building foundation - concrete vs poles

[beer batter]

I'm been hearing a lot about pole shed style foundations for homes these days instead of the traditional concrete slab foundation. Price is the main thing I hear where you can save quite a bit of cash with the pole style foundation and just pour concrete in as the floor, but not intend to use it as a foundation.

My question, why are 90% of homes still using concrete slab foundations if the pole foundations are cheaper and basically just as effective?

If the house is going to be a single level home, what are the advantages/disadvantages for both?

[josterbauer]

It depends on where you are building. Most cities will not allow a residential living quarters to be built on poles. Yes it is going to be cheaper, just be sure to check the local building codes. One disadvantage is going to be the loss of heat from the floor side of it. It seems like no matter how well you insulate it will always be on the cold side. I work for a builder of 150 homes a year, and also design them as well.

[cementhead21]

I am not exactly sure what you are refering to in a pole shed type of slab here ,, but heres my 2 cents worth .Mostly i think it has to do with building codes in certain areas, most what you to have some sort of footing( which is smart)...There are many Slab on Grade types of homes going in all over Mn . Most have a engineered slab that uses and over sized footing and are designed to be used with in floor heat.In Northern St Louis county the vast majority of Homes for Habitat are being built this way ,,,In floor heating is a nice way to go ,, pretty cost effective also.. I have a friend who also puts up pole type buildings on the same type of slab system. and with the in floor heat wow is it nice to work off of...Also as i get older ,, i am tending to think of one level living is the way to go ,, I do right now have a print of this style of home that I am considering building,,, with the new high efficent boilers out there which are realy small it only makes sense to me to go this route.. hope that helps ya

[cementhead21]

 Originally Posted By: josterbauer

It depends on where you are building. Most cities will not allow a residential living quarters to be built on poles. Yes it is going to be cheaper, just be sure to check the local building codes. One disadvantage is going to be the loss of heat from the floor side of it. It seems like no matter how well you insulate it will always be on the cold side. I work for a builder of 150 homes a year, and also design them as well.

Joster,,, see post i made

[sparcebag]

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[Roofer]

We are in the process of bidding a large garage for RV's. For everything to be finished (like inside a house), it is cheaper with a slab and stick framed rather than finishing a Pole Barn. I know this is a different type of thing, but it gives you an idea.

I would rather have a cement foundation and a basement rather than wood.

[josterbauer]

I see the post that you made cementhead21, I was saying that the poles raised above grade is a colder option. My next home is going to have in floor heat in the foundation as well as the garage. A little more expensive to start with, but I think that it pays in the end. Also think of going with closed cell spray foam insulation. My opinion is the best way to go as far as insulation.

[beer batter]

Thanks for all the responses. To answer a few questions:

This home is being built in Pope County in the west central part of Minnesota where there is no restriction from building this type of structure.

I am also planning in-floor heat possibly utilizing geothermal (which I learned from some of you on a separate thread).

Single level to make access easier in our retirement years. No basement or upper level involved.

Roofer, from your entry am I to take it that it costs a lot more to finish the interior of the pole style foundation than a standard concrete slab/wood frame foundation? That's the first I've heard that it costs more to finish, I've only heard the other side that it's cheaper to build initially. Interesting, thanks for the input.

[hanson]

Beer Batter-

Could you explain a little better exactly how this construction system works? The way I'm understanding it now, you are building a "pole barn", pouring a slab, and then infilling in between all the poles with studs & insulation to essentially create your house.

If this is the case, I can think of a handful of issues right off the bat that would concern me, add to the cost, and/or make construction/finishing difficult.

The bottom line is most homes in our area are built a certain way because thats how they've always been done. When you are looking at labor costs on a project, the further you stray from "traditional", the more money a subcontractor is going to throw at it to cover any unexpected things.

We're definitely starting to see newer technology make its way into homebuilding but it didn't come easy. A few examples would be insulated forms for poured concrete foundation walls, structural insulated panels, TJI's (wood I-Beams). These are things that have taken awhile for contractors to adapt to and now they are commonplace.

[John Mickish]

The reason for a foundation is to keep the house from moving as much as possible. I have to believe that with a design like what you are talking about you will be repairing drywall cracks for the rest of the life of the house.

