# Formula for working kn/m ????

Discussion in 'Builders' Talk' started by iprwolf, May 16, 2005.

1. ### iprwolfMember

I am trying to work out what width my footing would need to be. Is there a formula in lay mans terms how to work this out. Single storey , brick/block wall with 60mm cavity 260mm total. height 2.1 m supporting a lean to type roof. Soil/ sand quite firm ground.
Thank in anticipation

2. ### scutchMember

Approved Document A of the Building Regs gives guidance on concrete footings - page 46 is the one you want. http://www.odpm.gov.uk/stellent/groups/odpm_buildreg/documents/page/odpm_breg029383.pdf

All the trade material websites list the 'weights' of their products. Bulk density of some common materials:
bricks (Fletton) 18kN/m3, lightweight blockwork, say 15kN/m3, mortar 18kN/m3.

For the sake of argument, take a worst case (let's say it's all 18kN/m3). Every linear meter of your building will have a volume that is 1 (length) x 0.2 (wall thickness) x 2.1 (wall height) which gives 0.42m3. Multiply 0.42 by 18 and you get 7.56kN/m (that's about 3/4 of a tonne). You'll have to factor in roof loading as well - wld need to know span and pitch for this. Hope this makes sense.

3. ### iprwolfMember

Thanks for that, the span is 2.3m, with a pitch of about 30 degs, I just dont want to dig out 2much as it will cost in concrete.I have building technology 5th edition which gives sizes of footings but need to know kn/m
Thanks again

4. ### scutchMember

You'd probably still be under 10kN/m. Check this with Building Control before you do anything. As you probably realise, foundations aren't just about keeping the wall up, they're also need to keep the roots out, so even quite modest structures have relatively deep foundations. Also, many BCOs work on the assumption that single storey buildings may eventually be extended upwards, and might expect the foundations to reflect this. I'd give Building Control a ring - you don't have to tell them who you are or what you're doing. Good luck.

5. ### iprwolfMember

Thanks again for that. They just dont seem that keen around here, everythings top secret or so you would think.
Think i will just dig small and let him inspect, thats what I paid for, and he will have to let me know what he wants, but you have confirmed what I thought, Great help, thanks again.