# Attached garage without footings?



## ikessky (Aug 24, 2009)

I'm in the process of planning a 24x40 attached garage. One contractor is telling me that if I am commited to keeping the garage heated above freezing, I won't need to have a foundation poured and can just do a slab. I know the guy and trust him, but I just can't wrap my mind around why heating the garage above the ground would keep it safe from frost heave. It's tempting to do it this way and save some money, but I'm thinking it's better to just bite the bullet and have a foundation done. I understand the frost heave process, but I'm just looking for some information why heating the structure will protect the slab and the attached structure.


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## Daniel Holzman (Mar 10, 2009)

First off, no doubt you are aware of building code rules, so I assume you either live in an area where you don't need a building permit, else your building code allows for construction of an attached garage without footers below frost line. So let's move on.

In order for frost heave to occur, you need three things to happen:

1. You need free moisture in the soil. You don't get frost heave in the desert even if the soil gets below freezing for this reason. Similarly, you rarely get frost heave on clay, since the moisture is chemically bound to the soil, and is not free.

2. You need a relatively fine grained soil that traps the moisture between grains, allowing large ice crystals to grow. Most prone to frost heave is fine sand and silt. Coarse gravel does not normally frost heave because the moisture moves easily through the soil, and large crystals do not develop.

3. You need freezing temperature in the soil. In your case, the builder is assuming that by heating the garage, you will prevent the soil from freezing, due to the combination of insulation provided by the slab above the soil, and heat flow through the slab. I don't kinow where you live, what kind of soil conditions you have, and what kind of moisture conditions you have, but there are occasions where this approach works. There are also circumstances where you fail to generate adequate heat, the soil freezes, and you have potentially serious problems. If your building inspector allows it, and your contractor provides an IRON CLAD guarantee that it will work, assuming all responsibility for damage to your property if it freezes, and the costs to repair, I might consider it. Then again, I am pretty skeptical about this (you plan to leave your heat on when you go on vacation?). Your call.


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## ikessky (Aug 24, 2009)

The contractor that told me about this is a reputable guy and they've been in business since the 70's. He must know something about the codes, but what do I know?

I'm in northern WI, so freeze/thaw is a definite issue. I understand what frost heave is, but that's where my knowledge stops. Even with the heated structure/slab sitting on the ground, I still don't see what is going to stop the frost from going under the slab and pushing up from there. Unless we are assuming that the heated structure would keep a certain layer of unfrozen earth and moisture under the slab and when the frost pushes up, it would have some "give" to it and wouldn't move the structure above.

Either way, I think the proper thing to do is put the footings in. How about I go to sell the house and have to tell the prospective buyer, "Yeah, it's a nice garage, but you have to keep it heated at all times so it doesn't mess up your roof line."


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## Ron6519 (Mar 28, 2007)

ikessky said:


> I'm in the process of planning a 24x40 attached garage. One contractor is telling me that if I am commited to keeping the garage heated above freezing, I won't need to have a foundation poured and can just do a slab. I know the guy and trust him, but I just can't wrap my mind around why heating the garage above the ground would keep it safe from frost heave. It's tempting to do it this way and save some money, but I'm thinking it's better to just bite the bullet and have a foundation done. I understand the frost heave process, but I'm just looking for some information why heating the structure will protect the slab and the attached structure.


I can't see this as a logical building process in any zone, much less a freeze zone. Building code dictates what is needed, not the whims of a contractor. Call the local building dept and get their requirements.


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## jomama45 (Nov 13, 2008)

Your apprehension to the builder's suggestion are warranted, especially seeing as it goes against WI's own prescriptive code:

_*Comm 21.15 Footings (1) (e):*

Structures supported on floating slabs or similar shallow foundations may not be physically attached to structures that are supported by footings that extend below the frost line unless an isolation joint is used between the structures. This isolation joint shall extend for the full height of the structure._


In short, the code requires you to match the existing foundation type; Grade beam to grade beam, frost wall to frost wall. You can legally build it like stated in the last sentence of the code states, but it's alot more work IMO, and yields inferior results. I've done the foundations for 100's of additions, and only once have I done one with the isolation method. It was extremely complicated, nothing could be fastened between the 2 structures at all. The roof framing literally laid on the garage roof, with some intricate flashing. In all honesty for the amount of work it took, it would have been easier to tear the garage down & put frost footings under it. The only reason it wasn't is because it didn't meet current set-back requirements and the new garage would have been substantially smaller than the existing.


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## havalife (Mar 23, 2011)

ikessky said:


> The contractor that told me about this is a reputable guy and they've been in business since the 70's. He must know something about the codes, but what do I know?
> 
> I'm in northern WI, so freeze/thaw is a definite issue. I understand what frost heave is, but that's where my knowledge stops. Even with the heated structure/slab sitting on the ground, I still don't see what is going to stop the frost from going under the slab and pushing up from there. Unless we are assuming that the heated structure would keep a certain layer of unfrozen earth and moisture under the slab and when the frost pushes up, it would have some "give" to it and wouldn't move the structure above.
> 
> Either way, I think the proper thing to do is put the footings in. How about I go to sell the house and have to tell the prospective buyer, *"Yeah, it's a nice garage, but you have to keep it heated at all times so it doesn't mess up your roof line."*


:lol::lol: Classic I guess you answered your own question.


