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Concrete pad foundations?

P

parkland

Member
Joined
Nov 12, 2014
Messages
15
Location
Canada
I was hoping to get some input on this.

We just purchased some land in BC, and planning building site for the future.

This home isn't being built right now, but here is what were planning anyways.

What we were thinking, is a quonset home, not round, but where the sides are angled about 20 degrees, and the roof is about 40 degrees.

From what I've been told, this is the only style of metal building that can handle the snowload and have an importance factor of "1".

Or in other words, the rating of a home residence.

Where were building, there is no zoning. So aesthetics don't matter.

I actually think it will be a neat home, with lots of windows in the front facing the lake.

Maybe a 50x120 building, with a divider so the rear portion can be a large garage and shop.

We are planning to spray foam the entire metal building, installing wood stringers on the inside just strong enough to hold wall covering.

That seems to be the simplest most reliable method to go about this building type.

My main question, is the foundation.

The metal structure would be forcing outward, as the weight of the metal and snowload would force the walls outward.

So it seems to me like pilings are not a good idea, not only would they possibly shift outwards, but the building needs to be fastened along it's length, not just pilings.

To make it work, the pilings would need a footing poured across the top of them, also would need some type of tension cables from side to side,

to counteract the forces of the walls pushing the pilings outward. Seems elaborate and expensive.

I am really thinking the best way, might be a pad foundation. The pad foundation would provide the strength needed, and the mounting capability.

I have been reading, and I can find some information about pad foundations for homes, but it seems to be rare, so hard to learn much.

Ground contact foam seems to be key, to disrupt the freeze line under the ground under the pad.

A pad foundation seems like it would be ideal for this home, it could be poured over foam boards, and run in floor heating tubes when pouring it.

So wondering if anyone has any ideas or thoughts to say about this.

I have worked in construction when I was younger, I remember building a heated garage with in floor heating, the floor was 4" thick, but the edges went up to 6" thick

to support the wall weight. I'm basically thinking of the same design, but up-size the dimensions to accomodate the weight.

The goal is to have a long lasting home, little to no maintenance, and simplicity in design and construction.

With the metal building and closed cell spray foam, we should really never have to worry about things like moisture barrier or insulation installation quality.

With the pad above grade, and foam under it, along with plastic moisture barrier, we should never have any humidity coming in.

The pad brings up a different set of problems, like either elevating showers and toilets and running plumbing over the pad, or building a sub-floor.

Thoughts?
 
Hire an engineer to advise you and help prepare the construction documents.
 
As Mark K suggested, "hire an engineer!"

An engineered slab would be in order IMO. May have to have Styrofoam on the sides of the slab as well?

ICE must have dined at Denny's, yesterday, 23 hours ago?
 
Have your engineer start by looking here.....

R403.3 Frost protected shallow foundations. For buildings where the monthly mean temperature of the building is maintained at a minimum of 64°F (18°C), footings are not required to extend below the frost line when protected from frost by insulation in accordance with Figure R403.3(1) and Table R403.3(1). Foundations protected from frost in accordance with Figure R403.3(1) and Table R403.3(1) shall not be used for unheated spaces such as porches, utility rooms, garages and carports, and shall not be attached to basements or crawl spaces that are not maintained at a minimum monthly mean temperature of 64°F (18°C).

Materials used below grade for the purpose of insulating footings against frost shall be labeled as complying with ASTM C 578.
 
What is the soil like there? if you have lots of rock it shouldn't be a problem compared with places with lots of clay.

Unfortunately I don't have a whole lot of experience with the BC building code, but the National Building Code would require a a structural engineer to design the slab with integral perimeter footing (commonly called a thickened edge slab). The engineer will give you what the expected bearing capacity of your soils are. Then you need a geotechnical engineer to evaluate the soil on site and make sure the bearing capacity is reached, either naturally, or by removing the poor material and importing and compacting suitable material.

