Lintel question: I'm wanting to install a new 48" window in an existing, load-bearing, block, exterior wall. The existing block is 4x16x6, with 3/8" mortar gap. Can I grind out a row of mortar, slip a thick FLAT steel lintel into the gap, remortar, and then cut the window out below? Because the block is only 6" wide, I'm trying to avoid angle lintels (much more work). I would extend the lintel to 6" beyond the opening on each side. This lintel would need to transfer the weight of 3 more rows of block, a 2x6 sill plate, and two truss ends. My roof is a 12/4 pitch with basic 3 tab asphalt and I live in the desert, so no snow load or moisture issues. Do you think a flat lintel would work, or am I asking for collapse?? Thank you, thank you, and thank you again...

 

You need a local architect or engineer. No one here is going to tell you to take a chance.

 

In general, a flat steel piece like you are proposing will have very little support for a vertical load. Angle iron on the other hand have a lot more vertical strengths. You are definitely going to need an engineer's opinion before attempting to do what you are proposing.

 

I'm an engineer, and here's my opinion: Unless it's extremely thick, a flat steel lintel lacks the stiffness to properly support any substantial vertical loads without significant deflection. It probably wouldn't collapse, but could easily sag to the extent that the block wall and truss loads from above are likely to cause wall failure.

The vertical legs of steel angles are what provide the increased section modulus necessary to prevent deflection. And don't make the mistake of trying to find "angle iron"--if you managed to find any, it would be too soft to carry loads, and hasn't been manufactured for more than 80 years. Steel angle should be used, and is readily available from many sources. It can easily be incorporated into a block wall; just don't skimp on the leg sizes and thickness.

 

You will never get an exact answer on the internet, especially with the vague description of the wall (cross-section, thickness of the load-bearing portion of the wall, and the amount of masonry over the lintel).

I am somewhat familiar with construction in that area and my gues is the that the masonry masonry units are 5-5/8" thick wall, 3-5/8" high and 15-5/8" high ( nominally 6x4x16" and not 4x16x6" block). That is a very common unit and type of construction in AZ.

Most engineers in the area have seen this situation through the years and know exactly what needs to be done. The amount of masonry above the opening is important, since if it is high enough, the load on the lintel may be less due to the arch action of masonry.

Dick

 

Thanks. I was curious about flat steel because the adjacent lintels on that same wall and height appear to be flat steel (I see no vertical support on either side and no seam in the middle to indicate a double angle). I'm now wondering if there is a bond beam already up there, and the existing metal I'm seeing isn't really structural? Do you know of a clean way for me to determine in a reinforced bond beam exists? Our building permit department is pretty helpful down here, and they'll have to green light me before I do any chopping into a loaded wall... I'm just trying to figure out if I can do this myself without the expense of structural engineer (very tight budget). I do appreciate your feedback.

 

A bond beam usually the top course (or two ). Its purpose is not really structural, but provide a solid bearing surface for any construction above (more floors or roof trusses).

If your building department is any good you will have a bond beam as a top course for a wall and often have a bond beam as an intermediate support/continuity an a gable end of a home.

A better description of the wall (height, length, etc.) is needed and is the reason you will never get a firm answer to your question without it. Bond beams are usually not detailed on a plan because they are usuallt built but local conventions.

A 6" thick block wall has tremendous strength, as exhibited by the many 7 to 20 story 6" load bearing block apartment buildings (partially reinforced and not technically reinforced on the upper 2 or 3 floors). If all gets down to the dimensions (thickness, wall height, wall length, wall section height above openings) and a simple answer will not be possible without it.

If you are looking at other construction, the flat bar running horizontally may just be a plate that si there to support the masonry above DURING construction and is supported by props that are removed later to allow the window installation. If your window opening is NEW and is 48" wide, you may have to do some investigation yourself (drill, probe, etc.) IF you know what to look for.

If you have enough load bearing wall height above an opening, the "arch effect" of masonry actually reduces the load on a lintel above an opening, but that requires an engineer to save the money invested.

Dick

 

Thanks again, Dick. What I have is 8x4x16 CMU (7.625x3.625x15.625). The height of the wall is 98". With the .375" joint, that means I have 24 rows of block. Above the 24th row is a sill, 2x4 trusses (4/12 pitch), and comp shingles. This wall is not the gable end. The window I want to install is 48" wide and 36" high. I want the top of the window to be level with the other openings on this wall, which is at the joint between the 21st and 22nd row. Do you think those 3 rows above my cut line could be filled and reinforced? The other openings are at the same height and the only visible lintels on those openings is the flat steel. This is a Knoell spec home, and I'm thinking their masons set in the flat steel while they built the wall because above would be bond beam. Would that be reasonable, given my single level home? Frankly, I'd rather sound dumb to you than dumb to my permit department. I'd be grateful for any additional advice you could offer.