Prefab garage base - DPM, MOT depth etc.. The answer?

[studarude]

Morning all,

Ive been browsing the forum for some time now trying to tie down the details of the necessary spec for a garage base i'm looking to put down on the side of my house for a prefab approx 8ft 3 by 20ft 3.

Side of the house is here:



Ive read conflicting suggestions as to how to do the base for it. The garage will be entirely free standing, placed as close to the brick wall as possible to maintain the walk way between the drive and back garden.

So, how do you guys suggest i do the base?

The garage people say 4" aggregate, 4" of concrete in a uniform pad, but ive got my doubts about this, the garage will be used to look after the cars i run so its likely there will be jacks used frequently ( so a lot of point loading) and the odd use of an engine crane.

My Dad (who's a engineer who insists on over-engineering!) has suggested a strip footing, engineering brick upto finished height, small amount of aggregate and then back fill with concrete.

Is this a bit over the top?

Given the 'blank canvas', how would you guys construct the base?

Also, ive heard conflicting stories regarding the DPM, i think its necessary, but some folk are saying that its best without owing to the damp nature of these garages?

Help!

 

[Alastairreid]

150mm type 1 mot, 25mm sand blinding, 1200 guage dpm, 100mm c35 concrete.

 

[studarude]

Is that as in a uniform pad? No edges or 'footings'?

Will the 100mm really be enough for jacking cars up on etc?

Thanks for the reply!

 

[Alastairreid]

Strip foundations with 7n concrete block edgings.

Consider putting A4 mesh in the concrete.

http://buildriteltd.co.uk/shop/morris-100mm-concrete-block-pallet-p-157.html

C35 concrete mix uses

C35 is a very strong concrete mix and its recommended use is on industrial floors, reinforced foundations, piling and underpinning.

http://www.concrete2you.com/products/c35/

 

[studarude]

At the risk of being a pain (and owing to the fact i cant visualize what you're proposing) how would the base look like sketched out? What would i need to dig out, build up etc. Im a complete newb with this so please bear with me!

Probably make perfect sense to my old man however...

 

[^woody^]

Just imagine a cheese sandwich

 

[Alastairreid]

http://www.youtube.com/watch?v=rrs7QclgFZE

 

[studarude]

So, i dig a strip footing, block upto ground level, dig down in the centre 250mm to accomodate 150 type 1 mot and 100mm concrete?

How wide/deep does the strip footing need to be?

Can i then cast inbetween the blocks? like shuttering?

 

[Alastairreid]

350x200mm for footings!

Dont forget your sand blinding and dpm on top of hardcore.

 

[studarude]

Does it 'need' strip footings? Or are they just to provide a base for the block to shutter up to with the concrete?

I.e if i dig down uniformly, maybe 6" bigger all round, get my hardcore down and compacted, then blinded with the sand, could i use some reclaimed scaffold planks as shuttering and pour the concrete in?

Or is this making life more difficult?

Just wondering how i'd run/finish the DPM.

 

[Alastairreid]

Building the garage off the toe of the slab can cause it to crack.

You can use well supported scaffold boards, dig the edges deeper.

The membrane will lap up over the boards.

Something like this.