sit on, i already said that...its gonna be at least made out of 2 x 8 , i need to build a step up to it anyway. i could lay that on a layer of ply, which then sits on the floorboards i suppose...

 

[Leofric]

i could lay that on a layer of ply, which then sits on the floorboards i suppose...

- That won't be necessary then , you already answered the question :-

i'm going to build a frame under the bath anyway so the feet will not be in contact with the floorboards, but onto the timbers i place between the bath feet and the floorboards. bath is 850mm wide. joists are 350mm apart give or take. so there will be 2 joists under it.

- the new timbers will spread the load on to the joists if they are under the bath feet.
ps but I don't have a degree in physics ​

 

[Leofric]

The only suggestion concerning the Building Regs side is that "joists should be doubled up" where under the bath (Approved Document A).

Exactly, assuming timber boards as mentioned previously are placed under the bath feet to spread the load ,I can't recall Building Control, NHBC, a consultant engineer or anybody else ever asking for structural calculations for the loading imposed by a bath on a suspended timber floor.

 

[psychonaut]

leofric - i do have one, but its no use here, all iserves is to make me worried...but, maybe better to be worried than do something dumb...

 

[Leofric]

leofric - i do have one, but its no use here, all iserves is to make me worried...but, maybe better to be worried than do something dumb...

true, fair enough

 

[endecotp]

Don't forget the weight of the water.

OK, I reckon you can approximate to that with a third person

 

[psychonaut]

OK, I reckon you can approximate to that with a third person

sounds like fun! unfortunately it will probably be one of my kids....

 

[Bodgedbuild]

All the load/span calculations relate to acceptable deflection not the point at which the joist will fail. If you are taking boards up, you could fit noggins to stiffen the floor up, you could even sister the joists for as much as you could get at, the bending occurs in the middle of the span so the floor would be stiffer even with partial sistering of joists. I have the opposite "problem", my builder envisaged problems installing a steel that would cross under my joists to provide adequate stiffness because of its connection into a party wall. The engineer simply got around the issue with massive joists, doubled. Where my shower is (in my loft conversion) an extra joist were added because it is technically a bathroom. Some of the joist (not yet installed in the pics) are also flitch beams. You could park a lorry in my loft and it wouldn't bend!

 

[psychonaut]

Rather than sistering, what if I put 8 x 2 above the existing joists ..so we have a 8x2 --floorboard--8x2 sandwich. Will this have same structural effect as sistering? I'm going to puth the bath on a plinth anyway so this is a lot easier...

 

[tony1851]

It would be roughly the same structurally as sistering in terms of bending stress and deflection, though it will not reduce shear stress at the bearings
But aside from all the technical bo llock$ - you're probably over-thinking all this - your floor won't collapse!

 

[Nozzle]

If it’s OK for two people to stand close next to each other on the floor,
and it’s OK for them to lie next to each other in a bed on the floor,
then it’s OK for them to share a bath.

(Both morally and structurally.)

It's not just the bath they're sharing - it's also a huge amount of water. Nice, dense, water....

Much of which will have come from a DHW cylinder likely on the same floor of the house, possibly even in the same room, and maybe even loading up the same joists. And the cylinder is immediately re-filled. Likely a vertical cylinder rather than horitzontal, therefore higher point loading, size for size.

Nozzle