Deck Design and Post Hole Layout:
How to Lay Out a Solid Deck Foundation Using the 3-4-5 Method
© 2008 by Kelly Smith all rights reserved
Welcome to installment 4 of the deck design and building series of articles. It fills you in on laying
out the post hole locations. It also addresses setting your ledger board. These are the same methods
employed by professional deck contractors.
I highly recommend Angies List - Ratings,
reviews and sometimes revenge. See what local homeowners say about the service companies they hire.
Always be sure to check your local building code.
This series of articles begins with basic design issues and moves through to final finishing and
refinishing. The links to the entire series are located at the bottom of the page as they are posted.
Building your backyard deck is guaranteed to boost your property value and repurpose unused real estate
for some kick-back entertaining and leisure time. You can choose to hire a deck contractor or tackle
this great DIY project on your own and save money.
Squaring your Decks Layout
This explanation assumes youre building a rectangular, attached (to the home) deck with cantilevered
joists. It also assumes the plan is for the joists to start at one corner of your home. But if you are
building a deck on top of an existing concrete patio, the layout process explained here is still applicable.
- Deck Terminology: A cantilevered deck simply means that your outside
joists are secured to the ends of your ledger board as usual, however the ends of your beams are
overhanging the post line giving it a less block-like look. Think Frank Lloyd Wright design.
The numbers I use here are to make it obvious how you can use the 3-4-5 method to arrive at a
square foundation layout (in this scenario, 6-8-10 are used; however, you can use any similar multiple.
- Make a pencil mark on your house where an end of your deck is to be located.
- Now, measure down your wall the distance that your beam will hang over. Hammer a nail in
half way here.
- Next, measure 6 down your wall. Hammer in another nail.
- Tie your string line to the initial nail.
- Peel off a length of masons string thats longer than your finished deck will end up
extending. Pull it taut and tie it off to a 2 X 2 stake.
- Make a mark on the string with a Sharpie 8 from the nail.
- Tie another string to the second nail and mark it with a Sharpie 10 out.
- Keeping strings taut, one person should hold the first string, someone else holds the
- Move the strings until the marks intersect.
- Hammer in the stake. This spot is directly perpendicular to the house.
- Repeat the above process for the other end. A square area is now defined with respect to
Now Find your Deck Post Locations
You will have already determined the number of your posts and the distance between them from reading
the previous lumber sizing and spacing article. Now you'll use that knowledge to locate where your
supporting posts will go.
- For each row of posts parallel to your house, use your Sharpie to mark the two staked
- Using more stakes and strings, guided by the marks you just made to establish the rows,
make a matrix.
- Now use the sharpie to mark the lines where the posts will be.
- Using your plumb bob, mark the hole locations on the ground with carpenters chalk or
fluorescent spray paint.
Locate your Ledger Board
The lumber dimensions of your joists and the relative distance of your homes back door from the
ground level are used together to determine the location of your ledger board. If it happens that your
door is very close to the ground, your ledger board is actually two pieces of lumber, with one on the
left side of your door and another on the right. If this happens, you can design your deck to be stepped
up onto it. Be certain to make the ledger board level using a laser level or a water level.
The next article covers setting and leveling the deck posts in fast setting concrete mix.
- Part 1: Wood Deck Design Fundamentals
- Part 2: Deck Design and Framing Concepts
- Part 3: Lumber Sizes And Spacing for Deck Building
- Part 4: Deck Design and Post Hole Layout
- Part 5: Setting Posts in Deck Construction
- Part 6: Deck Building: Beams and Joists
- Part 7: Trex Composite or Aluminum Decking vs Natural Wood
- Part 8: Popular Deck Board Patterns and Decking Installation Instructions