Detach 48x28 Garage - Footings

[Pettrix]

About to break ground on my 48x28 detached garage and on my engineering footing schedule it doesn't show any footings where the two 18' wide garage doors are. I know they are not "required" as there is nothing being supported wall wise there but someone told me that it's "better" to pour the footing under those doors as to keep the whole garage footing as a rectangle, making it stronger. One would run the horizontal footing bars but no vertical bars would be run since there is no wall being stacked on top of that area.

Is that true? Should I run a continuous footing underneath the garage doors or stop at the door area, and then restart again?

My engineering calls for a footing that is 18" below grade, 24" wide, 12" tall, with three #4 rebars at the bottom of the footing. Garage will be ICF (Insulated Concrete Forms) so I will be stacking ICF (6" concrete core) for the garage walls. I am using 4,500 psi concrete footing pour.

 

[scootr]

That is correct. Pour a 12x12 footing under the doors and tie 1 or 2 rebar through so you have a complete loop around the perimeter for the strongest structure. ( Just my opinion from 45 yrs experience in this field)

 

[deezler]

In reality the floor slab you pour will support the vehicle in/out traffic just fine, and the rest of the foundation will not somehow just come apart because it's not tied together in a full rectangle. Its a huge concrete footer, full of rebar, it'll be fine. The purpose is to support the vertical weight of the building - there shouldn't be pressure trying to explode the footer apart horizontally.

Your location of "desert" implies dry, stable soils and I presume you will be doing proper compaction of all soils underneath the footer and then also the interior floor slab.

But! I would do it also, if the cost of extra concrete doesn't ruin you. You only get one chance, don't skip anything that could lead to regrets.

 

[Pettrix]

In reality the floor slab you pour will support the vehicle in/out traffic just fine, and the rest of the foundation will not somehow just come apart because it's not tied together in a full rectangle. Its a huge concrete footer, full of rebar, it'll be fine. The purpose is to support the vertical weight of the building - there shouldn't be pressure trying to explode the footer apart horizontally.

Your location of "desert" implies dry, stable soils and I presume you will be doing proper compaction of all soils underneath the footer and then also the interior floor slab.

But! I would do it also, if the cost of extra concrete doesn't ruin you. You only get one chance, don't skip anything that could lead to regrets.

Footings are poured on undisturbed native soil (once inspected by geo engineer). No fill or compaction is needed as long as the soil underneath the footing hasn't been disturbed after excavation. The interior slab (5") will have compacted 3/4"- AB (sand and 3/4" and smaller rock). Interior slab will be 5" thick, at a 4,500 psi mix, with #4 rebar at 24".

 

[Hay Dude]

I like having a footing under the opening. It supports the slab of concrete at the opening of the garage especially if heavy vehicles/equipment is entering there and keeps it from cracking or settling.

 

[scootr]

In reality the floor slab you pour will support the vehicle in/out traffic just fine, and the rest of the foundation will not somehow just come apart because it's not tied together in a full rectangle. Its a huge concrete footer, full of rebar, it'll be fine. The purpose is to support the vertical weight of the building - there shouldn't be pressure trying to explode the footer apart horizontally.

Your location of "desert" implies dry, stable soils and I presume you will be doing proper compaction of all soils underneath the footer and then also the interior floor slab.

But! I would do it also, if the cost of extra concrete doesn't ruin you. You only get one chance, don't skip anything that could lead to regrets.

The SW deserts are on the San Andreas fault. There are literally hundreds of fault line fingers running off of the main fissure. The soil is mostly sand and rock. No doubt that added $150 cost to pour a bond beam accross the 2 doorways at the weakest point in the structure is a reasonable caution in my opinion based upon 35 yrs building experience in this SW desert area. I've lived through more big quakes here in the last 45 yrs than I can name including the 7.3 Landers quake.

 

[deezler]

Good point, earthquakes are definitely not on our mind for building here in the midwest. Interesting that the engineer doing the plans found it unnecessary though.

 

[ponytug]

Good point, earthquakes are definitely not on our mind for building here in the midwest. Interesting that the engineer doing the plans found it unnecessary though.

Two words: "New Madrid"

Where were the largest earthquakes in the continental United States? (Hint--not San Francisco)

by Martha Hutchens Every now and then, a community has a terrible day. Or in this case, a terrible five months. Deposit Photos Our story st...

www.hhhistory.com

In addition to the size of the initial 1811 quake, there were reports of an earthquake every two hours for for five months.

I am not saying it should be top of mind for folks in the Midwest, but perhaps more top of mind than it is for most people. (tornados tend to be top of mind for me in the Midwest) I remember a small quake as a kid in the Midwest that jolted the house pretty good. The epicenter was over a hundred miles away.

FWIW: Earthquakes in the central part of the US tend to be felt at much larger distances. It is thought to be because many of them are caused by the North American plate cracking which then rings like a bell across the shield. The ringing tends to get buildings oscillating and that oscillation tends to increase the damage sustained for a given Richter level. That's one reason why buildings on fill do so poorly in earthquakes.

Did you know that Boston and San Francisco both have similar probabilities of Richter 7+ quakes in the next decade. Only one of them has seismic building codes...

Backto the OP's question
@Pettrix If you can afford it, I would definitely pour a footer across the door. It will be stronger, and will strengthen the floor, the driveway entrance ramp, and the integrity of the door.

All the best,

Peter

 

[deezler]

Yeah I'm aware of the New Madrid fault but thats like 700 miles from Michigan (I should have said "upper" midwest I guess). We occasionally get mag 2-3 quakes here but I've never even noticed one while it's happening.

Pattrix, sounds like a robust building coming together. Can you share some pics as things progress?

 

[LD1]

Have always done footers under the door. Even laid block under the door up to slab grade. We refer to that as a frost-wall. Laying block doesnt apply to you, as you are pouring walls.

Have you considered monolithic slab?