Dangerous deck (C) Daniel FriedmanDeck Post Installation Procedure
Deck Design-Build Online Guide

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How to install & connect deck posts: this article describes how to set the deck posts in place atop their piers, the use of temporary bracing, options for connections between the posts and piers and post tops and beams or girders that carry the deck.

This article series describes critical safe-construction details for decks and porches, including avoiding deck or porch collapse and unsafe deck stairs and railings. Our page top photo illustrates temporary bracing and support during replacement of unsafe deck posts. This deck was in danger of collapse.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Deck Post Setting, Bracing, Cutting

Deck post replacement (C) Daniel Friedman

A deck frame is composed primarily of three components: posts, beams, and joists. This article will show you how to prepare and install each of these parts for a typical deck, as well as how to tackle more advanced techniques such as framing around the corner of your house and building openings in the deck.

A special feature highlights the process of building a deck at ground level, m Much of the framing will be out of sight once the deck is complete, which is another way of saying that it will be hard to fix any errors you make.

So while looks may not count for much when framing, quality certainly does. Take a little extra time to build a frame for your deck that will last.

We (DF) replaced the unsafe deck posts shown at page top with these 6x6 posts back in 1985.

We sank the treated-wood post bottoms 36" into the soil after placing concrete and stone in the bottom of the hole.

Today I'd have used above-ground concrete piers and post anchors at the post bottoms. The cross bracing for this deck was not yet installed.

Setting the Deck Posts

Posts are a prominent visual feature of many decks. With good planning, they can be transformed from merely functional components into decorative design features.

Posts give decks most of their elevation. If you are building a high deck, you will need long posts. If, however, you are building a very low deck, you may not need any posts at all.

Bad deck post (C) Daniel FriedmanWatch out: Don't do what this contractor did. The "deck post" is comprised of a stack of 4x4" scrap with no actual structural connections. Gravity may seem to work to keep this deck in place - until my teen-aged cousin rams the deck with the lawn tractor.

Most decks are built with 4x4 posts, but 4 x 6s and 6 x 6s are often used as well, and even larger posts are sometimes required. Some people think that 4 x 4s look too weak and skinny on a high deck, even when they are structurally sound.

Feel free to use larger posts than are required if you prefer a bulkier appearance. Post size is also related to how far the beam spans from one post to the next.

Posts must be plumb, well secured, and cut to the right length. They are rarely the same length on a deck, however, since piers are usually not perfectly level with each other.

So it is best to avoid cutting posts to their anticipated length before setting them in place.

To determine the length of each post, use one of two methods.

The first, which may be easiest with short posts, is to set the post in the post base, check it for plumb, and mark the desired post height using a level or a water level. Remove the post, cut it to length with a power miter saw, and then attach it to the post base.

The more typical approach is to put all the posts in position, brace them so that they are plumb, attach them to the post bases, and then mark and cut them in place.

Post to deck rim joist connections (C) Daniel FriedmanIf you are using pressure treated posts, it is best to place the uncut ends into the post bases. But it is even more important that the bottom surface of every post be flat and square. Use a small square to check the ends of each post. If neither end is square, cut just enough off the bottom to make it square, then coat the cut surface with a water-repellent preservative before setting it in place.

Framing Options for Connecting Deck Posts to Beams

The most common means of joining posts to beams is to have the beam rest directly on top of the posts, to which it is secured by special connectors. This is also the strongest connection, and usually the easiest construction technique.

Our photo shows a tiny entry deck whose joists did not require a supporting beam. The front rim joist can be seen connected to the supporting post with three bolts.

Decks are sometimes built with posts that extend above the deck surface to serve double duty as railing posts. This requires that notches be cut carefully into the posts to fit the beam. This approach is feasible only when using posts that are at least 6x6.

Avoid building your deck with the beams bolted to the sides of extended posts, even though your building code may not explicitly bar this approach. It is not a recommended practice, since the entire connection relies on fasteners to support the load.

