Whether you start the layout of your deck with a ledger or are expanding an old deck from an existing framing member, the next step is laying out the site for footings and post locations. Here’s how to get things right.
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Making batter boards
Batter boards are a homemade tool that will help you make both the layout and excavation of the site more precise. To make a set of batter boards (you’ll need two for each corner, except where the deck abuts the house directly), cut scrap 2×4 lumber to 2-foot lengths, and point the ends so you can drive them into the ground.
Fasten a 15- to 18-inch crosspiece to the legs a couple of inches below the tops. The crosspiece will let you move the mason’s line so you can position it where you need it.
Set Batter Boards
Drive batter boards in the ground about 2 feet beyond the temporary stakes. Stretch mason’s lines from the ledger (or a framing member, if you’re expanding a deck) to the batter boards in all directions. Then tie a line between the other set of batter boards, across what will be the front edge of the deck. This line will be parallel to the ledger and will help you mark the footing locations. Don’t worry if your angles aren’t right on the money yet. That comes after you have all the lines tied.
Then square the corners with a 3-4-5 triangle. Keep the lines level with a line level as you square them.
Mark the post locations
When the mason’s lines are square and level, you are ready to transfer the footing locations to the ground. Depending on how you’ve drawn your plans, the intersection of the mason’s lines represents one of two points—either the corner of your posts or their centers.
Marking the ground
If your project calls for an excavation for a section of patio, for example, use the same methods described above to lay it out. After u have marked your corner locations with stakes, tie a taut line at ground level between the corners, and paint the line with spray paint. This provides a straight line on the ground for excavation.
Footings and piers
When all the footing locations have been marked, remove the mason’s lines and dig the footing holes with a posthole digger or power auger.
The building codes in your area may have a lot to say about the kind of footings you need and how deep they should be. In some localities, posts set in concrete or tamped earth and gravel may be OK. Other municipalities require above-grade posts to be set on piers and footings. In this case, footings must reach below the frost line to prevent them from heaving when the ground freezes.
To prevent moisture damage to the posts, set your finished footings and piers slightly above grade. If you plan to set post anchors directly in wet concrete without piers, use tube forms. If you plan to pour the footings first and add piers later, make sure your footings are high enough so the piers will keep the posts above ground level.
You can buy concrete in premixed bags (just add water) or purchase and mix the dry ingredients from scratch. Here’s what you should consider: QUALITY: If you mix dry ingredients from scratch—in the correct proportions— the quality will equal that of premix. CONVENIENCE: Premix is much more convenient. No mixing is required— except for water, of course. COST: Premix costs more than mixing from scratch, but the extra cost buys you convenience and time.
Have your hardware and piers handy before you mix and pour the concrete. You will be setting them in wet concrete. This is no time to run to the building supply store.
Digging the holes
With a clamshell digger or an auger, dig the footing holes to the size required by local codes and your design. Pour 4 inches of loose gravel in the hole to help water drain away from the footings. If you are using prefab forms, attach them to a 2×4 frame. If you’re installing posts below grade, put them in and brace them.
No matter what kind of concrete you use— premix bags or mix you own—it’s best to mix it in batches one hole at a time, unless you have a crew of helpers. Shovel the mixed concrete carefully into the footing hole, pushing the mixture down with a scrap 2×2 to force out any air bubbles. Once the hole is filled, smooth the concrete with a trowel and, if you haven’t used tube forms, slope its surface to let water drain away. Install the post anchor or J bolt. Once the footings and piers or anchors are in place, the concrete needs three days to a week to cure.
Setting Corner Posts
Treat the bottom of each post with a protective sealer at least one day before you set the posts in the anchors. This guards the posts against rot, infestation, and moisture damage. Pour the sealer in a shallow pan and soak each post for a few minutes before setting it up to dry.
Set the corner posts first. That way you will have a benchmark from which to level all the posts with the ledger.
Soften up hard soil
Wet soil is easier to dig than dry soil. If you run into hard, dense soil, pour a bucket of water into the hole. Water makes the soil softer, which lets the blades of a manual digger or a power auger cut through more quickly. Lifting the wet soil will be more difficult, but still easier than trying to cut through the hard earth. Let water drain out of the hole before pouring concrete.
Mixing your own Concrete
Here’s the recipe to use if you’re mixing your own concrete from scratch: 1 part Portland cement, 1 part sand, and 1 Vi parts gravel. Use a wheelbarrow, a mortar box, or a power mixer. Measure shovelfuls of sand and cement first and mix them thoroughly, then add the gravel and mix again. Hollow out the center of the mix and add a little water. Pull the dry ingredients into the center a little at a time, adding just enough water so the mix is stiff.
- Place a corner post in an anchor; hold it temporarily with decking screws.
- Brace the post with scrap 1×4 lumber angled to ground stakes.
- Check the post on two adjacent sides for plumb with a post level or a carpenter’s level.
- Adjust the bracing as needed until the post stands plumb.
- If you plan to cut the post in place, fasten its base securely with lag screws. If you are going to remove posts for cutting, don’t fasten them securely. In either case, leave the braces in place as you continue.
- Using a water level, a line level on a taut mason’s line, or a 48-inch carpenter’s level placed on a long, straight 2×4, mark the post level with the top edges of the ledger.
- If your posts will extend above the deck, use this line as a reference when you install the beams and joists. If the posts won’t extend above the deck, mark them as follows:
- Measure down from the line by the depth of the joists and mark this point.
- Use a combination square to make a line and to transfer the line to all four faces of the post. This is where you will cut.
- Mark an x on one side of a line to indicate the waste portion.
- Set and mark the remaining corner posts in the same way.
Measure twice, cut once
Use this old carpenter’s adage when preparing to cut posts. If your rail deck design includes any unusual features—cantilevers, extended posts, special hardware, or beams longer than the ledger—keep them in mind as you measure the posts for cutting. These features can affect post length. To avoid time-consuming mistakes, remember:
- You can cut a post shorter, never longer.
- The mark on the post that is level with the top edge of the ledger is where the decking boards will be fastened to the joists. Your cutting line represents the top of the cut posts, on which beams and joists will rest.
You can cut the posts in place or take them down to cut them. Each method has advantages and drawbacks.
- Cutting posts in place is difficult because you are sawing at an awkward angle. You risk making cuts that aren’t straight, but you avoid taking the posts down and resetting them.
- Cutting posts on the ground—on sawhorses—will likely give you a cleaner cut because your position is more balanced. But you’ll have to rebrace and replumb posts when you put them back up. Either way, there are common difficulties:
- Using a circular saw is difficult because 4x4s are too wide to cut in a single pass.
- Treated lumber gums up saw blades.
Whatever method, consider these tools:
- CIRCULAR SAWS usually make the fastest and cleanest cuts but can be awkward to use sideways. Make two passes.
- RECIPROCATING SAWS are easier to handle if both hands are free to hold on, but their blades can wander. These aggressive, hardworking saws are anything but subtle.
- HANDSAWS take longer, but they’re simple and safe. Use a sharp crosscut saw with teeth no smaller than 8 points. Some come with large teeth to cut through large framing.