Hyderabadghar/Do it your self/How to Install Deck Beams

There are four considerations when choosing the beam(s) for your deck. First, think about space. If your deck is built close to the ground, you may not have room to put a beam on the posts or joists on the beam. You can save room by using a bolted-on beam and/or by having the joists tie into the beam with joist hangers rather than sitting on top of the beam.

Next, think about whether the beam will be visible, and if so, what it will look like. If your beam will be visible, choose a style. Nicely installed bolts on a built-up beam can look good, while a massive timber has a classy yet rustic look. Be aware, however, of what sort of lumber is available—it may be that you can't get a good-looking 4x8, for instance.

If your deck is raised more than a few feet off the ground, there's another consideration: an on-top beam is more likely to need bracing than one which is bolted on.

Finally, consider weight. A 16-foot piece of 4x10, especially if it's still soaking from pressure-treating, can be a real back-breaker. And things can get downright dangerous if you have to lift it high in the air. So in some cases, it is simply easier on your body to use built-up beams.

PROJECT BASICS

Project: Moderate

Estimated Project Time: 1 hour

Estimated Project Cost: Varies with the height, number, and type of beams

Start Tips: Make sure your saw blade is sharp.

Safety Tips: Never use a power tool on a workpiece—large or small—that is not firmly supported.

Recommendation: Do-it-Yourself

TOOLS & MATERIALS

Lumber for the beams	Lag screws, 2-1/2 inch deck screws or 12d galvanized nails (for attaching beams to the posts)
Circular saw	Carriage bolts, if needed
Hand saw or reciprocating saw	Joist hangers, if needed
Safety goggles	Pencil
Hearing protectors (when cutting lumber)	Framing square
NIOSH-approved dust mask or respirator (when cutting lumber)	Caulk, if needed
Work gloves	Drill and bits
Heavy-duty work boots	Repellant-preservative
Pressure-treated plywood spacers	Line level or water level
Post caps and strap ties (to hold beams in place)	Shims, as needed
Square	Ladders, as needed

Fig. 1

INSTRUCTIONS

Types of beams
Here are some common types of beams:

A) A beam made of a solid piece of four-by lumber resting on top of 4x4 posts. If done correctly, this has a classic, clean look, but there's little leeway for correcting mistakes, and it can be difficult to find good-looking four-by lumber. (Fig. 1)

Fig. 2

B) A built-up beam made of two two-bys with pressure-treated plywood spacers sandwiched between them. This is actually stronger than a solid beam, and usually less expensive, but it does take some extra time to build. And once built, it may be just as heavy and difficult to maneuver as a solid beam. (Fig. 2)

Fig. 3

C) A beam consisting of two pieces of two-by lumber attached to opposing sides of the posts. Though a bit time-consuming, this is often the best type of beam for the do-it-yourselfer, since it involves little heavy lifting and is correctable. (Fig. 3)

Fig. 4

D) A laminated beam, made of two two-bys that have been joined together with many screws or nails. This is also simple to build and gives you the option of either attaching the two pieces together on the ground or putting the second piece on after the first, thereby avoiding heavy lifting. (Fig. 4)

Fig. 5

E&F) A solid or doubled beam set into a notched post (Figs. 5 & 6). The notching adds some strength to the beam but takes away some from the post. So this is recommended only when posts are 6x6s. The notches must be cut cleanly and accurately, with no gaps, or they'll invite water to seep into the newly cut lumber—always a bad idea.

Fig. 6

Joists can either rest on top of the beam (usually the simplest solution because you can hide the beam by cantilevering the deck)—or they can be attached to the side of the beam with joist hangers. All beams discussed above can accommodate either method.

Fig. 7

Beams on top of posts
For attaching beams on top of posts, choose from a variety of specially designed hardware. This hardware works better than pieces of wood that you cut and scab on, which always have exposed end grain and are prone to water damage. (Figs. 7 & 8)
Attaching the beams to the side of the posts gives you the option of bringing them to the same level as the joists. In fact, the beam takes the place of the header joist and so will be cut to exact length and marked for joists in conjunction with the ledger, as if it were the header joist. Make sure the beam is crown side up when you mark for the joists.

Fig. 8

Lag screws are strong if you drill the correct pilot holes for them. But some people prefer to run bolts all the way through the members, and this adds a bit more strength in exchange for extra labor. For laminating two two-bys together, a lot of 2-1/2-inch deck screws or 12d galvanized nails work much better than a few bolts.

Fig. 9

Installing beams
1) Mark the corner posts
Top a long, straight piece of lumber with a level, or use a line level or water level to mark the beam height on each corner post (Fig. 9). First, mark the spot that is level from the top of the ledger; this shows where the top of the joists will be (and the top of the beam if the beam and joists will be on the same plane). Note: if you want the deck to slope slightly away from the house for drainage, measure down from that mark 1/16 inch for every foot of joist travel. From the mark you just made, measure down the width of the joists—that's where the top of your beam will be if the joists rest on it. Mark the other corner posts in the same manner.

Fig. 11

3) Cut off the posts
Follow this step only if the beams will sit directly on top of the posts. If the posts are not cut accurately to height, you will have to top some of them with shims—not a great disaster, but something of an eyesore and a potential rot spot. Your beam may be crowned (remember, always put the crown up), which means that the posts in the middle will need to be a bit taller than the posts on the end. If possible, hold the beam in place to mark the interior posts.

Double-check your circular saw to make sure it cuts at a perfect right angle, or your cut will look sloppy. Using a square, draw a line completely around the post. Get into a comfortable position, take a deep breath, and cut two opposite sides with a circular saw (Fig. 11). For a 6x6 post, cut all four sides and then finish cutting the middle of the post with a hand saw or reciprocating saw.

Fig. 12

4) Make and cut the beam(s)
This is one of the few cases where letting a board run wild is probably not a good idea because it may be difficult to cut the beam cleanly once it's in place. Double-check your measurements; a wrongly cut beam is rarely correctable.

If you're constructing a built-up beam on the ground, position screws or nails so they do not go through the same grain lines or they could split the wood.

Fig. 13

Be sure to place any beam splices so they'll fall in the middle of your posts. For built-up beams, stagger the splices so that splices on the two-bys fall on different posts (Fig. 12). Cut the ends with a 45-degree notch for an attractive, finished appearance. This cut will not weaken the beam.

Fig. 14

5) Attach the beam(s)
If you need to wrestle a heavy beam into place, arrange for plenty of help and make sure that any ladders you use are extremely stable.

Put the beam in place, using screws to hold it temporarily. Measure to check that the beam is properly located so your deck will form a rectangle, not a parallelogram.

Install lag screws or bolts after predrilling pilot holes (Figs. 13 & 14). For an on-top beam, slide the post cap into place and attach it with deck screws. Drill more pilot holes—at least for the screws that go into the posts since these may split the wood.

If your beam will be covered by fascia, countersink holes so that the bolt or lag screw head and washer can sit just beneath the surface of the board, and fill the countersink with caulk after the lag screw or bolt is installed. For beams that will be exposed to view, a more attractive alternative is to through-bolt them with carriage bolts, if possible.

cut the posts flush to the top of the beam

Fig. 15

6) Cut off the posts
Unless your posts will rise up to become part of the railing or a bench, use a hand saw or reciprocating saw to cut the posts flush to the top of the beam (Fig. 15). This is a trouble spot, susceptible to water damage (since it is newly cut open grain that will be difficult to reach once the deck is built) so brush on a good soaking of repellant-preservative.