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Advice Needed for Suspended Timber Floor for Bathtub, Sink and Toilet over Existing Floor

Postby LAM1983 » Fri Aug 14, 2015 5:44 pm


I have a bathroom 3.3m x 2.2m.

I would like to build a raised floor to accomodate a bathtub, sink and toilet.

There already exists a floor. The timber joists run along the shortest axis of the room being approximately 2.4m wide accounting for the 10cm joist ends which sit into the brickwork.

The house is a mid-terrace. Built 1900.

To construct my new floor, can I overlay the joists on the existing floor - I presume this is not best practice?
If I am to build a new floor over the existing floor, which would be supported independent of the existing one, is the following construction suitable:

1. Hang one main joist (number 6 on drawing) across the shortest length of the room in the same direction as the current joists - span 2.35m - bearing 100mm
2. Hang other 5 joists (number 1-5) at a right angle to the first joist for 2.15m into the wall at the other side. 100mm bearing one end on brickwork // 450mm centres.
3. Adjoin Joists 1-5 to joist 6 by way of joist hangers.

Joists 125 x 47mm C16.
What specification should joist 6 be - I presume it must be larger to take the weight of 1-5?
Drawing attached with plan.

Many thanks in advance.

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