How to Install Deck Piers
Deck piers support the beams that create the joist spans for a deck. This is the foundation of the deck and if not properly installed will result in failure of part or the entire deck. Unlike a concrete footing that distributes the weight of the structure over a large area, piers concentrate the load to a small area. Ground stability and soil compaction are very important when you consider using this type of foundation structure. Be sure to determine the bearing capacity of your soil and keep a factor of safety of at least 4.
[edit] Steps
Before You Start to Dig: Call 811
Before you start this (or any other) digging project, call 811, A new, federally-mandated national "Call Before You Dig" number. 811 was created to help protect people from unintentionally hitting underground utility lines while working on digging projects.1 Deck Beam Pier
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This article will show you how to install beam piers to support a deck. Note the finished pier is set in the ground with a tapered fill so water won't collect around it. These piers are one foot into the ground because they are located in earthquake prone Southern California.
2 Center the Hole
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Based on your plan lay out your post positions. Be careful to center the hole on the position for the pier. Specification for distance between piers can be found in most books about deck construction. These holes are one foot square and one foot deep. The existing ground around the hole should be undisturbed as it provides the lateral support for the post. Poor positioning of the hole will result in a larger hole and less support.
3 Completed Hole
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This is the completed hole. Note the sides are vertical and the bottom is flat.
4 Level the Bottom
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Fill the bottom with about one inch of gravel, sand, or pea gravel. This will allow you to create a flat level surface to place the paver on. It also absorbs some of the expansion and contraction that characterizes some soils.
5 Compact Gravel
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Compact the gravel at the bottom of the hole. This is important to prevent the weight of the deck from pushing the piers down and creating sags in the deck.
6 Level the Paver
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Place the paver in the bottom of the hole and check for level by placing a post of with square cut ends on the paver. Then check the level in both direction on the posts top. You may also use a small 12" level on the paver. If it is not level, add more gravel or sand and recompact.
7 Length of Pier
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Once the paver is level in all directions it is time to determine the pier length. This deck is attached to a retaining wall and a ledger board is the basis for the level. Position the pier and strike a line on the pier level with the top of the ledger.
8 Cutting Piers to Length
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I use a radial, or chop saw to cut the piers to length. This assures a square cut that allows the beam to rest more completely on the end of the pier. These piers are 4" pressure treated peeler cores. You could also use pressure treated 4"x 4" posts.
9 Check Pier Height
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9. Once the pier is cut to length recheck the height by laying the level on the ledger and the top of the pier.
10 Locate Pier Center
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Locate the pier by measuring from two known points. Use the same points for every pier. Don't measure from pier to pier. If one pier if off, you will multiply the error.
11 Mark the Location
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Once you have the exact location, mark the bottom of the pier with a felt pen on the paver. This will allow you to relocate the pier if it is bumped or move accidentally.
12 Fill the Hole
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Carefully fill the hole with loose dirt until it is 4 inches deep in the entire hole. Hold the pier to prevent the dirt from moving it off it proper location.
13 Compact the Fill
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Carefully tamp the dirt with another pier or post while holding onto the pier to prevent it from moving. The dirt should compact to at least 3 inches, and the pier should be stable enough to stand on its own.
14 Continue Filling
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Fill the remaining dirt 4 inches at a time and compact. You should have more dirt that the remaining space in the hole because of pier, paver, and gravel .
15 Create a Sloped Cap Around Pier
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Use the extra dirt to create a sloped cap around the pier to discourage water from collecting near the pier.
16 Finished
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Your efforts should result in a level aligned resting place for the beam.
[edit] Tips
- Try a Cutoff Saw. A chop or cutoff saw can also be used. This will allow the cutting to take place at the deck site.
- Better Long than Short. Make the first cut a little long, you can always cut off more. It's hard to add length to a pier.
[edit] Warnings
- Undisturbed Soil. The gravel and paver should rest on undisturbed soil, not loose fill or soil filled with decomposed plant material. If this is the case, dig a deeper hole, compact it well before adding gravel, then compact it again.
- You must use only pressure treated posts.
