Foundation vs. Engineered Pad

[wonderfred]

Well - coming down to some finer details of my future garage but am torn between having a foundation (footings 4 ft. under ground and 1 ft. above) vs. an engineered pad (17" edge thickness).

My garage will be 35.5 ft. deep and 28 ft. wide allowing me to be just under 1000 sq. ft. which is what I am allowed. It will be 20 ft. to the peak with a walk thru attic truss. Probably going with garage doors (10 ft. wide and 9 ft. high). This should leave me with about 10.5 ft. ceiling and about 9 ft. floor to peak on upper floor.

I plan on insulating (live in Ontario) and will use 2x6's. There will be steps going up to the attic at the rear.

Just wondering what your thoughts are on the engineered pad vs. footings? And any other input would be appreciated. Thanks

 

[wildstyle]

I just built a 28x36 shop in BC and every contractor that bid on the job quoted on full foundation, including some very good friends that I trust who I ended up hiring to do the job. So that was the way I went.

 

[GYPSY400]

I'm in Ontario too.. My floor is an engineered slab with pretty much the same specs and size as you.. Check out the link in my signature, there are a lot of pictures there.


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[yeldogt]

I was thinking of doing one for a small addition a few years and ran into problems with my town. They wanted more engineering vs typical footing/ walls and I still had no guarantee of success ..... the cost savings of the mono pour evaporated. Did a typical setup.

If you need inspections and these are used around you then you may have a better outcome

 

[Kamn]

i did an engineered slab for my garage, kind of wishing I had done a foundation with footings as I am getting some cracking and a little heaving
Planning on changing it in a year or two, raising the structure and then digging down for footings and foundation

my 2 cents

And I'm in Ontario as well

 

[Elginz]

If you would be welding, it would be nice to have a couple inches of cement wall above the floor to keep embers from getting in the wall floor connection, also to keep the wall dry if using water inside. Just another reason to go with the footing. I did the slab with a 3" high curb.

 

[Jlbc212]

I also had a 1000sqft size limitation for my garage. It is 35'8" x 28'. Thankfully the height limitation was 25'. I had to build it into the side of a slope. I had about a 5' change in elevation from the back left corner to the front right corner. Consequently, I have a full foundation 10" thick and a minimum 4' below the surrounding grade. Make sure if you do an engineered slab, that the perimeter is at least 12" above the surrounding final grade level. This is absolutely necessary (IMHO) to keep the sill dry at all times. More height, 18" to 24" would be better. If I had a more restrictive height limitation, like you do, I would have foregone the attic to ensure that I had adequate height inside the garage to install a two post lift (scissor trusses instead of attic trusses). I also have 12' wide by 10' high garage doors. If you have a standard size pickup truck, you will greatly appreciate the wider door opening.

 

[earthworks]

In north western Ontario a frost garage wall foundation has to go down 4.5' and costs about 50% more in concrete alone. For that reason most garages (includingmy own) are built on slab on grades w/ 12" club footing. Our municipal building department only requires engineering for none conventional slabs as long as the truss width doesn't exceed 32'. Cracking only becomes an issue worth improper concrete mix ,insufficient compaction, or building on improper native soils. If your not on good non frost susceptible gravel or sand, then Make sure to excavate at least 1.5' and import good pit run while compacting in at least two lifts. Also insure that downspouts and drainage grading keep the area from remaining saturated as frost heading won't happen in dry gravel conditions. Built right it should perform as well as a frost wall and save you thousands.

 

[dirttracker18]

Also in Ontario and I just used a club footing. I had to have a permit and inspection and the municipality and inspector were fine with it.

I am 30 X 36 and in a deep frost region. I have had no issues with movement or settle at all. I can count the number of very fine hairline cracks in my floor on one hand with leftovers.

I am not sure what the benefit of your options presented will be other than a much higher cost?

 

[Radix2]

For those who have "engineered pads" - did your builders follow the specs for a "frost protected shallow foundation" - i.e the use of insulation below grade and outside of the foundation to prevent frost from forming under the pad ?

specs are here - and note that there are designs for both unheated and heated buildings - http://www.toolbase.org/PDF/DesignGuides/revisedFPSFguide.pdf


I did take a look at Gyps400's build and didn't see any insulation placed outside the perimeter - I think this is a major oversight that builders are making - perhaps inspectors are allowing this under rules that don't require proper foundations under garages vs. living spaces? With good well-drained and naturally frost heave resistant soils, you can have a good result even without proper design features (as many old SOG garages will attest).

