Large baths, reinforcing floor

[TomLane]

Anyone had any experience of installing a large bath? (1800mm x 1100mm x 440mm) (Ancona Double Ended Bath)

Customer is looking to get something like this & I have said that due to size of bath & larger water capacity that the floor underneath the bath would have to be reinforced!

Would most agree with this? I know it's probably a bit belt & braces but would rather do it right first time as it's the first of this size I have done.

 

[Ray Stafford]

Do you have the capacity of the bath? And is it a modern house, or an old one?

 

[tamz]

290 litre capacity is 290kg of water (45 1/2 stone)
Std bath holds around 175 litres (27 1/2 Stone)

It is unlikely the floor would need reinforced but the only person who could tell you is a structural engineer after a site visit, which won't be cheap.
Just write them a disclaimer and get them to sign it.

 

[Ray Stafford]

(disclaimer - I am not a structural engineer)

The theoretical minimum design standard for modern domestic floors is 1.5kNm2 loading or 1.4kN point loading.

Rule of thumb is to divide by 10 to get the loading in Kgs/m2 which would give you 150kgs per m2.

So if the 290 litres (=290kgs) weight was distributed over 2 square meters, it should be fine.

Remember these are permanent loadings, in the worst possible position (usually the centre of the floor).

A bath is very different from a permanent feature, (say a CWS tank) in that it is infrequently used. They are also usually right at the edge where the loading tolerance would be much higher. Also, almost every builder exceeds minimum specs as a matter of course.

However, if you really want to put your mind (and your clients mind) at rest, get a structural engineer in. If the house is old, or if you have other reasons to suspect the joists might be weakened, definitely get it checked.

 

[TomLane]

Thanks both, very informative & helpful as always!

Much appreciated!

 

[TomLane]

Just an after thought though. Taking into account the weight of the bath even before its filled with water, then filled, then adding a person this would tip it over the allowance with accordance to the calculations?!

I know that the likelihood of the bath being filled to its capacity is low but there is still obviously the potential for it to be filled to maximum!

 

[tamz]

Just an after thought though. Taking into account the weight of the bath even before its filled with water, then filled, then adding a person this would tip it over the allowance with accordance to the calculations?

With a bath that size you'd be better adding the weight of 2 persons :wink:
Advise the customer to get it checked and leave the responsibility (and liability) with them.

 

[Ray Stafford]

Just an after thought though. Taking into account the weight of the bath even before its filled with water, then filled, then adding a person this would tip it over the allowance with accordance to the calculations?!

I know that the likelihood of the bath being filled to its capacity is low but there is still obviously the potential for it to be filled to maximum!

To be honest Tom, I doubt it would make much difference. If you look at the theoretical threshold, three or four medium sized people having a group hug within 1 square meter would overload the floor. And if they were fat gits, bang in the middle of the floor, and they stayed there for 10 years, there might eventually be some noticeable distortion of the floor. But probably not.

We have guidelines at work for loading our mezzanine floors (4.7kNm2), but the bloke who erects them just laughs and reckons his floors would take miles more than the weight that its warrantied for.

 

[TomLane]

Good point Ray well made Ray! 🙂

I've been to the house today to have a look at the proposed bathroom & the guy said it's only for when his grandkids come to stay so they can chuck them both in the bath at the same time!

I asked him how old & politely how big were the children because even with a standard sized bath would fit 2 children with room to spare!

He's got more money than sense from what I can gather. Although saying that, he went into Homobase & bought the bath so he got it relatively cheap!

 

[Destroyer2813]

Tamz took the thoughts right out of my head

 

[chris watkins]

I think we are forgetting that the human body is mainly water & would displace some of the 290 L of water so only have to worry about what is above the water line wouldn't we ?
More to the point Tom is that as soon as a bath capacity goes over 230 Litres it becomes notifiable to the water undertaker under the Water Regulations 1999, I think that this is so that they can require the installation of a water meter because of the likely increase in water usage, are they on a meter ????

 

[snowhead]

I'd be just as concerned about the length of time to fill and the stored capacity to fill it.

 

[tamz]

Tamz took the thoughts right out of my head

Well it will be until the novelty wears off :lol:

 

[Destroyer2813]

Well it will be until the novelty wears off :lol:

Be a week then even, less if theve been married a while

 

[stevetheplumber]

we had a hotel room with a large semi circular bath in and just staying upright with no where to wedge yourself was a nightmare some of the luxury shapeddesigner ones must be even worse

 

[Guest123]

When taking out an old bath, and after checking the joists, I always lay new 18mm ply on the floor for the new bath. This not only reinforces the existing floor, but distributes the weight.

Dont think youve anything to worry about. Think of the weight of an old cast iron bath fully filled with water and containing a person, none of these were ever fitted on a reinforced floor and most have lasted for many years.

 

[tamz]

we had a hotel room with a large semi circular bath in and just staying upright with no where to wedge yourself was a nightmare some of the luxury shapeddesigner ones must be even worse

Thats where the wife comes in handy Steve. Gives you at least a toe hold :smile:

 

[chris watkins]

What do you recon the joisting was like for this one? Greek o Roman marble bath around 1.25 tonn empty.

 

[tamz]

You can see what side the fat lady sat facing the taps (looking at the floor) Chris :smile:

 

[chris watkins]

No fat ladies in that one Tamz, the client was the other way inclined, if you know what I mean. LOL
(He did however have a peep hole installed above the W.C.!!! very worrying when I saw this on the plan's )

 

[TomLane]

View attachment 10816What do you recon the joisting was like for this one? Greek o Roman marble bath around 1.25 tonn empty.

Wow, that's impressive!

I think I could be persuading him away from the large bath anyway as he only has small hot water storage (not sure of capacity as I haven't looked at tank yet!)

I also replace the boards under bath with at least full length floorboards as quite often they're not complete & in some installs plyboard as you said System!

Like I say, I'd rather do it right first time even if it takes a little more effort!

 

[chris watkins]

Just found it, for all though dis-believers a working peep hole !!

 

[TomLane]

View attachment 10832Just found it, for all though dis-believers a working peep hole !!

Odd! Very, very odd!

 

[Dannypipe]

View attachment 10832Just found it, for all though dis-believers a working peep hole !!

That is so very disturbing!! HA

 

[Dannypipe]

We've just had to sort out a floor in a bathroom we're doing. I say we but I've not been there much due to the hassles with my van.

Basically the last bloke who fitted the heating (many years ago) cut the joists down so that the whole floor is reduced to about 30mm at the edges.

So what we've (my chippy) has done. Is fit a floor over the floor. Using structural joist hangers so the new floor is being supposted off the brick work.

We could have run a new floor in the same way inline with the old joists, but that would have been more work, as it would have involved moving all the old services.

It was unforseen and has come as an extra to the customer, but they're fine about it. The old floor was so springy, and the bath was larger than standard.

If I'm not sure on something, I always use a structural engineer.

I'm on good terms with mine as I always reccomend him and use him a fair bit myself. A typical cost for a visit, and drawings still isn't cheap (betwen £200 and £500 depending on how complicated). They have to underwrite it. If I follow his drawings and something happens, it's his problem not mine.