It's easy to get a bottom or top stair tread that doesn't match the rest of your steps. Depending on how you plan to finish your stairs decking pattern, there are a couple of measurements to consider. Let's look at some rise and runs.
Stair Rise | Stair Run | Examples
Example:
2' 2 9/16" (Grade to top of deck frame) + 15/16" (Deck board) = 2' 3 1/2"
If you place a deck board on top of the framing, you can measure the total without any math.
For example, a quick stair count can be had by dividing the deck's total height by a Timbertech Terrain Riser board, 7 13/16" tall.
(total deck height) ÷ (riser board height) = number of rises
2' 3 1/2" = 27.5" (total deck height)
7 13/16" = 7.8125" (riser board height)
27.5" ÷ 7.8125 = 3.52 (rises)
Then round 3.52 up to four. We need full rises; decimal numbers need to be rounded. If we round down (fewer steps), our riser height increases. And, in this example, we would go over our 7 7/8" maximum step height in Edmonton.
Next is the exact riser heights: Divide the total height by the number of rises.
27.5" (total height) ÷ 4 (rises) = 6.88" ( 6 7/8")
Our example will have four rises at 6 7/8" and three steps.
For more details on step quantities and riser heights, check out this article: How many steps for my deck?.
6 7/8" (riser height) - 15/16" (deck board thickness) = 5 15/16"
So when laying out your 2x12 (stringer), use the same rise for every step. After all the steps are marked, add a trim line the same thickness as your deck board above the bottom of the last step.
You can also save this trimming step for when you install the stringers. First, make a reference line (6 7/8" below the top of the framing) marked on the rim board. Place a stringer up against the deck and measure how high the stringer sits above the reference line. Then remove that amount from the bottom.
It's common to do this if your stairs land on an uneven grade or surface. Each stringer will have a different height above the reference line. For aesthetics and safety, trim the bottom step.
5 1/2" + 5 1/2" + 1/8" = 11 1/8" run
With three steps, this is a total of 2' 9 3/8" away from the deck.
When installing composite boards, I like to hold two deck boards and a hidden fastener in between to measure the tread width.
Total width with nosing
decking + gaps - nosings
(6 x 5 1/2") + (1/8" x 3) - (1/2" x 3) = 33.38" = 2' 7 7/8"
In our example the run used to cut the stringers is this total width divided by three. 10 5/8"
This run will allow full deck boards (no cuts) with consistent spacing and nosing.
When the stringers are attached to the deck, on the top step, the first deck board starts at the rim board. The bottom two steps, however, begin after the riser board. The riser board pushes the decking forward to line up with the next riser board below. If the top step of the stringer is cut with the same run as the other steps, there will be a gap. The thickness of the riser board needs to be trimmed from the top stringer width.
e.g. With the three steps of two pressure-treated deck boards, if we add a 2x6 kicker. Our run is still 11 1/8". The top step will be shorter by the thickness of the 2x6 material (1 1/2").
(Tread width) - (Riser thickness) = Top step run
11 1/8" - 1 1/2" = 9 5/8"
Tip: cut one stringer and double-check your measurements with some scrap deck boards and fasteners. If it's all good, trace that stringer for the rest of your bundle.
