Tripled up 2x8 for beam

topic posted Sun, July 9, 2006 - 7:18 PM by  Witchy
Share/Save/Bookmark's getting down to the wire and none of the books I have give me an answer to this one. Hoping there's someone out there who can help.

The guy in the Building Department said we could, quote, "triple up 2x8's for the beam" to support the floor joists. The beam will be a little under 27' long.

I get the general concept, but how are they fastened together? First instinct says to bolt them together.

The longest I can get the wood is 20' pieces. Since I'm spanning more than the 20', I'm assuming you stagger the pieces so the cuts don't line up.

Any feedback is greatly appreciated.


posted by:
  • Re: Tripled up 2x8 for beam

    Sun, July 9, 2006 - 8:02 PM
    WE are totally redoing an old house totally gutted now and even pulled up the floors down stairs. Just asked my man to help with your problem. He wouldn't recommend free standing that distance. You will need a support in the middle. We put a support on a 13 ft span. you can use multile boards using yellow pine #2 or better with 2 layers of 5/8 to 3/4 plywood laminate together using construction adhisive 3 1/2 in screws or 15 galvanized nails. Build in place. Deffinately needs a support in the center. He just said he would use larger then 2 X 8. You can buy a laminated preenginered beam.

    Hope this helps.
    • Re: Tripled up 2x8 for beam

      Mon, July 10, 2006 - 5:37 AM
      Thanks for the info, Patty.

      There are 3 piers for support...1 along the wall that doesn't have the new foundation, and 2 more at 7' intervals. The floor will be over an 18" crawlspace that has a concrete surface.

      Re the preengineered laminate stuff...too pricey. I'm on a VERY tight budget on this project. 2x8's are code, and should be OK. It's only a single floor, and won't need to support a lot of weight.

      • Re: Tripled up 2x8 for beam

        Mon, July 10, 2006 - 5:54 PM
        Face nailing with 16d nails should do the job. The building code would determine spacing of the nails (or if they are acceptable at all.) If I had to guess, I would say 4 nails across the 2X8's every 8 in. Stagger them.

        Nail piece A to B with four nails at 8, 16, 24, ... inches
        Nail piece B to C with four nails at 4, 12, 20, ... inches if that makes sence.

        Yes stagger the joins. and put the joins immediatly above the intermediate support posts.
      • Re: Tripled up 2x8 for beam

        Mon, July 10, 2006 - 9:02 PM
        You say it's a one story house so although I'd like to see something bigger like a 2x10 or 2x12, I think 2x8 will work . With the pier supports along the beam span you should be OK or at least "code". Have you thought of how your gonna get the beam under the house and in place?
        • Re: Tripled up 2x8 for beam

          Wed, July 12, 2006 - 9:57 AM
          >Have you thought of how your gonna get the beam under the house and in place?

          The addition is all new construction, so we are literally building from the ground up. Lots of room to maneuver. The addition area is 15'x27'.

          The crawlspace will only be about 18" deep when it's done, so this should be fairly easy. The ground under the addition used to be a cement patio. They cut into it for the foundation (38" cement footer and 3 courses of block), and piers (also 38" footer and block), and left the rest of it intact. The space is completely cement covered and level, so we can fasten the 2x8's together and lift the beam a few inches on to the post/piers. I've got a crew who will be helping...definitely couldn't lift it myself. ; )

          • Re: Tripled up 2x8 for beam

            Wed, July 12, 2006 - 6:42 PM
            "The addition is all new construction,"
            Oh, then it's a piece of cake, Right... lap yr joints 4 feet and use construction adhesive and lots of nails... like everyone else said, but try to keep one edge straight when nailing up the beam. I' ve seen guys nail bows into beam by setting up the boards on the ground on edge and just nailing away not knowing if the ground was curved or something ...use a tight string line to set the edge.
  • Unsu...

    Re: Tripled up 2x8 for beam

    Mon, July 10, 2006 - 6:31 AM
    You are in Cleveland so this is something you might be able to pull off.
    Look for steel beams Steel I beamb is you can or Box beams I prefer I ( or H) beams.

    Steel is so very underused in residential construction but is is the cat's meow when it comes to spanning long sections with no support collumns in between the ends

    You should consider the load and the span. the beam will be rated in KiPs (Kilo inch pounds) Calculate the static and dynamic loading and multiuply it by four. Then go find a beam that will support that load over it's length Your construction will never move.

    An alternate to a steel beam is the laminating of wood and steel together. Many restorers use 3/8" or 1/2" steel plate cut the width of the wood beams and laminate the plating to the end joints overlapping a bout 2' on either side of the joint when mating two studs together end to end.

    You might also consider an engineered joist. I don't like them but they are way strong and you can get 'em from any lumber yard.
  • Unsu...

    some passing ideas

    Wed, July 12, 2006 - 9:41 PM
    sorry, no real experience in house building.

    i make furniture and when i need something as strong as possible i will use the proper joint, use wood glue, and screw or nail it as well.

    you are using a 27' floor beam, supported in 3 spots, built with 3 pieces of 2x8 stacked together. will this beam be running horrizontally or vertically? not an expert here, but would vertically running 2x8's provide more strength for top weight, but less support for sideways straying. i am assuming here that horizontally running is the proper way as long as the beam is thick enough.

    what if you could provide both axis's of support. what if you made your own beam? stack 2 or 3 boards up horizontally, glue and screw them together, then "dado joint" the next board, vertically, in from the bottom, glue and screw this as well and make your dado 1" deep. this would make a "t" shape. (imagine if you could do a sliding dovetail joint here instead of the dado joint).
    your pier can now attatch to this beam with a huge 7" deep open mortise cut into the top of the pier, only bolt it, no glue or nails. if you are using a metal pier you will need a welder to attatch a U shape to the top of the pier.

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