# how to make an opening in an existing concrete block wall?



## 3bar (Jan 14, 2011)

i need to add a couple windows in an existing concrete H block wall. 8' and 5' openings.

there are roughly 5 or 6 courses of blocks above where the window would be. one problem is the blocks are not staggered. they are lined up vertically. 

obviously, i will build a temporary wall inside to support the roof(spancrete), but how would i go about supporting the blocks above where the window will be? i have steel coming that was spec'd by an architect. should i just remove the blocks above where the window will go, install the steel, then reinstall the blocks above?


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## Dirtywhiteboy (Oct 15, 2010)

OK I have never heard of CMU not being staggered??There is no interlocking that way? So the corners just but each other:blink: But I have cut these holes and and knocked the top inside of the block out and put the steel in head out with 2x8 and drilled big holes above and piped in concrete. You should also fill the block on each side of the window to the floor to act as trimmers for your header you pour. I used a big piping bag and a vibrator to do this and it worked very well I must say:thumbsup:


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## concretemasonry (Dec 1, 2006)

You did not say where you are located, so the term "H block" could mean anything.

In any event a stack bond building has lower strengths in some ways. Cutting the opening could hit some vertical rebar if the building is in a seismic area.

Opening of that size will require filled block cores on both sides to carry the load of the lintels. The lintels will have to be determines to be long enough beyond the opening width to allow enough bearing on the filled block cores. Fortunately most real "H block" or "double H block" can be filled easier than block laid in running bond because the block webs align. - Make sure the steel ordered meets the architects plans to provide enought bearin length.

Since building has a "real" roff system of Spancrete, there is probably some vertical reinforcement if the wall is carrying any load from the Spancrete.


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## rblank (Feb 18, 2008)

I've only dealt with a stack bond a few times, and in both cases it was on a college campus. I think you have two options.

1. Bust out the course(s) of CMU above the opening, sliding in the lintel as you go. On the 8' span, it may require you to get some temporary shoring in there for the cmu anyway. Once the lintels are installed, cut out the block below.

2. Take out ALL the CMU, including the 5 - 6 courses above, and fill it back in after you install the lintels. If you have to add rebar above the lintel, or at the jambs, and grout fill, it might be easier this way anyway.


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## stuart45 (Oct 7, 2009)

As stated above, taking down the blocks above might be the easiest option. If you decide to prop the blocks try and get hold of a strongboy as shown below.







Knock it into the joint above where the lintel is going and support it with an acrow prop. It can save putting needles through in many cases.


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## 3bar (Jan 14, 2011)

Dirtywhiteboy said:


> OK I have never heard of CMU not being staggered??


the blocks have an indentation on the edges to create a diamond effect when stacked vertically. its an old school thing.





concretemasonry said:


> You did not say where you are located, so the term "H block" could mean anything.


Illinois. no seismic requirements here.





stuart45 said:


> As stated above, taking down the blocks above might be the easiest option. If you decide to prop the blocks try and get hold of a strongboy as shown below.
> View attachment 49289
> 
> Knock it into the joint above where the lintel is going and support it with an acrow prop. It can save putting needles through in many cases.
> ...


i like this idea. would you put them on both sides of the wall?


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## Diamond D. (Nov 12, 2009)

Short of Stuarts recommendation,
if you don't have the equipment,

I have cut out for a 10' garage door, with steel lintel, by through bolting 2x12x16's , either side, every 16", with some, but minimal vertical support. (12" block,1/2 bond)

It was about the same, 6 or so courses above it, with bar joist sitting on top of that.

Worked well. Not a single crack.
Maybe I was just lucky, I don't know.

I did an 8 footer last fall, with concrete lintels.
That was cake. cut out one side and webs. Install 2 lintels.
Go around, cut out other side, install lintel.
Cut jambs, knock out the rest of the opening.

Good luck, 
D.


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## stuart45 (Oct 7, 2009)

3bar said:


> .
> 
> 
> 
> ...


No, one side is enough. They give you room to work from the other side if needed.


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