Engineer and builder disagreement on floor joists, who's right?

[renovationsnewbie]

Hello everyone!

I’m looking for your opinion on a disagreement between my structural engineer and my builder regarding a bathroom renovation.

We are renovating a bathroom and adding a new bathtub. Span: 2.35 meters Existing Joists: 5x2 (120mm x 50mm)

One end of the joists is notched into the web of a 4-inch (approx. 100mm) tall steel beam

The problem is, the Structural Engineer has calculated that the existing 5x2s are inadequate for the new load. Suggested adding new 6x2 joists at 400mm centers.

The Builder (who is a friend trying to help, and keep it cheap) is pushing back. They suggest sistering new 120x50mm joists to the existing ones instead.

The Builder's reasoning: Because the RSJ web is only 4 inches tall, installing a 6-inch joist would require excessive notching at the bearing end to make it fit or drilling the beam to install packers and hangers would cost more.

Any advice is much appreciated!!!

 

[noseall]

Hello everyone!

I’m looking for your opinion on a disagreement between my structural engineer and my builder regarding a bathroom renovation.

We are renovating a bathroom and adding a new bathtub. Span: 2.35 meters Existing Joists: 5x2 (120mm x 50mm)

One end of the joists is notched into the web of a 4-inch (approx. 100mm) tall steel beam

The problem is, the Structural Engineer has calculated that the existing 5x2s are inadequate for the new load. Suggested adding new 6x2 joists at 400mm centers.

The Builder (who is a friend trying to help, and keep it cheap) is pushing back. They suggest sistering new 120x50mm joists to the existing ones instead.

The Builder's reasoning: Because the RSJ web is only 4 inches tall, installing a 6-inch joist would require excessive notching at the bearing end to make it fit or drilling the beam to install packers and hangers would cost more.

Any advice is much appreciated!!!

Whilst 120's might just nick it, I wouldn't bat an eye at notching half a dozen joists, safe in the knowledge it will satisfy Building Control.

 

[stevie888]

I think this is one case of a sensible builder and an over the top SE.

I doubt I would have even queried the existing unless it's a really mahoosive tub (in which case is the steel ok?) or the joists were suffering from plumber pox.

That said I fear BC are likely to side with the SE: maybe a quick phone call to test the water.

 

[robinbanks]

or drilling the beam to install packers and hangers would cost more.

Simpler to just pack the web with a single long timber, than mount multiple packers on multiple drilled holes

Whilst 120's might just nick it, I wouldn't bat an eye at notching half a dozen joists, safe in the knowledge it will satisfy Building Control.

Are you proposing 5 inch or 6 inch joists? (Are you responding to the concern about notching a 6 inch, or approving use of a 5inch sister?)

 

[noseall]

Are you proposing 5 inch or 6 inch joists? (Are you responding to the concern about notching a 6 inch, or approving use of a 5inch sister?)

I'm not really proposing anything, other than on paper 120mm might work. I suppose you have to factor in the reduction in performance where the joists are cut (into the web), but the cut will occur no matter what section you were using. I'm not really sure about the loadings, is all, what with the bath and all.

 

[Dereekoo]

Short on facts, but c16 5 x 2 spaced at 400 centres satisfies structural requirements for a standard floor load of 150kg/m2 so depending how your SE is adding on the weight of the bath the 150 x 50 could be in the right field if he means to replace the existing joists, if he means in addition to the existing joists then they seem well over the top and complimenting the current joists with joists of the same size would seem appropriate, but, as stated, short on facts and figures

 

[robinbanks]

Because the RSJ web is only 4 inches tall, installing a 6-inch joist would require excessive notching at the bearing end

If that's what the SE has specified, just get on with it. Takes about a minute to cut a 2x2 block out of a joist end (or two 1x2, depending on how the existing joists align with the web) and as long as the extra inch isn't fouling on anything like a ceiling below, it's an easy install..

 

[^woody^]

Your engineer should be devising a solution to take the floor load, not just having a narrow mind set of "bigger load = deeper joists".

Doubling up the joists, or alternate joists or having the same size joists at smaller spacing is as good as using deeper joists.

A proper engineer should be able to work out loading per m2 and design a joist section and spacing to deal with that, not just look at span tables (which are themselves over rated). That's just either lazy or inexperienced.