Putting a doorway in a concrete block wall


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Old 11-29-06, 11:53 AM
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Putting a doorway in a concrete block wall

Here's the situation:

I have a concrete block home that was built in the 60s. Small, one story, nothing fancy, 8' ceilings, no attic to speak of, etc.

Oddly, the house has no view into the back yard, because there is a small concrete block laundry room tacked onto the back of the house. This room has a 6' wide window in it that I want to slice to the floor and replace with a door.

I would like to open up a corresponding 6' wide hole in the "inside" wall (exterior wall of the main house) so that I can walk from my living room into the laundry room, then out the new back door.

According to the original plans the house has a poured concrete beam along the top of the wall. I am not sure how tall this would be, it may be at normal header height already?

I would have approx 3-4' of undisturbed wall on either side of my opening.

What is the right way to go about doing this safely? What should I plan on for reinforcing the opening? Is a header a necessity even if I find a solid concrete beam already in place along the top of the wall?

Thanks, don't want to cut corners - eyeballing the job I don't think there will be any immediate problems just cutting it out but want to make sure to do it right so it is structurally sound long term.
 
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Old 11-29-06, 12:27 PM
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Putting a doorway in a concrete block wall

Is the wall you are considering putting a hole in a loadbearing wall?

Your "concrete beam" may actually be a bond beam (8" high) that is intended to tie the top ring of the block together. They usually are not designed to span a 6' opening. Is possible it could carry the load, but it will be difficult to tell what the spanning capacity is.

An engineer could give you better advice and options after looking at it. Maybe your original plans could help him. most people are not fortunate to have the original plans.

Dick
 
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Old 11-29-06, 01:03 PM
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Yes. The wall supports the roof trusses. Since the house is small and a simple layout, I wouldn't consider it to be under tremendous load but obviously I would prefer the roof to stay where it is. You are probably right in that what is at the top may just be a bond beam (tie beam?). It looks like in current code it would be 12" high but not sure if that was the same 40 years ago.

I'm trying to get an idea of what my options would be before going to a pro. If the beam is not in fact intended to be unsupported - is this something I could work around by cutting a "T" shaped hole and inserting a homemade wood beam (four 2x8s?) as the header?

I should also point out that I am flexible (to a point) in the size of the interior opening. While 6' would match the outside opening, I can shave a couple feet off of that if there is a safety concern. Tonight I can try to cut out a square of sheetrock on the inside and see what I've got.
 
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Old 11-29-06, 01:15 PM
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Putting a doorway in a concrete block wall

The pro will give you the options.

You do not use wood to reinforce concrete (it is too flexible), but it could be a good nailer.

Most standard block bond beams are 8" high, since that is all that is really necessary it it is not spanning more than a couple of feet.

If you have an older home in Florida, you may have a 12" deep poured in place beam that has much more spanning capacity and could work. Get an engineer to tell you.

Dick
 
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Old 11-29-06, 07:55 PM
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OK I've got some more info.

I ripped out some drywall on the inside, and dug up the original plans, and here's what I found.

The wall is plain old cinderblock... up until 80" tall. At the 80" mark, it turns into what looks like cinderblocks turned on their side. (16" Tall) Testing with a drill tells me they are solid.

Looking at the original plans, I see that these are "U" shaped blocks (the plan says "U Block Belt" with a small diagram) apparently with concrete poured inside and reinforced with 7/8" rebar.

Now here is where things confuse me again. Just eyeballing what is there, while I'm sure it is sound - it does not look like something I would necessarily want to walk under. HOWEVER - it is at the same height as all the window and door openings. Measuring it, it would be impossible for the windows and doors to have more than 2" of anything above them before hitting this beam. Ditto for the garage door opening. (actually it looked more like 1" )

So ... Do my windows and doors really not have any other header above them? (can't find any reference to one on my plans) Does that mean this poured beam is "safe" for openings?

Also, after some measuring, my new plan is to go with a 4' opening, NOT 6', on the "unknown" wall.

I can't see any way to create a "thick" header and still have an 80" tall opening without cutting into the u-blocks, which does not seem wise. The best thing my neighbor and I came up with, if it is needed at all, would be to reinforce the opening with a steel plate bolted in place. Does this make any sense?
 
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Old 11-29-06, 08:13 PM
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Putting a doorway in a concrete block wall

It looks like you have a very substantial beam around the top of your home. Don't let the looks scare you or influence you about the strength. An 8" wide by 16" deep reinforced (7/8" rebar) concrete beam is very substantial and definitely is stronger than any wood header.

You probably have the remains of a 2x "buck" that was used to form the window openings left in place at the existing windows. This makes a good nailer for doors and windows.

I had a large masonry home built and opted to go with the 8" deep bond beam around the structured, but dipped down to 16" deep in the areas over my openings. I did this to keep the amount of grout down for the masons to mix. I had four 6'-8" openings separated by 8" block columns. It also carried the brick veneer weight over the door openings. I also used a 2x "buck" to form the openings and support the beam over the opening during construction.

Dick
 
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Old 11-29-06, 08:22 PM
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It is doable, but you will still need a structural engineer's stamp so that you can sell the house down the road. If it were me, I would slice the 6' exterior doors out of the window, and put a regular door on the interior wall. You do not want to cut the bond beam in any case.
 
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Old 11-29-06, 09:03 PM
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Thanks for the comments, guys. The thing that makes the beam look "scary" is simply the joints between the U-blocks. Although yes I imagine that if the whole thing is poured the length of the house, it isn't going anywhere.

I'll do some more investigation and see what I can find out. One of the reasons that I don't mind tackling this project as a DIY adventure is because I hope to do a substantial addition to the house in a few years, which would involve removing this whole section of wall anyway. In the meantime I am trying to keep it to an affordable (but safe) level, part of the reason for me to narrow the span from 6' to 4'. I'd rather put up with the reduced asthetics and not take quite so much wall out. But I will seek an informed decision on it.
 
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Old 11-29-06, 10:00 PM
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The joints are there to keep the CMU apart, not to hold them together. There is a solid reinforced concrete beam inside the form created by the u-block.
 
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Old 11-30-06, 06:18 AM
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Putting a doorway in a concrete block wall

For the beam you are concerned with, the mortar joints on the bottom are of no consequence structurally. The structural analysis assumes the joints and concrete in the bottom part of the beam do not exist and the steel carries all the load (tension) in the bottom of the beam.

Contrary to other opinions, the block in the upper portion of the beam does carry some of the small load (compression). The concrete assembly (block and mortar) is very strong in compression. In normal compression, mortar has very little effect on the strength of a block and mortar assembly because of the types of stresses and the "false" low strengths given by the unique testing methods used for mortar. I have seen 4500 psi block and mortar prisms made using 1900 psi mortar.

If you really want a standard 6' opening, the low cost of an engineer may show you that you have a lot more flexibility than you think you have.

Dick
 
 

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