how to use concrete deck blocks

You will need a foundation for the new deck you intend to build. Concrete footings, piers, and deck blocks are some options for deck foundations. And while deck blocks are cheaper and quicker to install, you may wonder if they are up to code.

Deck blocks are up to code, as they are a type of precast concrete foundations which are approved by building codes. However, local building code offices may not permit the use of deck blocks if the soil is prone to frost heaves, or there is a tendency for high or uplift winds.

Continue reading, as this article discusses deck block foundations, how they compare with concrete footings, and when to use deck blocks.

What Are Deck Blocks?

Deck blocks are precast concrete blocks used to hold up beams for supporting structures, especially floating decks.

There are different types of deck blocks; some have notches to hold beams, joists, and posts, which makes them excellent for constructing freestanding decks (decks not attached to the building.) Other blocks have grooves or slots that can take 2×4 wood (or composite materials) used at the edge as floor joists for low-level decks that require little or no support.

Though their sizes vary according to the manufacturers, deck blocks are generally 10 to 11-inch squares, and 7 or 8 inches high, and weigh about 48 pounds.

Are Deck Blocks up to Code?

Building codes approve the use of precast concrete foundations, and deck blocks are classified as precast concrete foundations.

However, the size, bearing capacity, and composition of the blocks must be appropriate for each location. Also, it is advised to confirm from the local building code office, as some areas may require the use of additional anchors.

Are Deck Blocks a Good Option?

Deck blocks are appropriate foundations for low freestanding structures. They do not decay and are largely corrosion-resistant.

The blocks are preformed concrete units, as such, makes it easy and quick to construct decks. They make excellent foundations for small to medium decks when used correctly, as they have considerable load-bearing abilities.

Additionally, blocks also remove the complexity of deck construction, with rudimentary carpentry skills, one can successfully construct a deck as a DIY project. Deck blocks are great options for building a grade-level deck that requires no permits.

When to Use Deck Blocks

While deck blocks may be code approved, it is best to restrict their use to low, floating decks.

Additionally, do not use deck blocks if:

The soil is susceptible to frost heave.
The location experiences high or uplift winds.

How Do Deck Blocks Compare to Concrete Footings and Piers?

Concrete footings and piers are popular options for deck foundations, and you may want to know how deck blocks compare to these.

Accordingly, the two will be compared under the following:

Ease of installation. Deck blocks are much quicker to install than concrete footings, as they are preformed units. Also, concrete footings require considerable amounts of soil to be excavated, whereas minimal digging is required to install deck blocks.
Price. Deck blocks are fairly cheap and do not require much labor to install. On the other hand, the cost of in-situ concrete and the associated cost of soil excavation makes concrete footing the more expensive option.
Bearing capacity. Concrete footings will support greater loads than deck blocks due to the increased mass and wider bearing area.

Can I Use Deck Blocks?

For simple low or ground-level decks, deck blocks are your ideal bets for foundations, as with simple tools and some skill with working wood, you can build a simple floating deck using deck blocks.

Deck blocks are readily available in many home and garden stores; they are relatively cheaper to use and are best for low or ground-level decks requiring small framing materials.

There might be some concerns about their load-bearing capacity in moderate wind areas, but if a lateral restraint is applied at the base of the post, there is no cause for concern. The blocks have a low bearing area, so you must take care when selecting the dimensions of beams and joists to be used with the blocks.

Building codes recognize deck block foundations; thus, they get subjected to the same requirements as typical deck footings.

The requirements for deck blocks are:

They must have a sufficient bearing area (the area of the block sitting on the earth).
There must be a minimum of 12 inches below the local frost depth.

Here's a good explanation video showing how to use deck blocks to give you an idea of how these are used.

Are Deck Blocks Safe?

All things being equal, deck blocks are safe. Deck blocks placed on sandy or gravel-like soils work best. These soils will let the excess water drain away during autumn and prevent frost heaving during the winter, remaining largely unchanged despite the seasonal freeze and thaw cycle. On the other hand, heavy clay soils will hold too much water affecting the integrity of the deck block foundation.

Level ground is ideal, but not always possible. If the ground slopes slightly downward, no matter the material used for foundation, there's a high chance for lateral movement.

Prevent lateral movement by digging the higher part of the gradient deeper than the lower end so that the deck can level out.

Make sure to confirm the load-bearing capacity of the blocks you are about to purchase, to ensure that they are the right fit for the size and purpose of the oncoming deck.

If you are concerned about the safety of the deck you are building, I recommend looking into HomeAdvisor Decks to find local professionals in your area that can help you out. I've been able to find some good companies on there, and a good company will warranty their work.

How Far Apart Do You Put Deck Blocks?

The positioning of deck blocks may vary depending on the load and type of soil. Depending on the land's topography, dig the holes in such a way that all the blocks are even. Use a tape to measure the blocks and make sure they are equidistant from each other. Also, measure from corner to corner to make sure the diagonals are equal, make sure the corners form a square.

Another spacing method is to put blocks 5 feet longitudinally and 4 feet laterally so that the arrangement is in the form of a rectangle. Doing so allows for a 10′ by 8′ deck using 9 deck blocks in total.

As a general rule, put a deck block every 3-4 feet for heavy loads and 4-6 feet for lighter loads.

Additionally, note that the number of blocks needed for a deck foundation depends on the size of the oncoming deck and the soil properties. Softer soils require the loads to be more evenly distributed, as concentrated loads will cause differential settlements.

Accordingly, more blocks will be needed to spread the load evenly, and the guidelines for spacing may not apply. Still, what is essential is that the blocks are spaced uniformly.

How Much Do Deck Blocks Cost?

The price of deck blocks varies depending on the size and manufacturer. However, prices range from $4 to $6 and can be purchased from local hardware stores and home improvement centers.

Now a days they make hardened plastic versions of deck blocks that you buy in packs, like these TuffBlock Deck Blocks (link to Amazon) that have great reviews.

Conclusion

Deck blocks are types of precast foundations. As such, they are approved by code. However, they may not be suitable for every location, especially frost susceptible soils.

In setting out deck blocks, it is important to space the blocks equally from each other (three feet apart) so that the load is spread evenly to avoid differential settlements, especially in soft soils.

Compared to concrete footings, the blocks are cheaper and easier to install, but not as strong. Consequently, deck blocks are suitable for small to medium-sized low freestanding decks.

Helpful Links:

TuffBlock Deck Blocks (link to Amazon)
Are Decks or Patios Cheaper? Cost Compare Guide
Is A Deck Considered A Structure?
HomeAdvisor Decks (local professionals)