New Suspended floor in bathroom

[John]

I`m going to build a suspended floor in a small downstairs bathroom so that all the drainage & pipes can go underneath. The room is approx 1.89m by 2.46m and I plan to batten out the wall and then hang joists inbetween using joist hangers at 400mm intervals using the shortest span (1.89m). What size joist should I go for?, one book I read says I can use 100x50mm (4x2) but I`m not sure. On top of this will be plywood screwed down and then tiles. There will be no bath in the room, just a bog, shower and basin. If necessary I can supplement the span with a sleeper wall (I think they call it) to provide rigidity to the floor (don`t want it flexing with tiles on top!).

John

[jerrybuilt]

What's the floor now? Are you digging out? If so, I'd be inclined to put a sleeper on each side, allowing for existing ventilation, on in the middle of you're using 4x2, and be very careful about plane, and be careful about the timber you use to keep it plane!

Anyway, I get the feeling I want to know a bit more about the current and intended set-up!

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[Christian McArdle]

A 47mm x 97mm joist on 400mm spacings with SC3 timber and 0.25-0.5 kN/m2 allows a span of 1.92m, making it just compliant with building regulations. If you had wanted a bath installed, you would double up the joists supporting it.

If your intended flooring weighs more than 0.5kN/m2, you'll need 122mm (5 inch) joists.

A sleeper wall or thicker joists would improve rigidity, if required. If you install one, ensure ventilation is adequete. In fact, you must ensure ventilation is adequete anyway. Ensure you install good insulation and airbricks. Take the time to install underfloor heating for a new floor.

Christian.

[fred]

In article , Christian McArdle writes

Is there an existing floor?

[John]

regulations.

Yes, about 2ft below the proposed (new) floor. Its concrete (no damp).

John

[fred]

In article , John writes

Ah, now I see why you're suspending it ;-), that was my only query.

Sleeper wall sounds OTT, but if 4" is the min for joists then I'd be inclined to use 5" to limit flex.

[Lobster]

Spookliy enough, I'm probably about to do something very similar; building a raised floor in bedroom 3 (formerly bathroom) to enable soil pipes etc from what will be an internal bathroom to reach the external wall. (I can't see any other way of doing it given the layout of the house and joists etc).

What I was going to do was essentially nail new joists parallel to and directly above the existing structural joists (not sure whether its worthwhile/necessary to remove the floorboards first - may do so just to ensure I can see any hidden wiring/pipes!). The soil pipe will be traversing the structural joists diagonally (which is why I can't 'bury' it below floor level), so the new timbers will just have a gap where the pipe goes through. (This is upstairs in a terraced house BTW).

Given that my new timbers (I hesitate to call them joists, cos they aren't!) are not a structural part of the house as such, I was going to use much less substantial wood for them than the real joists; just using my common sense. Or is that wrong - do I need to fulfil any building regs by using stinking great 5x2's? Would it make a difference if I left the original floorboards there or not?

Thanks David

[Christian McArdle]

You should calculate the dead load of your proposed timbers and floorboards and ensure that this loading does not make the existing joists too small. What is the span and dimensions of the existing joists?

Christian.

[Lobster]

Hmm, that aspect hadn't occurred to me!

The overall span is about 12 feet; the raised area where the timbers would sit is about half that. The existing joists are varied in size, but are all at least 5.5 x 2.5 inches.

As regards loading; there is a stud partition down the middle of the span, ie at right angles, and the non-raised area will need to bear a bath and shower.

What d'you reckon?!

Thanks David

[Lobster]

While I haven't ruled out the above, an architect visiting the property has suggested a Plan B which would not involve raising the floor, but having the soil pipe traverse the kitchen ceiling concealed within cladding to make it look like a beam. Visually it would look OK but I have my doubts on two fronts:

(a) Would building regs object to a soilpipe basically attached to the kitchen ceiling?!

(b) I can get adequate fall on the soil pipe, but it would probably need to have 4 or even 5 90-deg bends between the bathroom floor and the entry to the stack. Although I'll be able to cover the whole pipe from suitably positioned rodding access points, it doesn't sound like great plumbing practice to me to have that number of corners. Is this normal and is it likely to work OK? What does the uk.d-i-y panel think? (Note I will be selling the property once work is complete, so personally wouldn't be too bothered if we're only talking about a very small increased risk of blockages...)

Thanks David