# How to calculate load for ceiling



## newirishman (16 Nov 2009)

Hi,
I am trying to figure out how much load my ceiling can hold.
The joist are 1.5 inch by 7 inch, and one every 14 inches (that means, 12.5 inch between two joists). Length as around 4 metres (distance between the walls)
The build is a mid-1950's house.

There is quite a few tables to be found in the interweb but most of them are to calculate the distance or max length.

Anyone who has a good link or some maths formula to calculate psf or N/sqm based on the above? 

Not aiming for engineering grade numbers just an idea.

EDIT: reason for asking is that the floors upstairs are rather "bouncy" and not sure if I should consider doing something against it.


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## Pope John 11 (16 Nov 2009)

newirishman said:


> Hi,
> I am trying to figure out how much load my ceiling can hold.
> The joist are 1.5 inch by 7 inch, and one every 14 inches (that means, 12.5 inch between two joists). Length as around 4 metres (distance between the walls)
> The build is a mid-1950's house.
> ...


 
A rule of thumb I have learnt previously, 1/2 inch depth for every foot of span, assuming joist spacing of one foot. This would equate to 6.56 inch depth for your 13.2 foot span, & you have 7 inches, joist depth.

Another one, if its not broken, don't fix it.

Haven't said that, is there any deterioration to the ceiling below?



newirishman said:


> There is quite a few tables to be found in the interweb but most of them are to calculate the distance or max length.
> 
> Anyone who has a good link or some maths formula to calculate psf or N/sqm based on the above?


 
It really depends on the strength grade of the timbers.


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## newirishman (17 Nov 2009)

Pope John 11 said:


> A rule of thumb I have learnt previously, 1/2 inch depth for every foot of span, assuming joist spacing of one foot. This would equate to 6.56 inch depth for your 13.2 foot span, & you have 7 inches, joist depth.
> 
> Another one, if its not broken, don't fix it.
> 
> ...



Hi, thanks for that. As far as I can see there is no deterioration to the ceiling, and understand that point of "not broken don't fix it." 
Reason for asking is that I am not used to bouncy floors and sometimes just find it a weird sensation.
I guess it is now tricky to get the strength grade of the timber - wood looks all the same to me so not sure that timber was used back then.


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## onq (18 Nov 2009)

Hi Newirishman,

The fact your floors are "bouncy" indicates your floor joists could be marginal - "bounciness" is one of the signs. If the floors are heavily loaded now you should consider reducing the load. In addition you should be careful of any notching or drilling of holes in the floor joists.

If you go here:

[broken link removed]

And look for "domestic timber floor" under Building Control Guides on the lower right side of the page you'll fine a document in which the sizes of joist are related to spacing and spans.

195mm x 47mm C16 structural grade timber at 400mm centres supports a max span of 4.07M 

This is qualified as follows:

_"All the figures are based on normal domestic floor loadings where the floor construction is typically 18-25mm floor boards/sheets with up to 12.5mm thick plasterboard and skim underneath. For any other situation these tables may not be appropriate and you should refer to the Trada Document – ‘Span tables for solid timber members in floors, ceilings and roofs for dwellings’.  When choosing a joist spacing, check that your floorboards (or sheets) are strong enough to span over the width chosen. As a general rule - floorboards should be a minimum 16mm thick for joist centres up to 500mm and 19mm minimum for centres up to 600mm._"

As a general rule of thumb I'd specify 200 x 50mm up to 4.0M and 225 x 50mm up to 4.5M, all at max 400mm centres, with Trimming and Trimmer Joists doubled.

FWIW

ONQ.

[broken link removed]


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