Bathroom floor loading- waste pipe running through each joist...

I have inherited a wetroom with floor tiles and underfloor heating.

Plan is to put a bath in.

I had concerns previously about the combined weight of the floor tiles, screed for ufh when adding a bath. I was reassured that the additional weight of a bath, the water etc isnt more than a few people.

Anyhow, got the bath and taken a section of ceiling away in the room below to work out the best place to connect up the bath drain.

Whoever fitted the wetroom decided to cpnnect the sink (at the opposite end of the room) to the waste pipe underfloor, so had used a hole saw through every joist.

Joists are 18cm tall and spaced 40cm apart.

This means that hole is cut through around 8 joists in the same place.

It also looks dead center.



Had the bathroom floor been compromised structurally, or, is it "ok"?

What's the consensus on the additional weight of the bath? Is plumbing it in a bad idea without reinforcing the floor? Or, am I good to go?

 

If by 'dead centre' you mean the centre of the depth of the joists, you should be OK, assuming the span isn't too great, and that the bath is near the ends of the joists.

 

Thank you @tony1851.

Span is 4.5m. Holes are positioned at the centre of the depth of the joists.

Bath is around 1.5 from the end of joists.

We are considering false ceiling below in the kitchen. Would it be prudent to build it out of a stronger joist, butted up to the joists above to provide additional support from deflection?

Or would that a waste of money/effort?

 

Hmm.. 4.5m is a long span for 180mm deep joists without the holes - you might need to consider some way of strengthening the floor.

 

Hi @tony1851,

I really appreciate your help here.

Darn. I just finished fitting it and was considering a much needed bath.

How would you suggest strengthening the floor?

We were considering floating ceiling below. Could we use that? E.g., use floor joists, running at 90 degrees to the existing ones, butted up tight?

If so, what size and grade timber would you suggest?

And, could we use brackets to attach these to the masonry? Unsure how we could use hangers and still butt it up tight

Thank you

 

I had a thought and more of a rummage with the ceiling off more, and, with a tape measure out.

The bathroom is at the top of the stair, and, offset partially as the staircase has a landing halfway up where you turn 180 degrees to get up stairs (hope thats clear)

So the first six bathroom joists are 3.2m spans. These have the bath on top, bath sitting at right angle to the joists (so over most of them, not sitting on just one)

The rest are 4.2m as they extend into the hallway (the 3.2 are shorter as they are terminated by the wall od the landing halfway up the stairs.

Unsure if this paints a rosier picture?

 

I've spoken to a SE, who is visiting this afternoon.
He's said, for the joist size, span and spacing he'd always recommend doubling up under a bath.

He said, probably, he'll recommend removing the offending waste pipe and bracing all the joists with a second joist.

Either way, until he gives me the report this is all "probably". I assume it will be "certainly" though.

What sort of costs is reasonable to brace 8 to 10 3.2m to 4.2m? Assuming full access from the room below and ceiling of that room already removed?

 

Ouch.
Ok.

SE spent an hour and called it "one of those things you read about but never expect to see"

All joists are 4.5m span.
There's a brick wall upstairs resting on the joists.
This wall is taking some of the roof load, which is at 90 degrees to the main walls, with bracing and plates on this wall.

He joked that, even without underfloor heading, screed, tiles and bath he's surprised there's not more deflection. That's not even considering the holes for the waste pipe.

Oh, and the ground level supporting wall has 2 doors with a half brick pier between them.

Seriously though, he said its safe in terms of it wont catastrophically fail.

However, the first 6 joists holding the bath and brick wall will need additional bracing, that will take most of the remaining space between them. He called them "very thick" supporting joists.

Report due by end of week.

Glad I called him

 

Oh dear, that's a shame to see.

You may have fallen foul of a bathroom installer who was a jack of all trades and a master of none, see it more often these days.

Any experience plumber would always reject cutting in a waste pipe perpendicular through joists, the pipe is just too large to run through the joists without compromising its strength, that would then drive a change in the design with the waste/basin being relocated.

All that hassle and cost for such an easily avoided design faux pas.

Seriously unfortunate for you but it's a great example for a DIY site where anyone else may be considering doing the same to their bathroom.

 

It's a shame I inherited this mess, however, am OK with it. Not happy, but, it's not soured anything.

The daft thing is the wastepipe could have followed the joist runs to the external wall and connected to the stack there with no cuttting.

However, it's a blessing really, because I'd have never called the SE out. The additional issues he found warrants the extra work and explains the 60mm deflection in the joists. 100 year old buildings eh...

 

Ok, SE plans avail.

3 options

1) 6 new joists bolted to side of existing. Min 3.2m long. Will require rerouting plumbing. M12 bolts at 600mm centers.

2) 6 new joists butted up underneath, using wall plates, and packed out above to deal with deflection. Existing plumbing remains

3) 1x steel beam, 3.4m running at right angles to the joists. Existing plumbing remains.

Have invited some builders to quote.

Thoughts on what will be the cheaper option?

I am almost tempted to DIY option #1, if I could think of a way to get 3.2m beams 3m in the air safely...

 

Would it not be accepted to glue and screw pieces of suitably thick ply around the plumbing holes to strengthen... often seen that suggested here?

 

The problem isnt just the drain holes.

The joists are 4.5m and over extended for their size. With a brick wall on top. And the roof reconfigured later to put load on the wall. Then the wetroom was added with screed and tiles etc.

Currently at 60mm deflection, with hairline cracks in kitchen walls where they sit.

 

If you are keeping the existing joists and considering putting new joists underneath in an attempt to reduce the deflection, this is unlikely to work.
Timber which is heavily-loaded over a long period - which the over-spanned floor joists are - assumes its deflected shape permanently; it's known as 'timber creep'. Any attempt to straighten the joists in the middle from below may result in the joists lifting at the ends.

In this situation, the best you could do would be to either strengthen the floor, eg by adding more joists between the existing joists. Or alternatively support the floor from below.
Neither of these will reduce the deflection, but would probably ensure that the floor does not fail structurally, or suffer further deflection.

 

These are my favourite options (options #1 and #3).

I'm guessing, based on the thought that option #3 installing 1x steel at right angles to support will be easier than 6x additional joists (either underneath or alongside), and will be the builder's preferred/cheapest option.

However I have no clue.