Floor Joists

[PrenticeBoyofDerry]

Just out of interest/concern,
I am aware of this document http://www.rushcliffe.gov.uk/upload/public/attachments/39/TA006timberfloors.pdf
But what is the stance taken by building controls, when the joist sizes do not comply to these in an old building.
The reason I ask is I have just been asked to carry some work out in a new refurb, the joist span approx 4-5m between supporting walls.
The joist depth is 75mm(3inch) x50mm(2inch) wide, in some places. These are the joist between downstairs ceiling and upstairs floor.
Some false ceilings will be going in and the above joist will not be used to support these.
So these joist will neither be plasterboarded and plastered or carry any weight from the underside.

So my question is, are they still suitable for the above floor to layed on to and what take on it would building controls be, taking in to consideration that it is an existing building not a new build.

 

[DSA]

A 75mm deep joist spanning 4m and carrying domestic floor loading would be massively overstressed, assuming softwood and fairly standard centres. Is this an existing or proposed situation? If existing, are there large deflections apparent?

 

[PrenticeBoyofDerry]

It's an existing property, that i have been asked to do some work on. The property is at least 100 years old.
Some of the work will need to be notified to LABC, so the plan is to wrap everything up in to one application.
But my concerns are the floor joist, the property was previously owned by a gentleman that has died, the property has not been maintained well, but has now been bought via auction. The new owner has started to gut the place and is at a stage now where things can go back. So nearly everything is bare or exposed internally.
I have been upstairs and the deflection in laymans terms did not seem to be to great, so was not an issue as such. But my work means I need to comply to certain requirements, which will mean either notching or drilling through some of the joists (I am fully versed in these requirements/regulations) Where the false ceiling is being installed, I can avoid this.
So my concerns are the suitability of the joist and what LABC stance would be on them, taking in to consideration it's an existing build where the original joist are still in place, they are not damaged or suffered from infestation or rot. Although not a suitable dimension.
I have expressed my concerns to the owner, who is as always trying to keep the budget down and not wanting to do work that is not needed.

 

[Deluks]

What do you mean by 'in some places' ? Have other timbers been removed prior to you arriving on the job? 3x2 would struggle to hold the ceiling up properly over that span, let alone the floor as well.
And don't take any mérde from penny-pinching customers. Rules is rules and if any problems come to light in the future you don't want your name bandied about as being the builder in 'question'

 

[PrenticeBoyofDerry]

What do you mean by 'in some places' ? Have other timbers been removed prior to you arriving on the job?

No timber removed, just not all the timbers downstairs are of the same dimension. Some joist in other rooms a slightly deeper but I'd be a brave man to say they were more than 100mm.

And don't take any mérde from penny-pinching customers. Rules is rules

That's what I am trying to determine, what are the regulations.
Do they need to comply to current ones or because it is already in existence and has been for some time is allowed?
He is aware that building inspectors will visit the site.
I think it could be a good idea to have chat with them before hand, to see what is what.

 

[RonnyRaygun]

Have you stood on the floor in question?

I remember once standing on a floor made from 4x2 timbers at 400 centres and spanning around 5m.
I was bouncing like I was on a trampoline!

If you're interested, I just did a calc, and according to BS5268, at 5m and 400mm centres, 50x75 C16 is overstressed under just its self weight and the weight of the floorboards...

 

[Deluks]

Don't rely on the regs to convince him. It's your professional opinion that these joists are too small and they will need replacing or strengthening. That should be enough. He trusts you enough to give you the work in the first place and he should take your advice. Get some 8x2's in there at 400 centres. Minimum.

 

[PrenticeBoyofDerry]

Have you stood on the floor in question?

I remember once standing on a floor made from 4x2 timbers at 400 centres and spanning around 5m.
I was bouncing like I was on a trampoline!

I have and to be honest, although some the existing floorboards were a little delicate. The joist themselves seemed sound and if you didn't know what lies beneath, you would not have questioned it.

 

[PrenticeBoyofDerry]

Don't rely on the regs to convince him. It's your professional opinion that these joists are too small and they will need replacing or strengthening. That should be enough. He trusts you enough to give you the work in the first place and he should take your advice. Get some 8x2's in there at 400 centres. Minimum.

I'm up again at back end of the week, to get the layout square footed for notified application and a bit more info of the work required.
See if I have overlooked anything on my first but brief visit.
It only struck me, as I was thinking about how best to comply to the holing and notching of joist.

 

[RonnyRaygun]

Have you stood on the floor in question?

I remember once standing on a floor made from 4x2 timbers at 400 centres and spanning around 5m.
I was bouncing like I was on a trampoline!

I have and to be honest, although some the existing floorboards were a little delicate. The joist themselves seemed sound and if you didn't know what lies beneath, you would not have questioned it.

Have heard that older timber can often be stronger than new...and amazing how floors have the ability to redistribute loads...
Plus the factors of safety in the British Standards helping out...

 

[DSA]

Even with a D40 hardwood, a 75x50mm section would be more than 2x overstressed. I think whether or not LABC would require a change is rather irrelevant - clearly the size is inappropriate and (based on what you have said) should be replaced. I would like to think that any reputable builder would not leave a floor like that, and you should be able to explain to the owner that it is potentially a very serious issue, assuming an occupied room is being supported.

I am intrigued though why the floor does not appear like a 'trampoline' (as previously mentioned) - do you have a photo?

Have you tried to actually measure the deflection of the floor? And these are definitely not roof joists??

 

[PrenticeBoyofDerry]

I have not measured the deflection, just stood on the joist with both householder and another, A bit a tentative jumping about.
Not roof joist, joists between downstairs ceiling and upstairs floor.
I had originally gone in to plan for the electric installation, then noticed the joist sizes, knowing that at some point the cables could be required to be routed through the joist, that's when I started to stratch my head!