How to Install the First Deck Board Perfectly
This single board determines the alignment of your entire deck. Get it right, and every subsequent board falls into place naturally. Get it wrong, and you'll fight the alignment for every board that follows.
Quick Summary
15-30 minutes
Easy but critical
1/4 inch
Why the First Board Matters So Much
Think of your first board as a reference line for the entire deck. Every board after it will be spaced off the one before. If your first board is 1/4 inch off-parallel to the house, by the time you reach the far edge of the deck, you could be off by an inch or more—creating an obviously crooked final board.
The time you spend getting this first board perfect is the best investment you'll make in your deck project. Measure twice, measure again, then fasten.
Pro Tip: Some builders install a temporary "starter board" at the house to establish the gap and reference line, then remove it and install the real first board once they're confident in the alignment. This gives you a do-over without leaving any visible mistakes.
Tools and Materials
Essential Tools
- Tape measure – Accurate measuring is everything
- Chalk line – For snapping a reference line
- Speed square – For checking 90-degree angles
- String line – For checking board straightness
- Drill/driver – Impact driver works best for deck screws
- 1/4-inch spacers – Maintain gap from house (pencils work in a pinch)
Materials
- Your straightest board – Sort through lumber to find it
- Deck screws or hidden fasteners – Appropriate for your decking type
Step-by-Step Installation
Step 1: Select the Best Board
Before you begin, sort through your entire deck board supply. Look for:
- Straightness – Sight down the edge of each board; pick the one with no bow or curve
- No twist – Lay the board flat and check all four corners touch the surface
- No major defects – Avoid large knots, splits, or checks near the edges
- Good color match – If visible, pick one that represents the average color of your lumber
Important: Save any bowed or twisted boards for shorter spans or locations where imperfections matter less. A bowed board can often be straightened when fastened across multiple joists.
Step 2: Establish Your Reference Line
The house wall (or ledger board) is your reference for parallel alignment. Measure out from the house to establish where the first board's outer edge will sit.
- 1.Measure from the house: 1/4" gap + board width = outer edge distance
- 2.Mark this distance at both ends of the deck
- 3.Snap a chalk line between the marks
- 4.Verify the line is parallel to the house by measuring at several points
Pro Tip: If your house wall isn't perfectly straight (many aren't), establish your reference from the longest straight section. The small gap variations near the house will be less noticeable than a crooked outer edge.
Step 3: Position Your Spacers
Place 1/4-inch spacers against the house at each joist location. Options for spacers include:
- Commercial deck spacers – Designed for this purpose, easy to remove
- Carpenter's pencils – About 1/4" thick, readily available
- 1/4" plywood scraps – Cut to consistent thickness
- 16d nails – Standard 16-penny nails are approximately 1/4"
The gap between the first board and the house is critical. It allows water to drain away from the house, provides air circulation to prevent rot, and accommodates wood expansion. Never install decking directly against the house.
Step 4: Position the First Board
Lay your selected board against the spacers with the best face up. Check:
- Board is pressed firmly against all spacers
- Outer edge aligns with your chalk line
- Board ends have appropriate overhang (typically 1-1.5")
- Board spans joists properly (no joints except on joist centers)
Step 5: Verify Straightness and Alignment
Before driving any fasteners, double-check everything:
- 1.Run a string line along the outer edge of the board
- 2.Hold the string about 1/8" off the surface at each end
- 3.Check that the gap is consistent along the entire length
- 4.Measure from the house at multiple points to verify parallel
If the board has a slight crown (curve), install it crown-up so foot traffic will flatten it over time.
Step 6: Secure the Board
With alignment verified, fasten the board at each joist:
- Face screwing: Two screws per joist, 3/4" from board edges, pre-drill near ends
- Hidden fasteners: Install first clip against house, follow manufacturer instructions
- Drive depth: Screw heads should be flush or slightly countersunk, not proud
Avoid This Mistake: Don't overdrive screws. Driving screw heads below the surface weakens the hold and creates pockets that collect water and debris.
Step 7: Remove Spacers and Check Again
After securing, remove the spacers and make a final inspection:
- Gap from house is consistent along the entire length
- Board hasn't shifted during fastening
- Outer edge is straight and on your reference line
- All fasteners are properly seated
What If the House Isn't Straight?
Many houses have walls that bow slightly or aren't perfectly plumb. Here's how to handle it:
Slight Variation (1/4" or less)
The 1/4" gap can accommodate minor variations. Install the board parallel to an average line along the house, letting the gap vary slightly. These small differences are nearly invisible.
Moderate Variation (1/4" to 1/2")
Establish your reference from the straightest section of the house. Increase the gap at the problem areas so it varies from 1/4" to 1/2". This keeps your board straight while maintaining minimum clearance.
Significant Variation (1/2" or more)
Consider scribing the first board to match the house profile. This involves marking the house contour onto the board and cutting along that line. It's extra work but results in a consistent gap along the entire length.
Common First Board Mistakes
Using a bowed or twisted board
A bad first board means every following board will be fighting against it. Take the time to find your straightest lumber.
Installing directly against the house
No gap means no drainage, no air circulation, and accelerated rot at the most vulnerable point of your deck.
Not checking parallel to the house
Measuring only at one end leads to a board that's off-angle. The error compounds with every subsequent board.
Fastening before verifying alignment
Once screws are in, adjustments are difficult. Take an extra minute to double-check before committing.
Skipping the string line check
Your eye can't detect subtle curves. A string line reveals imperfections you'd otherwise miss until it's too late.
FAQ
How far should the first deck board be from the house?
Leave a 1/4-inch gap (about the width of a carpenter's pencil) between the first board and the house. This allows water drainage, air circulation, and accommodates seasonal wood movement. Never install decking directly against the house.
Should the first deck board be the best board?
Absolutely. Use your straightest, most defect-free board for the first position. This board sets the alignment for every subsequent board. Sort through your lumber before starting and reserve the best board for this critical position.
Do I need to predrill deck boards?
Predrill within 2 inches of board ends to prevent splitting, especially with hardwoods and treated lumber. Modern self-drilling deck screws usually don't require predrilling in the middle of boards for softwoods. When in doubt, predrill.
How do I know if my first board is straight?
Stretch a string line from one end of the board to the other, held about 1/8 inch off the surface. The gap should be consistent along its length. If the board bows toward or away from the string at any point, it's not straight.