I'd like to build one on a slab for a garage/shop.  Would want it to be about 25x40 feet and I'd like to do as much of the work myself as possible.  

I'm not concerned about wall insulation - Could poured walls be similar cost to buying blocks and mortar?  
Good idea to have rebar put in the slab to anchor walls to the slab?  
If it's block walls I'd like them to be filled with concrete.  How much concrete does it take to fill 8x8x16 wall and is it worth the cost?
What sort of roof trusses should I consider?  Ie. Wood or metal?

Never built a block building - what do I need to know?

I’m not an estimator but if I recall correctly, 1.2 cubic yards of grout per 100 square feet. It’s $110 off the truck, and you need a pump.

You will need rebar connecting the wall to the slab and then vertically and horizontally in the wall itself.

You’ll want to use water repellant on the block of its single wythe, and integral water repellant in the block and mortar.

Block are cheaper than poured walls.

I have a farm with a larger garage that Is block walls with no rebar and walls are hollow.  It's been around since at least the 60s and maybe 50s.  
Walls were last painted... over 30years ago.  

Stupid question time:

1.2 yds per 100 ft2 is to fill the block?  You say grout - is it just a thinner mix so it flows down the blocks easily?
How "necessary" is the rebar and filling the walls?  I want to do it, but I'm negotiable depending on cost/benefit.
Water repellant?  Is that something sprayed on after building?  

What part of the country are you in? I’ve only done CMU in the west so maybe some places don’t require reinforcement still. 1.2 yards is to fill 100sf of CMU wall. Water repellant goes on last. If you get waterlogged block you can get water inside. If you do it yourself it’s not outrageous. Grout is a fine aggregate concrete for pumping with less strength than most concrete. Even if there are places that don’t require grout and rebar I would want it kn case someone drove a car into it or shot at the garage.

Why not icf?

Deep South, this would be in AL/TN area.  Haven't bought the land yet, but many rural locations have no building code requirements.  Frequent tornados, but a wooden roof would come off before the walls collapse.  Again, Im sure no requirement for fill/rebar but I'd like it if it's affordable.  

How do you attach a wood roof?  If walls are filled it'd be easy to set anchor bolts in and bolt down pressure treated 2x8 to attach roof.  What about attaching to unfilled walls?

I'm kinda surprised at how inexpensive the blocks are.  The waterproofing stuff costs almost as much as the block.  Windows, garage doors, and people doors will cost more than the block too!

As I understand you have to sheath the inside and outside of icf walls?  
All that wood eats up $$ and results in lots of wood and foam which are susceptible to critters and insects.  

Gotcha, fair point

LOL that is a big NO You will need some wood for temp. bracing other than that I have never seen a icf house that required sheathing inside and out

Honestly I know very little about unreinforced masonry.

When I worked with bricklayers back in the late 70's, every wall we built was unfilled.
Every fourth or fifth course(maybe sixth) would be reinforced with Dura-Wire.
If you want to put rebar in, you'll have to do it no later than the fourth course, because the cells don't always line up and, and snots can fill the cells, making it difficult to drop rebar down from a height.
Lay four courses or so, and put 5' or 6' rebar in the cells.  Continue laying the courses over the rebar, install your Dura-Wire, and continue.  A pain, but it's possible.
I wouldn't fill the cells with mud until at least a week after the block has been laid, to give the joints plenty of time to set up.
Skip the rebar, use Dura-Wire, and fill the cells with a very loose concrete mix.  A vibrator might be nice to have, but we survived without one.

Here you have to have vertical rebar on 32" centers and horizontal bond beams every 48". Horizontal beams are 'u' shaped blocks with no web or end panels that you can run continous horizontal bar in and then fill with grout.

The only concrete block building I’ve done we used surface bonding cement for the blocks. Wood rafters and plywood sheeting on the roof then asphalt shingles for the roof. Nothing special.  Neither my father nor I wanted to deal with conventional block laying and the surface bonding cement seemed like a much faster option. It was.  

Basically stack the blocks and trowel on the cement.

Cover yes sheath no. Metal outside and drywall inside is fine

The outside of ICF can be stuccoed directly on the foam.
The inside of icf residences should be drywalled for fire/offgassing reasons but a detached garage with no sleeping/living areas doesn't matter as much.

