Marrying a 12" block wall to 8"

[Sparticle]

We were going to do slip form to build two houses, but after a couple years of research have just changed it to concrete blocks. We have to get done before next winter and there are just 3 of us (and one is 72 years old. No she won't be lifting the blocks and yes I know how heavy they are).

It's an earth bermed house so the North wall needs to be 12" concrete blocks. The East side however isn't bermed so we really only need 8" blocks which are cheaper. I can't think of a reason (other than aesthetics) that we couldn't marry the two walls together and I drew a rough idea of what it might look like before camouflaging it with something to stuff in the cavities and then plastering over it. That N. E. corner is just the mud room, so there will be coats hanging in that corner anyway.

The beams for the roof will rest on the North and South walls.

Can anyone think of a reason structurally why this wouldn't work?

P.S. I KNOW the rebar is off in the drawing when you compare the two views and that it needs to be surrounded by 3" of concrete. I was just playing around with it.

edit: just noticed I put 1 sq = 2ft. hehe, meant 2" oops, did it too late at night.

[T-Bone 369]

Typically when we do a transition in block we do it at the corner - in your detail diagram of the corner exchange the 12" block on the east for 8". That will make the transition smooth. In a nutshell, you build the corner with an 8 on the first row ands then a 12 then back to an 8 on the third row and so on. It does effect the bond slightly but probably someone without a trained eye would not notice it. I'll try to draw a picture as it is easier to show than tell. There is another option that we will do from time to time - hiding an offset at an interior wall. Turn your corner with the 12's and lay them out to the inside corner of where your interior frame wall will be when it is build. At that point you make a vertical control joint that is hidden by the fraome wall. The major disadvantage of this is there is a vertical joint (read weak spot) at that point. You have to reinforce across the joint with wire but still will never be as strong. Hope that helps.

[T-Bone 369]

Forgive my lack of artistic ability but this should show the correct way to do your transition at the corner (not to scale lol). Obviously the third course should be laid the same as the first, the fourth the same as the second. Good luck and be careful.

[omnicat]

"Do you, 12" block, take this 8" block to be your masonically joined continuum? To have and to hold, from this day forth, until gravity and time do you decay?"



(sorry, couldn't resist adding my stream-of-consciousness associations)

[Sparticle]

T-Bone, Well aren't you wonderful. Off to study your drawings. Thanks a million! I couldn't find any drawings of it online or in my books so I was just guessing (obviously). We're doing dry stack with surface bonding which is stronger than mortar joints, so it should work pretty well.

Thanks again!

[seedspreader]

Why does the north wall need to be 12"?

Plenty of underground basements are built with 8" blocks.

[Sparticle]

Originally Posted by omnicat

"Do you, 12" block, take this 8" block to be your masonically joined continuum? To have and to hold, from this day forth, until gravity and time do you decay?"



(sorry, couldn't resist adding my stream-of-consciousness associations)

Bahahaha!

[Sparticle]

Originally Posted by seedspreader

Why does the north wall need to be 12"?

Plenty of underground basements are built with 8" blocks.

The North wall is 10 feet tall and will be bermed all the way to the roof. We've got a bunch of books on earth sheltered houses and they all recommend 12" blocks. We've been studying this for several years and since we have no personal experience, we're just trying to do it right "by the book".

[seedspreader]

Oh, I am sure it won't hurt a bit, I was just wondering why you said that it had to be 12". If that's what the experts recommend for underground houses, I guess they would know.

[Sparticle]

Originally Posted by seedspreader

Oh, I am sure it won't hurt a bit, I was just wondering why you said that it had to be 12". If that's what the experts recommend for underground houses, I guess they would know.

We'd sure like to go 8", it'd be cheaper. Maybe I'll see if we can find any bermed houses that used it and see how it's doing for them.

[Sparticle]

I lay in bed thinking about this stuff. This morning I was thinking that I drew the 12" block into the 8" wall some so that the corner would be strong to resist lateral forces. Sort of like a pilaster for the corner. DH worried that the 8" block on the first course on the end wouldn't be strong enough?

[blooba]

I'm no engineer but i would flip the 2nd and first courses around since the majority of the horizontal force will be coming from the back (12" wall). Would that be better T-Bone?
I think it would be alright either way but might as well make it as strong as possible.

[wy_white_wolf]

Originally Posted by Sparticle

I lay in bed thinking about this stuff. This morning I was thinking that I drew the 12" block into the 8" wall some so that the corner would be strong to resist lateral forces. Sort of like a pilaster for the corner. DH worried that the 8" block on the first course on the end wouldn't be strong enough?

