Deck Building 9 - Digging Foundation Holes and Setting Pier Blocks

Intro - Prep - Tools and Materials - Ledger - Holes - Attach Ledger - Joists - Foundation - Set Pier - Girders - Layout Joists - Install Joists - Deck Boards - Cutting Ends - Facing - Railing - Waterproof

Digging the Foundation Holes

Margin of: 1”

Most Common Mistakes

Not digging deep enough for local codes and frost lines.
Not digging into stable, undisturbed soil.
Not squaring off walls at the bottom of the hole.

You should get Adobe Flash Player so you can view our video.

I won’t insult you by trying to tell you how to dig a hole, but I need to say a few things about the hole before you start to dig. The size of the hole is important. The diameter is usually about 16”, but check your local code. More importantly the depth of the hole is often regulated by code. Distances of 12” - 60” are the range, depending on the frost level in your area (the colder the climate, the deeper the hole).

Once you have determined the diameter and depth, simply dig your needed holes, being sure to dig good, straight (not sloping) walls. Dig until you hit stable undisturbed soil that will not settle. Never backfill a hole with loose dirt before pouring concrete. This compacts and causes settling.

Tip: Keep the concrete damp while hardening for a stronger pour. This can be done by sprinkling water on the pour as it dries or by laying wet cloths across the top.

Pouring the footings and Setting the Pier Blocks

Margin of Error: 1/2”

Most Common Mistakes

Top of pier blocks not level.
Pier blocks not properly aligned
Neglecting to use the metal connector where required.

Now you are ready to mix up some concrete, pour it in your hole, drop a pier block in the fresh concrete, level and align it, and continue.

A few words on mixing concrete. On small deck jobs I recommend that you simply buy the ready-mixed concrete with all needed ingredients in a bag, mix it with some water, and pour it in the hole. Purchase enough bags to fill your holes; you don’t want to run short and have to rush back to the store to finish off a hole. You will be surprised how many bags a hole can require.

Mix the concrete in a wheelbarrow or pan with a cement hoe, and be sure to follow the instructions as to the proper mix. Pour the concrete in the hole within an inch or so of the top and smooth it out with a piece of 2 x 4 or a trowel until it is relatively level. You can now place the pier blocks.

Pier blocks serve as a transition from the posts supporting the girder to the concrete foundation footings. Although they can be built at the site, they are available at all home centers and hard- ware stores in a range of styles and sizes and are therefore not worth the hassle of pouring them yourself. The most common type is simply a small truncated concrete pyramid on top of which the wooden post sits. The weight of the deck keeps the post in contact with the pier block A version of this is a pier block that has a small piece of redwood or pressure-treated lumber embedded in the top so that the post can be toe nailed to the block. Often metal fasteners are used in areas where there are earthquakes. They are embedded in the fresh concrete and the posts are bolted to them. This pre- vents the posts from shaking off the pier blocks in a quake.

After the hole has been filled with concrete, and the concrete leveled and smoothed, drop the pier block into the fresh concrete and work it down until at least 3” - 4” of the base of the block are embedded. As you set the block, be sure of two things. that they are properly aligned and that they are level. It should be rather easy to check both. To check alignment, simply drop the plumb bob from the marks on your string to be sure the tip of the plumb bob is in the centers of the pier blocks. To check level, use a small torpedo level, placing it in both directions as well as diagonally across the top of the pier blocks until the tops are level. Tap and move the blocks around to make any needed adjustments. After your pier blocks are property set, allow the concrete to harden (this can take anywhere from 2 to 24 hours). Then you can begin building the girders and posts. We recommend keeping the concrete damp while hardening for a stronger pour. You can do this by sprinkling water on the pour as it dries or by laying wet cloths across the top.