# Block Joists



## NJ Brickie (Jan 31, 2009)

Does anyone have any experience with the Block Joist flooring/roof system? I found some info on the web about it and it seems like a newer system. One of their designs states that it can be done without concrete topping. Seems like it may be a good system for a concrete floor with out needing pumps or cranes.


ftp://imgs.ebuild.com/woc/j980127.pdf


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## Rockmonster (Nov 15, 2007)

Well I'll be dipped in $&@*......I think I like the idea...set it up with almost NO skilled labor....I imagine it would be good for soundproofing as well....I'm going to look into this further...tks for the link..


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## stuart45 (Oct 7, 2009)

We often use a system called block and beam for ground floors.
http://www.cube6.co.uk/
I've never used one with steel beams, but I suppose it's the same idea.
It can also be used on upper floors on blocks of flats. 
Timber ground floors are quite rare here now.


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## concretemasonry (Dec 1, 2006)

Joist Block was developed by a man in Virginia about 30 years ago.

It was attempted to be a lighter weight steel joist instead of the heavier traditional concrete joists that were used sucessfully in Europe for more than 40 years earlier. The system is also used for high slope roofs with concrete block or clay tile.

I was at job west of Richmond, Virginia in the early 1980's that had the joists up, most of the block set, but grout not dumped. It was amazing how rigid and tight it was and how little movement or deflection there was were a few people jumped and try to cause something to happen. - Even sounder than a wood joist/beam system with the decking on and installed.

In Europe, the all concrete system (lightweight concrete beams instead of steel joists) has been used for many, many years (maybe over a century). Both block and hollow structural clay tiles are manufactured for the system. For interior floors, it is usually topped with 1 1/2" to 2" of concrete or "grout" to cover the heat radiant heat above the block in colder countries. Heating cost for these homes (1 or 2 stories above a basement, if needed) is very, very low and comfort level is very constant. One advantage of the concrete beams/joists is that the bottom side is all in the same plane and can be easily finished.

Obviously, wood is not used in the common homes, so the weight is not a factor - out of question for weaker wood structures.


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## stuart45 (Oct 7, 2009)

Here's a few floor systems that were used in the 60's and 70's.


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## concretemasonry (Dec 1, 2006)

There are coutless variations on the concept since most people in Europe will not accept the noise and deflection of wood construction.

About 10 years ago, I saw a floor system in Hungary made from pre-stressed concrete beams and blocks even made from shredded wood scraps, sand and cement. They put in supports for the beams (longs spans) during construction before the block were placed. The block were then placed and a smooth topping applied and the supports/props were removed in a week or to complete finishing. Very well engineered and constructed (for a few centuries of life). - This was not necessarily based on initial construction costs, but on liveability, life and resale. It was common in apartments and condos also.


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## CJKarl (Nov 21, 2006)

Sounds crazy to me, guessed I learned something new today.


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## 4th generation (Mar 28, 2008)

At first glance it looks like a brilliant idea, there must be some drawbacks though.


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## masonryworks (Dec 24, 2009)

Wow, that is an interesting concept. It does seem like a solid floor.


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## stuart45 (Oct 7, 2009)

There are a few drawbacks to a block and beam system. The beams have to be worked out and ordered in plenty of time, and you are relying on them being delivered on time.
The brickwork and blockwork has to be built spot on, whereas with timber floors the chippys can easily cut the joists to size if there's any cock ups.
You can easily alter a timber floor in the future, such as putting in another staircase.
The sound insulation put into modern timber floors is a lot better than in the past. 
Most low rise housing in the UK has concrete ground and timber upper floors, unless they are flats.


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## cleveman (Dec 28, 2007)

Any standard engineering out there for spans without joists?

For example, you can span 8 feet with 4" concrete with no rebar, 12 feet with 4" concrete with rebar every 1' on center, blah blah blah for different thicknesses of concrete and different spacing on the rebar and rebar diameter.

Same question for spans with joists-what joist depth, rebar diameter and spacing, and concrete thickness.


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## NJ Brickie (Jan 31, 2009)

cleveman said:


> Any standard engineering out there for spans without joists?
> 
> For example, you can span 8 feet with 4" concrete with no rebar, 12 feet with 4" concrete with rebar every 1' on center, blah blah blah for different thicknesses of concrete and different spacing on the rebar and rebar diameter.
> 
> Same question for spans with joists-what joist depth, rebar diameter and spacing, and concrete thickness.



There is span info up to 20' in the link. I think I am mis-understanding your question though.

stuart-I have seen floors similar to the ones in your post. I just finished up a job which included adding a elevator in a school that was built in 1909. The floors where terracotta tubes similar to very large flue pipe with a concrete topping. The terracotta rested on a few beams in the span and was built into the triple+ wythe brick walls at either end. The total thickness was about 2'.


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## cleveman (Dec 28, 2007)

NJ Brickie,

I was trying to ask if there are some standards in spans for unsupported concrete floors.

For example, you want to have a floor spanning 12'. The standards would tell you that you could use 4" thick concrete with x diameter re-bar spaced every x", or 6" thick concrete, or 8" thick, etc. 

Compare this to spanning 12' with lumber. You could use x species of 2x8 floor joist spaced every 16", or 2x6's spaced every 12 inches, maybe you could even use 2x4's spaced every 8 or 6".

There must be some standards specifying that with a design load of x lbs./square foot, you can span x' with 4" concrete, or x' with 4" concrete with #4 rebar every foot, etc. etc.

As a practical problem, lets say that I have a 6' wide porch which I want to frame a floor underneath and pour a slab on top of it, then strip the floor. Can I span the 6' with 4" concrete, or do I need to go 6 or 8" thick or thicker? What size rebar would this require, and what spacing?


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