Wooden garage footings/slab

[welshcottage]

Hi all

Have used the forum before and been very useful so thank you in advance in this one.

We are building a garage after much discussion we have decided on a wooden structure ( as it will tie in nicely with he lol of an ajoining barn)

This will need its own slab, but will but up the the barn wall, it's been suggested as the barn has shallow footing as built in stone slabs ( 150us year ago and stable) that we do not excavate to deep as could undermine the foundation.

The garage just for info will be three sides, made of wood with a pitched roof that will run upto the adjoining barn on slate.

It's been suggested buy our local builder that we, use the following method as using a wooden structure, did did down around 6 inches, add 6 inches of hardcore, soft sand couple of inches, DPM, and 4 inches of concrete reinforced. This way though we will have a floor around 4 inches above the ground ( which makes no difference to us) this effectively is the slab and footings in one.

Any thoughts on this method, garage for info will be about 3.5m X 6m

 

[theprinceofdarkness]

I think that you should put some sort of retaining "wall" around the sand layer. To stop rodents making their home in it or water washing it out.
Top soil is very soft, your barn has been compressing it for 100 years +, your garage will also compress its base unless the hardcore is truly wacked down. My postman who delivers about twice a week has worn a path 3" deep in virgin meadow in about 5 years.
FWIW I have just laid a concrete floor in a Victorian barn, walls had to be underpinned, built ON the top soil!. The clay subsoil within the barn was so hard that I had to "dig" it out with a bolster and a lump hammer, that was last summer. Concrete went in last September. The 4" thick C35 readymix is now cracking. But I think that is because the whole barn is sliding down the hill albeit slowly, is your site flat?
Frank