need to make hole in structural cmu wall larger, then add reinforcement

[paulmars]

Hope proper forum.

Existing 18 wide x 12" height hole near floor, thru cmu structural wall. Wall supports roof rafters. Need to enlarge hole to 18 x 18".

1-Hole was cut thru wall by previous owner or their contractor. I don't know if they put a header in that hole.

2-It looks like one of the rafters is laterally very close to one side edge of the hole. Not sure if it is above the hole or just beside it. See diagram.

I won't know either #1 or #2 until I pull the old air handler.

Im getting quotes on new hvac system. So far quotes say new air handler requires 18 x 18" return.

Im thinking of adding 2x4s, straps, and cross member. Also a header above the hole.

Points on diagram. Sorry it's pretty bad, but kinda scale.

Red is 2x4s (can I liquid nail to walls opposed to screwing?)

Blue is ends of rafters sitting on top of 2x8/10 on top of CMUs. Ill push the red 2x4s tight below those and strap them together.

Brown is what Im calling a cross member. Maybe it should be higher? If I dont need to stagger the right red 2x4 should I still use that cross member?

Cutting the cutouts shown at top sides of 18x18 hole for header will be tricky.

Your thoughts?

Thanks,
P
.

 

[paulmars]

Why did this post before i clicked post?

 

[paulmars]

I uploaded 5, not 4 pics

 

[PJB12]

Liquid Nails doesn't have any structural strength. Construction adhesives in general have little or no structural strength.

I'm not exactly following what you have to accomplish, but while studying the opening consider if an angle steel lintel will help you support the load from above. They are commonly used above openings in masonry or block. It will span the opening , plus some distance on each side.

You will cut mortar out of the joints at the top of the opening on each side of the opening. The horizontal leg of the steel angle will slide into the slots you just made. The vertical leg is often, but not always, attached to the masonry above the opening. The mortar is then patched.

My own home has 1/8 x 2 x 3 angles holding 2 stories of brick above doors & windows, some are on gable ends some on eave ends. No problems. No cracked joints.

You can also temporarily support the framing and create a build-in-place a concrete lintel. But, you'll have to let it cure 28 days before loading it. (Or buy a pre-cast one)

Paul

 

[paulmars]

Liquid Nails doesn't have any structural strength. Construction adhesives in general have little or no structural strength.

I'm not exactly following what you have to accomplish, but while studying the opening consider if an angle steel lintel will help you support the load from above. They are commonly used above openings in masonry or block. It will span the opening , plus some distance on each side.

You will cut mortar out of the joints at the top of the opening on each side of the opening. The horizontal leg of the steel angle will slide into the slots you just made. The vertical leg is often, but not always, attached to the masonry above the opening. The mortar is then patched.

My own home has 1/8 x 2 x 3 angles holding 2 stories of brick above doors & windows, some are on gable ends some on eave ends. No problems. No cracked joints.

You can also temporarily support the framing and create a build-in-place a concrete lintel. But, you'll have to let it cure 28 days before loading it. (Or buy a pre-cast one)

Paul

As suggested else where im thinking of cutting slot in mortar above hole & of course out past hole 6" on each side & pushing in a 3"x3" angle iron. Both sides of cmu wall. Cold rolled hi carbon angle iron. Not as strong as a full lentil, but maybe enough. Kinda depends what I see when i expose the existing hole. Cancel the 2x4s. That was silly .

 

[PJB12]

As suggested else where im thinking of cutting slot in mortar above hole & of course out past hole 6" on each side & pushing in a 3"x3" angle iron. Both sides of cmu wall. Cold rolled hi carbon angle iron. Not as strong as a full lentil, but maybe enough. Kinda depends what I see when i expose the existing hole. Cancel the 2x4s. That was silly .

I think you have a very good plan, depending on what the wall is holding. Eighteen inches isn't a very wide hole and lots of weight is being sent to adjacent blocks on the way down to the hole. (I'm not an engineer, so this is based on the "doing stuff & seeing stuff" method.)

The high carbon angle you mentioned is probably A36 HRS. (Hot rolled). I would imagine it is far, far more than adequate for your load, especially because of the vertical leg which adds a tremendous amount of resistance to deflection versus a piece of flat stock. Tremendously More!


The masons would do pretty much what you said above when we needed a large opening in a load bearing block wall for electrical duct runs. (Sometimes 4 or more feet wide)

The steel was usually A36. The length past the opening was greater than half of a block on each side. They wanted to catch the center web wall.

Usually the width of the horizontal leg of the angle steel (the leg in the slot) was wider than half the depth of the block. Sometimes full block depth was used, depending on the engineering call out.

For Example- If the block was nominal 8 x 8 x 16", half the depth would be 3-4/5" (7-5/8" divided by two). A 5" leg was used to let it go more than half of the block depth. Four inch was too close due to the inside radius of the steel. Typically, I'd see 1/4 x 4 x 5 or 1/4 x 3 x 5 angles. (Sometimes 3/16")

Other times, for the same block dimensions, a 3 x 3 was put inside and a 3 x 3 was put outside.