Build the Best Porch Flooring Structure

Joists, Bridging and Decking Materials

Your porch flooring structure must be structurally stable to not only maintain functionality but also its beauty over the years. What may surprise you is that floor joists on a traditional front porch foundation, unlike decks, run horizontal to your home and support the actual flooring (see diagram below).

By doing so, your decking material will be perpendicular to your home. For those who have built backyard decks, you are basically rotating the structure for a front porch. By doing so you eliminate the need for butt joints as you will normally be using shorter decking materials.

We'll show you how porch flooring is constructed and offer some good tips along the way.

collage of different kinds of porch decking
The anatomy of a porch floor. Time to learn about it!

Enjoy Our Short Slide Show

Our slide show (2:44) is about the anatomy of a porch floor. I narrated it myself and hope you find it interesting.

These pictures were taken at our son's home during their recent porch renovation.

traditional front porch decking perpendicular to house
Traditional front porch with Azek porch decking material

Porch Floor Anatomy

typical front porch flooring construction graphic
Front Porch decking materials laid perpendicular to house

Although traditional porch decking runs horizontal to your home many porches today run perpendicular. There is no distinct advantage to either. Remember; however, if building a traditional porch, it may change the number of beams you need and the direction of your joists.

In this section; however, our porch flooring graphics will be shown from a traditionally constructed front porch perspective.

Before we get started, you may want to explore our porch foundation section to see how to construction the footings, piers, posts, and beams.

concrete anchors for posts
Constructing a front porch foundation

Front Porch Floor Joist Spacing

There are a few different types of joists. The rim, band, or end joists are floor joists that are the outer most joists.

These are typically the only joists you will see when looking at the porch. Typical floor joists connect to the beam(s) and directly support your decking materials.

diagram showing joist spacing at 16 inches on center

In the diagram above, an additional beam is shown to depict situations where the joist span is too long for the length of the joist. In those cases, installing additional beams adds stability to your porch.

No matter which structure you choose, space your joists 16 inches on center (o.c.). Measure from the center point of one joist to the center of the next.

You could also choose to space them 12 or 24 inches apart. (If you space them 24 inches apart you may need to add bridging to keep the platform from swaying).

The closer together, the more stable your platform. Check with your local codes department to determine specific requirements for your area.

Calculating Joist Spacing and Spans

For DIYers, no matter whether you are buildng a front porch or back deck, it is really important to understand joist spacing and spans. Exceeding the limits of your chosen wood can be disasterous, so avoid any problems by adhering to local building codes and making the right calculations.

Here are a few common planning factors from a floor joist span table:
  • A 2x8 yellow pine joist spaced 16 inches on center can span approximately 13 feet 7 inches.
  • A 2x8 yellow pine joist spaced 24 inches on center can span approximately 11 feet 11 inches.
  • Whereas:
  • A 2x10 yellow pine joist spaced 16 inches on center can span approximately 17 feet 4 inches.
  • A 2x10 yellow pine joist spaced 24 inches on center can span approximately 15 feet 2 inches.

  • There are a myriad of factors involved in the calculations so to make it easy use this link to the American Wood Council's free joist spacing and span calculator where you can even download an app for your phone.

Attaching Joists

The easiest way to attach joists is by using joist hangars like those pictured below. Y ou can either use galvanized nails or deck screws (which I prefer).

photo of a single joist hanger double joist hanger for porches or decks

For decks you would attach the joists to the ledger board and if you are making your porch the same as a deck you would do the same. If building a traditional front porch, you would attach the joists to the band joists or to the band joist and beam (if you installed additional beams - see our foundation section).

picture of a hurrican tie for joists In some cases you will lay the joist over the beam to create an overhang. In those cases, use a hurricane tie (photo at right)to attach the joist to the beam.

Start by marking your band or end joist in 16 inch increments. (I recommend you use a double end joist for stability). Measure from the back edge of your ledger board as shown in the diagram below. Place a mark every 16 inches.

You may have to add an additional joist if the last segment exceeds 16 inches. Continue marking through to the beam.

diagram showing joist spacing along beam
Measuring for joist locations

Make a Joist Hanger Jig

Joist hanging can be fairly easy if you make a jig first. As a woodworker I make lots of jigs for use in my shop and know how useful they can be. If working alone, a jig is a must. Jigs will ensure you are consistent throughout and make the job a lot easier.

This joist hanging jig is quick and easy to make:

diagram showing joist jig
Quick and easy joist hanging jig

Watch Your Crowns

Pay attention to your lumber too. It is almost impossible to purchase joist lumber without crowns, that is, they tend to have an inherent curve in them as depicted by the graphic below.

You will want to install your joists with the crown side up. By doing so the weight of the decking materials will "flatten out" your porch floor. Otherwise, you will have an uneven porch floor.

diagram of joist board with crown

Why Won't It Fit!?

No matter how careful you are installing the joist hangers, some joists will extend above the beam or ledger or even be a bit short. Not to worry. If too tall just chisel out the bottom of the joist so it sits lower on the hanger. For joists that are too short use shims to raise them a bit.

