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How to Build a Strong Deck Foundation

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“Can’t we just lay some decking already?!” That line echoes a kitchen project post from last December about all the small prep steps that came before painting cabinets—and it perfectly describes where we are with the deck. We’ve made real progress, but we’re impatient DIYers. After setting all the joists, we were itching to put decking down… until I noticed a handful of small but important tasks to finish first. Womp womp. Don’t worry — you’ll see decking being installed at the end of this post (and the work continues), so we’re definitely moving closer to the finish line.

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The very first step after rough framing was to get an inspection. Not a required one — an optional framing inspection — but worth doing. Our next mandatory county inspection would have been the final sign-off, and the thought of finishing everything only to be told we’d made a mistake made me nervous. Sherry called the county and scheduled the optional framing inspection so we could confirm we were on the right track. A smart move.

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Short version: we passed. I did make a small error by notching my 4×4 posts, which our county technically allows only for 6×6 posts. The code expects 4x4s to be attached with a specific bracket at the top of the post. Fortunately, this inspector was understanding — he noted the county’s guidance isn’t crystal clear and, because the deck is low to the ground and only eight feet wide, wasn’t worried. He even joked that “this thing’ll hold up five elephants and about 500 of those (points to Clara through window).” I’ll take that as encouragement.

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With the green light, I moved on to finishing the exposed framing. The exposed edge of the deck had some uneven joists sticking out, so I added two band boards to create a clean, finished rim along the angled portion where the stairs will be.

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This angled section required precise miter cuts. I trimmed the ends of the two joists to accept a 2×8 band board, using a nylon string to mark the 45-degree angle for the cuts.

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With the tops marked, I used a pivot ruler to transfer the angle and then adjusted my circular saw to make the angled cuts right on the joists.

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Here are the two joists cut to angle. I then measured and cut the 2×8 band board to match, including a mitered end that would sit flush against the house.

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After temporarily nailing the band board in place to hold it while I drove screws, the edge looked far more finished and stable.

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I repeated the process for the open end, cutting another 2×8 with a matching miter so it would sit flush against the band board. Before fastening it permanently, I trimmed the excess from the girders below — I had left them intentionally long during rough framing to allow for this exact adjustment.

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I cut most of the girder length with the circular saw and finished through with a reciprocating saw when needed. Once trimmed, I screwed the new board into the rim and angled band board and trimmed the final excess to create clean finished edges.

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With the rim and band boards addressed, I added counter-flashing to protect the ledger boards where they meet the house. This was a condition from the earlier failed inspection and it’s an important step to prevent water damage.

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On the siding side I slipped the flashing under the bottom siding and nailed it into place. For the brick side I folded a small piece of flashing and tucked it into a cut in the mortar where the original flashing had been set.

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I trimmed the vinyl flashing around the joists and formed a small drip lip so water will run away from the brick. I also ran clear silicone into the mortar crevice to hold the flashing in place and seal against moisture — a tidy and practical step to protect the ledger and house interface.

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Flashing is tedious but not technically difficult. It felt good to check that off the list and to be one step closer to installing deck boards.

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Before laying boards, I decided to address stairs and guardrail posts while the framing was still exposed. Planning and installing attachments or reinforcements now is far easier than retrofitting them after decking is in place.

I used two spare 2×10s to mark the stair placement based on the holes already dug for stair posts, which helped determine where guardrail posts would sit on the deck.

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I elected to place the stair railing inside the stringers so the steps wrap around the posts. Once I marked each 4×4 post location, I reviewed the county’s attachment requirements and searched for appropriate hardware.

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After a few trips and some head-scratching, we found Deck Tension Ties and followed recommended practices for secure post attachments. The older method of bolting posts to the outside of the deck isn’t considered as secure anymore, so these tension ties give a much stronger connection and will help us meet inspection standards.

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I screwed a tension tie to the rim board against the house, drilled matching holes in the 4×4 post (trimmed to the county-required 36″ railing height), and bolted the post in place. For posts not adjacent to the rim, I added blocking between joists and attached a tension tie to each side before bolting the posts — a method that provides a solid, code-friendly connection.

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Installing all of the hardware took two days — partly because of tight spaces that required hand-driving fasteners and partly due to pop-up thunderstorms that put a halt to work more than once. Life happens; we balanced deck work with book deadlines and childcare, but steady progress continued.

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The payoff: actual deck boards are finally going down. We’re mitering corners to create a framed border and adding a few “zipper” seams to the layout for visual interest — a pattern we teased earlier and are excited to see come together. So far we love how it looks and can’t wait to install more boards and share the finished layout.

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All this careful prep is paying off. It’s about time, right?

What small but important tasks have you checked off lately? Maybe you finally caulked the trim, changed filters, swapped batteries in smoke detectors, or weeded the patio? If not, consider this your friendly nudge — those nitty-gritty jobs really do matter.