[hanson]

 Originally Posted By: mnfishinguy

The reason for a foundation is to keep the house from moving as much as possible. I have to believe that with a design like what you are talking about you will be repairing drywall cracks for the rest of the life of the house.

That is definitely one of the reasons I was going to mention.

We have one big enemy living in Minnesota and that is frost and the freeze/thaw cycle. Building Code requires foundation footings to be below frost depth. The depth frost penetrates is different from northern MN to southern MN so the typical depth of footings is different from north to south.

Like 'mnfishinguy" said, a continuous reinforced concrete footing acts as a system to combat differential settlement as well as spread the load from above to the soil. A pole system as a handful of concentrated point loads placed on the soil and is more susceptable to differential settlement. Quality of the soil and bearing capacity of the soil are important in a system that relies on point loads. You'll more than likely need engineered fill with very good compaction at the pole locations to prevent them from settling differently.

[beer batter]

Hanson, your description of building a pole shed, then a concrete slab, and filling in the gaps to finish things off sounds about right to me. I would also assume they'd have to fill in a class 5 (or something similar) under the concrete slab to help prevent frost heaving.

I don't know a whole lot about it other than I spoke with 2 different builders in that area that recommended looking into a pole shed style house foundation rather than the more traditional concrete slab foundation. Easy way to save lots of money, but they didn't go into a whole lot of pros and cons. They each said from the outside looking at the house, you can't tell it's pole foundation. The differences lie between the walls and under the concrete floor.

That's why I created this thread, to find out more about the pole style foundations. So much knowledge on this site, I figured someone would have some background on them.

[cementhead21]

Here is the design that is being used in northern mn right now for in floor heated slabs.. It is a 6" slab with a thickened edge that is 24" x 20". The this design calls for 4 #4 rebar in the footing with hoops 24" oc and #4 rebar 24" oc in the main part of the slab. The heating tubes are placed on top of 2" of high density foam.. This is a engineered slab design with 4000psi concrete mix.

Personally I would go with a 6" sand base over the foam and tubes. I would also go with a 16"oc rebar pattern.This not only creates a larger thermal mass, but also places tubes low enough that you dont have to worry when anchoring all the walls..

Things to consider in this type of building are : Heating, the heat is not instant. It takes time to heat that mass. : Cooling, I personally do not know of a central air unit that would work .It also takes time for the mass to cool down.

Hope this helps ya out also ,, if you got any other questions feel free to ask .

Oh and Beerbater.. concrete is only as strong as the base it is poured on.. and you can place poles for old style pole building or i would suggest doing normal stick framing and sheeting it with steel panels

[Roofer]

Beer batter, it is less expensive to finish a stick framed building than a pole building. being the pole building you would have to frame all the walls and ceiling in afterwards, your savings is gone. If it is going to be an open building with no heat, the pole building is cheaper.

I finished my pole barn and it is nice IMO, but a stick framed building would actually be better.

Building from new, and completely finishing, it is cheaper to build a stick frame garage. It also looks nicer and can match your house closer. I also feel much better with shingles and siding rather than pole building tin.

[sparcebag]

concrete is only as strong as the base it is poured on..

What about bridges,poured ceilings????

[cementhead21]

 Originally Posted By: sparcebag

concrete is only as strong as the base it is poured on..

What about bridges,poured ceilings????

Now you are going into mix designs of concrete and renforcement... even in poured floors that also serve as a ceiling there are columns that are placed that are tied in with rebar,, Those columns are typically placed on a large footing for large buildings, Or on a pile cap. which we are now traveling into an area that this post is no where near needing unless he is building in a area with problems to start.. take a look at what they are doing on the supporting of the new I35 bridge..... Remeber this also ,, concrete does not reach its full strength until 28 days have past and it has cured out.. in most cases concrete cured under water is the strongest...

Gee i wonder how i came up with the name i use here , think it may have something to do with something i have worked with all my life

[sparcebag]

Cement thought I'd ask I worked on most bridges from Denver to Eisenhower tunnel I-70 and the tunnel also.So some crete doesnt need a base only designed support system.

