InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
How to build & install a built-up structural beam for decks, porches, & similar structures. This article describes how to build a beam used to support a deck or porch floor or similar structure. We describe building the beam out of 2x lumber in four easy-to-follow steps.
The article concludes with a description of different methods used to make a secure structural connection between posts and beams in wood-framed structures. This deck design-build article series describes construction details for decks and porches, including avoiding deck or porch collapse and unsafe deck stairs and railings.
The beam, or girder, is the structural member that spans from post to post.
Modest-sized decks typically are built with a single beam, but larger decks may require two or more.
[Click to enlarge any image]
There are several ways to make and mount a beam.
Regardless of the style of beam you use, you can be sure that it will be heavy. Plan to have a helper or two available when you need to lift a beam into place.
How to Construct a Built-up Deck Beam
When the design calls for placing a beam made of two 2 x boards over 4x4 posts, a very common arrangement, many deck builders like to construct the beam with Vi-inch spacers between the boards. This produces a beam that fits perfectly on top of the post, since 2X lumber is 1 1/2inches thick.
Additionally, the spacers allow water to drain through the boards, which prolongs the life of the beam. Use pressure-treated plywood for the spacers.
Note, however, that if your plans call for a single 4X beam, which would be 3 ½ inches thick, this built-up beam will not be sufficient. Structurally, it amounts only to a 3-inch-thick beam.
You can also make a built-up beam without spacers. Attach boards to each other with l0 d nails driven through both sides at least every 16 inches.
Apply a bead of silicone caulk to the joint between the boards to keep any moisture from penetrating.
The structural connectors shown at left are used at inside corners where a joist hanger or post & beam connector doesn't work - for example at the inside corner formed by the side rim joists and the ledger board or the inside of side rim joists and the front rim joist.
When Constructing a Built-Up Supporting Beam, Center Joints over Posts
When buying stock to use as beams, plan to have each joint fall directly on the center of a post. The adjoining sections of the beam should be cut as squarely as possible to provide maximum bearing on the post. With built-up beams, stagger the joints between boards, still making sure that each joint falls on the center of a post.
When Building Up a Beam Set All Lumber Crown Side Up
Lumber that is used for beams and joists nearly always has a visible crown, or arch, as shown below. Install both beams and joists with the crown facing up. That way, once the deck load begins pressing down on the crown, it will level itself out. In constructing a built-up beam, make sure the crown on both boards faces the same way
4-Steps to Build & Install the Deck Support Beam
Step 1: Find the Framing Lumber Crown
Locate and mark the crown for the beam. You can usually spot the crown by sighting down the edges of the board. Alternatively, set the board on edge on a flat surface, such as a concrete driveway or garage floor. You might want to mark the board with an arrow clearly indicating the crown.
Framing Note: Always install the board crown side up. When building a built-up beam, sight down each board, mark for the crown, and attach the boards with both crowns up.
Step 2: Assemble the Deck Beam
It is smart to build a beam that is a bit longer than needed. That way you can shift the joists slightly to square up the frame if necessary.
Once that is done, the beam can be cut to finished length. Assemble a built-up beam on a pair of sawhorses. Attach spacers to one board every 12 inches, then set the other board on top and drive three 12d nails at each spacer location.
Flip the two boards over and repeat the nailing pattern. Stagger joints between boards, and secure each joint with a spacer and nails.
Step 3: Set the Deck Beam in Place
If possible, position or reattach string lines representing the sides of the deck.
Align the beam with the string lines at each end. If you made the beam a bit longer than needed, overlap the string an equal distance on each end.
Lifting a typical deck beam overhead may require three or more relatively strong workers.
The safest way to install a high beam is to use scaffolding, which will also make joist installation much easier.
If you are concerned about a heavy beam tipping over as you try to set it in place, temporarily attach 2 x 4s to a couple of posts so that the 2 x 4s stick up by 8 to 10 inches.
Set post caps on the other posts and fasten them to the posts with a single nail each. Remember to install the beam with the crown side up.
Deck girder flashing tip: In our photo the deck beam and some deck joist top surfaces have been protected by additional flashing. Keeping water out from between the segments of built-up deck beams can substantially increase the life of the structure.
Obviously the time to make this decision is before nailing the deck flooring in place.
Since the deck fasteners will puncture flashing you might ask what good it's doing. Water enters an un-flashed deck girder at the gaps between the deck boards.
Step 4: Attach the Deck Beam to the Posts
With the beam safely in place, add post caps to any additional posts that need them.
Check the beam’s alignment with the string lines.
You can also check the alignment by measuring the diagonals; provided that the beam is equally spaced from the ledger on both sides, the beam will be properly positioned when the diagonals are identical.
Once you are confident that the beam is squared up with the ledger, attach the post caps to the posts and the beam with nails as recommended by the post cap manufacturer.
Our photo (left) illustrates a typical steel post-to-beam connector that ties a 4x4 post to a built-up deck girder. Other sizes of post and beam connectors are available for virtually every combination of post dimension and beam dimensions.
Post-To-Beam Connection Methods for Decks & Similar Structures
The strongest and most secure way to install a beam is directly on top of the posts. In most cases, the easiest way to connect the beam to the posts is with galvanized post caps.
Post caps are available to fit most typical post-and-beam configurations, even where the beam is narrower than the post. The top three illustrations at right show some of the more common connections.
Beams and posts can also be fastened together with wood cleats made from framing lumber, which must be bolted to both members.
Although the cleat method requires a bit more work, some people prefer the look of wood to less attractive metal caps, especially when the connection will be fairly visible.
Continue reading at DECK JOIST LAYOUT or select a topic from the More Reading links or topic ARTICLE INDEX shown below.
Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
Ask a Question or Search InspectApedia
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
 Steve Bliss's Building Advisor at buildingadvisor.com helps homeowners & contractors plan & complete successful building & remodeling projects: buying land, site work, building design, cost estimating, materials & components, & project management through complete construction. Email: firstname.lastname@example.org
Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education.
Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com
 Mark Morsching, Everflashing, Tel: 800-550-1667, Email: email@example.com. The Everflashing product comes in G-185 and Stainless Steel and is intended for use with treated lumber with copper in it. Everflashing produces a variety of specialty flashing products including flashings for use with decks at deck ledgers and deck perimeters.
 Claudia Hudson, Asheville NC, Tel: 828-252-0644
Email: firstname.lastname@example.org . Ms. Hudson is an SEO copyrighter / content writer. She has provided background research and text for InspectApedia's articles on deck and porch construction methods & procedures. April 2013.
Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program. Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
The Home Reference Book, a reference & inspection report product for building owners & inspectors. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
The Home Reference eBook, an electronic version for PCs, the iPad, iPhone, & Android smart phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones
Wikipedia provided background information about some topics discussed at this website provided this citation is also found in the same article along with a " retrieved on" date. NOTE: because Wikipedia entries are fluid and can be amended in real time, we cite the retrieval date of Wikipedia citations and we do not assert that the information found there is necessarily authoritative.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
The ILLUSTRATED HOME illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
The HOME REFERENCE BOOK - the ENCYCLOPEDIA of HOMES, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
The HORIZON SOFTWARE SYSTEM manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones