How to Mount a Deck Frame to Concrete Foundation

If you are planning on building a low deck or wood patio next to the concrete foundation(check out how to remove concrete slabs from patio), you might have an excellent opportunity to really solidify the deck frame by mounting it to the foundation itself. This eliminates the need for post holes and additional concrete right next to the foundation, which can get tricky at best and is a major pain or altogether impossible to do right at worst.

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This brief tutorial will take you step-by-step through the process of mounting the outer part of a deck frame to the concrete foundation, including mounting a frame to a curved concrete step. We hope you find this tutorial helpful.

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The first, and probably most important, tool that you’ll need access to in order to mount the deck frame to the concrete foundation is a rotary hammer drill. A rotary hammer drill produces a pounding force while drilling that makes it an excellent tool for effectively drilling into (or through) concrete.

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Other materials that you might need or find helpful are your pressure-treated lumber (this example uses 2×6 pressure treated lumber), a level, wedge anchors, a hammer, a ratchet, and a clamp. And a miter saw for making your lumber cuts. You might find a chalk line helpful as well, to mark your level line.

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This example uses 1/2″ wedge anchors, 4-1/4” long. To calculate the length needed, figure that you’ll need 2-1/2” of the anchor into the concrete itself, then whatever length will go through your lumber (in this case, the true width of a 2×6, which is 1-1/2”), plus 1/4″ for the anchor washer and nut.

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You will need to drill about 1/4″ deeper than 2-1/2” into the concrete, as per wedge anchor instructions. Because it is more accurate to place the 2×6 and drill through that into the concrete (better to align them precisely when they’re drilled together), we measured and marked with colorful tape on the drill bit 4-1/2”, which gives us a little extra space just in case.

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Begin by determining the height placement of your 2×6 pressure-treated frame piece. Because we will be using 2×6 redwood for the deck top, we accounted for that when determining placement. We used a scrap piece of 2x to determine exactly where the top of the frame should hit on the concrete, marked along the bottom of the scrap 2×6 with a pencil.

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Here you can see the pencil guide line for the top of the frame lumber.

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Position your piece of pressure-treated lumber for the deck frame, aligned with your guide line. Use a level to make sure it’s, well, level.

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Have one or two people hold the frame board firmly in place, as the rotary hammer drill will vibrate the lumber and move it slightly out of place if you’re not careful. Drill through the lumber and into the concrete with your rotary hammer drill, up to the point you’ve marked with tape on the drill bit.

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Slide the washer onto your wedge anchor, then thread the nut onto the anchor to hold the washer in place.

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Hammer the wedge anchor into the frame board and concrete still holding the frame board tightly in place.

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Hammer the wedge anchor all the way into the board. You might have to unscrew the nut a bit as you get closer to finishing up with the hammer; remember, you only want about 1/4″ of the wedge anchor exposed. After you unscrew the nut a little, hammer in the anchor a bit more.

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Once the top of the wedge anchor is flush with the outer edge of the nut, you’re ready to tighten the anchor into place.

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Use a ratchet to tighten down on the anchor nut.

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The lumber might bend inward slightly as you tighten; this is okay. Don’t worry about cranking it down too tightly, though. You don’t want to damage or weaken your frame board.

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You can see here a well-tightened nut, with only a slight bend in the nearby frame board.

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Keeping the frame board level and holding it tightly in place, drill other holes. A good rule of thumb is to place an anchor every few feet. Cut and butt additional frame boards up next to the first one, if needed.

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Be sure to keep the boards level, even at the connection points. You can mount the boards up to about 6” in from the end of the board.

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Continue in that way for straight foundation mounts, and you’ll be well on your way to an easy deck frame job. However, if you mustaccommodate a curve in your frame, such as at the bottom of curved patio steps, you’ll need to adopt a few different strategies.

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First, cut smaller boards that will allow you to work around the curve. Each board should extend about 4”-6” past the curve on each side.

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Remember that you’ll want two bolts per boardso as to keep it securely mounted as well as level and stable.

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Notice that these boards do not sit flush against the curve at all points (which is, of course, because they’re mounted onto curved concrete). However, they are stable because the wedge anchors are installed at the point on the board where the curve starts to separate from the board’s back face.

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Second, use a clamp to hold the pieces level; because they are smaller boards, everything (including fingers and faces) gets much closer to the drill bit, which can make everyone nervous. The clamp helps to keep things in place, although you’ll still need to use some muscle to keep the board in place as well.

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Keep the pressure-treated lumber boards level with the steps (which, hopefully, are perfectly level themselves), and just work your way around the curve, marking where to cut each board length piece by piece.

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You’ll notice that the ends of these frame boards touch but are not end-to-end flush (as in, the ends aren’t cut at angles to join precisely with the neighboring ends). This is perfectly fine for a deck frame. The boards are secure, with their double wedge anchors into the concrete, to provide plenty of support for the deck frame.

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Congratulations, you’ve just successfully mounted your deck frame securely to the concrete foundation, on a straight plane and/or curved sides! You can start to visualize the final result now, can’t you?

Happy DIYing.