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Slab in unheated garage

I'm not debating your points red-eye, but take my two 600+ sf examples and make them both 500 sf accessory buildings to my main house, heat both, etc., store cars in one and let a relative live - sleeping and bathroom - in the other. And I'll support plumbing etc. off the walls which are on a frost protected foundation.

I am just struggling where this floating slab subject to frost heaves is permitted, besides accessory structures under 600 or 400 sf, or more specifically in garages larger than 600, heated or not, with plumbing or not. Maybe it's in IBC. Haven't looked there yet. I've spent my life in 4.10 and 10.30 (I think .30 in 2021) so IRC is new to me. I used CABOs O&TFD last time I built residential.
 
bill1952 said:
I'm not debating your points red-eye, but take my two 600+ sf examples and make them both 500 sf accessory buildings to my main house, heat both, etc., store cars in one and let a relative live - sleeping and bathroom - in the other. And I'll support plumbing etc. off the walls which are on a frost protected foundation.

I am just struggling where this floating slab subject to frost heaves is permitted, besides accessory structures under 600 or 400 sf, or more specifically in garages larger than 600, heated or not, with plumbing or not. Maybe it's in IBC. Haven't looked there yet. I've spent my life in 4.10 and 10.30 (I think .30 in 2021) so IRC is new to me. I used CABOs O&TFD last time I built residential.
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I guess it will take posting R403.1.4.1 three times for you to actually read it.

You can't live in an accessory structure. You can only live in a dwelling and that comes with a LOT of other requirements that negate your arguments (heat, insulation). A floating slab in an unheated garage is not a foundation, it's just a slab and it can be supported by frozen ground (it is, all winter, in northern climates). A floating foundation is allowed for accessory structures, that's not the same as a slab.
 
In your referenced section do you refer to:
"R403.1.4.1 Frost Protection
Except where otherwise protected from frost, foundation walls, piers and other permanent supports of buildings and structures shall be protected from frost by one or more of the following methods:.."

because a s.o.g. is not "a permanent support of a building or structure"? And this would apply to accessory structures as well as living space? It certainly is not the 600 sf accessory space exception below this.

I'm also not seeing where sleeping in an accessory structure is prohibited by the IEC. Isn't a detached office on a lot with a main dwelling an accessory structure? Label it a cabana or pool house, same thing, as long as not designed, built, or intended for living. I'm sure zoning ordinances and hoa rules treat this differently but I was addressing just the IRC.
 
bill1952 said:
In your referenced section do you refer to:
"R403.1.4.1 Frost Protection
Except where otherwise protected from frost, foundation walls, piers and other permanent supports of buildings and structures shall be protected from frost by one or more of the following methods:.."

because a s.o.g. is not "a permanent support of a building or structure"? And this would apply to accessory structures as well as living space? It certainly is not the 600 sf accessory space exception below this.

I'm also not seeing where sleeping in an accessory structure is prohibited by the IEC. Isn't a detached office on a lot with a main dwelling an accessory structure? Label it a cabana or pool house, same thing, as long as not designed, built, or intended for living. I'm sure zoning ordinances and hoa rules treat this differently but I was addressing just the IRC.
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Dude, read the exceptions.

If you're living in the structure it's a dwelling, not an accessory structure. It's a matter of occupancy. If you want to sleep in your garage that's up to you and local ordinances. If you want to build anything you start with occupancy.

You sure know how to beat a dead horse.

I'm out, arguing your inane comments is no longer amusing me.
 
Well, at least I've been respectful.

No one has shown me where in the IRC the supports for a floor of a greater than 600 sf accessory structure does not have to be frost protected. The very question I asked starting this thread. You point to a section that excepts 600 or less sf accessory buildings, but that is all, and implies greater than 600 sf do require frost protection. If the floor of any size accessory building is exempt, or all garage floors, why not say that?

Thank you for attempting to answer the question.
 
Bill....I did.....A foundation stem wall is not frost protection for any slab (by code), a 42-48" deep footing is frost protection of a "structure". In reality, the frost typically doesn't like to creep under stuff, or through the stem wall, so we accept it as "otherwise protected"....

And I reiterate, if the slab does not support the structure, it needs no frost protection...its a bad idea (IMO), but morton buildings have been getting away with it for years, so it must not really be an issue...

"R403.1.4.1 Frost Protection
Except where otherwise protected from frost, foundation walls, piers and other permanent supports of buildings and structures ...
 
