Substructure – Decks By E3

If you are attempting to build your own deck, then there are a lot of different options available to you during your project. One choice that stumps a lot of DIY deck builders is whether to support their deck with flush beams or dropped beams. If you’re not sure what the difference is or which is best for your deck, then this is the place for you. Let's first discuss the differences between flush and dropped beams on a deck. Then the various factors you should consider when determining which type of beam installation is the best one for your deck. Flush Vs Dropped Beam - What’s The Difference? As you may have guessed already, or maybe not. The name describes the beam placement in relation to the deck joists. The substructure supporting the decking of your deck. The bones of your deck, giving it form and strength for deck pleasure. What Is Flush Beam? Flush beams are structural support that is installed at the end of deck joists level with the top of the joists. The name ‘flush’ beam comes from the fact that the top of the beam is set flush (level’ or ‘even’) with the joists. Often of the same material and dimension as the joists, but not always. Similar to a rim joist but with additional plys to add strength to the deck and hold the weight of the deck along with people and furniture of the deck. The depth and number of plys depend on the span (distance between supports/posts) and the length of the joists supported. As determined by the International Residential Building Code (IRC), along with national codes such as the Canadian Wood Council. Combined with your local jurisdictions. Wow, that was a lot of lawyer speak to say check with your local building code to determine the sizes of your deck beam both flush and dropped. A flush beam is installed using joist hangers and can be installed at either end of your deck, or even in the middle. They are commonly used for ground or low decks, as well as for framing angled decks (such as stair landings or fashionable octagon deckings). What Is Drop Beam? A drop beam is installed underneath the deck joist rather than level with them. It can still be installed at the end, in the middle of the deck (like the flush beam) but is commonly installed slightly back from the deck’s end too. With the joists cantilevering over the beam. The joists bearing directly on top of the beam not requiring any structural support like hangers. As the name suggests, the beam is "dropped" underneath the deck joists. A way I keep it clean in my head is a simple question. Do I drop the joists on the beam or flush them up? Flush Beam Vs Drop Beam - Which Should You Choose? There are a few factors to consider when choosing to use a drop beam or flush beam in your deck project. It’s important to note that both work great for providing your deck with support and strength, but they may not always be interchangeable. There are deck designs or placements which are better suited for a flush beam or vice versa. Below area few things to consider when choosing the best beam for our deck. Under Decking Space The most important factor to consider when choosing between a flush beam or drop beam for your decking project is the amount of space you have underneath your decking. If your decking is built close to the ground, then you probably won’t have enough space underneath the deck frame to install a drop beam. Drop beams require more space underneath your deck, and as a result, it’s usually the deciding factor on whether or not a deck builder opts for a drop beam or flush beam. As a result, drop beams are more widely used for decks that are a minimum of 18" (457 mm) above grade. The height of the joists plus the beam. Yes, you can build a lower deck with a drop beam, but additional steps will be needed to protect the grade beam from rotting. This is why most deck builders choose to use flush beams on low decks instead. Where there's not enough room underneath the deck’s frame for a drop beam. But at times, aesthetically, a deck will look better with a flush beam. Such as around window wells, angle stairs, etc. This doesn’t mean that you have to go for a drop beam if you have a tall decking. You can still use a flush beam to support your deck, but in my experience, most people choose to use a drop beam. Why? Let's answer why you may want to use one over another beyond space restraint. Strength Although both drop beams and flush beams are great for strengthening and supporting your deck substructure, drop beams are generally considered to be the stronger option of the two. This is because a flush beam holds the joists on the ends using hangers., while the drop beam supports the joist from underneath. Meaning that your deck will rely on the wood structure itself to support its weight when using a drop beam, while decks with flush beams rely on metal fasteners for joists to beam connection. The difference in strength is pretty minor, but metal fasteners can break or rust over time. Especially if you use non-zinc-coated hangers, but that's a different story. The strength of wood is far stronger and