Hadn't heard of durawire - Looks like a simple and effective product, will definitely use it.

I think I may go with filling just the bottom couple rows of block for better anchoring to the slab and then fill around each door opening to allow more than animal/weather door security.  

What about roof?  Wood trusses seem like the fast/east/cheap solution?

You  need to pour a bond beam around the wall at the top and they make a cement block just for this purpose

Bond beam

Required here every 6 courses (48") minimum reinforcement I think is 2 #4 bar.  Knock out the vertical cell so vert bar can run through.


Durawire was popular years ago, it is no longer allowed in our seismic area.  Check with your local building department and see if it can be used for horizontal reinforcement.

If you’re not going to grout it, I’d recommend a metal building.

Perkins Builder Brothers farmhouse build has a block foundation/walkout basement.  Might be a good way to get an idea of what you're in for.

Lay two courses of block, then hammer drill thru the cores into the slab, drive a chunk of rebar into the hole and that is the core to fill with grout

Why would you drill after the fact? Why would you not cast it into the slab? What core are you going to drill through? Why not drill through a cell?

I did a concrete block pool five years ago with no issues, I poured footers and built 2 courses of block around the perimeter and drilled in 2" rebar shanks.  Then used durawire every couple courses going up, the durawire is obviously used horizontally between the block courses.
I then came back and poured about 2" of mortar into the base, I think I might of done that after I layed another couple courses on the bottom two courses, after I drilled in the rebar.

Anyways, it was a fun project and I would seriously consider using concrete block building an out building and unless you really want to spend the money, I don't think you need to fill every core with rebar and mortar. . It wouldn't hurt but it will take time & money.  

I also don't think the concrete block of today is anywhere as near strong as the concrete block of the past, maybe its just the stuff you buy at HD, Lowes, Menards, etc - but I found some local guy that had truckkloads of concrete blocks at .50/ea and it was old school stuff, heavier and finer concrete - not like the large 'cell' block you find at the home centers.

One last thing, just like any other project, the expenses is in the special stuff, I mean you can get block for less than $1 ea, mortar isn't too expensive, or you can blend it yourself,, but those special items like the bond beam, those are the things that really drive up overall cost, and yes you can buy it or find a more affordable alternative.  I've always enjoyed procuring the material for my projects, accumulating things over a period of time, shopping around finding things on sale, etc.  Being frugal isn't a bad thing

Florida uses lots of concrete block in buildings, I would look into the building codes used there for roofing attachment.  Might be overkill but some of the things done like metal straps are cheap parts and fairly quick and easy install.

I discovered that - there are tons of options for metal rafter attachments but the ones I found are all set in concrete, i.e. The walls have to be filled with concrete.  The  bond beam thing around the top would make this the cheapest/easiest/strongest solution it looks like.  

What about the size for a steel wide I-beam lintel over a normal 1-car width garage door?

Why not just use grouped block to cross over the garage door opening? That works to like 60 feet wide.

I don't now what grouped block is.

Grouted, but autocorrect got me. You add steel and 3-6 courses of grout and you can span any common garage door. You’ll have to grout around the door jambs also. Steel itself is cheap but you’d need equipment to hang it and you’d either have to grout the block you attached it to, or use vertical steel to hold the steel beam, and then you have to do something to keep the rust at bay.

Gotcha.  That's what I would do because I can get steel scraps very cheap.  I assume any 4-6-8 inch steel I beam is plenty strong for a 8ish door wide garage door opening?

Might want to compare a metal building . The outfits that do them knock up a sizeable building in a couple of days .



Does anyone build the frame and roof like a metal building then build up the walls with block instead of metal sideing?


Then there are pole barns to consider.

The slab for a pole barn is built different than one you are going to be building a block wall on , basically a bigger footing

We have a metal building with block walls. It’s a thing.

Still grouted it solid.

Research Florida building codes. Just about all the houses being built are block covered with stucco. The trusses have metal hurricane straps attached, where they meet the wall every 24 inches, cement is poured into the hollow block and filled securing the metal strap into the cement. once dry, the roof sheathing is nailed, and either shingled or tiled.  It's going to take more than a cat 5 hurricane to rip that roof off, those bricks attached to a cement pad, isn't going anywhere either and won't burn.