Thank you. I interpret your R403.1.4.1 reference to suggest a s.o.g. floor is not a part of the "buildings and structures" and therefore does not have to be supported by a frost protected foundation to comply with the IRC. It doesn't quite seem to mesh with R401.2 and the reference to "accommodating all loads in accordance with Section R301" but I'll ignore that.

Can you point me to where in the IRC this is limited to accessory structures (>600 sf) or isn't it?
 
Limit for small garages not being on a full foundation is 660 sq. ft. in the Great White North as well.

Always interesting to see the consistency between our two codes.
 
My understanding of the "why" it is allowed for a garage up to 600 Sq. Ft. is not that the building will not be subject to frost heave, it absolutely will (well, depending on your soils and temperatures), it is allowed because there is unlikely to be differential movement in the structure due to the small size. Even if there is an issue, because it is "only" a garage, it is unlikely to become a life safety issue or damage the structure to the point it is unable to be used for it's intended purpose. Basically, the risk assessment allows it.

This isn't to say that it is a good idea to do this everywhere, it is a minimum code after all. Certainly, if you have an area with vastly different soil types, you might want to ensure the foundation is below frost.

While there are sometimes where frost will come in underneath a garage slab that is independent of the building foundation and cause it to heave, it is relatively unlikely. Remember, for frost to heave the ground, there has to be water in it. The only way that the ground is going to have water in it with a building overtop is either really poor water management, or soil particles that are small enough to engage capillary action and hold water instead of letting it drain away.
 
tmurray said:
Limit for small garages not being on a full foundation is 660 sq. ft. in the Great White North as well.

Always interesting to see the consistency between our two codes.
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Well I'm longing for the fantastic canoe routes of the truley great white north now but are you saying a garage over 660 sf has to have a full foundation where you live?

I need to look more at IBC and type U buildings perhaps, treating a 1000 sf building for vehicles as something other than an accessory structure to an IRC dwelling. Or just submit for permit and assume (safely I'm sure) reviewer will not care the 1000 sf garage floor is not supported on a frost protected foundation.
 
You mean this?:

R403.1.4.1 Frost protection. Except where otherwise
protected from frost, foundation walls, piers and other
permanent supports of buildings and structures shall be
protected from frost by one or more of the following
methods:
1. Extended below the frost line specified in Table
R301.2.(1).
2. Constructed in accordance with Section R403.3.
3. Constructed in accordance with ASCE 32.
4. Erected on solid rock.
Exceptions:
1. Protection of freestanding accessory structures
with an area of 600 square feet (56 m2) or less,
of light-frame construction, with an eave
height of 10 feet (3048 mm) or less shall not be
required.
2. Protection of freestanding accessory structures
with an area of 400 square feet (37 m2)
or less, of other than light-frame construction,
with an eave height of 10 feet (3048 mm) or
 
I'm trying to focus on what the IRC requires, not what I'd require or what makes sense or what some people believe the IRC requires but can't quite point to it.

As far as the driveway, if it were a load scheduled in R301 that R401.2 said had to be "accomodated" and thus supported by a frost protected foundation, I would say the code says yes. But all "passenger vehicle garages" are scheduled and no concrete driveway nor dirt nor any driveways are scheduled. As pointed out there are exceptions to the frost ptotection requirement but none apply to a >600 sf garage. I'm just reading the words in the IRC.
 
There is no reference from R401.2 to frost protection to the loads in R301......THERE IS NO IRC SLAB THAT IS "SUPPORTED" BY A FOUNDATION...It is supported by the base per R506
 
tmurray said:
My understanding of the "why" it is allowed for a garage up to 600 Sq. Ft. is not that the building will not be subject to frost heave, it absolutely will (well, depending on your soils and temperatures), it is allowed because there is unlikely to be differential movement in the structure due to the small size. Even if there is an issue, because it is "only" a garage, it is unlikely to become a life safety issue or damage the structure to the point it is unable to be used for it's intended purpose. Basically, the risk assessment allows it.

This isn't to say that it is a good idea to do this everywhere, it is a minimum code after all. Certainly, if you have an area with vastly different soil types, you might want to ensure the foundation is below frost.