sturdier. Bearing the weight of the joists, decking, furniture and let's not forget, people more easily than individual metal components like fasteners. A whole wooden beam is much less likely to snap or break compared to an individual hanger or nail. This is why many deck builders prefer supporting the decks they construct with dropped beams over flush beams. But strength is only one reason to use a drop beam if you can. Cost On that note of metal fasteners, it’s worth mentioning that flush beams will cost more compared to drop beams. Because of the need to purchase metal hangers and fasteners to attach the joist to the flush beams. Not bank breaking but an additional cost. A hanger goes for roughly a buck fifty plus add in the screws and nails, and you are roughly at $2 per joist per beam. For a simple attached 12' x 12' deck, 16" on centre joists, that is an extra $24. Drop the beam and go order a couple of combos from Wendy's. Even better, order that grill mat for under your grill to protect your decking from all that grease dripping from your burgers. If your deck is bigger, big enough for grilling and dining, it will save you even more to drop the beam. Beyond cost is a design consideration. Design Another reason why you may want to choose a drop beam over a flush beam for your decking is more flexibility for your deck design. Drop beams allow for cantilevers off the end of the deck. Increasing size by a couple of feet without adjusting the footing locations. It can also work better for under-deck drainage. With the drop beam supporting the trough directing the water away from below your deck. Again depending on your local building codes but some do not include the cantilever in the joist span calculation. Allowing additional deck depth without increasing the size fo the joists. Unfortunately, this kind of flexibility is not available with flush beams. Aesthetics Plus, there are deck aesthetics. A lot of people prefer the look of cantilevers and the design feature they bring to a deck over flush beams. They also add some additional dimension to the look of your deck, bringing some depth and shadows, which can increase your deck's appeal. Ease of Construction As a professional deck builder, this is the biggest reason to integrate a drop beam instead of a flush one. A drop beam is easier to work with and is faster to install joists on. Joists can be placed on beam without requiring hangers to be installed. Even holding one side while flushing up the other side on the ledger. Additionally, it takes way less time to nail a joist down to a beam than install a hanger. Plus, joists can be installed without cutting to length in advance. Then snapping a line and cutting all the joists in place. Saving time and ensuring the deck rim will be straight. Probably my favourite reason is tolerance in footing location. Now don't go overboard and become a hack. Digging in your footings without measuring and all. But a beam post misplaced a 1/4" will never be noticed with a drop beam. You can adjust the beam to line up with the post and no one will notice. The same flush beam cannot be adjusted without changing the overall look of the design. Yes, there are ways to hide that too, but a drop beam is so much easier to make minor adjustments without changing the overall look of the deck. These and many more are why I favour dropped deck beams over flush beams. Unless, of course, I don't have enough height under the deck for a drop beam. Which Type Of Beam Is The Most Popular? The type of beam you choose for your deck often comes down to the amount of space you have underneath the frame. If there’s no room for a drop beam, then you have no choice but to use a flush beam instead. Flush beams are great for reducing vertical space required and so are commonly used for ground-level decks. Not just the code ones that don't require hand rails but the true ground-hugging decks. However, drop beams are probably the most popular type of beam out there. Because of the reasons I listed. I have built more decks than I can count with drop beams. They are the most common design. Just looked out my back window. Over 20 decks and every one of them has a dropped beam. Not scientific, but this is not unusual. Flexibilty, cost, strength, ease of construction have all played a reason why this is so. And why dropped beams are the most popular deck beam option. But there are times for flush beams which should not be overlooked. Reduce headroom clearance. Lower deck height. Just to name a few. Final Thoughts How I often go about choosing between a drop beam or flush beam. I start designing the deck using the easier and cheaper option of a dropped beam. Then while drawing and designing the deck, I ask. Would there be any advantages to raising this beam and making it flush? If none come to mind, then I stay with a drop beam. If there is a reason, then I adjust my plans to include a flush beam. That way, I only include them if there is a deck benefit. a benefit that makes it worthwhile. Dropped or flush, enjoy your deck. https://www.youtube.com/watch?v=sEaOoZ3NkJs