Skip to Content

6 Great Ways to Support Floor Joists in a Crawl Space

6 Great Ways to Support Floor Joists in a Crawl Space

Share this post:

This post may contain affiliate links. If you click one of these links and make a purchase, I may earn a commission at no additional cost to you. In addition, as an Amazon Associate I earn from qualifying purchases.

Crawl space foundations are famous among homeowners because they allow easy access to the plumbing and electrical wiring of your home.

However, how do you support your joists to prevent the flooring from sagging or getting wobbly?

If you’re wondering how to support floor joists in a crawl space, you’ve come to the right place. In this article, we’ll show you how to keep your floor joists stable and secure.

Let’s get started!

How Do You Support Floor Joists in a Crawl Space?

Over time, floor joists can lose their stability. Usually, the culprits are mold, excess moisture, and dry rot. Lucky for you, here are some methods you can try to reinforce your joists:

Method One: Joist Sistering

Sistering is when you add more joists alongside the existing ones. This way, the new joists can take the strain off the old joists.

In addition, this method can provide better support for holding up the flooring.

Preferably, use new joists made of lumber-engineered wood, like plywood. It should also be of the same length as the old joists and should be installed at the same span.

Before you start sistering though, you have to remove all obstructions, like water pipes and electrical cables. Then, lift the joists to a desired height using an adjustable steel column.

After that, apply a construction adhesive to the existing joists. Next, put the new joists in an X pattern every six inches. Lastly, secure them with 10d nails.

Method Two: Install a Beam

Installing a beam to the structure can provide more support to the floor joists. Plus, the beam can take some of the pressure off.

In this method, you’re going to use jacks to lift the floor joists. Once you’ve adjusted them to your ideal height, use lally columns and set the beam vertically.

After that, make sure that there’s a snug fit between the joists and beams by using shims and adjusting the lally columns. Lastly, remove the temporary jacks.

Method Three: Bridging

Over time, joists can start to twist and lean sideways. Eventually, the structure becomes unstable and results in uneven floors.

Luckily, bridging can help reinforce the joists. To do so, you’re going to add plywood or lumber strips to the structure.

Then, you’re going to connect the joists to the ones directly adjacent to them.

Install the wooden strips in between the joists following an X shape position. This will secure the joists and prevent them from moving sideways.

Use ½ inch of plywood and split it into strips that are three inches wide. If your joists are less than 12 feet, you only need a set of bridging in the middle.

However, if the joists are over 12 feet, you’ll need two sets of bridging. In addition, joists that are over 18 feet require three rows of bridging.

Use 8d nails or structural screws to start installing the strips. Another tip is opting for a nail gun or a pneumatic palm nailer to get the job done more easily.

Method Four: Blocking

Blocking has the same concept as bridging. For blocking, you’re going to use wood pieces that have the same widths as the spaces between the floor joists.

Then, install the lumbers in one row if your joists are 12 feet. If your joists are 18 feet though, you’ll have two rows. Moreover, if the joists are over 18 feet, they’ll require three rows.

You can use two or three 10d nails per block to secure the structure. For best results, lay out the blocking in a straight line.

Then, ensure a snug fit by cutting the blocks into tiny fractions longer than the width of the ‘joist-bay’ or the spaces between the joists.

Method Five: Use a Steel Plate

Another way that you can support floor joists is by installing a steel plate. In this method, you’ll need the steel plates to be the same length and width as the floor joists.

In addition, make sure that there are pre-cut holes on the plates to bolt them in place. Use ⅝ inch carriage bolts for best results.

Overall, steel plates ensure an improved stability in the crawl space. However, keep in mind that, unlike joist sistering, you can’t drill through the steel plates to access plumbing or wiring.

Method Six: Consider Jack Posts

Jack posts are adjustable steel columns that come at a variety of heights. Typically, the jack posts have steel plates you can use to set them at their general heights.

On top of that, the posts have screw plates at the top to adjust according to your desired height. Then place a piece of lumber or a beam across the jack posts.

This way, you can lift multiple joists at the same time.

Final Thoughts

There you have it: your guide on how to support floor joists in a crawl space.

Adding a beam to reinforce your joists is a great way to improve the rigidity of your crawl space. Other methods you can try include bridging, blocking, and sistering.

Additionally, you can consider using jack posts or steel plates to add more support to the flooring.

Whichever method you choose, it can reinforce your crawl space’s stability. Plus, it prevents your home from having wobbly floors in the future.

Therefore, you can have the peace of mind that your crawl space flooring is safe every time you walk over it.

Share this post: