Garage Slab 20' X 20' Edge Concerns

 
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Old 03-27-2010, 10:02 PM   #1
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Garage Slab 20' X 20' Edge Concerns


I am a carpenter by trade but have decided to build my own garage here in Ottawa. I will be using a 4" concrete slab on grade with 6" wide by 12" high perimeter wall to keep wood walls away from the ground. After digging down 2' of pure sand, I decided to stop, compact it and fill the hole with gravel. I plan on reinforcing the slab with 15M bars on 12" centers both ways and put two around the slab perimeter and one inside the perimeter wall. I will be building 10' high walls with 2X6 then put on the roof. There will be a 16' X 8' garage door for entry. I have never done any work with rebar or concrete before so don't know if this plan will be adequate? Should I thicken the slab around the edge or maybe the whole thing? Should I use more reinforcement or use it differently? It gets very cold here in winter (-30C) and hot in summer (+30C), should I use any expansion joints? Should I take special care at the opening of the garage?

The old garage was built around 1913 directly on the ground and held up until now. There was no bottom plate left and the stud ends were rotten. the whole thing sank at least 6 inches. I can't believe it lasted 100 years. I want the new garage to last even longer. Probably going to use pressure treated for bottom plate. The concrete is what worries me in this situation, don't want it to crack or crumble too quickly.
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Old 03-27-2010, 10:17 PM   #2
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Re: Garage Slab 20' X 20' Edge Concerns


Your local code will dictate how the footing should be done.
I like the idea of the footing to elevate the wall. Your rebar idea sounds a bit over kill. If your in rain country provide a depression in the slab where your door closes, about an inch deep, 6" wide and about 3" wider than your door opening to keep water out. Yes, use expansion joints. I'd also provide a 3'man door for entry.

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Old 03-28-2010, 12:52 AM   #3
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Re: Garage Slab 20' X 20' Edge Concerns


You can build a frost protected slab on grade if the building is heated.

http://www.nahb.org/assets/docs/publ...00244041PM.pdf

Last edited by mics_54; 03-28-2010 at 01:03 AM.
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Old 03-28-2010, 01:17 AM   #4
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Re: Garage Slab 20' X 20' Edge Concerns


dont belive it would pass code up here
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Old 03-28-2010, 09:25 AM   #5
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Re: Garage Slab 20' X 20' Edge Concerns


thickened edge slab detail for Canadian climate
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Old 03-28-2010, 10:30 AM   #6
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Re: Garage Slab 20' X 20' Edge Concerns


Quote:
Originally Posted by CanCritter View Post
dont belive it would pass code up here
#1) I wouldn't have suggested it had I thought it wouldn't.

#2) More than one million FPSFs have been built over the past
45 years in Norway, Sweden and Finland, where they have
been approved by code since the 1970s. In Scandinavia, the
method is standard practice for low-rise construction,
including homes, townhouses, shopping malls, stores, office
buildings and schools. In the lower U.S., an estimated 3,000
FPSFs had been built by 2000, including single family
houses, townhouses, housing for the elderly and disabled,
additions, apartments, stores, and other commercial
buildings.
Additional FPSFs have been built in Alaska and Canada.
The U.S. Army has built several FPSFs, including an
addition to a conventional deep foundation for an airport
control tower in Galena, Alaska, near the Arctic Circle,
where the frost depth is 13 feet and winter temperatures
reach -60 F for weeks at a time. No frost heave or differential
settlement has been observed. For more information
see www.geofoam.org/pdfs/CRREL9707.pdf.
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Old 03-28-2010, 11:01 AM   #7
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Re: Garage Slab 20' X 20' Edge Concerns


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Originally Posted by griz View Post
Your local code will dictate how the footing should be done.
I like the idea of the footing to elevate the wall. Your rebar idea sounds a bit over kill. If your in rain country provide a depression in the slab where your door closes, about an inch deep, 6" wide and about 3" wider than your door opening to keep water out. Yes, use expansion joints. I'd also provide a 3'man door for entry.
Yes, I forgot to say, there is a 3' man door at the left rear and window somewhere on the left side. I don't believe in overkill, only underkill. Rebar is already ordered so it is too late anyway. It will be here tomorrow. I like your idea for the depression at the door, will definitely do that. What spacing should be used for the expansion joints? Should they be in the floor and ledge? I have included pictures taken today to show what I am talking about. I will finish the ledge formwork around the right side today. We will be placing the rebar tomorrow.
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Garage slab 20' X 20' edge concerns-img_1754a.jpg   Garage slab 20' X 20' edge concerns-img_1755a.jpg  
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Old 03-28-2010, 11:05 AM   #8
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Re: Garage Slab 20' X 20' Edge Concerns


Quote:
Originally Posted by HHC View Post
I am a carpenter by trade but have decided to build my own garage here in Ottawa. I will be using a 4" concrete slab on grade with 6" wide by 12" high perimeter wall to keep wood walls away from the ground. After digging down 2' of pure sand, I decided to stop, compact it and fill the hole with gravel. I plan on reinforcing the slab with 15M bars on 12" centers both ways and put two around the slab perimeter and one inside the perimeter wall. I will be building 10' high walls with 2X6 then put on the roof. There will be a 16' X 8' garage door for entry. I have never done any work with rebar or concrete before so don't know if this plan will be adequate? Should I thicken the slab around the edge or maybe the whole thing? Should I use more reinforcement or use it differently? It gets very cold here in winter (-30C) and hot in summer (+30C), should I use any expansion joints? Should I take special care at the opening of the garage?