 

[mostheman]

i did an engineered slab for my garage, kind of wishing I had done a foundation with footings as I am getting some cracking and a little heaving
Planning on changing it in a year or two, raising the structure and then digging down for footings and foundation

my 2 cents

And I'm in Ontario as well

I have the same results. Mine (constructed by Previous Owner now 6 years old ) is on engineered slab on a gravel pad that had been build up from imported material. Cracking and Heaving in the centre.

If I were to do It I would do a frost wall and have a Knee wall 1 to 2 feet above the slab. It makes for a much nicer end product and don't have all the slush and water melting off your car running to the wood walls.

 

[wonderfred]

Thanks for all the excellent info...I am waiting for an estimate for both. Now kind of leaning towards the foundation. Thanks again.

 

[Radix2]

Thanks for all the excellent info...I am waiting for an estimate for both. Now kind of leaning towards the foundation. Thanks again.

please let us know the results and what building techniques are included in the comparable quotes

 

[machsnell]

Footing and block for a building that size will be more but not substatially. I am concrete guy and I like the thought of having my walls on non freezable ground. On the other hand if you import stone compact REALLY well and keep it dry and insulate then you would be ok. Insulation is key for both on cracking. Request rebar and microfiber in you slab and up the concrete to 4000 or 4500. All of those don't increase price substatially but add a great deal to the strength and survivability of your concrete slab.

 

[BeachBoy]

For those who have "engineered pads" - did your builders follow the specs for a "frost protected shallow foundation" - i.e the use of insulation below grade and outside of the foundation to prevent frost from forming under the pad ?

specs are here - and note that there are designs for both unheated and heated buildings - http://www.toolbase.org/PDF/DesignGuides/revisedFPSFguide.pdf


I did take a look at Gyps400's build and didn't see any insulation placed outside the perimeter - I think this is a major oversight that builders are making - perhaps inspectors are allowing this under rules that don't require proper foundations under garages vs. living spaces? With good well-drained and naturally frost heave resistant soils, you can have a good result even without proper design features (as many old SOG garages will attest).

my builder does insulate past the foundation (horizontal). I have posted a few pictures somewhere on this forum.

 

[earthworks]

Around my slab I used 2"vertical insulation and 4"horizontal (wing) 4' out. Is not done exactly according to fpsf model, but very close. It is the standard commercial engineered method for our region though. Most large commercial shops, garages and hangars are constructed with this insulation and club footings.
I'm Also a ********, and with concrete in our region at $210 / yard, there's no way a frost wall foundation would be comparable in price to a slab.

 

[Beemer533]

Those of you with engineered slabs talking about keeping the walls dry, why couldn't the OP just lay a "stub" wall on the perimeter (poured or block) and then just frame on that like you would on a regular foundation?

Maybe I am missing something..

This post edited by the NSA

 

[Jlbc212]

Around my slab I used 2"vertical insulation and 4"horizontal (wing) 4' out. Is not done exactly according to fpsf model, but very close. It is the standard commercial engineered method for our region though. Most large commercial shops, garages and hangars are constructed with this insulation and club footings.
I'm Also a ********, and with concrete in our region at $210 / yard, there's no way a frost wall foundation would be comparable in price to a slab.

WOW! I paid $105/ yard for 5000psi concrete last summer. Water and cement must be awfully expensive there!

Those of you with engineered slabs talking about keeping the walls dry, why couldn't the OP just lay a "stub" wall on the perimeter (poured or block) and then just frame on that like you would on a regular foundation?




Maybe I am missing something..

This post edited by the NSA

Ideally, it should be monolithic from bottom to top. But, I suppose you could apply some waterproofing material along the exterior seam between the block and the slab.

 

[ddawg16]

My slab goes down 3' with 8" stem walls





It was all poured at once. While we don't have frost heave, we do have expansive soil.

