question about garage foundation/slab?

[ninedriver]

Hello all!
I am currently in the designing and info gathering stages of my future garage build. I've been looking at a lot of pics/threads on this forum and have a question about the garage foundation/pad.
It appears most people dig a perimeter trench for the footings and then poor a level slab over the top. Then, they line the perimeter with a few courses of cinder block. That's my first question: What's the purpose of the block? When houses are built don't they build the walls on the flat slab? And is that threaded rod protruding from the blocks to bolt a footer too?
Anyway, any info regarding the foundation/slab process(s) would be greatly appreciated. Thanks!

 

[Stuart in MN]

It's fairly common to have one or two courses of block on top of the slab before the wood structure begins, mostly to keep the wood up off the ground and away from moisture. Yes, the threaded rods are used to bolt down the footers.

 

[Falcon67]

That seems to be a trend up north. You almost never see that around here. We put the slab between 4" and about 6" off the ground for a shop and around 12" for a house and go up with framing from there. My slab will be 4" above grade on the high grade end of the building. It'll be plenty if we ever get any more rain. Plate anchors are required per IBC 2006 at 1' from corners and at no more than 6' intervals between. Must be hot dipped galvanized for use with treated plates.

For some general specs, review IBC 2006.
http://publicecodes.citation.com/icod/ibc/2006f2/index.htm

 

[holdover]

slab is about 4" above grade, and the first three plates of my wall are treated ground contact lumber (first one bolted to the slab, second one nailed to the first, third one bottom of wall where studs are nailed to) standing water will never reach studs or T11 siding, unless Noah floats by.

 

[Stuart in MN]

Sometimes it's not just standing water you have to worry about, the frozen kind can get piled up pretty high too.

 

[holdover]

with drifting in the snow area I'm in sometimes the wall is covered to above the windows.. But it melts, and is not a concern

 

[brownbagg]

I have never seen it done in my region but I like the idea, especially if you wash the car inside the garage, like winter time.

 

[ddawg16]

Welcome Ninedriver......

First off.....PLEASE put your location in your profile....it makes it a lot easier to give you a meaningful answer. Where you live has a big impact on how things are done.

In the north, they are going to dig down deep to get below the frost line. Failure to do so means your house will quickly fail. One of the reasons you see basements up north....if your going down that deep...might as well make a room out of it.

In California? Frost line? Yea....right...

A lot has changed over the years as to how certain things are done. We had a discussion a couple of years ago about why houses were built differently in different parts of the US. For example, Stucco is common in California...but not way up North...why? Moisture gets behind the Stucco....freezes...and distroys it.

Cinder blocks....makes for cheap walls. But does not do that well in earthquakes....but does very well in Huricanes. Get the idea?

Regarding what you have seen....a 'good' foundation will have a good footing. The footing is what really supports the walls. Case in point....my house was built in 1952. The footings are 12" below grade, the bottom 'pad' is 10" thick and only 12" wide with the footing wall being 6" wide. The addition I am now doing has footing walls 8" thick with the footing pad being 18" wide and 16" thick.

Click on the link in my sig....my garage has a similar footing....but I have stem walls. Basically, the stem wall gets the mudsill (bottom plate of the wall) at least 8" above the ground. This means I don't have to worry about water getting into my garage.....or termites climbing up.

 

[Falcon67]

Sometimes it's not just standing water you have to worry about, the frozen kind can get piled up pretty high too.

OY. The only frost line around here is in our freezer.