How to make large doorway in load-bearing concrete block wall?


Old 12-10-13, 09:56 AM
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How to make large doorway in load-bearing concrete block wall?


I hope you can help. I'm looking for advice and instructions for making a fairly wide open doorway in a concrete block wall. I need help for how to make the header so the wall above the door doesn't fall down.

Please see the attached picture. It is a load-bearing wall between our dining room and garage. The concrete blocks are 20x20x50cm (8" X 8" X 20").

The doorway I want to create is about 155cm (about 6') wide. I've marked the proposed door in red. It will just be an open space with no doors.

I understand that I will need to somehow make a concrete header that is reinforced with rebar… but I'm not sure how to do that.

- Should I just rent a masonry saw and cut out the door hole (following the red lines), build a wood form around where the header should go, and then fill up the form with cement? How do I keep the roof from falling down? (I think I need to use a large wooden beam on the roof lintels and then some bracing?)

- Should the new header "connect" to the existing small header you can see that wraps around the whole wall? I marked in green the proposed header. For example, should I drill holes into the existing small header and epoxy some vertical rebar pieces that go into the new header?

- How do I pour the concrete into the wood form for the new header if the wood form covers the whole thing? (ie: I won't be able to pour the cement "from above" the new header since it will butt up tight against the existing header above it… I don't want to have any big air bubbles trapped or a layer of air between the existing small header and the new header. Should I make a few holes in the side of the top part of the wood form and then somehow pour in a really runny mix of concrete?

- I was thinking to make the new header so each end "sits" on at least 1/4 of a block on both ends of the doorway. Is that enough? Too much? I want to make the doorway as wide as possible.

- Is there a better way to cut out the doorway from the blocks besides renting a saw? I have lots of time, so that's no problem. Should I use a hammer and chisle? Or a hammer drill with a chisle attachement? The garage is enclosed, so I worry that it wouldn't be good for my health if I used a saw and created a massive concrete dust cloud I am sucking into my lungs…

- Any "gotchas" or things that I am not thinking about? Is this job just too big for me to handle? I had a contractor quote $1500 for this job, which is why I am wondering if I can do it myself. (I'm an electrician, so no stranger to tools, etc… but I have not really got much experience with concrete or block walls.) Is it better to just suck it up and pay the contractor?

Thanks for any help!
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Old 12-10-13, 10:46 AM
canuk's Avatar
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Is this garage remaining as a garage ? If so , then would this connection to the living space meet fire codes ?

It's difficult to really comment on what you can do here. The main reason , when it comes to structural considersations no one over the internet can give you any definite answers sight unseen. Besides, the only real information should come from a qaulified engineer.
For example, an engineer would have to design the concrete structral member with the appropriate rebar size and quantity. Perhaps steel could be used, but an enginee rwould have to specify type , thickness and fastening method.
Old 12-10-13, 03:55 PM
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I'm an engineer, and there are too many issues (and missing information) for me to address for your situation. For starters:
1. Why do you not want a door in the proposed opening? Doesn't it get cold where you live? Or is the garage heated, and no longer used as a garage?
2. Do you have a local building department that issues permits and requires inspections of such an undertaking? If so, they need to be brought into the picture early in the process.
3. If loads require it, the header will have to be supported by appropriate columns on either side. Hollow block walls are normally insufficient to provide adequate support. Moot point if block walls have been filled with vertically-reinforced concrete.
4. A heavy timber header and support columns (much lighter than concrete, and considerably easier to work with) might suffice, but without knowing the roof loading, correctly sizing them would not be possible. Not good when a heavy concrete roof is involved.
4. CIP concrete or structural steel would obviously work, but as already stated, such would require design by an engineer. One of several methods could be used for gaining form access with concrete, depending on the geometry involved. Of the two options, structural steel would get my vote, as it would be considerably faster and easier to work with.

Last edited by BridgeMan45; 12-10-13 at 06:10 PM.
Old 12-10-13, 05:18 PM
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Not an engineer but am willing to put in my 2 cents.

You for a support header I would think you would just need to add a steel lintel to both sides of the wall. How large, I couldn't tell you, but lets just say "big". The lintels would need to go past your opening similar to green box. Install the lintels first and then make your opening. You would likely want to fill the block cores on both sides of your opening with concrete or mortar.

Again, Not a engineer.
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