Are you changing from a dirt floor to raised floor? Or was there a raised floor before and you tore it out to be replaced?

Mitsy --- We're swapping over, but only on that one side. It had the worst holes in the roof, so you can't even really walk there for the foot deep potholes and the strong slope. I figured it wouldn't be much harder to put in a floor than to shovel the floor flat again, and then we could store chicken waterer supplies on the ground without worrying about the bottoms of the boxes rotting out.

Congratulations on putting a floor in, it will make the space much more useful. However, don't use cinder blocks turned sideways like shown in your photo, they aren't meant for a load in that orientation. For a load bearing situation, they need to be oriented with the cells upright, as if you were building a brick wall.

Good luck!

James --- Mark was waiting for someone to say that, but he thought it would be Roland. Our building helper did that, and Mark plans to talk to him about it. He's usually such a pro that we're surprised he put the blocks in that way. I suggested that he was only using them as a support while scabbing pieces together and didn't mean to leave them there afterward, but we haven't talked to him yet....

well, I must admit that the construction of the supports looked less than stellar to me, to put it mildly. But I don't want to be the person who complains about everything.

Besides, structures are usually quite overbuilt. You could lose one or two supports without strength problems once the floorboards are in place and screwed down, I think. The reasons for that are multiple, but they boil down to two things. First, it is common to multiply expected loads with a safety factor, and use that higher load for laying out the structure. This is reflected in building codes and engineering training worldwide. Second, if you built a structure out of wood that was just strong enough, it would flex so much that nodoby would want to walk on it.

Incidentally, in this case the orientation of the cinderblocks doesn't matter, since the joiste only rest on the ends; the loads from the joists are transmitted through the vertical end faces of the blocks only. But if you were to shift the blocks so that the joist rested on the horizontal face inbetween the vertical "walls" of the cinderblock, James would have a very good point indeed. You would be bending a concrete plate, producing compression loads in the top of the plate and tension loads in the bottom. Now, cement and concrete can withstand huge compression loads, but only very small tension loads. That is why those slender concrete bridges that one sees are made out of pretensioned reinforced concrete with embedded steel bars or cables to carry the tension loads. The steel is pretensioned to prevent the concrete from cracking.

Roland --- I think it helps that the flooring going down is a solid inch. When I went out there to bounce on the first piece this evening, it felt extremely sturdy.

Very good info about the strength of concrete!

I have been following your blog for a while and it looks like there is nothing you cannot do. I just like the fact that you have pictures to illustrate the text, and the pictures are very descriptive on their own. In relation to concrete flooring, a good thing to have especially when you are working in potentially rainy weather are concrete blankets.