Foundations?? huh?

stifz

Hi All,

I'm looking into building a garage, have the p.p. for a 9m x 6m garage. I've never done anything like this before so i'm wondering how should i go about laying the founds for a cavity block built shed?

How far should i dig for founds?

What size concrete foundation is req to support 9m x 6m? Will i need to re-enforce with steel?

Also how do go about working out how much concrete i need to order.. is there a particular mix i should get?

??

Johnniep

Hey Stifz,

Alot of questions in one little post

How far should i dig for founds?

Typically, foundations should have a minimum cover of 450mm of soil to prevent freeze / thaw action of the concrete footings, however, if you are building up off poor ground conditions, you may need to go deeper depending on the soil conditions.

I would not use hollow blocks below ground level as these can fill with water and cause problems further down the line :eek:

What size concrete foundation is req to support 9m x 6m?

this depends on a number of factors ie height of wall, roof buildup, ground conditions etc, but a minimum footing withh of 3 x wall thickeness would be the absolute minimum - say 750mm x 300dp

Will i need to re-enforce with steel?

I would always recommend a layer of A252 (high yeild, ribbed steel) mesh as a minimum!

Also how do go about working out how much concrete i need to order.. is there a particular mix i should get?

For all sub structures, for durability purposes, you should use a 35N20 mix. Any readymix supplier will know what this means! You are building a 9x6m shed which gives 30 linear m of footings. Based on a 750x300dp footing you would need in excess of 6.75m^3 of concrete (plus a little extra for comfort!)

All the above are mimimum values I would recommend but it really does depend on the site and ground conditions. If you in anyway unsure, I would recommend that you get someone to have a look at the ground for you before you start the building works!

Hope this helps.....

J

stifz

Legend! Fair play to you.

So if i guided 7m^3 of cement i'd get the rough cost of that end of it. Any idea's what the average truck load carries? Would i do it in one load?

Any idea's how the steel work is done.. do i put it up right in the ground or make it into boxes to enforce 750mm x 300mm and lay it in place then fill will concrete?

Thanks

Mellor

this depends on a number of factors ie height of wall, roof buildup, ground conditions etc, but a minimum footing withh of 3 x wall thickeness would be the absolute minimum - say 750mm x 300dp

Most of it is spot on IMO but you could I ask why you added so much to the size of the foundations. "3x the width, and a depth equal to the wall thickness" is the rule everyone uses. Which for a 215 wall would give you 645x215. And is you wanted to round it up so its even, about 650x215.
I know that foundations are often oversized for peace of mind, but this is a single story structure with probably a light weight roof. So the load won't be too much.
It probably adds 1.5-2 cubic metres of concrete to the job.
Not sure what thats would cost, but if it wasn't too much then i'd go with the oversized ones.
BTW not nitpicking, just curious. Wondering if there was any reason other than being safe.

muffler

Mellor wrote:

Which for a 215 wall would give you 645x215. And is you wanted to round it up so its even, about 650x215.

BTW not nitpicking, just curious. Wondering if there was any reason other than being safe.

Not nitpicking either but the OP is building a cavity wall so the least thickness would be 2 x 100 block leafs + 50 cavity = 250mm. 3 times wall thickness is 250 x 3 = 750mm. which would suit the bucket size on a JCB

Johnniep

No worries on the "nitpicking" Mellor but the reason I went with 750 is cause I dont think you can get a 645w bucket for a digger Also, I assumed that when the OP said "cavity block built shed" they meant that it would be a single leaf of 215 hollow block. When it comes to footings, I always error on the conservatve side. Getting access to increase the size of a footing or having to underpin a strip is a very expensive!!! I know this is "just" a shed but the same principals apply!

Anywho, the steel should be installed in a single layer at the base of the footing with a minimum of 50mm concrete cover to all steel. The mesh should be lapped by a minimum of 375mm.

I think the average concrete truck will hold about 6 cubes, but larger trucks are available.

Oh, and just be sure you order concrete. Ordering 6 or 7 cubes of cement could be an expensive mistake :eek:

squire1

Johnniep wrote:

I think the average concrete truck will hold about 6 cubes, but larger trucks are available.

Oh, and just be sure you order concrete. Ordering 6 or 7 cubes of cement could be an expensive mistake :eek:

A man with experience:D

You will probably be able to order up to 9 cubes for delivery in one truck if you need but beware of the space needed to get a truck this size in and turned. You can possibly get a truck with integrated conveyor belt for placing the concrete if required. Just ask your supplier.

stifz

thanks lads. Much appreciated.

Mellor

muffler wrote:

Not nitpicking either but the OP is building a cavity wall so the least thickness would be 2 x 100 block leafs + 50 cavity = 250mm. 3 times wall thickness is 250 x 3 = 750mm. which would suit the bucket size on a JCB

Well i took his original post as "cavity block" wall. And not a cavity wall made from blocks. Good point on the digger bucket.
Anyway thanks for the reply JohnnieP. And your right it is safer to spend the extra now then have to come back.

stifz

Just pricing up this project.. does 460 for 8m^3 of concrete 35n20 sound about right?

Also any idea's how much? the cost? and where to get a252 ribbed steel? It strikes me a general builders yards would nail me on the price.

Getting excited now! looks like this maybe a runner.. need to dry store a boat so it would be fantastic if i could get it started this year.

thanks

karltimber

ever thought about a slab of concrete

saves a lot of hassle. just make the out edges deeper and shutter if all off.
Scrape the top soil off and put in some hard core, and pour your concrete.
(( quick explanation - not that quick))

It saves on footings and extra blocks etc.
There will not be much weight on the walls at all.
I used 6" solids due to my limited wall laying abilites - and believe me when I say it's a solid shed --aka nulcear bunker

just an idea --- also something I regret and may change -- put an apex roof and you will get extra storage also.

K