It will take 18 courses to reach the 12' you want. It makes no difference in strength which way you start.

If you are worried about the bottom of the wall kicking in than pour your floor on top of the footer instead of inside it. That way it helps to lock the bottom course in place.

[fordy]

Originally Posted by Sparticle

The North wall is 10 feet tall and will be bermed all the way to the roof. We've got a bunch of books on earth sheltered houses and they all recommend 12" blocks. We've been studying this for several years and since we have no personal experience, we're just trying to do it right "by the book".

.............Why can't you attach a piece of 3 inch angle iron too the slab with anchor bolts so that the inside edge of the bottom row of blocks "Pushes" against the angle iron when you add the backfill ? That way , the wall won't beable too move even IF it wanted too ! , fordy

[fishhead]

Could you fill the voids on the corner with concrete and rebar to strengthen it?

[Sparticle]

Originally Posted by fishhead

Could you fill the voids on the corner with concrete and rebar to strengthen it?

Yes in the corners and about every 4 feet or so, the blocks will be filled with concrete and rebar insterted. Then other blocks will be filled with sand maybe.

Wy-wolf, I was actually going to have 2" of the floor (adobe poured) over the grade beam (footer) which will support the bottom blocks some.

Fordy, having to process what you've said.

[T-Bone 369]

Originally Posted by Sparticle

I lay in bed thinking about this stuff. This morning I was thinking that I drew the 12" block into the 8" wall some so that the corner would be strong to resist lateral forces. Sort of like a pilaster for the corner. DH worried that the 8" block on the first course on the end wouldn't be strong enough?

wy_white_wolf is correct - makes no difference - had to draw it one way or the other so drew it this way. Strength wise it matters not - you have the same amount to material in the corner. Truth is depending on the length of the wall you may have one corner with the 8's on the corner while the other may have 12's. It all depends on the bond when you do your layout.

The advantage to using 12" block is not the mass of the block but the cavity size. Bigger cavity = more room to pour your concrete and rebar = stronger wall. Most residential construction here uses 8" block unless there is a brick ledge then we lay 12's except for the last row which is 8's. On comercial work we often lay 12's if there is the possibility of lateral push (stair well walls and elevator shafts come to mind). I will say that very few basements are built from block here any more - there are a few but it's not common. On your back wall if you choose to use the 12's I would fill the cores closer that 4 feet. Frankly with the type of application you are looking at I would go every other if not each core. You're laying 12's because you worry about the lateral force but on 4' cores you are not taking advantage of the block size you have chosen. The amount of material required is fairly minimal to slush the voids full. With that and re-bar drilled into the footer the wall should be fine. The weakest point of the wall will be the joint between the footer and the wall. However, if you do pour the floor higher inside and have re-bar in the footer into the cavity it will not go anywhere.

Try not to over think what your doing - find a good book with diagrams and use it for a reference. Make sure the footers are perfectly flat and level especially since you are thinking of drystacking. Also, be very careful of these 12' block. Our experience is that if you are trying to work above the middle of your chest you are way too high - build some scafold and work between your knees and chest. The shoulders just can not take it (rotary cuff surgery is not all that much fun).

[ErinP]

Make sure the footers are perfectly flat and level especially since you are thinking of drystacking.

And by all means, when you pour, make sure you screed them perfectly. No little bumps near ties or anything.
Otherwise you'll be out there with a chisel, chipping them flat.
(Don't ask me why I know this )

Then other blocks will be filled with sand maybe.

I just read this part aloud to DH as I thought it sounded like a super idea.
He didn't as he said the sand would have to be perfectly dry and there could be no seepage later. Otherwise it'll expand and contract and damage blocks.

Anyone have thoughts on this?

[Sparticle]

Thanks again. We have about 15 books or so we're using to help us and it's amazing how much is still left out. after you read it you think you have it down pat. Then when it comes to the drawing phase you realize there are little things here and there left out.

Good thought about the sand and the cavity size, we should do better with that.

[cfabe]

If you are building under code your 10' tall wall will probably need to be engineered. It may require 12" block and it may also require an interior brace wall depending on how long it is. If you don't have codes there, you really need to get a very good handle on how strong that wall needs to be by actually doing the calculations. Most how-to books I've seen don't actually get into how to do the load calculations necessary to size building components, they just give some general rules of thumb with the disclaimer "consult local codes."