I'd go footings any day...with stem walls. It gets all that wood up above grade (and water)

 

[GYPSY400]

For those who have "engineered pads" - did your builders follow the specs for a "frost protected shallow foundation" - i.e the use of insulation below grade and outside of the foundation to prevent frost from forming under the pad ?

specs are here - and note that there are designs for both unheated and heated buildings - http://www.toolbase.org/PDF/DesignGuides/revisedFPSFguide.pdf


I did take a look at Gyps400's build and didn't see any insulation placed outside the perimeter - I think this is a major oversight that builders are making - perhaps inspectors are allowing this under rules that don't require proper foundations under garages vs. living spaces? With good well-drained and naturally frost heave resistant soils, you can have a good result even without proper design features (as many old SOG garages will attest).

If you look at the pic below , you will see 2" foam along the stem wall.. This was installed after the forms were removed. Granted I don't have the insulation horizontally in the ground around the perimeter , but there is no where on my pad where cement touches dirt.



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[gdh33]

I had my pad poured last year, 30' x 40'. I looked at slab vs foundation and is was 1/2 the price and the most common method for unattached residential garages around here (northern ontario). My patio and half of my driveway are poured concrete and they are crack free and have not heaved, except one corner of my driveway from water issues. That is what sold it for me. Pad did not need to be engineered (because they are so common around here) and like earthworks said, a frost wall foundation required twice the amount of concrete, so twice the price. I am going to build a concrete curb around the perimeter of my pad to raise the wood higher from the ground and for see no problems.

edit to say: No insulation under the pad, plan on insulating around the perimeter and horizontal wings this year.

 

[Jlbc212]

One more thing to consider - I see lots of people using ridgid foam board insulation on their foundation wall or slab curb. Carpenter ants love the stuff. If the insulation is placed right up to the wood sill, it provides an unseen (to you) path for the ants or termites to infest the wood frame.

 

[BeachBoy]

we don't have termites in our northern weather.

we have flys, mosquitoes and ladybugs... all no issue for wood.

and in winter.. absolutely nothing

 

[NUTTSGT]

You guys up north get way more cold temps and frost than we do down here in Ohio. I'd still prefer to have a foundation wall that goes down and a short stem wal lthat goes aup above the floor for the wall to sit on.

 

[Radix2]

If you look at the pic below , you will see 2" foam along the stem wall.. This was installed after the forms were removed. Granted I don't have the insulation horizontally in the ground around the perimeter , but there is no where on my pad where cement touches dirt.

I saw on your build thread that you are well insulated to keep the cold out of your building.

The horizontal insulation is not really related to that however - it is the design feature that is intended to replace the normal below frost deep footing.

In the case of a deep footing, it is the depth that makes sure the footing will not get frost under it to heave and crack.

In the case of a frost protected shallow footing, it is the horizontal insulation that creates the frost free area under the foundation at the building edge.

Without the horizontal insulation, the ground can freeze under the perimeter of the building, there is no protection from the vertical insulation, and the slab is unprotected until well under the building.

As folks have mentioned, driveways, garages of all sorts usually get away without heaving with no protection or deep footings - and many building codes allow construction of garages without proper footings - but to me these are not Apple to Apple comparisons - the deep footing is engineered to prevent the issue, the FPSF is engineered as well - a shallow foundation not incorporating specific elements is relying somewhat on luck to work properly.

It could be argued that extensive free draining base might be a frost heave prevention element, but there are no generally accepted standard designs based on that that can be inspected for that I know of (anyone know of a third option to deep footings or FPSF?)

If you look at the design guide for FPSFs, it should possible to add the horizontal protection to an otherwise insulated slab to move the frost zone away from the walls.

 

[dirttracker18]

I'm not sure why you are ignoring a much more cost effective club footing. I am in a deep frost zone and EVERYONE builds garages with club footings here without any issues.

 

[Radix2]

I'm not sure why you are ignoring a much more cost effective club footing. I am in a deep frost zone and EVERYONE builds garages with club footings here without any issues.

Who's ignoring it?

A club footing or thickened edge slab foundation is what the op is talking about I believe ? It is also what the FPSF is based on. The issue is that a common club foot foundation has no protection against frost damage and is not appropriate/code compliant for living space in frost zones.

It doesn't make sense to me to compare a frost proof deep foundation with a foundation only allowed for sheds and garages in these zones. Especially when there is an engineered solution for shallow foundations in cold areas available - although in many jurisdictions it is new and not well understood.

As far as "everyone with no issues" - there are posts on this very thread with people living with issues in their garages.

I can see taking the chance on a simple garage or shed, but for a fancy garage journal project, I'd want to take a look at the cost to engineer out the possibility of having frost damage.