1. Set Up Temporary Bracing for Deck Posts During Construction

Missing deck pier (C) Daniel Friedman

Our photo (left) illustrates what can happen if the deck contractor is a good finish carpenter but one who is not so sharp with deck construction.

His post was left floating atop a wood scrap that we later replaced with an excavated shallow block pier. The deck (as well as his cabin's slab floor) floats.

Real post piers and good connections between the post base and pier top are important for a durable structure.

If you are using adjustable post bases, first attach the hardware to the anchor bolts. (Fixed one-piece bases will already be in place.) Set a post in each post base.

Drive one nail through the base and into the post just far enough to hold the post in place; you may have to remove and reposition the nail later. Plumb the post by checking it on adjacent sides with a carpenter’s level. If you are working alone, it may be easier to attach a post level (inset) to the post to leave both hands free to continue working. With the post plumb, attach temporary braces to two adjacent sides.

If you are using adjustable post bases, first attach the hardware to the anchor bolts. (Fixed one-piece bases will already be in place.) Set a post in each post base.

Drive one nail through the base and into the post just far enough to hold the post in place; you may have to remove and reposition the nail later. Plumb the post by checking it on adjacent sides with a carpenter’s level. If you are working alone, it may be easier to attach a post level (inset) to the post to leave both hands free to continue working. With the post plumb, attach temporary braces to two adjacent sides.

Use 1 x 4s for braces, securing them with screws to stakes in the ground and with clamps to the posts

Details about permanent deck post bracing are below at DECK POST BRACING

Keep the Deck Posts in a Straight Line

Church sisters installing plastic-wrapped 6x6 deck posts SummerBlue Arts Camp Two Harbors MN (C) Daniel FriedmanWe hope you used your batterboards and string to get those piers exactly where you need them to carry the deck posts.

But if some piers are centered exactly in position, as long as the post bottom will be close to the pier center, you'll be able to get the post to its exact-desired position by using adjustable deck post base connectors that we describe below.

First let's be sure our piers and posts are lined up. If your batterboards are still set up, you can run a string line to help align the posts.

Since this string line relates to the sides of the posts, rather than their centers, reposition the string on each crosspiece by one-half the thickness of the post

If the batterboards have been removed, you could set a couple of them back in place quickly. Just be certain that the string line is perfectly parallel with the ledger, so that it’s the same distance from the ledger on both sides.

We used batter boards and string to lay out and keep our deck posts aligned for the SummerBlue Arts Camp stage decking in Two Harbors MN (photo above left). These 6x6 treated wood posts were set in augur -drilled holes in the hard clay soil.

We wrapped each post with 6-mil poly to reduce the chances of frost lensing and heaving - a procedure that has worked well in this climate. More than sixteen years later we can report that the stage has not moved.

The original construction, installation and long term performance of this outdoor performing arts stage floor are described in a series of articles beginning at BATTER BOARDS LAYOUT METHOD.

2. How to Attach the Deck Posts to the Piers using Adjustable Post Bases

With all the posts plumbed and aligned (see below), if you are using wood post bases, drive nails through the post bases into the posts. Use only the nails recommended by the manufacturer of the post bases you are using. More often we use a steel post connector plate that is tied to the pier top - an "adjustable" post base.

The adjustable deck post base is bolted to the top of the concrete pier. If you planned ahead, you inserted the anchor bolt into the pier top when you poured your concrete piers. If you forgot that step all is not lost. Use a masonry drill bit of matching diameter and bolt-to-concrete mounting epoxy to install the anchor bolts for the post bases.

With the anchor holts in place, place the deck post connector atop the post and add washers and hex-nut as provided by the manufacturer. The adjustable base will permit movement of the post bottom anchor to exactly the right final position before you tighten its mounting bolt.

If you are using adjustable bases, be sure that the nuts on the anchor bolts are tightened snugly, but not so tightly that you strip the threads.

3. Find the Final Deck Post Height

The first step in determining post height is to mark each post at the spot that is level with the top of the ledger. Place a carpenter's level on the straightest 2x4 you can find.