Generally steel buildings like this come with stamped plans and may or may not include foundation plans.
 
steveray said:
Have your engineer start by looking here.....R403.3 Frost protected shallow foundations. For buildings where the monthly mean temperature of the building is maintained at a minimum of 64°F (18°C), footings are not required to extend below the frost line when protected from frost by insulation in accordance with Figure R403.3(1) and Table R403.3(1). Foundations protected from frost in accordance with Figure R403.3(1) and Table R403.3(1) shall not be used for unheated spaces such as porches, utility rooms, garages and carports, and shall not be attached to basements or crawl spaces that are not maintained at a minimum monthly mean temperature of 64°F (18°C).

Materials used below grade for the purpose of insulating footings against frost shall be labeled as complying with ASTM C 578.
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Canada does not have any provisions similar to this one.
 
tmurray said:
What is the soil like there? if you have lots of rock it shouldn't be a problem compared with places with lots of clay.Unfortunately I don't have a whole lot of experience with the BC building code, but the National Building Code would require a a structural engineer to design the slab with integral perimeter footing (commonly called a thickened edge slab). The engineer will give you what the expected bearing capacity of your soils are. Then you need a geotechnical engineer to evaluate the soil on site and make sure the bearing capacity is reached, either naturally, or by removing the poor material and importing and compacting suitable material.

Generally steel buildings like this come with stamped plans and may or may not include foundation plans.
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Depending on the location on the lot, some places are shallow sandy loam, other places it's rock, as in mountainside rock.

I don't believe theres clay.

I believe it's shallow enough that you could excavate to the rock, and pack a-base tight with a packer to grade it.
 
The engineered plans often come with the building, but I don't necessarily think they have longevity in mind.

If I recieved engineered plans for a pad, would it require another engineer to re-stamp it, if the thickness was increased for example?

I don't know how practical it would be with the insulating foam going into the ground around the foundation, as there is lots of rock.

I was sort of visualizing this as a thickened edge slab, that would float on foam panels.

Now that I'm thinking about it, it seems like a stupid idea.
 
parkland said:
The engineered plans often come with the building, but I don't necessarily think they have longevity in mind. If I recieved engineered plans for a pad, would it require another engineer to re-stamp it, if the thickness was increased for example?

I don't know how practical it would be with the insulating foam going into the ground around the foundation, as there is lots of rock.

I was sort of visualizing this as a thickened edge slab, that would float on foam panels.

Now that I'm thinking about it, it seems like a stupid idea.
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It would depend on your inspector. Most are ok as long as you are meeting the minimum requirements the engineer specified for the construction.

The foam could work as long as it has been tested for the loads that it would be exposed to (that's a big if). The only issue would be in the energy efficiency portion of the code. 9.36 has some pretty specific requirements for integral perimeter slab on grades which generally include insulation on the face of the concrete and sloping away at an angle from the bottom of the footing (skirt insulation)to prevent heat from short circuiting around the insulation. you could likely convince your inspector that this complies as an alternate solution by drawing similarities between provisions requiring insulation below regular basement slabs.
 
Looks like you Canadians have put your "Tuques" together on this one. :0

Could you heat the slab, like they do inside a car wash bay?

pc1
 
Pcinspector1 said:
Looks like you Canadians have put your "Tuques" together on this one. :0Could you heat the slab, like they do inside a car wash bay?

pc1
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The main problem is the energy code. You could heat the slab, but it would be required to be insulated underneath. To deal with the perimeter footings we still would need skirt insulation around the exterior according to the black and white of the code. The other possibility would be a performance based design completed by an energy advisor. That actually might be the bast way to gain compliance with the energy code for this type of construction.
 
I just realised a "thickened edge" slab has an inherent flaw for this type of building;

All the weight from the steel arches would apply along the outermost edges where the concrete is thicker, but with foam under the whole works,

I can see the outsides sinking a touch as the foam compresses, and causing cracks along the ouside walls close to the thickened edges.
 
parkland said:
I just realised a "thickened edge" slab has an inherent flaw for this type of building; All the weight from the steel arches would apply along the outermost edges where the concrete is thicker, but with foam under the whole works,

I can see the outsides sinking a touch as the foam compresses, and causing cracks along the ouside walls close to the thickened edges.
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Generally, with this type of construction you would not apply foam below the thickened edge, just under non-loadbearing sections of the slab, hence the requirement for skirt insulation. If you found an appropriate high density foam you could have a low compression if placed below the thickened edge, but I wouldn't hold out hope.
 
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