While there are sometimes where frost will come in underneath a garage slab that is independent of the building foundation and cause it to heave, it is relatively unlikely. Remember, for frost to heave the ground, there has to be water in it. The only way that the ground is going to have water in it with a building overtop is either really poor water management, or soil particles that are small enough to engage capillary action and hold water instead of letting it drain away.
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I agree with all of this except the last paragraph. There must be moisture in the soil but not necessarily water. You also need clay in the soil to create the lensing which is what drives the force exerted in frost heave. You can certainly have frost heave below buildings with clay soils and all other water management done correctly.

To a different post, frost doesn't like or dislike anything, it's all simple thermodynamics. The only barrier to heat moving through a stem wall is the very little insulating properties it has. What you're actually seeing when there is no frost under a floating slab is the insulation of the structure above it reducing the heat radiating up. The roof is helping you, the stem wall is negligible.
 
bill1952 said:
I'm trying to focus on what the IRC requires, not what I'd require or what makes sense or what some people believe the IRC requires but can't quite point to it.

As far as the driveway, if it were a load scheduled in R301 that R401.2 said had to be "accomodated" and thus supported by a frost protected foundation, I would say the code says yes. But all "passenger vehicle garages" are scheduled and no concrete driveway nor dirt nor any driveways are scheduled. As pointed out there are exceptions to the frost ptotection requirement but none apply to a >600 sf garage. I'm just reading the words in the IRC.
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You're reading words and not definitions. Frost protection is required for structures, slabs are not defined as such unless they are elevated.

Are you purposely being thick? Your continued questioning is absolutely pointless. This topic has been explained to you by multiple posters but you continue to ignore their comments.
Get a dictionary and read Ch. 2.
 
Rick18071 said:
In PA you can build a garage up to 2,000 sq ft without a permit. And not need frost protection. This doesn't mean it's a good idea to do it.
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Rick, my family is from Montrose PA area, great grandfather settled there I 1840, and we almost moved there for retirement.

I'm unclear if that is two separate amendments. In the IBC, the work exempt from permit is often misinterpreted to mean the work does not have to meet code. Not so. Sure, it isn't necessarily inspected and you will probably get away without meeting code if you so desire. I know of at least one instance in my very narrow area of speciality where permit exempt work was reported, subsequently inspected, and red tagged.
 
redeyedfly said:
I agree with all of this except the last paragraph. There must be moisture in the soil but not necessarily water. You also need clay in the soil to create the lensing which is what drives the force exerted in frost heave. You can certainly have frost heave below buildings with clay soils and all other water management done correctly.

To a different post, frost doesn't like or dislike anything, it's all simple thermodynamics. The only barrier to heat moving through a stem wall is the very little insulating properties it has. What you're actually seeing when there is no frost under a floating slab is the insulation of the structure above it reducing the heat radiating up. The roof is helping you, the stem wall is negligible.
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What "moisture" are you seeing that is not water?

Water is all H2O, regardless of phase. In the world of building science, if we want to talk about a specific phase of water we say phase [vapour/liquid/ice] water. We rarely refer to moisture as it means either vapour or small amount of condensation.

With this in mind, I assume you are indicating that there would be phase vapour water contained in the soil that can cause frost, I would question how often this happens. Typically, there will be an intermediate phase change to phase liquid water before the ultimate phase change to phase ice water. There are conditions that can be present that causes deposition where phase vapour water undergoes a phase change directly to phase ice water, but the conditions are extremely demanding for this to be able to happen naturally.

The capillary force holding water is not just present in clay, but any soil particles small enough to ensure the adhesion of the water molecules to the soil particles overlaps sufficiently to defeat gravity.
 
bill1952 said:
Well I'm longing for the fantastic canoe routes of the truley great white north now but are you saying a garage over 660 sf has to have a full foundation where you live?

I need to look more at IBC and type U buildings perhaps, treating a 1000 sf building for vehicles as something other than an accessory structure to an IRC dwelling. Or just submit for permit and assume (safely I'm sure) reviewer will not care the 1000 sf garage floor is not supported on a frost protected foundation.
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Sorry, Typo. 600 Sq. Ft. and yes they have some sort of full foundation under them. Typically we see a frost wall, just a 4' wall with footings to get them below the frost line, but we have people provide an engineered design for a slab on occasion as well.
 
Decades ago we had a local engineer design a mono slab that could be used on an unheated garage/shed. His design is 6" of washed gravel and install gutters to direct water away from the foundation. He limited his design to a 1080 sg foot building with no plumbing installed. There have been hundreds installed in the past 30 + years and no failures or frost heave problems.
 
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