deck step measurement (confused)

I have stumbled onto something that I don't know how to accurately measure.
I've got a low deck (21" above ground), and I am trying to cut 2x8 stringers to enclose the two required steps. I probably need some support in the middle as well (3' span).
I want to make sure that the ends of the stringer are flush to the deck and to the ground. Side view would look something like this:
| <-- side of deck | \\ | \\ <-- stringer | \\ | \\ | \\ ________________\\_______ <--- ground
Ideally the angle between deck and ground would be 90 degrees. Any ideas on how I can measure this accurately?
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Borrall Wonnell wrote:

You're going to need to use 2x12s Your stairs will require 7 inch risers and 10 inch treads. Bob Vila's site has a video of this. http://video.bobvila.com/m/21320810/building-a-deck-and-stairs.htm
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As with all things that Boob Vila is involved with this almost has something worthwhile. It didn't answer the OP's question about the angle of the deck relative to the ground.
Nice catch on pointing out the need for 2x12's instead of 2x8's.
G.S.
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Lay a 4' level on the side of the deck and on the ground perpendicular to the deck. That will give you a good idea if its square. From my calculations, at 21" above the ground, you need 2 steps @7" high, and the tread should be 11". So the end of the stringer will be approx 22" away from the deck. Even if its not perfectly square, you could always trim or shim a little under the stringer. Its a small set of steps. Also you might get away with using 2 stringers if you overhang each step 6" on each side. Then you would have 24" span between stringers ( provided you use 2X6 steps). Which means less likelyhood of problems trying to level the steps and stringers.
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Gordon Shumway wrote:

I'd put this in the 'life's too short' category, and buy precut treated stringers from the deck aisle at the Borg. At most, they will need a little trimming to match the as-found conditions, and to make sure the rise and tread depth are the same for all the steps. (Some assume a face board on the top, some don't, some assume bottom riser will be buried in a lower deck, some don't. ) But all the hard parts will be done already. I wouldn't pay the premium if I was putting up a dozen decks at a condo complex, but for a one-time job, the convenience is worth it, IMHO. If there isn't a concrete landing pad for the stringers already, scrape a level spot with a shovel and put down 2-3 precast pavers- you don't want the stringers sitting in dirt. You can dry-fit all the pieces basted together with a few long spikes not driven home, to make sure it is all square and level, fine-tuning as needed, before you do the final assembly with hangers and deck screws. For 36" wide, I would use 3 stringers. Even with 2x6 treads, a 24" span in center will feel bouncy for larger folks.
-- aem sends...
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I agree. It is a simple set of steps but just using a carpenter square to lay out the stringers even after you know what the run and rise has to be is not something that is common knowledge.
My first set of steps (1 story into basement) took me some studying to get the layout right and I already knew how to use a square.
Harry K
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Those "pre-made" stringers are fine provided they are the correct riser and tread, in the OP's case it must be 7" step and 11" tread.

A 2X6 can safely span 24" with no problem. I have a 5 foot wide stairs with 3 stringers and there is 25" between each stringer and I have no problems with bounce
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Since most codes allow a riser height from 7" to 8" overall, what makes you think the pre-cut stringers are going to be at the 7" riser height that the OP requires? If they are, say, 7 1/2", they won't work, no matter how much "trimming" you do. With a little careful planning, cutting a set of stringers is a pretty easy project.
JK
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Wow, I never expected so many responses!! A few comments:
1) I considered the pre-made stringer (including metal) but the rise was too tall.
2) This will be an enclosed step, so the 2x8 will not be notched like a traditional stringer. Won't this be strong enough? I was planning on slotting each step into the side of the 2x8s, and finishing up with a traditional 2x12 stringer in the middle.
3) Love the 3-4-5 idea. Cardboard sounds like a nice follow-up. Now if only I could cut a straight line with my circular saw :)

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re: Now if only I could cut a straight line with my circular saw
That's what a...
- Speed square - Framing Square - Clamped on straight-edge - Edge guide - T-Square
...is for.
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I don't like that idea. A 2X8 will not work for that anyway. Use the 2X12 and just cut out the desired riser and treads. Don't notch. Also as someone suggested, because you might be securing the stringers to the framing below the deck, you might have to add a 3rd tread on top level with the deck.
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On Mon, 15 Jun 2009 16:13:24 -0700 (PDT), Borrall Wonnell

An inclinometer.
G.S.
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[--]
1.To check for 90 degrees --
Measure the distance from ground to top of deck - = 21" Measure out from the deck 28" and mark the spot Measure the distance from the top of the deck to the spot you just marked - it should be 35" if it's a 90 degree angle. (3-4-5 triangle)
2. If it's not 90 degrees, get some cardboard and make a template., or just lay out 3 2x4s at the location and nail them together - that'll give you all the dimensions and the proper angle.
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With the way most decks are built you will need 3 treads in order to securely attach this to the deck.
The top tread will be equal to the surface of the deck.
I also vote for buying the pre-cut ones at the BORG. Trace the outline onto heavy cardboard of a scrap of plywood and then adjust that until it fits.
Use that pattern to modify the rest of the stringers.
Ideally steps should be level or have a minor backward pitch toward the deck. Never pitch them away from the deck.
Colbyt
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Since you will only need two steps to reach your 21" high deck, you might consider "stacked boxes" instead of the usual stair stringers. While I normally cut stair stringers for longer stairs, I used the box approach for the front and back steps of our house. Easy to build, and rock solid.
With your 21" deck, you would have three risers 7" high. If you're using regular 2x decking material, you would subtract 1-1/2" from that 7", and rip the boards for the lower box to 5-1/2" (I would rip down a 2x8, rather than relying on the width of a 2x6). Build a simple box from that lumber for your first step.
Now rip lumber to the full 7" for your second step (since you're not subtracting the thickness of the decking material). Then build the second box on top of the first.
I added vertical 2x4's in the corners to tie everything together. Then screw on your decking and you're done.
If your steps are more than 3' wide or you use thinner deck material, I would add a middle support on each box.
If your steps are resting on the ground, rather than a concrete patio or sidewalk, I would probably pour a concrete step for the bottom "box", and then build a single wood box on top of that.
For a 7" riser you would need about a 10-1/2" tread. A couple of 2x6's, with a slight space between them for drainage would work well (11-1/8" total) and give a small "nosing" overhang.
Be sure to use pressure treated lumber for your outdoor stair structure, no matter what construction method or decking you use. I ripped the front and back of my "boxes" about 1/4" narrower to allow drainage, so the "support" is only on the sides and middle support of the boxes.
Just another option to consider.
As for squaring off the building, mark one side of your steps on the deck. Then measure 4' along the wall, and 3' out from the wall. Move the 3' measurement back and forth until the distance between the tips of the 3 and 4 foot measurements equals 5'. This triangulation is the Pythagorean (sp?) theory, and is a great way to check for square. You can scale up the basic 3-4-5 triangle if you need to square up larger areas (6-8-10, 9-12-15, etc...).
If you use my "box" method of building, your steps will also be square when the diagonal measurements are equal. In other words, measure from the back left corner to the front right corner. This measurement should be identical to the back right corner and front left corner. If not, shift things around till they are equal.
Or, just use a framing square. :)
Anthony
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That did the trick...simple and solid. The concrete pavers that the 'box' rests on weren't completely level, so I shimmed it with narrow strips cut from spare shingles.
I avoided the angle measurement problem, but I'm sure it will crop up again in the near future.
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