Strength of a First Floor in a Victorian Middle Terrace

[sallyjc]

Hello

I live in a Victorian Middle Terrace and am having the first floor redecorated.

I or rather the Builder has pulled up the old carpet and floorboards as we had to fit some new electric sockets and also move a radiator.

We have now laid some flooring grade OSB I think he said it was called. And now my question/concern.

I would like to have electric underfloor heating in this room which is 420cm x 340cm. And then on top some engineered oak flooring which is 18mm thick. The builder says that we will use a self leveling flexible material on top of the electric underfloor heating. And then the wood is glued on top of that.

I am am worried about the weight of all this material and the strength of the floor. He said the self leveling flexible material would be heavy and it would 5mm to 10mm thick.

The floor joists in the room sit on top of brick walls. When we had the floorboards off we saw the joists and they are in good condition. They occur every 25cm or so and there are lots of joists in the room. He says they are at least 4" x 2", maybe 6" x 2".

The room will be a child's bedroom afterwards with a bed, wardrobe etc.

Am I worry over nothing about adding all this extra weight to a first floor?

Thank you very much for some advice!

Sally

 

[tony1851]

You need to be specific about the sizes of the joists, their centres (spacing) and their clear span.
(25cms seems unusually close - usually they are at 35-40cm).

 

[sallyjc]

Hello

I have just check by measuring the screws that are poking out and they have mostly 34-35cm gaps between them

Thank you

 

[tony1851]

It's not the gaps between the joists that you measure, it's the distance between the centres of the joists. So if your gaps are 35cm, your centres will be about 40cm, which is what would be expected.
Assuming the span was 3.4m (ie the short span) the 6x2s would not nowadays be accepted as suitable.
But in practice, the floor won't collapse; all that will happen is that it will deflect that little bit more - you might not even notice it.

 

[sallyjc]

Hello

Thanks.

The floor is already laid so I am looking at the screws that are holding the floor down which I am guessing the Builder screwed roughly in to the middle of the joists. So the 34-35cm gap would be centre of joist to centre of next joist I think?

Is 4x2 better than 6x2? Or are they even bigger these days. It is a Victorian house though!

Also, would you or anyone here be able to say roughly what the floor would support in kg?

I mean, we know the room size, the number and size of the joists that are supported by "load bearing" brick walls. Is there a formula which would say roughly XXX kilograms?

Thanks

Sally

 

[tony1851]

Hello



Also, would you or anyone here be able to say roughly what the floor would support in kg?

It doesn't quite work like that. It depends on what deflection (sag) of the floor you are prepared to accept.
The higher the load, the greater the deflection and the more risk there is in cracking the plaster ceiling below. But with the loads you are putting on it, the worst that will happen is that you may possibly get a few extra small cracks in the ceiling.
The joists will support far more weight than you have before they become overstressed and collapse.

 

[sallyjc]

Thank you.

The question about it actually falling down in really one of curiosity that stems from a very basic O' level in Physics. I remember having to work out formulas with something called the second moment of area. That's all I do remember though!

I have often wondered if a car somehow got in to a first floor bedroom would it collapse. Or maybe a 500 people in a small bedroom (a squash I know!).

Thanks

 

[tony1851]

I have often wondered if a car somehow got in to a first floor bedroom would it collapse.

Why?!

 

[sallyjc]

Like I said, it's curiosity as to just how strong the floor would be and how many kilograms it could take.

The car is just an everyday object that I know is heavy!

 

[tony1851]

Depending on which way the car was oriented (ie axles parallel or perpendicular to the joists) the floor as a whole probably would support it, assuming a load of around 1T.

But if the joists didn't give way, the floor boarding immediately under the wheels might, and the car would drop down a little until the body shell was supported across the joists.

 

[phatboy]

But if the joists didn't give way, the floor boarding immediately under the wheels might, and the car would drop down a little until the body shell was supported across the joists.

Much like if you fit a bath with its feet not on the joists and without any load spreading battens, there is the risk it could drop through the floor, so the bottom of the tub is actually on the joists