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Thread: Crawl Space Beam and Joist Support Questions

  1. #1
    DIY Junior Member Leaky1's Avatar
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    Question Crawl Space Beam and Joist Support Questions

    Our townhouse experienced significant damage to the framing in the crawl space due to water infiltration. We spent the last two years investigating where the water was coming from and believe we have done all that can be done to eliminate the sources. With that resolved we moved on to rebuilding the foundation and framing in the crawl space.

    We were in the process of replacing some rotted floor joists and decided to replace the entire support structure for the landing after seeing the extent of the rot and poor condition of the piers.

    I have some questions regarding how much end bearing is required for the ends of joists and beams and the best method of terminating a beam at a CMU wall.

    Regarding end bearing for joist and beams. I found the following in Principles of Home Inspection: Systems & Standards.

    Joists require 1 1/2 inches of end bearing, considerably less than the 3 1/2 inches required for beams. That's because the live load carried by individual joists is much smaller than the beam's load. Note: Some jurisdictions call for 3 inch end bearing on masonry. Check standard practices in your area.

    Where joists rest on beams, best practice is to have the joist rest on the full width of the beam, rather than just 1 1/2 inches. Good practice also includes splicing joists that overlap from opposite side of the beam.


    Based on the above I believe I should go with the following:

    ORIGINAL FRAMING Only 1 of joist bear directly on 4x6 beam.

    http://www.fototime.com/7D02FCEE01A6ED3/orig.jpeg

    Photo link below shows typical condition of the original joist after I removed the rim joist.

    http://www.fototime.com/65FC521A44909B7/standard.jpg


    PROPOSED REVISED FRAMING 3-1/2 of joist bare directly on 4x6 beam.

    http://www.fototime.com/510E5027526A10A/orig.jpeg

    Last week we poured new footings and pilasters for the posts that will support the middle of the new 4x6 beam and floor joist. The new 4x6 beam will replace the existing 4x6 beam and plywood shown in the original framing drawing above.



    I would like to support one end of the 4x6 bean with a Simpson HU46 hangar nailed to the 6x6 beam that replaced the rotted triple 2x6s. This will leave a gap between the new 4x6 beam and an existing 4x6 beam below.



    The other end of the 4x6 terminates at a CMU wall. Currently it bears 1 on a pressure treated 2x6 secured to the CMU wall with corroded pins and washers.



    I believe I have three options that meet code.

    1. Remove the current pressure treated 2x6 ledger and secure the end of the new 4x6 beam in a Simpson HU46 secured to the CMU wall with Simpson Titen screws.

    http://www.fototime.com/EE5EAA1DC8FB014/standard.jpg

    2. Remove the current pressure treated 2x6 and replace with another pressure treated 2x6 that is located 5-1/2 higher and secured to the CMU wall with expoxied 5/8 bolts, washers and nuts. The new 4x6 beam would be secured in a Simpson HU46 secured to the new pressure treated 2x6 with 1-1/2, 9 gauge, HDG nails



    3. Remove the current pressure treated 2x6 and replace with a pressure treated 4x6 secured to the CMU wall with expoxied 5/8 bolts, washers and nuts. This will allow the 3-1/2 of the new beam to bear completely on the new 4x6 ledger as recommended in Principles of Home Inspection.

    Comments appreciated.

  2. #2
    Moderator & Master Plumber hj's Avatar
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    Default joists

    It is somewhat tedious to read the entire message. But, your existing joists may only be bearing on the beam by 1", but the 2.6 "rim joist" attached to the ends, PLUS the 2x6 attached to the face of the beam under the joists alter the entire dynamics as far as support is concerned. BUT, you also have to figure in the fact that there is also an upper level "something" being supported by those joists also. Then add in that a 2x6 joist has limited support and span capabilities, and one has to wonder if there were calculations made at some time to ensure that they were adequate. As for expoxying the support bolts, that would only work if the concrete blocks are internally grouted. Otherwise you would need through bolts.
    Last edited by hj; 06-27-2009 at 03:11 PM.

  3. #3
    DIY Junior Member Leaky1's Avatar
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    I talked with a structural engineer yesterday and he said any of the options above for the attachment of a beam to a CMU wall are acceptable. Based on some efflorescence on the CMU wall I am hesitant to use Option #1. Since we are in a seismic area I am hesitant to use Option #2. Im not comfortable with the 1-1/2 10D nails if things start moving around. I think I will go with Option #3. The structural engineer suggested using 3x6 ledger instead of 4x6 ledger as another option, but I see the Simpson BC4 he suggested for the 4x6 ledger will not work with the 3X6 ledger. I will ask him if I can use Simpson A34 ties if I use the 3x6 ledger.



    He also said the revised framing is acceptable, but he wants me to add blocking under the 4x12.

    Thank you to everyone who responded.

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