PDA

View Full Version : One course of block


Burt
08-01-2008, 11:34 AM
Hello All,

Novice here. I have helped friends over the years frame their cabins and garages but have never laid any brick.

I am building a garage. I am having a concrete slab poured by a contractor but I am planning on doing the rest of the work myself (with friends).

I need to lay one course of cinder block which my sill plate will rest on. First can a novice to this? Seems like a fairly straight forward project ... basically making sure everything stays level.

Do I need to anchor this one course of block to the slab? If yes, how is this done? Drill holes ... place rebar ... secure with cement (or epoxy?) ... set bricks ... fill brick cavity with concrete? How many feet per anchor? (the garage is 36'x24')

Also, I will be using 2x4 studs, what size cinder blocks should I use? Should I use the standard 8dx8hx16w or 6dx8hx16w?

Thanks for your advice.

Burt

Richard A Hetzel
08-01-2008, 12:57 PM
Depending on where (what region?) you live, the block may need to be carried down to below frost level, not just built on the slab. Also, the slab should not rest on the foundation, it should be entirely within the foundation. Building a course of block on the edge of a slab and then building a superstructure above that will almost guarantee cracks in the slab. I think you need some advice from a qualified design professional, so you don't make expensive and senseless mistakes in construction. How do you plan to build the roof over the 36x24 space? Clear-span trusses? If so, the loads on that slab edge will be considerable, and the slab will crack. Worse, the edges may settle also. How about the garage doors? Are they in a load-bearing wall, and who will design the headers for them? If not clear-span trusses, then who will design the center girder? Who will design the foundations for the columns that support the center girder? Your original question suggests that there are some major design issues that haven't been addressed, and the time to do that is before you start building. Paper is cheap; wood and concrete are expensive.

concretemasonry
08-01-2008, 01:22 PM
What you are proposing in a very common form of construction in many areas of the country. It just makes sense to have a floor that can be cleaned easily and can give you additional headroom if desired. You can also get a door that gives you a higher opening , if desired.

The additionof one course does not add any appeciable load to a proper garage slab, since the wall and roof loads are really the same. In many cases, the 8" block spread out the load from the 2x4 stud wall and improve the situation. - That is from an experienced, qualified engineer. The garage structure above is the same irregardless of the extra course of block. just make sure your garage and slab are designed/constructed properly.

Since your garage must be anchored to the foundation, the easiest and most logical mentod is to use longer anchor bolts projection so the block can be laid over the bolts and the sill bolted to the foundation is that way. It is best to fill the cores with bolts in them. The block can be either 6" or 8" thick. Some people often choose to use a 4" or 6" high block in place of a traditional 8" high block, but that is a personal choice. An additional benefit of the course of block is that the raised sill provides extra insurance at a man door on the walls other than the front in case the grading and drainage is not ideal in the future.

As I said, this is very common in many areas and your building official or builder should be familiar with this long accepted practice.

Richard A Hetzel
08-02-2008, 04:32 AM
I stand by my post. I can't tell you how many times I've seen something done wrong, and heard "Oh, we've been doing it that way for 25 years," Longevity doesn't equal correctness, unfortunately.

concretemasonry
08-02-2008, 08:38 AM
Every area has its own needs and ways of building.

This morning, I was consulting on a $1.5 million home that used a 1 course concrete block curb in the garage to protect the wood and make the cleaning easier.

On the home, the attached 3 car garage had a course of 6" block laid on top of the monolithic floor frost/wall, but it could have been a poured foundation with a slab poured on top since it was a poured foundation. - Already backfilled. The anchor blocks appeared to be set using epoxy to eliminate the need for setting them during pouring the concrete (chalk marks on the poured floor to located the bolt loacations). All the framing above appeared to be normal.

The detatched 4 car garage had 8" block foundation/frost walls at least 5' below grade with a 8" high course of block above the floating slab inside the block walls. All the cores of the block were filled, but that may have been done for cleanliness and ease of construction. These anchor bolts extended full depth into the wall below. The owner is a car entusiast, so the floating slab was insulated and had radient heat installed. Obviously, the course of block was done for ease of cleaning and to keep the finsihed floor level near the exterior grade, but provide enough elevation to keep the wood at the required distance above the exterior soil. This door was oversized for height because of the need for a higher opening and interior headroom.

There are many ways to build correctly.

