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Building a Deck Addition

Get the most out of your backyard space with a 300-square-foot addition for about $1,200.

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Hosts Pat Simpson and Amanda Rosseter expand a cramped deck by building a second level. Maximize space by creating a two-tiered outdoor living space (figure A) with about $1200 in materials.


Protective construction gloves and safety glasses
2' x 6' and 2' x 8' ledger boards
5 ¼" decking boards
5 ½" decking boards
2" x 6" pressure treated boards
2' x 8' beams
batter boards (1" x 2" wooden stakes)
4" x 4" posts
2" x 2" baluster boards
masonry string
tape measurer
hole digger or rent a gas powered auger
pre-mixed concrete
joist hangers
galvanized nails
16 pd shanked galvanized nails
3/8" x 4/8" lag screws
3/8" x 7/8" carriage bolts
#8, 2 ½" galvanized deck screws
½" galvanized deck screws
clear water repellant or stain with water repellant

*Note: Before undertaking a construction project of this size, check the local building codes and obtain a building permit, and find out the location of any underground utility lines. Determine the details of the deck plan such as railing system, and note any potential problematic drainage areas.

1. Wearing thick construction gloves and safety glasses, tear down the old deck portions, starting with the railing and stairs. Watch out for any sharp nails or rough edges. If the posts were originally set in concrete, saw off the posts flush with the frame.
2. Construct the deck frame with 2' x 6' and 2' x 8' ledger boards.
3. Support the boards temporarily with the 16 pd ring shanked galvanized nails driven partially into place. Then, secure the boards permanently by pre-drilling four holes along each ledger board. Use a ratchet to attach 3/8" x 4/8" lag screws along the boards.
4. Square off and level your addition, drive batter boards into the ground at the corners, and run masonry string between each along the outside perimeter starting near the house and working your way around. Don't use nylon string for this process because it stretches.

5. Following the 3, 4, 5 rule, use a tape measurer to locate 3' from a corner and mark the measurement with a marker. Next, measure 4' from the corner along the string, and mark with the pen. Once you get an exact 5' measurement between two points on perpendicular strings, the corner is square (figure B). Repeat the process for all the corners.
6. Dig post holes about 2' deep with a hole digger, or rent a gas powered auger for larger jobs. Pour about 2" of gravel in the bottom of the hole to facilitate drainage.
7. Place a post in the hole and shovel pre-mixed concrete around the post in the hole. Use a level to make sure the posts are vertically straight, and allow the concrete to cure.

8. Use 2' x 8' beams to support the deck sub-structure. Pre-drill and attach the beams to either side of the posts using 3/8" x 7/8" carriage bolts (figure C).
9. Finish the deck framing by attaching the joist hanger 16" on center, meaning there is 16" between each joist with galvanized nails. Hold a scrap piece of wood perpendicular to the ledger board to measure if the deck will meet the desired height.
10. Put the joists in place and toenail the ends of the beams to keep both sides spaced evenly.

11. Lay the 5 ¼" decking boards perpendicular to the old deck floor boards (figure D), and pre-drill the ends of the boards to prevent any wood splits. Butte the pressure treated boards and a ¼" gap will naturally occur over time. Use #8 2 ½" galvanized deck screws to secure the boards in place.
12. Attach the 4" x 4" posts that have a lap cut 1 ½" to fit over the lip of the deck for the railing system with lag screws. Always check to make sure your work is level.
13. Once all the posts are in place, attach the rail supports with 2" x 6" boards. Pre-drill pilot holes on an angle and use 2 ½" screws to secure the boards in place.
14. Cut the 2" x 2" baluster rails on a 45-degree angle along the bottom edge.

15. Line the rails flush with the screws along the railing supports. Use a 2" x 4" scrap piece wood to evenly space the rails (figure E).

16. Leave an 8' gap in the railing system to install a built-in bench (figure F). Use 2" x 6" materials for the four support frames. Attach the bench frame to the posts and deck surface with 1/2" deck screws. Pre-drill pilot holes, and toenail the screws in place. Make sure your work is level and square.
17. Build the bench seat height at 18" with a 7-degree slope for the back support.
18. Use 5 ½" decking boards for the bench, and leave open space beneath the bench for user's feet.
19. Finish the deck with clear, water repellant or stain with a water repellant.

Quick Tips

  • Protect your eyes with safety goggles when sawing and sanding.
  • Use earplugs when working with power tools.
  • Always wear a dust mask sawing or sanding, especially if you do so indoors.
  • Make sure your workshop has good lighting and ventilation.
  • Wear gloves to prevent splinter wounds.
  • Keep a first aid kit close by for any unexpected accidents.
  • Maintain the sharpness of tools like wood chisels to keep them working properly.
  • Make sure the handles of top-heavy tools are attached well to prevent any accidents.
  • Look for double insulation on electrical tools, and read the instructions before use.
  • Wear a tool belt to keep materials close at hand.

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