Decks California - builder - contractor - design - construction
Decks California - builder - contractor - design - construction
Three basic rules for a comfortable stair rise
The sum of two risers and one tread should be 24 to 25 inches.
The sum of one riser and one tread should be equal to 17 to 18 inches.
The height of the riser times the width of the tread should equal between 70 and 75 inches.
Definitions used for stair design
Stringer :: The angled sawtooth framing member that makes up the stair steps
Skirt :: The angled framing members that are on the two outsides of the stringers.
Run :: The tread width minus the nosing.
Total Rise :: The height from the top of the decking to the top of the slab. From finish of where it goes to, to finish of what it sits on.
Total Run :: The entire length you have to work with. From the deck face to the end of the bottom tread.
Determining the total rise
You kind of have to do this twice, you know measure twice cut once.
Level it out from top of the decking to the top of the landing where you figure the stair will end.
Get that height, and divide it by 7. A 2x4 checked with a string line works well.
7 is the rise of each step we are going for.
It gets a bit tricky here because it never seems to work out perfectly.
We are just trying to find how many steps though so round it off.
If it's over .5 than round up and down if under.
I know... what?
Okay an example then.
Say the total rise is 78" I divide by 7 and I get 11.14
.14 is under .5 so I have 11 rises. If it was 11.72 it'd be 12 rises
With the number of rises we can get the total run
There is always one less run (tread minus the nosing) than there are rises.
Two 2x6's with a space for expansion minus a 1" nosing is a 10 1/4 run
Nosing :: The tread overhang
So if I have 11 rises I have 10 runs times 10.25
102.5 so now I can get my exact total run at 102 1/2 inches from the deck
What if the total run doesn't work
You measure 102 1/2 and you find you don't have a full tread width on the landing.
You go back and divide by 8 if it's too long and 6 if it's too short
That will add or take away a tread, but if you can't get a comfortable stair
within code you have to move the landing or the stair location.
Finally the calculations for the stairs
Okay we've double checked the total rise and it is 78"
and we now know we have 11 risers in our example.
So to get the exact height of each rise we divide 78 by 11 or by the number of rises.
78 ÷ 11 = 7.09 The Total Rise divided by the Number of rises
If you're in the field and only have a decimal calcualtor :: Take the first number and divide it by the second number. For example (1/8) 1 divided by 8 equals .125 1/16 is .0625
.09 is closer to 1/8 so 11 risers at 7 1/8
What if the landing is on an angle like a sidewalk on a hill
Where the bottom or top riser adjoins a sloping public way, walk, or driveway having an established grade and serving as a landing, the bottom or top riser may be reduced along the slope to less than four (4) inches in height with the variation in height of the bottom or top riser not to exceed three (3) inches in every three (3) feet of stairway width.
I treat these like a winder, so at the walk-line or most common path that is where I'll match my rise.
The stair rise calculation table
Now that I put you through all of that I have made a stair table.
You might be able to refer to it and not go through all the math.
Personally I always have the construction master pro
calculator (right) with me, one in the shop and one in the truck.
It'll not only do the math in feet & inches it'll tell me the run, rise,
length of the stingers the angle... it almost builds the stairs.
Get the book too (left), these tools are just as valuable as a hammer for a carpenter.
The layout and cutting your stairs
Site down the 2x you are using and if there is a slight crown work from that side.
Using our example place your stair clips at 7 1/8 and 10 1/4.
Mark off the number of steps.
After you have the stair laid out if you are using a 3/4 risers take that off of the top rise like in the picture right, if you are adding a riser there later leave it on.
Then you take the tread thickness off the bottom for the first step where it sits on the landing, this will make all the steps the same height.
Cut the very top vertical (plumb cut) and the bottom horizontal (level cut).
Now is the time to place it and check the treads with a torpedo level and if the length is working.
If you fluffed up at least you still might be able to salvage the stringer at this point.
After you have checked the stringer in place copy it and cut the others.
Before you install the stringer use it to layout the skirts.
At the bottom reverse the square and add on enough for the nosing.
At the top take into account if you are adding a riser or not.
Also for the top just make the plumb cut for now.
After you place it you can get the exact level cut from the decking.
That section of the skirt is called the horn.
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This page last modified on Wednesday, February 02, 2011
Decks building codes relating to stairs - California - ICC 2010
1013 Guards (railings):
1013.1 Where required.
Guards shall be located along open-sided walking surfaces, including mezzanines, equipment platforms, stairs, ramps and landings that are located more than 30 inches measured vertically to the floor or grade
R312.2 Height. shall be not less than 42 inches high measured vertically above the adjacent walking surface, adjacent fixed seating or the line connecting the leading edges of the treads.
1. Guards on the open sides of stairs shall have a height not less than 34 inches measured vertically from a line connecting the leading edges of the treads.
2. Where the top of the guard also serves as a handrail on the open sides of stairs, the top of the guard shall not be not less than 34 inches and not more than 38 inches measured vertically from a line connecting the leading edges of the treads.
R312.3 Opening limitations.
Required guards shall not have openings from the walking surface to the required guard height which allow passage of a sphere 4 inches in diameter.
1. The triangular openings at the open side of a stair, formed by the riser, tread and bottom rail of a guard, shall not allow passage of a sphere 6 inches in diameter.
2. Guards on the open sides of stairs shall not have openings which allow passage of a sphere 43/8 inches in diameter.
Stairways shall not be less than 36 inches in clear width at all points above the permitted handrail height and below the required headroom height. Handrails shall not project more than 4.5 inches on either side of the stairway and the minimum clear width of the stairway at and below the handrail height, including treads and landings, shall not be less than 31 1/2 inches where a handrail is installed on one side and 27 inches where handrails are provided on both sides.
1009.4.2 Riser height and tread depth.
Stair riser heights shall be 7 inches maximum and 4 inches minimum... Rectangular tread depths shall be 11 inches
5. In Group R-3 occupancies; the maximum riser height shall be 7 3/4 inches; the minimum tread depth shall be 10 inches ...
A nosing not less than 3/4 inch but not more than 1 1/4 inches shall be provided on stairways with solid risers where the tread depth is less than 11 inches
1009.4.4 Dimensional uniformity.
Stair treads and risers shall be of uniform size and shape. The tolerance between the largest and smallest riser height or between the largest and smallest tread depth shall not exceed 3/8 inch
SECTION 1012 HANDRAILS
Handrail height, measured above stair tread nosings, or finish surface of ramp slope, shall be uniform, not less than 34 inches and not more than 38 inches
Stairways shall have handrails on each side
3. Decks, patios and walkways that have a single change in elevation
4. In Group R-3 occupancies, a continuous run of treads or flight of stairs with less than four risers does not require handrails.
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Serving North Marin & West Sonoma Counties in the San Francisco North Bay area of Northern California
With the exact total run we can get the total rise
Now we can double check the exact total rise from our earlier guess.
Level out again and measure to get the new total rise.
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