Garage Foundation Question ?
 

I want to build a small garage at a vacation cabin in the mountains.
Several years ago, I had a spot cleared at a spot that I intended as a level
parking spot. I had some rock delivered, so that the spot was level. So,
I have an area of about 25 feet by 35 feet, where the rock (because of
the land slope) is about 1 foot deep on one end, and about 6 feet deep on
the other end. (That is quite a pile of rock, and has been a good parking
spot).

Here is my question: I know that foundation footers should be dug to below
the frost line, which in this area is about 3 feet. This is because of
frost heave, as I understand it. But, it is very unlikely to me that I would
experience frost-heave in an area where I have 3 to 6 feet of rock, right ??

I can't remember the type of rock, but I think it is limestone. It is 2-3
inch size. It has some "fines" in it, so that is has bonded together very
well. It is VERY hard , and stable.

Questions:

1. What type of footer would I need, and how deep should I did it ?

2. I am assuming that I would have a footing around the perimeter of the
garage, and then the concrete floor of the garage would just be poured 4-5
inches thick, right? Is that what is called a monolithic slab? Would I
still need some pea gravel and/or sand, to be put over the rock described,
before the concrete is poured ?

-------------------------------

I know these questions are basic, but I don't want to sound too green to my
contractor.

Thanks for any advice !!

--james--

James Nipper wrote:

I want to build a small garage at a vacation cabin in the mountains.
Several years ago, I had a spot cleared at a spot that I intended as a level
parking spot. I had some rock delivered, so that the spot was level. So,
I have an area of about 25 feet by 35 feet, where the rock (because of
the land slope) is about 1 foot deep on one end, and about 6 feet deep on
the other end. (That is quite a pile of rock, and has been a good parking
spot).

Here is my question: I know that foundation footers should be dug to below
the frost line, which in this area is about 3 feet. This is because of
frost heave, as I understand it. But, it is very unlikely to me that I would
experience frost-heave in an area where I have 3 to 6 feet of rock, right ??


Correct, if the stone has adequate drainage.


I can't remember the type of rock, but I think it is limestone. It is 2-3
inch size. It has some "fines" in it, so that is has bonded together very
well. It is VERY hard , and stable.

If it is too many fines and has hardened into almost a concrete like
state, then it may not be porous enough to drain the water fast enough
to prevent heaving.


Questions:

1. What type of footer would I need, and how deep should I did it ?

You may not need one at all, just a slab.


2. I am assuming that I would have a footing around the perimeter of the
garage, and then the concrete floor of the garage would just be poured 4-5
inches thick, right? Is that what is called a monolithic slab? Would I
still need some pea gravel and/or sand, to be put over the rock described,
before the concrete is poured ?

If the drainage is good, you likely need little else on top. If the
drainage is poor, then you'll need to dig footers to below the frost
line, which could be rather deep on the deep side of your rock pile.

Matt

On 1/3/2005 9:12 PM US(ET), James Nipper took fingers to keys, and typed
the following:

I want to build a small garage at a vacation cabin in the mountains.
Several years ago, I had a spot cleared at a spot that I intended as a level
parking spot. I had some rock delivered, so that the spot was level. So,
I have an area of about 25 feet by 35 feet, where the rock (because of
the land slope) is about 1 foot deep on one end, and about 6 feet deep on
the other end. (That is quite a pile of rock, and has been a good parking
spot).

Here is my question: I know that foundation footers should be dug to below
the frost line, which in this area is about 3 feet. This is because of
frost heave, as I understand it. But, it is very unlikely to me that I would
experience frost-heave in an area where I have 3 to 6 feet of rock, right ??

I can't remember the type of rock, but I think it is limestone. It is 2-3
inch size. It has some "fines" in it, so that is has bonded together very
well. It is VERY hard , and stable.

Questions:

1. What type of footer would I need, and how deep should I did it ?

2. I am assuming that I would have a footing around the perimeter of the
garage, and then the concrete floor of the garage would just be poured 4-5
inches thick, right? Is that what is called a monolithic slab? Would I
still need some pea gravel and/or sand, to be put over the rock described,
before the concrete is poured ?

-------------------------------

I know these questions are basic, but I don't want to sound too green to my
contractor.


Check with your local building inspector. See what he will accept.
I don't think that having 1-6 feet of stone piled on top of the ground
meets the requirements of a 3' frost free footing.

--
Bill

I know several people including my Father who have large shops on what's
called a "floating slab" there are not any footers, the whole slab is
designed to move and "float" as the frost comes and goes. My Dads shop even
has a hoist in it without any problems in cold Ontario for over 15 years,
not even a single crack...

Some areas (inspectors) understand floating slabs, and some don't.
They work great, however.
Another alternative I've used on shop buildings is to have the structure
supported by piers (sonotube, whatever)
that go well below the frost line, and then an ordinary slab floor.
hth
bill

"HotRod" wrote in message
...
I know several people including my Father who have large shops on what's
called a "floating slab" there are not any footers, the whole slab is
designed to move and "float" as the frost comes and goes. My Dads shop even
has a hoist in it without any problems in cold Ontario for over 15 years,
not even a single crack...

"James Nipper" wrote in message
...


I want to build a small garage at a vacation cabin in the mountains.
Several years ago, I had a spot cleared at a spot that I intended as a
level
parking spot. I had some rock delivered, so that the spot was level.
So,
I have an area of about 25 feet by 35 feet, where the rock (because of
the land slope) is about 1 foot deep on one end, and about 6 feet deep on
the other end. (That is quite a pile of rock, and has been a good
parking
spot).

Here is my question: I know that foundation footers should be dug to
below
the frost line, which in this area is about 3 feet. This is because of
frost heave, as I understand it. But, it is very unlikely to me that I
would
experience frost-heave in an area where I have 3 to 6 feet of rock, right
??

I can't remember the type of rock, but I think it is limestone. It is 2-3
inch size. It has some "fines" in it, so that is has bonded together very
well. It is VERY hard , and stable.

Questions:

1. What type of footer would I need, and how deep should I did it ?

2. I am assuming that I would have a footing around the perimeter of the
garage, and then the concrete floor of the garage would just be poured 4-5
inches thick, right? Is that what is called a monolithic slab? Would I
still need some pea gravel and/or sand, to be put over the rock described,
before the concrete is poured ?

-------------------------------

I know these questions are basic, but I don't want to sound too green to
my
contractor.

Thanks for any advice !!

--james--


A monolithic slab is a one-piece unit. It consists of beams on the
perimeter, and a much shallower surface within the beam perimeter. How much
stone, road base, or other fill depends on what you intend the slab to
support. Yours will probably require at least one beam down the center as
well. You will need steel (1/2" rebar) in the beams and to support the
surface of the slab.

The garage wall bottom plate should be secured with 1/2" J-bolts embedded in
the slab's perimeter. Where exactly these should NOT be depends where you
intend to put the garage door and any other entry door. So you need to come
up with floor plan now.

Frost-protected shallow foundations.

Google it.