The old garage was built around 1913 directly on the ground and held up until now. There was no bottom plate left and the stud ends were rotten. the whole thing sank at least 6 inches. I can't believe it lasted 100 years. I want the new garage to last even longer. Probably going to use pressure treated for bottom plate. The concrete is what worries me in this situation, don't want it to crack or crumble too quickly.
Sounds good, 12"high curb maybee a little high, 8" above grade is a good alternative. I would pour a footing 36"depth or a 16"depth thicken edge, you can also run your rebar into footing and slab and pour it monolithic. A 4" concrete slab is good, 6 1/2 sac with 6% air, no10 wwm, and a fiber is good for a secondary reinforcement. I would not pour anything thicker, unless you plan on exceeding 4500psi. No need for expansion joint in slab.

Last edited by CONCRETE MIKE; 03-28-2010 at 11:56 AM.
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Old 03-28-2010, 11:10 AM   #9
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Re: Garage Slab 20' X 20' Edge Concerns


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Yes, I forgot to say, there is a 3' man door at the left rear and window somewhere on the left side. I don't believe in overkill, only underkill. Rebar is already ordered so it is too late anyway. It will be here tomorrow. I like your idea for the depression at the door, will definitely do that. What spacing should be used for the expansion joints? Should they be in the floor and ledge? I have included pictures taken today to show what I am talking about. I will finish the ledge formwork around the right side today. We will be placing the rebar tomorrow.
Not a bad set up, i would dig futher down below grade for a thickened edge. Are you going with a 12" over hang on front of garage? And are you going to have a 1" lip at front of the slab? I would also brace your outside walls better, i see that you are using 1" x 12" plywood for your outside forms, they might bow. Run your strong back and kickers every 2', it is better to over kick than under kick. I looked again at your set up, you need to run a strong back and kick at bottom and top, or your form work will bow and blow out. And for your inside curb forms i would also run some 3' steel pins to prevent bowing also. Well i see that you ran wall ties at the bottom, or are they spreaders?

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Old 03-28-2010, 11:40 AM   #10
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Re: Garage Slab 20' X 20' Edge Concerns


Here in cleveland ohio we also have alot of sand near lake erie and very bad winters, our local codes require a 36" footing on slabs 400sf or more. That is going to be a pain in the ass to strip and rub the inside walls, are you pouring the walls and floor monolithic? Remember most of your pressure will be at the bottom of your wall, brace bottom! Pour walls stiff and vibrate.

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Old 03-28-2010, 11:54 AM   #11
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Re: Garage Slab 20' X 20' Edge Concerns


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Originally Posted by CONCRETE MIKE View Post
Not a bad set up, i would dig futher down below grade for a thickened edge. Are you going with a 12" over hang on front of garage? And are you going to have a 1" lip at front of the slab? I would also brace your outside walls better, i see that you are using 1" x 12" plywood for your outside forms, they might bow. Run your strong back and kickers every 2', it is better to over kick than under kick. I looked again at your set up, you need to run a strong back and kick at bottom and top, or your form work will bow and blow out. And for your inside curb forms i would also run some 3' steel pins to prevent bowing also. Well i see that you ran wall ties at the bottom, or are they spreaders?
Digging at the edge will not be a problem, there is 30 tons of stone in this hole, 2 feet deep in some places. I will definitely do that today. I will have a gable roof, 4/12 pitch to not exceed height restriction, 2' overhang at front and 1' overhang at sides and rear. There is at least a 1" lip at front of the slab. The new driveway will be paved to meet in on a 1-2% incline. All formwork is 3/4" plywood. The outside forms are actually 3' wide, 2' below ground to the sand. We placed those before the gravel. The bottom of the outside form can't go anywhere as it is filled on both sides below grade. The top edge of the outside form is not fully braced yet. It may not show well in the picture but I screwed 6" steel ties at 3' spacing 1" above bottom of inside form to the outside form to prevent bottom of inside form kicking out. The top spreaders are spaced every 4'. All forms are screwed together with 1.5" screws. I will probably add a few 2" screws before pouring the concrete. Thanks for the advice. I must get out there and work!
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Old 03-28-2010, 11:55 AM   #12
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Re: Garage Slab 20' X 20' Edge Concerns


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Originally Posted by jlhaslip View Post
thickened edge slab detail for Canadian climate
Thanks for the detail! It makes sense. What do the blue lines represent? I assume the dots are rebar.
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Old 03-28-2010, 12:04 PM   #13
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Re: Garage Slab 20' X 20' Edge Concerns