Set one end of the 2 x 4 on top of the ledger, then adjust the other side along the post until it is level. Mark the post at the bottom of the 2 x 4. If the posts are too far from the ledger for this method, use a water level.

4. Mark the Cut Line on the Deck Posts

Deck post that can be kicked down (C) Daniel Friedman

With the height of the top of the ledger now marked on each post, you need to determine where to cut the posts. Place a short piece of joist stock under the mark on one post, then mark the post again.

If the joists will attach on top of (rather than beside) the beam, set a piece of beam stock under this line, and again mark the bottom. This final line is the height at which you need to cut the post. (Of course, you can also measure down the post with a tape measure rather than lumber, but using the latter is a bit more foolproof.)

You can repeat this process at each post, but it might be quicker to transfer the cut line from post to post using a 2 x 4 and a level.

5. Cut the Deck Post Tops to Final Height

Use a square to transfer the cut line to all four sides of each post. Set the blade of your circular saw to cut as deeply as possible. For a 4 x 4 post you will need to cut the post twice, on opposite sides. For a 6 x 6 post, cut along the line on all four sides, then finish the cut with a reciprocating saw or handsaw.

Deck Post Cutting Tip: measure twice, cut once. With all of your post cut lines marked, use a string and your level, or a straight 2x4 and your level to double-check that all of the post tops will be cut to the same height. Better now than l later.

Our photo (above left) taken during a field visit conducted for ASHI staff, shows how easily one might kick down an improperly supported and un-braced deck post. This entry deck and stair would have collapsed.

Deck Post Bracing Methods

Deck post to beam bracing (C) Daniel Friedman

Bracing is a way to stiffen and strengthen a deck’s substructure with diagonal boards. Bracing is required on some decks, so check your local building code for specific guidelines.

Even if it is not mandated, as a general rule it is wise to add bracing to decks with 4x4 posts more than 4 feet high and 6x6 posts more than 8 feet high.

Freestanding decks over 3 feet high also should be braced.

Post-To- Beam-Bracing

The most common type of bracing is called Y bracing. The simplest form of Y bracing, and the style that many codes demand, has one 2 X 4 on each side of the post and beam.

Carriage bolts are used to secure the connections. Cut the ends of the 2 x 4s plumb, as shown, so that water and dirt will not have a place to accumulate.

A single 2x4 brace can also be used on the sides of the deck to tie posts to joists, once the latter are installed.

Illustration used with permission from Best Practices Guide to Residential Construction, by Steven Bliss,

Many people prefer the look of solid 4x4 braces, which can be used with solid beams. The ends must be cut at 45-degree angles, and lag screws secure the braces to the bottom of the beam and the side of the post.

For 6x6" posts we cut our braces out of 6x6's as well.

Diagnoal sway bracking for decks and porches (C) J Wiley & Sons, S. Bliss

Post-to-Post Bracing

Scary tall deck with bad post base but using bracing (C) Daniel Friedman The scary tall multiple-level deck and stairway detailed at left left posts standing on sloping rock - something I (DF) found very scary.

You can see that the builder included a bit of 6x6" bracing between the posts and deck floor structure to add some stiffness and security.

The posts should have been anchored or tied to the rocks, cut to fit properly so that we're not just bearing on an edge of the post, and I'd have felt safer if the builder had made sure there was tie-back bracing between the post and the deck side joists back towards the building.

Post-to-post bracing is often necessary for decks with high posts (such as those built over a steep slope);

for decks with long spans between beams; or along the sides of decks where post- to-joist bracing is not feasible.

You can normally use 2 x 4s for braces up to 8 feet long.

Make longer braces from 2 x 6s. Use ½ inch carriage bolts at all connections. X-shaped bracing also requires blocking between the crossing braces. Local codes may stipulate the type of post-to-post bracing you can use.

If not, choose the style that looks best to you.


Continue reading at DECK BEAM CONSTRUCTION or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see RAILING POST CONNECTIONS for a description of connections for posts supporting guardrails or stair guards

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