Floor Joist load strength

[mdurkin]

Hi All,
I'd like to fit a heat-store in my airing cupboard on the 1st floor. I can see 2 joists in the cupboard, 8" apart. They're 2.5" x 7" (is this an unusual size?) with a span of 13ft. This is a 1930s house, and I believe the joists are original. Does anyone know what the maximum load I could reasonably expect to put safely on these 2 joists?

Thanks,
Matt

 

[jeds]

The problem isn't one of immediate failure. You could probably put whatever load you like (within reason) on those joists and they won't immediately collapse. The main problem with over-loading is that it will cause excessive deflection, which in turn causes damage to finishes (cracked plaster and paint etc.) and over a longer period of time the joists to bow out of shape.

In a modern construction it is normal to double the joists beneath baths and tanks. Otherwise you can work out the load and design joists to suit.

 

[mdurkin]

Thanks Jeds.
As this is an existing install, and I want to cause minimal disruption, adding extra beams isn't really an option as it really would involve tearing the house apart. Are there any load ratings for beams I could use to accurately calculate the safe load?
If the load is too great, I might look to see if I could suspend the load from the loft conversion joists by bouilding a frame attached to both floors that the store sits in. Anyone see any issue with that (other than the logistics)? The loft conversion was well done with large joists and no really heavy weights up there.

Thanks,
Matt

 

[Chukka63]

The loft conversion was well done with large joists and no really heavy weights up there.

Thanks,
Matt

except the floor and roof maybe.

 

[JohnD]

I can see 2 joists in the cupboard, 8" apart.

That is strangely close. I wonder why?

If you take up a board or two, you should see at least one more. They are likely to be round about 18" apart.

 

[mdurkin]

yes - I'm going to have to take up some floorboards and find out why those joists are so close together. If I'm lucky one is resting on something solid - like the wall below which might just be supporting. Maybe someone added one to take the weight of a water tank...
As regards the loft - the roof does not sit on the floor joists. The whole floor sits on 2 masssive steel joists the width of the building with the floor joists hung on those steel joists. Very strong. The roof doesn't sit on those joists - it sits on the outside walls - the loft conversion is the whole of the upstairs space so the only possible support is where the stairs come up. In any case, the floor of the loft is separate to the roof structure and very strong.

Will check out those joists and see if I can see anything more...
Thanks,
Matt