[FishDepot]

Beer Batter, Hanson is really correct in his rendition of the construction requirements. In addition, even though Pope County is a non-code area of the state, all residential building contractors (with few exceptions) are required to build to code, regardless if permitted and inspected - or not. Ultimately, they can be held liable for code violations, even in a non-code area of the state (based on consumer complaint). Make sure you hire licensed residential building contractors for any work you contract out.

The MN Energy Code requires the heated dwelling to be insulated to frost depth below gound - either vertically, or as an alternative, down to a certain depth and then out horizontally below grade. That means around the perimeter down 42" deep (in Pope County). As I said, there are code alternatives that allow for slab on grade construction, but what you describe does not sound as if it fully meets code. You may want to call the Minnesota Construction Codes & Licensing Division at 651-284-5068 for specific details on what is required. Ask to speak to a residential building code representative or the energy code specialist. They will give you the specific requirements and direct you to additional information sources on approved slab on grade construction. Heated slabs (with hydronics) are not abnormal by any means. They are in fact, very common. Nevertheless, you still need perimeter building foundation insulation per the energy code - even in a heated pole shed style building.

Another note. Build a 100% code compliant home. If you do not, you may have re-sale or other liability issues in the future. And,... oh yeah,... your castle will be much safer for you, your family, and all your friends. I could say more, but I'm here for fishing info. Good luck!

Fish Depot

(one of those helpful code guy's during the day, an average wanna-be fishing guy any other time)

[beer batter]

 Originally Posted By: FishDepot

As I said, there are code alternatives that allow for slab on grade construction, but what you describe does not sound as if it fully meets code.

I wouldn't base my description on whether or not code is being met. I'm a computer guy, I'm sure my description is far from reality. Thanks for the helpful suggestions though.

[cementhead21]

Fish ,,, In the design that i posted above , there is 24 " of 2 " foam around the peremiter of the slab.. Now i have seen some where they place (horizontally) 4'x8'x 2" foam sheets under the dirt grade around the slab also..In fact if braced correctly you can use the foam as forms for the slab instead of useing something like simons(sp)pans or building stiff back forms... As a matter of information Fish ,, I heard from a very reliable source that Mn Power requires you to use the extra 6 inch sand base( larger heated mass) when installing in floor heat with the design i mentioned.

Fish,,, One other comment I have about the design i posted ,, From your post I took it to mean that it may not be in line with the state codes.. This leads me to this question for you ... Do you realy think that an organization such as Northern St Louis County Homes for Habitat would be building homes (with the design i mentioned) that are not in MN Code? This would Also mean that many of the city and county building inspectors are not enforcing the codes across the iron range area .I will agree with you that in what Beer Bater is thinking about may not be in code(and probly isnt).

Sorry if i got the wrong take on this,, but it is my first impression

[FishDepot]

Cementhead21: The MN Energy Code currently (prescriptively) requires foundation insulation installed vertically around the perimter of a heated building down to the frost depth. It goes on to tell you that for slab on grade construction, you can run R10 down vertically to the base of the heated slab and then horizontally (out) for a distance equal to the design frost depth. It does not allow for any other installation practice.

In my original post, I used the word "alternative." This was on purpose, because many code officials will allow slight deviations to the specific requirements - just as you reference - but as an "alternate" to the code. MN HUD, and Habitat, both have slab on grade home designs that have been reviewed as a alternative designs. They have features that have been deemed to be "equivellant" to what the specific code requires, so they have generally been accepted around the state. I happen to know that for one of the referenced agency's homes, soil type is a big factor in this alternate design though. So as you can see, not everything is equal with slab on grade construction.

Another note,... an "alternate to the code," is project and site specific. Each project must prove within its own merit that it is equivellant or better than what the code expects. If the local code guy agree's, they will usually allow it. As for the sand layer thing, the code has never specifically required a "sand base" under a building slab or footing. Although usually considered good design practice, it is normally done due to poor soil conditions or for the proper/easier leveling of the base material underneath the construction. If some power agency wants more sand bedding for these buildings, and if they have some kind authority to require it, I say give it to 'em. Maybe they own the sand supply company along with the power plant.....

Good fishin'