Dick

Richard A Hetzel
08-02-2008, 01:17 PM
The original question was about placing one course of block on the edge of a slab, with no mention of any foundation, stem wall, slab thickening, or anything else...just a slab with a block on its edge, with roof load coming down on it. We don't know what region, we know very little other than what was posted. Sure, if there is a foundation, or even monolithic stem walls, it's a whole diofferent animal, but that's not the way the question was asked.

swhobie
11-28-2008, 08:29 PM
I am preparing to build a 24 x 30 freestanding garage at the back edge of my city lot that has an alley running behind it and want to put a 14 ft wide 9 ft tall roll up door on back and have the same type of door on yard side. This is for two reasons: 1. open them up for flow thru of air in summer. 2. Have the ability to pull small boats thru the garage and into the yard. Garage will be a workshop for doing fiberglass restorations of small sail boats and I want to work in the shade of the garage and then roll trailer into yard for curing of glass.

Having said that I want the floor (slab) to be on the same grade as the alley and yard for ease of moving boats in and out. Code requires that wood frame construction be minimum of 8 inches above grade. I am wrestling with a poured footing, cinderblocks on top to reach 8 inches above grade and then poured floor at grade level or monolithic pour at grade level with 1 row of blocks on top.

I would love some advice from the pros as to the pro's and con's of each. I will be doing the construction of the garage myself and that does not bother me as I have the necessary skillsets to work with the framing, joists, roof and vinyl siding. I am not experienced in the concrete side of this project. I am looking for ideas and help so that I can talk intelligently with local concrete contractors about this project.

If I do the monolithic pour so the top surface (floor of garage) is at grade, how does one attach the 1 row of blocks so that everything is tied together. I am leaning in that direction as it will be one pour and then the blocks can be set as opposed to pouring a footing, building a wall, then pouring the floor to the garage inside of the walls.

I am in Richmond, VA so my frost line is at 18 inches. Having said that do I pour my footings at a certain thickness and then block up with multiple courses of blocks or pour the footings thicker and only use one course of block?

Richard A Hetzel
11-29-2008, 04:06 AM
Why not just build a block foundation to whatever height you need it to be, and then just pour the floor slab inside the foundation, the way iy's supposed to be. A "monolithic pour" will require some careful detailing and reinforcing at all the edges if you want to avoid cracks. It doesn't sound like those things are within your area of expertise.

At the two doors, drop the block to one course below floor level, and taper your subgrade so that the floor wiill increase in thiskness from 4 inches to 8 inches over a distance of at least four feet as it rests on the walls in those places. Otherwise, float it between the walls.

swhobie
11-29-2008, 12:35 PM
Richard, thanks for ringing in on this. Your advice sounds like a good approach and makes sense to me. I found this site by Google search on "Concrete and Footings" and have spend considerable time browsing in the forums. It is Professionals like yourself that make the Internet such a valuable resource for those of us needing help in areas that we are not strong in.

I am confident that I will be hiring professional concrete and block contractors to do this part of my project but I want to be able to understand the options when discussing the project.

Thanks again and I would be interested in any other opinions that others may have to offer.

bernie
11-30-2008, 03:33 PM
Where the garage door meets the floor, have a inch and a half or less step so to speak in the concrete. This will trap out rain, wind, and light and make for a better seal. Also needs to be dead level.

bernie
11-30-2008, 03:57 PM
One question for the pro's please.....the footer goes in, then why not a 10" wide first course block,then 8 inch block thereafter, with the exposed 2 inches for slab rest. figuring 1/2 inch x 4 inch expansion material against block. And isn't it proper to water heavy before pour to settle earth ?

BDN Masonry
11-30-2008, 08:55 PM
You sould have a footing below the frost line. With the desired block on top of that with rebar every 32-48 inches. Best if that last coars could be a bondbeam poared solid with lag bolts ever 2ft. And make the floor a floating slab. Less cracking and much easier to replace.

Richard A Hetzel
12-01-2008, 02:44 AM
the footer goes in, then why not a 10" wide first course block,then 8 inch block thereafter, with the exposed 2 inches for slab rest.
Slabs on ground should not rest on the walls, unless required by openings such as large doors. The slab should be poured entirely within the foundation, not resting on it al all unless absolutely necessary for openings, and then it must be thickened and tapered as described above.