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Here in cleveland ohio we also have alot of sand near lake erie and very bad winters, our local codes require a 36" footing on slabs 400sf or more. That is going to be a pain in the ass to strip and rub the inside walls, are you pouring the walls and floor monolithic? Remember most of your pressure will be at the bottom of your wall, brace bottom! Pour walls stiff and vibrate.
I was planning on pouring all at the same time , monolithic, but don't have the confidence to do it without an expert. I want to have it all set up properly then bring in a finisher to help on pour day. Was planning on renting a vibrator for sure.
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Old 03-28-2010, 12:05 PM   #14
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Re: Garage Slab 20' X 20' Edge Concerns


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Digging at the edge will not be a problem, there is 30 tons of stone in this hole, 2 feet deep in some places. I will definitely do that today. I will have a gable roof, 4/12 pitch to not exceed height restriction, 2' overhang at front and 1' overhang at sides and rear. There is at least a 1" lip at front of the slab. The new driveway will be paved to meet in on a 1-2% incline. All formwork is 3/4" plywood. The outside forms are actually 3' wide, 2' below ground to the sand. We placed those before the gravel. The bottom of the outside form can't go anywhere as it is filled on both sides below grade. The top edge of the outside form is not fully braced yet. It may not show well in the picture but I screwed 6" steel ties at 3' spacing 1" above bottom of inside form to the outside form to prevent bottom of inside form kicking out. The top spreaders are spaced every 4'. All forms are screwed together with 1.5" screws. I will probably add a few 2" screws before pouring the concrete. Thanks for the advice. I must get out there and work!
I see. Good luck, put expansion at front of garage where drive will meet garage slab.
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Old 03-28-2010, 12:09 PM   #15
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Re: Garage Slab 20' X 20' Edge Concerns


this is canada..not alaska sweden or germany so those codes arent prevalant here...l was just looking into building a garage a mnth ago in manitoba..they said no go for slab foundations...my foundation would have to be below the frost line to pass code....personaly ld sooner go with a slab as its cheaper and easyer but alas codes say no in Manitoba or l was missinformed...in anycase the codes across canada are pretty much standard so will have to look into it more and have sent inquireies to both Manitoba and Ottawa for clarification....do you have a building permit for slab on grade desighn?
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Old 03-28-2010, 12:18 PM   #16
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Re: Garage Slab 20' X 20' Edge Concerns


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this is canada..not alaska sweden or germany so those codes arent prevalant here...l was just looking into building a garage a mnth ago in manitoba..they said no go for slab foundations...my foundation would have to be below the frost line to pass code....personaly ld sooner go with a slab as its cheaper and easyer but alas codes say no in Manitoba or l was missinformed...in anycase the codes across canada are pretty much standard so will have to look into it more and have sent inquireies to both Manitoba and Ottawa for clarification....do you have a building permit for slab on grade desighn?
So you live on mars?
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Old 03-28-2010, 01:23 PM   #17
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Re: Garage Slab 20' X 20' Edge Concerns


if you have something inteligent to say please do...baiting me aint gona git you nowhere son
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Old 03-28-2010, 01:46 PM   #18
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Re: Garage Slab 20' X 20' Edge Concerns


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Thanks for the detail! It makes sense. What do the blue lines represent? I assume the dots are rebar.
the blue lines are re-bar running across the slab/footer.

used this design on my own shop/garage 5 years ago. a few hairline cracks popped up the first winter, but have not gotten any worse in 5 years.
Area it was built does not required a building permit, but I have done the same design in town several times under permit. no issues.

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Old 03-28-2010, 02:53 PM   #19
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if you have something inteligent to say please do...baiting me aint gona git you nowhere son
If I was baiting you I would have used a zara spook or a hj12 huskey jerk, with 10 lb spider wire!
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Old 03-28-2010, 04:13 PM   #20
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Re: Garage Slab 20' X 20' Edge Concerns


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Originally Posted by CanCritter View Post
this is canada..not alaska sweden or germany so those codes arent prevalant here...l was just looking into building a garage a mnth ago in manitoba..they said no go for slab foundations...my foundation would have to be below the frost line to pass code....personaly ld sooner go with a slab as its cheaper and easyer but alas codes say no in Manitoba or l was missinformed...in anycase the codes across canada are pretty much standard so will have to look into it more and have sent inquireies to both Manitoba and Ottawa for clarification....do you have a building permit for slab on grade desighn?
You are allowed to use slab on grade design for accessory structures up to 592 square feet. This applies to all of Ontario, I don't know about other provinces. I am waiting on truss drawings and will be issued permit when they are submitted. Check out: http://www.cambridge.ca/relatedDocs/...ril%202009.pdf
This is the best site I have found for garage requirements.

Here are some updated pictures of my garage. I haven't done the digging around the perimeter to give it the shape in the drawing posted a few above. That will be tomorrow's work.
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