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-   -   Lintel block requirement in CMU crawl space foundation (http://www.diychatroom.com/f105/lintel-block-requirement-cmu-crawl-space-foundation-174578/)

Gunn317 03-15-2013 10:32 AM

Lintel block requirement in CMU crawl space foundation
 
I'm building a CMU block foundation (crawl space) for an addition onto my house. I have and planned on using a 48" long lintel block to span the opening of the crawl space. But I'm unsure of the length of bearing surface I need for the lintel. I can't find anything in the 2009 IRC specific to it, and no instructions from the place I got the lintel from.

I had assumed 8" bearing surface. But when I got to thinking about it, this would make my crawl space opening 32" wide (and it will be 24" high). This meets code in both directions, but if I only need a bearing surface of 4" on each side, then my opening becomes 40" wide, a big difference.

And then again, I've seen newer homes where no lintel block is used; the crawl space opening goes right to the sill plate. This would increase my opening height another 8" too. But that may depend on the load bearing above. In my case, my floor joists will run perpendicular to the wall this opening is going in. So I think a lintel block would be required in my case.

Any thoughts?

brockmiera 03-15-2013 10:40 AM

I would strongly suggest going exactly by the plans that were obviously drawn by the structural engineer who designed your foundation.

Gunn317 03-15-2013 11:10 AM

Quote:

Originally Posted by brockmiera (Post 1137771)
I would strongly suggest going exactly by the plans that were obviously drawn by the structural engineer who designed your foundation.

No structural engineer involved here. This is the simplest of additions. Single story 14x37, no interior bearing walls. Crawl space CMU foundation using 8" block.

brockmiera 03-15-2013 11:17 AM

Quote:

Originally Posted by Gunn317 (Post 1137793)
No structural engineer involved here. This is the simplest of additions. Single story 14x37, no interior bearing walls. Crawl space CMU foundation using 8" block.

Really? You didn't need a foundation plan to get a permit?

dakzaag 03-15-2013 12:53 PM

I can't recall a crawl space build that had a block header over the entrance.

I have probably constructed 15-20 per year for the last 5 years.

You can always put a hatch in a closet or something and avoid the opening altogether.

To answer your question regarding lintels, block lintels usually have 8" bearing. Iron lintels are usally sized by what is being supported.

jomama45 03-15-2013 02:08 PM

We do these all the time as well, so I'll offer a few suggestions.

First, IIRC, precast concrete lintels only need 4" of bearing peer side, but they need to be on solid masonry. SO, you would need to fill the cavity of the 2 jambs. 8" is the most typical though, as it keeps the block on bond.

To get additional head room, and avoid the need of a precast lintel, typically an additional piece of 2x lumber is attached to the existing rim joist, creating a header over new opening. Once attached, the 2-3 existing floor joists are attached to the new "header" with joist hangers.

You may also be able to find a longer lintel, and just allow for 8" of bearing on each side to simplify it. I can't speak for everywhere, but it's suddenly become extremely hard to find precast lintels here since the housing market tanked. We used to be able to get lintels 4", 6", and 8" width, from 40" to 144" in 8" increments just 5-10 years ago, now we're fighting over leftover stock...........:censored:

concretemasonry 03-15-2013 02:53 PM

jomama45 is correct because he in involved in the construction end of the business.

If I recall correctly (no code copies handy now), the IRC does adopt the ACI 530 code by reference, just as the IBC does. You will just have to read closely and find the referred code. The ACI 530 got rid of the old "running bond" and "stacked bond" definition problems by using a term "other than stack bond" that normally makes a 4" bearing perceptible for most wall patterns as a minimum. For higher loaded structures than homes, the 4" minimum may be acceptable, but not architecturally pleasing. The ACI 530 masonry standard is not a code, but is written by engineers, contractors and suppliers as the optimum standard for masonry and is adopted by most model codes in the U.S. and many international authorities. The standard is not written by ACI, but they participate in the creation and maintence and ACI does the printing and distribution and the ACI 530 designation commonly used short identification.

Dick

stadry 03-15-2013 09:27 PM

zzzzzzzzzzzzzzzzzzzzzzzzzz this is making my hair hurt :laughing:

Gunn317 03-18-2013 06:18 PM

Quote:

Originally Posted by brockmiera (Post 1137799)
Really? You didn't need a foundation plan to get a permit?

No. All I actually needed was a top view plan of the exterior and interior walls and the room designation. I designed the house addition/renovation myself and then consulted with an architect to finalize them. While I am an engineer in real-life, I am not a structural or civil engineer.

Quote:

Originally Posted by jomama45 (Post 1137918)
We do these all the time as well, so I'll offer a few suggestions.

To get additional head room, and avoid the need of a precast lintel, typically an additional piece of 2x lumber is attached to the existing rim joist, creating a header over new opening. Once attached, the 2-3 existing floor joists are attached to the new "header" with joist hangers.

Great suggestion here! I think this is the ticket and makes complete, and obvious sense to me. I've been thinking about it and my only question is:

What do you do with the sill plate in this location? Eliminate it, or continue it across the span? Reason I ask is I'm visualizing that the joist hangers may interfere with the sill in this spot. The sill could be eliminated and then 2x material fastened to the underside of the joist to frame out the crawl space opening, to attach a door. Am I on the right track? And I am planning on using engineered rim boards and I-joists for the floor system. Could I just double up on the rim board in this location, instead of using 2x lumber?

I've updated my model to include your suggestion (disregard the incorrect joist hanger, it was the closest I could find :)). http://www.mulberryhall.us/pub/house...aceOpening.png


Thanks for all the help, much appreciated!

GBrackins 03-19-2013 07:39 AM

Quote:

Originally Posted by Gunn317 (Post 1140279)
And I am planning on using engineered rim boards and I-joists for the floor system. Could I just double up on the rim board in this location, instead of using 2x lumber?

http://www.mulberryhall.us/pub/house...aceOpening.png


Thanks for all the help, much appreciated!

do not mix solid sawn lumber with engineered wood products such as I-joists as the shrinkage percentage is different.

If you know the manufacturer of the engineered wood products you can either download their literature or obtain their engineering software. These will allow you to determine if two plies of LSL rim will support your load based upon the span.

myself I'd probably use an LVL as a header to connect my joists to. I'd still use the single ply rim around the perimeter.

Good luck! :thumbsup:

Gunn317 03-19-2013 08:51 PM

Quote:

Originally Posted by GBrackins (Post 1140643)
do not mix solid sawn lumber with engineered wood products such as I-joists as the shrinkage percentage is different.

If you know the manufacturer of the engineered wood products you can either download their literature or obtain their engineering software. These will allow you to determine if two plies of LSL rim will support your load based upon the span.

myself I'd probably use an LVL as a header to connect my joists to. I'd still use the single ply rim around the perimeter.

Good luck! :thumbsup:

Yes, I figured as much about using solid lumber, one of the reasons for my question. LVL does seem the way to go. My span is only 14'; I already have product literature and span tables that I can reference.

I also called and talked to our local building inspector this morning about what I drew up and posted based on the recommendations here. He said it was all good to go.

At this point I'm assuming the sill plate will need to be removed over this crawl space opening so as not to interfere with the joist hangars. Can anyone confirm my thoughts, or steer me true?!

Thanks!

jomama45 03-19-2013 08:53 PM

Absolutely, no need for the sill plate under the opening. As you mentioned, it will only be in the way of the joist hangers..................

Gunn317 03-20-2013 07:03 PM

Great, problem solved! I've updated my drawing to reflect the final look.

Thanks!


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