Joists for Bathroom

[hammyhammy]

I'm swapping my bathroom with a smaller bedroom and trying to decipher the various building regulations that I need to comply with.

I'm happy with the requirements of ventilation, electrics and drainage but i'm stumped by the issue of strengthening joists because of the introduction of a bath where there wasn't one before.

My question is, do I actually categorically have to double up on joists?

The joists are spaced at only about 330mm, span the room by 2700mm and the joist themselves are a mighty 195mmx47mm

They seem quite closely spaced to me and the span is reasonably short too, then again the house is over 100 years old.

So, should I double up? If so, can I do this myself? (i'm highly experienced/capable DIYer) or do I need a structural engineer and builder to carry this out? Ir is it not necessary at all?

Should I just leave it and get on with the job since the existing bath is on the same structure and orientated in the same direction without reenforcement. The old bath is plastic as is the new one...

What do you think? Thank-you

 

[hammyhammy]

I have just thought of a few other things to add

(The 'doubling up' comes from 'Building Control Guidance Note 7, Page 2)

The new bath will be positioned in the corner against 2 load bearing walls and the other load bearing walls are 2.7meters and 4meters away (plus a partition)

 

[maltaron]

I have never seen bathroom joists any different from other rooms. When you consider that the bath sits on 4 little feet it's the strength of the floor boards which matters. I personally do not like chipboard floors in bathrooms but nowadays there must be hundreds of baths sitting on chipboard with no problems. Your joists are way over spec for the span so you should not have problems.

 

[hammyhammy]

That's what I assumed!

...Then you read a thing like in the guidance notes like: 'Floor joists must also be doubled up and bolted together under timber partition walls, and in bathrooms due to the weight of a filled bath additional joists must be provided under the bath'

...Gets your mind racing. The thought of pulling up a finished floor to satisfy an inspector worries me.

I intend on replacing the floorboards anyway (which are ancient and have cupped a bit) then overboarding with 18mm ply and finishing with a wood effect waterproof vinyl flooring to match the height of my tiled level access shower area.

 

[ban-all-sheds]

The thought of pulling up a finished floor to satisfy an inspector worries me.

Look at what the recommended joist size would be without a bath, and when you submit the plans say that you'll be using oversized ones because of the bath.

The you'll know one way or the other before you start work whether your LABC are happy with that.

And I would have thought the BCO would want to inspect before the floor goes down, not after.

 

[hammyhammy]

Thanks for the replies. I intend to do all my own drawings and go the full plans route instead of buildings notice. (unless you guys recommend otherwise).

With constructing my new bathroom in this other room from scratch, what will they be expecting me to cover in my plans and specifications? I assume ventilation and drainage. Will I have to cover electrics and fire or anything else? I was going to do the electrics myself??? (as it's just wiring the extractor into the lighting and moving the light switch and single socket to outside the room) I'd appreciate as many pointer as possible please.

I'm doing 1:20 scale for details. What scale for an overall plan?

 

[pedantician]

Although the room may be 2700mm across, the actual span of the joists may be longer as this depends on the positions of load bearing walls below.

If the structural span IS 2700mm, the joists will be fine as they are and won't need doubling up. Any building control officer should recognize that, although there are some who might ask for a calculation to prove it. You might then need to get a structural engineer (or anyone who can do the required calculations) to do it, or just add the additional joists.

The note to the span tables which suggests doubling the joists up is based on the assumption that the joists will be near their capacity already. Yours certainly aren't.

A couple of things you will need to do which you may not have considered:
- ensure that there is a fire escape window in the room which will become a bedroom: minimum clear opening of 450x735 (horiz or vert) with bottom of opening between 800 & 1100 above floor level
- you may also be required to install self contained interlinked smoke detectors in circulation spaces. It could be argued as unnecessary as you are not increasing the number of bedrooms, but is advised in Approved Document B. Advisable thing to do anyway though, if you haven't already got them.

 

[ban-all-sheds]

Advisable thing to do anyway though, if you haven't already got them.

I'd say have them in other places too - there are different sorts of detectors, some do smoke, some heat, some rapid heat rise. Smoke detectors are not a good idea in the kitchen, but fire detectors are. They can all be interlinked via wireless.