Don't Make This Mistake

When building the porch framing, i.e., the joists, be sure to allow sufficient time in which to install the joists and lay the decking materials within a reasonable time.

While building a large deck for a neighbor, I had to stop construction due to an emergency just after I installed twenty-one 16 foot long joists. Because I couldn't install the decking boards before I left, I knew I was going to encounter problems when I returned.

Needless to say almost all of the joists had warped considerably. It took many hours of measuring, cutting, clamping, and installing blocking between the joists to rectify the problem.

If faced with a similar situation in the future, I will lay boards perpendicular to the joists (on top and below) and temporarily fasten them in place to keep the joists from warping.

I'm also going to reconsider volunteering to help build decks for neighbors!

Recommend you start by hanging your end joists (or double end joists for the traditional porch structure). That, in essence will form your framework upon which you will hang the remaining joists. Be sure to allow extra length for the end joists to cover both the ends of the ledger board and the outer beam.

Floor Joist Bridging

Floor joist bridging is added between the floor joists to add strength and to prevent the porch from swaying or bouncing. I also use bridging to ensure the joists run parallel.

diagram showing bridging between joists
Bridging installed between joists

Select Your Porch Decking Material

Now's the fun part as you will get to see all of your hard work paying off. You probably have a good idea as to your porch flooring; however, we encourage you to visit our porch decking section to learn all of your options.

mahogney porch flooring You will discover materials you may not have previously considered like the mahogany wood porch floor pictured at right. (photo courtesy of Ryan Dingman)

You have lots of options ranging from many different types of wood to stone, brick, concrete, interlocking deck tiles, and more.

Installing Your Porch Decking

Unlike your backyard deck, wood porch flooring runs perpendicular to your home (if you so choose). typical front porch flooring construction graphic
Front porch decking materials laid perpendicular to house
Wood applications range from nailing (or screwing) you wood boards to the joists or installing traditional tongue and groove flooring to using your structure to hold a myriad of stone-type flooring as illustrated in the photo below.

wood to stone decking system
Use brick, stones, or other decking materials

wood to stone decking system The Silca System® (above photo) allows you to install their special grids over your joists. The grids will support all kinds of decking materials transforming an ordinary porch floor into an exquisite one!

Learn more and see the possibilities for your porch or deck.

Installation Tips

  • Spacing: If installing a wood floor understand that wood shrinks over time. If your boards are heavy and contain a lot of moisture, chances are they will shrink considerably. Install these tight against each other. If your boards are kiln dry space them approximately 1/8 inch apart.
  • Nails: Pound straight down and avoid hitting the surface of the wood.
  • Screws: If using screws always drill pilot holes first to avoid splitting the wood. I prefer to use a small bit with a countersink to place the head of the screw slightly below the surface of the wood.
  • Plan Your Last Row: The video below provides additional information but plan your last row well before you get there and make adjustments as you go. Otherwise, you are apt to finish with a very narrow board which not only doesn't look very nice but also will cause you issues later.
  • Use Clamps: Have a several long clamps available as you lay down your decking material. They come in real handy for staightening warped boards or as a second pair of hands if working alone.


Porch Flooring Installation Series - Step by Step

Mary and I recommend you see our videos and accompanying information, and tips courtesy of Vintage Woodworks, detailing how they repaired and installed a new porch floor. They are highly instructive and no matter your porch situation, we are sure you'll glean some great tips.

Handle Corners, Rim Boards, and Thresholds

laying porch floor around corners
See how to install around corners, rim boards, and thresholds
Square Your Porch

photo showing how to square a porch
Square your porch
Install Porch Boards

installing azek porch flooring
Installing your porch boards
Finish Your Porch Flooring

photo showing how to square a porch
Finish your floor to perfection
video introduction slide

Other Porch Floor Construction Considerations

Don't Forget Your Electrical Requirements

If you haven't already, now's the time to plan for your porch electrical requirements. If you have to run cable to electrical outlets, now would be the time to do so. We highly recommend you use our porch electrical section as a starting point for determining all of your electrical needs like lights, fans, receptacles, etc.

Keep Your Porch Dry

Often times porch owners encounter water issues whether on or under the porch or the surrounding area. If you believe you may have such issues, be sure to see our waterproofing a porch floor and our lawn drainage problem resolution.

Repairing Your Porch Floor

Now that you know your flooring anatomy, pay particular attention to the porch's structural components, i.e., existing porch decking, joists, rim joists, footers, and support posts.

Pay attention to these:
  • Make any necessary repairs before laying down a new porch floor, or painting or staining your existing floor.
  • Walk across your floor to see if there is any "give" to it.
  • Your floor should have a solid feel to it. If not, removing the old flooring will give you access to the framing underneath.
  • Once exposed, you can replace any rotting or decayed boards, add bridging, and even add additional joists to prevent sagging or to reinforce other joists.
  • Contact a local contractor if needed and remember to comply with local building codes.

Have a porch flooring height question. See our response to a recent inquiry about floor height for a porch.

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