Most locations have added it to their deck framing code. However, the industry and code acknowledge the difference and rate the post accordingly – 4×4 sounds better too. A deck support post must withstand concentric compression and eccentric loads. During your planning stage, don’t forget to consider the spacing for your beams. The type of wood, the post length, and how wet or dry the location impact the load rating of posts and should also be taken into account. I will attach 2 x 6 or 2 x 8 deck joists to these posts. They are commonly secured at or above ground level with a metal bracket to a footing, pier, or deck block, and to the beam at the other end to prevent twisting. The pier size is in the intersecting box of the row that corresponds with your joist span and the column that corresponds with your pier spacing. When we design decks for our area these are the building practices we follow. Use an 18” galvanized steel post sleeve or two 18-inch galvanized steel plates. With the min. If you have to use a built-up I suggest placing a flashing cap or membrane that won't break down and not use the ardox (threaded nail) as prescribed but use sds screws or thru-bolts. You should also know the size of the post you are considering to use. Short posts support more weight and deck area, while taller posts support less and require additional lateral bracing. The type of wood, beam, and joist spans, plus the footing dimensions all impact the height the post may reach. A “cantilever” is the unsupported end of a joist that extends past the last support post at the edge of your deck. Posts at the end of a beam carry less than the posts in the middle of a beam or deck, so the middle posts may need to be thicker than the end posts. © Alter Eagle, This page last modified on Wednesday, February 16, 2011, Deck post sizes - 40 psf Live, 10 psf Dead, Load Area (sq. Fasten the ends of each with (two) 1/2” diameter through bolts or approved equivalent connectors. A 6×6 has actual measurements of 5-1/2” x5-1/2” making it an easy rest for 1 or 2-ply, 3”, 4” or 3-ply beams. Any post more than 8 feet long we use 4x6 or 6x6. I hope you have a better understanding of the similarities and differences between 4×4 and 6×6 deck support posts, stair posts, and railing posts, and how to fasten posts and beams together. As always, your comments and suggestions are appreciated. Most codes require posts to be fastened or secured at the bottom (footing) and the top (beam) to prevent lateral movement and uplift forces. Keep in mind that these figures depend on the size and spacing of … code for nailing they will still check, may warp and will shrink at the splices which allows moisture to get trapped with dirt promoting the compromise of the beams over time. 6×6 deck posts offer a solid, stable base for most decks. What is Better, 4×4 or 6×6 for Deck Railing Posts? The beam should be centered or flush to the post sides so the weight is fully supported. On my own deck, I had to replace a 6x6 after a year, when it bowed almost 1 1/2 inches. Caps and connectors are fabricated to fit 4×4 or other sized posts, so make sure to get the correct piece. Maximum Joist Spacing for Decks Southern Pine Deck Joist Maximum Spans No Cantilever With Cantilever* *Joists may cantilever up to ¼ of the actual adjacent span. However, an 8-foot 4×4 supports 6468-pounds and 2339-pounds at 14-feet, while a 6×6 is 18032 and 10550-pounds respectively – or 64% and 78% more load capacity. Also on triples use 20d like we used to not the 10d. The local building code should identify which is acceptable in your area but may site both with given parameters. Post Anchors are made to support a maximum raililng height of 42 inches. Note: The 2018 IRC Table R507.3 identifies Tributary Areas of 20 to 160sq.ft. Paint the cut ends with waterproof sealer and then cover the post top end grain with self-adhesive water-proof tape to further reduce the risk of rot too. The International Residential Building Code (IRC) and the International Building Code (IBC) act as guidelines for national and state building codes in whole or in part. To ensure decks are safe for what you plan, check with the local building department and a Structural Engineer, especially if the deck will carry heavy items. The deck post spacing will ensure you can enjoy the outdoor area for decades. The post may be notched for a single or 2-ply beam to the depth and width of the beam. 3. A 6×6 will work as a railing post too but is over-kill unless there are other aesthetic or structural reasons for the heavier posts. Size your deck beams and headers with our easy-to-use span table, which allows you to cross reference the post spacing and joist length to determine the right deck beam size. As a general rule, the best “bang for your buck” is most typically spaced every 12 feet, although 10 foot and 14 foot spacings are often a close second. Caps sit on the post and the beam sits on and inside the upper part of the cap. A cut stringer must be supported every 6-feet and a solid stringer every 13¼-feet. Eugene has been a DIY enthusiast for most of his life and loves being creative while inspiring creativity in others. The load capacity of a 3-foot #2 grade 4×4 is 17,426 pounds, and a similar 6×6 is 20,834 pounds or 16% better. For example, a 2 x 12 joist placed 16” OC. The Tributary Area is determined by the joist span between supports and beam span between posts. A corner post supports a 1/4 of the area defined by the joist and beam span, and an edge post supports 1/4 of two areas. Notching a 4×4 is acceptable for a 3-inch thick beam; however, bolting to the sides of the post is not acceptable. For my money, I’ll use a 6×6. 5. Plan in advance by knowing the correct deck beam span to use. The type of wood and length of post influence how much it will support before snapping. Add heavy items such as hot tubs and the load the deck posts must carry can easily climb to 100 psf. The nominal 6×6 is actually 5-1/2” x 5-1/2” and offers ample support to 3-ply dimensional lumber beams, which is why many deck builders and DIYers use them for all deck support purposes. Let's make it a present that will last for generations with these top 5 tips on how to build a deck frame and substructure. Your post footings are the foundation of your deck and just like your house, the deck is only as strong as its foundation. It is advisable to check your local ordinances as neighboring jurisdictions can have differences – deck posts being a common difference. I'll use the PCz post caps (left) if I have a condition on a slope with possible lateral movement or a heavy load with a large joist over a longer span. Try it out at Decks.com. An intermediate landing must be built if the stairs exceed a vertical height of 12’-0” but may be used to shorten smaller stringer spans. How much they support is based on the tributary area and post height. Thicker beams will support more and allow for wider post spacing. for Live Loads of 40, 50, 60, and 70psf. 2. spanning 16’-6” between supports may cantilever up to an additional 4’-1 ½” for a total maximum length of 20’ -7 ½” Southern Pine Deck Beam Maximum Spans* Lumber Size Total D Always refer to your local building codes or a structural engineer. We’ll also look at posts for deck stairs and deck railings. Once they are tied in with the top and bottom rails and the railing cap board attached, they’ll resist twisting and bending. Solid blocking over beams should be mandatory for decks. These are the beam size tables I use from the UBC code I find they still work well, I laid them out so they are easier to read and I found them better than the interior IRC table or the new deck prescriptive. Hit + and - buttons to open or close spacing, re-calculating the deck to find how different spacing options effect cost and materials. Trim | Cabinets | Mantels, Deck Contractor
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