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## ikessky (Aug 24, 2009)

The question is not so much of "Can it be done this way?" It's more of "How would this work?" I guess on a larger scale, it's kind of like when you cover your carrots in the fall/winter with straw and then you can dig them all winter long. Except in this case, if you don't cover your carrots, they are going to mess your roof up!


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## tpolk (Nov 7, 2009)

much power outage where you are?


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## concretemasonry (Oct 10, 2006)

tpolk -

Good comment about the power outages. All it takes is a long period of not power or fuel to allow the frost to get under a shallow footing and cause long term damage to both the house and the garage.

I had a lake home in northern Minnesota and accidently hit the furnace breaker in October as I left. I finally got back in the area in late December and found the temperature inside was lower than I expected. Anything is possible if you rely on un-natural means to control conditions. Even a clerical/computer error could shut down a system.

Despite a few 3 or 4 day stretches of -0F weather, the temperature in the lake home only got down to 60F when the thermostat was set at 65F, which was surprising for uninsulated structure for about 3 months. I guess the all masonry structure had more thermal storage/inertia than I thought. In any event, if it can happen, it will happen eventually.

Dick


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## ikessky (Aug 24, 2009)

In the 8 years I've been in this place, we lost power once for about 30 minutes max. Also, I have a generator. I use wood heat in the house. Plans are being drawn up currently. I think I'm going to talk to the people that issue the building permit and the contractor, show them the code posted above and just tell them I want it done right the first time so I don't have to ever think about it again.


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## AGWhitehouse (Jul 1, 2011)

ikessky said:


> show them the code posted above and just tell them I want it done right the first time so I don't have to ever think about it again.


Sounds like the best plan. If you went with the non-footing you'd probably end up spending your savings rather quickly on continually heating the garage. With the footing, it's a pay once and done deal...


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## Joe Carola (Apr 14, 2006)

ikessky said:


> I think I'm going to talk to the people that issue the building permit and the contractor, show them the code posted above and just tell them I want it done right the first time so I don't have to ever think about it again.


Talking to the building department is what you're supposed to do anyway. No need to show them the code posted above because they will tell you what the code is.


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## jomama45 (Nov 13, 2008)

Joe Carola said:


> Talking to the building department is what you're supposed to do anyway. No need to show them the code posted above because they will tell you what the code is.


I take it you're not very familiar with Northern WI................


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## kjr6306 (Jul 29, 2011)

Have you considered a pole building with concrete floor?


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## Joe Carola (Apr 14, 2006)

jomama45 said:


> I take it you're not very familiar with Northern WI................


 Building department has no codes?


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## concretemasonry (Oct 10, 2006)

Joe Carola -

Just a clue, you are referring to the Republic of Wisconsin, as it was referred to a few years ago in a friendly way. They are famous for adding local conditions, but not always enforcing them. In the past they would poorly change the model codes and not realize the loop holes they created or that prevented some nationally known products from being used.

I am not far from northern Wisconsin and am there frequently. The knowledge and affect of the codes are hit and miss situation. - Good people, but poor administration and controls from the top.

Dick


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## not mike homes (Jul 22, 2011)

*Ive done it*

Ok here's the way it's done in northern Ont. Canada.
First your building dept. will give you what is required
in your area. In my case it required an eng. drawing of
the slab showing how it was to be done. This drawing
showed all insulation that is required around the slab 
and under it, pinning to the existing building ect. It 
also must be heated to a min. of 40 F all winter.
If there is little traffic around the garage the frost will not 
be a problem.
By the way the gentleman that said clay does not move
is out of his mind! It;s the worst there is! I've seen it heave
2-3 feet.

Hope this info is of some help


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## Tom Struble (Dec 29, 2008)

frost heave and expansive soil are 2 different things


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## jomama45 (Nov 13, 2008)

Joe Carola said:


> Building department has no codes?



In alot of the more rural areas of N. WI, there simply aren't building departments. Until maybe 5-8 years ago, most of these areas didn't even require building permits for new dwellings, much less remodeling, additions, alterations, etc... The state passed legislation requiring the entire state to require building permits & subsequent inspections at that time, but most areas never put together their own depts, so the state supplies them with the inpection companies. It's put out to bid on a multi-year contract, and the results are less than stellar. Oftentimes, the independent inspector is onlyy available 1 day a week, they can be very un-responsive, and typically won't help guide you along the way. They often feel their job only entails a "pass or fail" inspection, and it's up to you to do the legwork.




concretemasonry said:


> Joe Carola -
> 
> 
> 
> ...



See Dick, here we refer to it as "The Peoples Republic of Madison", as what happens there usually doesn't represent the balance of the state accurately. We do indeed have some differing "opinions" from inspectors on code issues, but they are fairly uniform from area to area.


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## Daniel Holzman (Mar 10, 2009)

*Clay vs. silt*

The comment that clay moves 2 - 3 feet likely refers to silt. Clay is a mineral that tightly binds water to it chemically. The water in clay is not free, and cannot freeze. Silt, on the other hand, refers to small (less #200 sieve) particles which do NOT bind water tightly. Silt is notorious for frost heave, as is very fine sand.

Unfortunately, silt and clay feel similar, and in some cases look similar, hence are often confused. There are sections of the US that have "red clay", which is often silt. So my point is that true clay almost never heaves, but since silt is often mistaken for clay, clay gets a bad reputation for frost heave.


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