Tread Width = Deck boards + Spacing
5 3/8 + 5 3/8" + 3/16" = 10 15/16"
Stringer Run = Tread Width - Nosing
Flush (no overhang) = Tread Width
Total Width (Stair Reach) = Total Tread Width - Total Nosing (overhangs)
(4 x 10 15/16") - (0) = 3' 7 5/8"
Top Tread Width = Tread Width - (kicker + riser + nosing) + top riser
10 15/16" - (0) - 0" = 10 15/16"
Tread Width = Deck boards + Spacing
5 1/2 + 5 1/2" + 1/16" = 11 1/16"
Stringer Run = Tread Width - Nosing
11 1/16" - 3/4" = 10 5/16"
Total Width (Stair Reach) = Total Tread Width - Total Nosing (overhangs)
(4 x 11 1/16") - (4 x 3/4") = 3' 5 1/4"
Top Tread Width = Tread Width - (kicker + riser + nosing) + top riser
10 15/16" - (0) - 0" = 10 15/16"
Tread Width = Deck boards + Spacing + Riser
5 3/8 + 5 3/8" + 3/16" + 3/4"= 11 11/16"
Stringer Run = Tread Width - Nosing
Flush (no overhang) = Tread Width
Total Width (Stair Reach) = Total Tread Width - Total Nosing (overhangs) + Top riser thickness
(3 x 11 11/16") - (0) + 3/4" = 2' 11 3/4"
Top Tread Width = Tread Width - (kicker + riser + nosing) + top riser
11 11/16" - (1 1/2" + 3/4") - 3/4" = 10 3/16"
Tread Width = Deck boards + Spacing
5 1/4 + 5 1/4" + 3/16" = 10 11/16"
Stringer Run = Tread Width - Nosing
10 11/16" - 1/2" = 10 3/16"
Total Width (Stair Reach) = Total Tread Width - Total Nosing (overhangs) + Top riser thickness
(4 x 10 11/16") - (4 x 1/2") + 3/4" = 3' 5 1/2"
Top Tread Width = Tread Width - (kicker + riser + nosing) + top riser
10 11/16" - (1 1/2" + 3/4" + 1/2") - 3/4" = 8 11/16"
Stair Rise | Stair Run | Examples
Stair rise
Rise is the step height; each rise should have a consistent size. When cutting your stringers, this measurement is the vertical portion. First, you will need the total height of your deck located at the stairs. The full height includes the top of the frame to the landing location, plus the thickness of your decking.Example:
2' 2 9/16" (Grade to top of deck frame) + 15/16" (Deck board) = 2' 3 1/2"
If you place a deck board on top of the framing, you can measure the total without any math.
Step Heights
Your step height is equal to the rise in your stringer. The exact riser dimension comes from dividing the total deck height by the number of steps needed.For example, a quick stair count can be had by dividing the deck's total height by a Timbertech Terrain Riser board, 7 13/16" tall.
(total deck height) ÷ (riser board height) = number of rises
2' 3 1/2" = 27.5" (total deck height)
7 13/16" = 7.8125" (riser board height)
27.5" ÷ 7.8125 = 3.52 (rises)
Then round 3.52 up to four. We need full rises; decimal numbers need to be rounded. If we round down (fewer steps), our riser height increases. And, in this example, we would go over our 7 7/8" maximum step height in Edmonton.
Next is the exact riser heights: Divide the total height by the number of rises.
27.5" (total height) ÷ 4 (rises) = 6.88" ( 6 7/8")
Our example will have four rises at 6 7/8" and three steps.
For more details on step quantities and riser heights, check out this article: How many steps for my deck?.
Bottom Step Height
When cutting stair stringers, this is the step that often gets missed. The bottom step of the stringer needs to be trimmed by the same thickness as your deck boards. Suppose this bottom step was cut exactly like the others. This last step would be the stringer rise plus a deck board's thickness away from the ground after decking. This doesn't happen with the other rises because the deck boards above and below add and take away height. The additions cancel each other out.6 7/8" (riser height) - 15/16" (deck board thickness) = 5 15/16"
So when laying out your 2x12 (stringer), use the same rise for every step. After all the steps are marked, add a trim line the same thickness as your deck board above the bottom of the last step.
You can also save this trimming step for when you install the stringers. First, make a reference line (6 7/8" below the top of the framing) marked on the rim board. Place a stringer up against the deck and measure how high the stringer sits above the reference line. Then remove that amount from the bottom.
It's common to do this if your stairs land on an uneven grade or surface. Each stringer will have a different height above the reference line. For aesthetics and safety, trim the bottom step.
Stair run.
Run is the tread width; each step should have a consistent run. Cutting your stringers uses this measurement and may include trimming the top run shorter based on kickers and nosing.Total width
The total width is how far the stairs reach past the deck. It is each steps run combined. We will use the deck board widths, spacing, riser, and kicker to set the tread width (run) in our examples. To have the steps end by a specific point, you would adjust the run's quantity and size.Tread width
A tread width includes deck boards and spacing. For instance, standard 5/4 x6 decking has a width of 5 1/2". With two deck boards per step being the most common and adding a 1/8" gap between those boards. This equals eleven inches and one eighth.5 1/2" + 5 1/2" + 1/8" = 11 1/8" run
With three steps, this is a total of 2' 9 3/8" away from the deck.
When installing composite boards, I like to hold two deck boards and a hidden fastener in between to measure the tread width.
