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Framing

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  • Introduction to Framing
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How-To

Installing Support Beams

Here's how to assemble and set the long built-up beams that bear the weight of the floor framing.

By Roe Osborn
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Lay out a slightly oversize notch in the plate to allow for fitting the support beam, then cut out the notch.

The mudsills support the ends of the floor framing, but most houses require support for the middle of the floor framing as well. Support beams or girders provide that support. A support beam can be made of various materials, including steel, LVL, and glue-laminated 2× stock. Most often, though, it is made from built-up layers of dimensional lumber such as 2×10s or 2×12s.

Locating the support beam

The support beam for this project consists of three layers of 2×12s assembled into a beam 36 ft. long. Lally columns sit on concrete pads or footings and support the beam. The beam ends typically rest in pockets formed directly in the foundation walls. These pockets are oversize to provide an air space around the sides and ends of the beam, a detail that encourages air circulation and discourages rot. Beam pockets are deep enough to allow room under the end of the beam for a moisture-blocking pad.

Before you lay out the position of the beam, check the plans and confirm that the beam pockets are the right size and in the right places. You have some wiggle room but major discrepancies could require new beam pockets or a change in the length of floor joists.

If the pockets look good, lay out the location of the beam on the mudsills. Check the plans for the distance from the front of the house to the centerline of the beam and mark this point on the mudsills at both beam pockets. Now lay out the width of the beam (4½ in. in this case) by measuring from the centerline. We also marked the location for the end of the beam because the 2×6 mudsills overlapped the beam pockets and had to be notched. The layout included a ½-in. allowance for airspace at the end of the beam.

It’s easy to figure out the thickness of the pad under the beam. Simply set a scrap of beam stock on the bottom of the pocket and measure up to the mudsills. A pad exactly this thickness will position the top of the beam flush with the top of the mudsill. Metal plates or a piece of composite decking make a good pad that won’t rot or compress.

Set a scrap of the beam material in the pocket and measure to the top of the mudsill to determine the thickness of the beam’s support pad.
Set a scrap of the beam material in the pocket and measure to the top of the mudsill to determine the thickness of the beam’s support pad.

Assembling the beam

Once the beam pockets are prepped, determine the exact length of the support beam by stretching a 100-ft. tape between the notches in the mudsills. Reduce this distance ¼ in. to ½ in. at each end so that the beam will slip in easily. Regular lumber doesn’t come in 36-ft. lengths, however, so you have to build the beam out of shorter boards layered together. The joints between the boards should be staggered from layer to layer so that no two joints line up at the same place. And for maximum strength, joints should fall over a Lally column.

Start building your beam by gathering the stock. Check each board for crown by sighting down one edge. The crown is any bow across the width of the board. The crowned edge should face up when the board is installed so that the weight of the building will straighten it. Mark the direction of the crown clearly as you work through a pile of lumber. Keep the straightest boards for the longest lengths; cull the worst boards to be cut into shorter lengths.

The crown is the natural widthwise bow of a board and must face up when the board is installed. Sight down each board and mark the direction of the crown.
The crown is the natural widthwise bow of a board and must face up when the board is installed. Sight down each board and mark the direction of the crown.

Take the location of the support columns from the plans, and cut boards for each layer of the beam. As you cut the boards to length, make sure the ends are square. Label each board to indicate its position both by layer number and sequence in that layer.

Working from the framing plan, measure and cut individual lengths of lumber for the beam so that every joint will land over a Lally column.
Working from the framing plan, measure and cut individual lengths of lumber for the beam so that every joint will land over a Lally column.

On this project, the basement slab provided a nice flat surface to work on. To assemble the beam, we arranged the first layer on the basement floor. The boards for the second layer were positioned on top of the first according to layout marks made earlier, and a quick measurement of column locations confirmed the layout. The two layers were nailed together according to the nailing schedule spelled out on the plan. The location and size of nails are details that must be followed to the letter. For this beam, four 16d nails were required every 16 in. and wherever a board bridges a seam, a row of nails must be driven on both sides of the seam.

A poured concrete basement floor offers a perfect working surface for beam assembly. Double-check every layout measurement as the labeled pieces go together.
A poured concrete basement floor offers a perfect working surface for beam assembly. Double-check every layout measurement as the labeled pieces go together.
Where a board in the beam bridges a joint in the layer below, drive a row of nails on both sides of the joint (note the joint in the middle layer).
Where a board in the beam bridges a joint in the layer below, drive a row of nails on both sides of the joint (note the joint in the middle layer).

When nailing two layers of lumber together with 16d nails, angle the nails so that they don’t go all the way through the other board. And as you nail the boards together, be sure to keep the layers flush at the top edge of the beam. Usually all that’s needed to align the edges is a hammer tap. If more force is required, drive a toenail into the misaligned board to draw the edge flush (see “Toenailing Boards Flush”).

When the third layer is nailed off according to the nailing schedule, carefully roll the beam over and nail through the back face as well, again nailing on both sides of any seam. As an added precaution against rot, nail a length of aluminum flashing around each end of the beam.

Aluminum flashing nailed to the ends of the support beam provides added protection against rot.
Aluminum flashing nailed to the ends of the support beam provides added protection against rot.

Toenailing Boards Flush

To align boards edge to edge, drive a toenail into the edge of the overhanging board, then pound the nail with a hammer until the board edges line up.
To align boards edge to edge, drive a toenail into the edge of the overhanging board, then pound the nail with a hammer until the board edges line up.
There are many places in house framing where two boards must be nailed together face to face with their edges flush. Unfortunately, two boards rarely have the same amount of crown and sometimes a tap of the hammer isn’t enough to make them align. In that case, drive a 16d nail at an angle through the edge of the board that must be drawn in. Then hit the nail with a hammer until the edges of the two boards line up. Drive additional nails on either side of the first if more force is needed. When the edges are flush, drive a nail into the face of the top board, near the toenails, to hold everything in place.

Setting the beam

The framing contractor on this project rented a rough-terrain forklift with a telescoping boom, a machine that makes moving lumber a breeze without straining anyone’s back. More common on West Coast building sites, a lift can be rented and easily pays for itself over the course of a project. Just make sure that anyone using it has been checked out thoroughly on its safe operation.

Before a beam is lifted into place, make temporary posts to support it until the Lally columns can be set. Each post is simply a pair of 2×4s nailed face to edge to increase stiffness. To determine the height of a post, stretch a string across the sills and between the beam pockets as tight as you can make it. Then at each temporary post position, set a scrap of 2×12 (the height of the beam) on the slab on edge and measure up to the string.

For the height of the temporary support posts, first stretch a taut string between the beam pockets. Then measure to the string from a scrap of beam material.
For the height of the temporary support posts, first stretch a taut string between the beam pockets. Then measure to the string from a scrap of beam material.
A forklift or crane makes setting the heavy support beam a safe and simple operation. Slip one end of the beam into position, then the other end.
A forklift or crane makes setting the heavy support beam a safe and simple operation. Slip one end of the beam into position, then the other end.

Assembling a Beam in Place

A built-up beam can be assembled in place if it’s too long or too heavy to be lifted. Lay out, cut, and label all the pieces as described above. Starting from one beam pocket, assemble two layers of the beam and support them with adjustable A-frame trestles. Nails staggered every few feet or so are enough to hold the layers together for now. Continue assembly to the other beam pocket, placing trestles as needed for safe, solid support.

When you’ve finished the first two layers of the beam, make the entire length parallel to a mudsill and hold it in position temporarily with 2×4s nailed to the plates. Then nail the two layers together according to the nailing schedule and add the last layer (or layers), checking frequently to make sure the top edges are flush, the beam is straight, and the top of the beam is in the same plane as the top of the mudsills. Many contractors use a transit to set the height of the beam, but it’s just as easy to stretch a length of mason’s twine between the mudsills and over the beam at every Lally column position.

When assembling a beam in place, support it on temporary trestles as you work. Keep the pieces in order and be sure to follow the nailing schedule exactly. (Note the double mudsill on this project.)
When assembling a beam in place, support it on temporary trestles as you work. Keep the pieces in order and be sure to follow the nailing schedule exactly. (Note the double mudsill on this project.)

When everything is ready, roll the beam upright onto blocks and make sure the top is facing up. Next, measure and mark the exact middle of the beam. Lifting chains can then be wrapped around the beam and positioned at equal distances from the middle so that the beam is perfectly balanced as it is lifted. Once the beam clears the foundation, carefully swing it into position over the beam pockets and lower it into position. When the beam is fully seated in the pockets, set the temporary support posts in place and tack them to the underside of the beam. Be sure to set the posts where they won’t interfere with the Lally columns later on.

Temporary posts nailed in a T-shape can be tacked to the underside of the beam for support.
Temporary posts nailed in a T-shape can be tacked to the underside of the beam for support.

Steel and LVL Beams

You can minimize or sometimes even eliminate the need for Lally columns in a basement by using materials that are stronger than lumber and that come in longer lengths. A steel I-beam can often span the width of a house without the need for any columns. However, steel is costly and has to be positioned with a crane or a forklift due to its weight. A wooden plate must be secured to the top of the beam with powder-actuated fasteners to provide a nailing surface for the floor joists. Also, many municipalities require that steel I-beams be enclosed in fire-code drywall before the house can be occupied.

An LVL beam is another alternative. LVLs come in long lengths and can be bolted together to form strong beams of various dimensions, and these beams are somewhat less costly than steel. The long lengths of built-up LVLs minimize joints, but the material is much heavier than conventional lumber, and a long beam may require crane placement. The density of LVL makes hand-nailing all but impossible.

A steel beam can span greater distances than wood, but you’ll definitely need a crane to get it into place.
A steel beam can span greater distances than wood, but you’ll definitely need a crane to get it into place.

 

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Previous: How to Air-Seal Mudsills Next: Installing Floor Joists

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Framing

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View Comments

  1. kentss | Jan 23, 2025 11:23pm | #1

    The article says, "Aluminum flashing nailed to the ends of the support beam provides added protection against rot." But the end is in contact with concrete. Doesn't aluminum flashing corrode in contact with concrete?

  2. patrick_mccombe | Jan 24, 2025 02:38pm | #2

    Hi Kent, The aluminum is more of a capillary break so the beam end doesn't absorb water moving through the concrete. Aluminum will rust when in contact with concrete but it's slow without water and a corrosive agent like salt. Peel and stick flashing tape or sill seal would perform the same job.

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Introduction to Framing
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