Stringer Run
The stringer run size differs from the tread width based on the size of the nosing. You see, the overhang (nosing) is not included in the stringer run. Each nosing hangs past the riser board on the step below. So the total reach of the stairs is smaller because of this overlap. Tread width remains the same, but the stringer run and total distance of your stairs will be shorter.Total width with nosing
decking + gaps - nosings
(6 x 5 1/2") + (1/8" x 3) - (1/2" x 3) = 33.38" = 2' 7 7/8"
In our example the run used to cut the stringers is this total width divided by three. 10 5/8"
This run will allow full deck boards (no cuts) with consistent spacing and nosing.
Top tread width
Let's say you have a pressure treated deck and you want all the risers to be closed off with a 2x6.When the stringers are attached to the deck, on the top step, the first deck board starts at the rim board. The bottom two steps, however, begin after the riser board. The riser board pushes the decking forward to line up with the next riser board below. If the top step of the stringer is cut with the same run as the other steps, there will be a gap. The thickness of the riser board needs to be trimmed from the top stringer width.
e.g. With the three steps of two pressure-treated deck boards, if we add a 2x6 kicker. Our run is still 11 1/8". The top step will be shorter by the thickness of the 2x6 material (1 1/2").
(Tread width) - (Riser thickness) = Top step run
11 1/8" - 1 1/2" = 9 5/8"
Tip: cut one stringer and double-check your measurements with some scrap deck boards and fasteners. If it's all good, trace that stringer for the rest of your bundle.
Examples and combinations
Flush Treads
Tread Width = Deck boards + Spacing
5 3/8 + 5 3/8" + 3/16" = 10 15/16"
Stringer Run = Tread Width - Nosing
Flush (no overhang) = Tread Width
Total Width (Stair Reach) = Total Tread Width - Total Nosing (overhangs)
(4 x 10 15/16") - (0) = 3' 7 5/8"
Top Tread Width = Tread Width - (kicker + riser + nosing) + top riser
10 15/16" - (0) - 0" = 10 15/16"
Overhang Treads
Tread Width = Deck boards + Spacing
5 1/2 + 5 1/2" + 1/16" = 11 1/16"
Stringer Run = Tread Width - Nosing
11 1/16" - 3/4" = 10 5/16"
Total Width (Stair Reach) = Total Tread Width - Total Nosing (overhangs)
(4 x 11 1/16") - (4 x 3/4") = 3' 5 1/4"
Top Tread Width = Tread Width - (kicker + riser + nosing) + top riser
10 15/16" - (0) - 0" = 10 15/16"
Flush Riser | Kicker
Tread Width = Deck boards + Spacing + Riser
5 3/8 + 5 3/8" + 3/16" + 3/4"= 11 11/16"
Stringer Run = Tread Width - Nosing
Flush (no overhang) = Tread Width
Total Width (Stair Reach) = Total Tread Width - Total Nosing (overhangs) + Top riser thickness
(3 x 11 11/16") - (0) + 3/4" = 2' 11 3/4"
Top Tread Width = Tread Width - (kicker + riser + nosing) + top riser
11 11/16" - (1 1/2" + 3/4") - 3/4" = 10 3/16"
Kicker | Riser | Overhang
Tread Width = Deck boards + Spacing
5 1/4 + 5 1/4" + 3/16" = 10 11/16"
Stringer Run = Tread Width - Nosing
10 11/16" - 1/2" = 10 3/16"
Total Width (Stair Reach) = Total Tread Width - Total Nosing (overhangs) + Top riser thickness
(4 x 10 11/16") - (4 x 1/2") + 3/4" = 3' 5 1/2"
Top Tread Width = Tread Width - (kicker + riser + nosing) + top riser
10 11/16" - (1 1/2" + 3/4" + 1/2") - 3/4" = 8 11/16"
Triple Deck Boards | Kicker | Riser | Overhang
Tread Width = Deck boards + Spacing
(5 1/2 + 5 1/2" + 7 1/4") + (1/16" + 1/4" + 1/4") = 1' 6 13/16"
Stringer Run = Tread Width - Nosing
1' 6 13/16" - 5/8" = 1' 6 3/16"
Total Width (Stair Reach) = Total Tread Width - Total Nosing (overhangs) + Top riser thickness
(3 x 1' 6 13/16") - (3 x 5/8") + 1/2" = 4' 7 1/16"
Top Tread Width = Tread Width - (kicker + riser + nosing) + top riser
1' 6 13/16" - (1 1/2" + 1/2" + 5/8") - 1/2" = 1' 4 11/16"
