Building Codes - Make sure to check your states International Residential Codes (IRC).  I live in Washington state so I will be using these codes to reference.  Here are the important codes to know.

• Stair width shall be no smaller than 36"
• There must be a minimum of 6'8" headroom from the sloped plane or the end of the stair tread.  This can be tricky but all you have to do is measure straight up from the edge of your stair tread to the ceiling and see if you have at least 6'8" clearance.
• Maximum riser height shall be no larger than 7 3/4"
• Minimum tread depth shall be no smaller than 10"
• A flight of stairs shall not have a vertical rise of more than 12' without a landing.
• The landing must be no smaller than 36" X 36"

There are a lot of handrail codes but we do not need to know these to build a simple set of stairs.

1. Find out your riser height.

• Measure from your lower floor to your upper floor.  Make sure to calculate the final height of your upper floor.   For example; If you are building deck stairs and the actual decking material has yet to be put on calculate that in.
• If you are on a sloped surface then you will need to find out where your stairs will be ending and calculate that in (this is more advanced stairs).
• Now that you have your measurement from the top of the lower floor to the top of the upper floor we need to find out how many stairs we need

A typical house has a wall height of (8' 1 1/8" wall height) + (9 1/2" floor joist) + (3/4" decking plywood)leaving us with a total height of  8' 11 3/8 " .  I will be using this number as an example for the stairs.

• So now we take that number 8" 11 3/8" and divide it by 7"  ( This is a standard number used to determine the amount of steps you need)  In this case we get the number 15.34, so we now know we need 15 stairs total.
• Now take the number of stairs you have and divide that by your total height.  In our case this is 8' 11 3/8"  divided by 15 which gives us the riser height of  7 3/16"

So we will need a total of 15 stairs at 7 3/16"

2.  Find out your run or tread length.

• Measure from where your stairs are going to end to where you would like them to being or vice verso.  Keep in mind that your minimum tread length cannot be under 10"
• Take your number of stairs and multiply by 10'.  In our case we have 15 steps and multiply this by 10" which gives us 150" ( we will actual only need 14 stairs because our upper floor counts as on step.  So we really only need 140".  This will be typical with most stairs.
• So in our  simple stair case lets say we have the 140".

3. Cut your stringers (stairs)- You will need a simple framing square for this.

• You will need to cut 14 stairs since your upper floor will count as the 15th.
• With your framing square simply make 14 triangles with it at 7 3/16" X 10" out of  2 X 12" Material.
• Your top and bottom stairs need a little extra attention. 
  
• On the subtract your kick plate (this is usually 3/4 X 8")  This is nailed or screwed onto your riser so that you can nail carpet to it, do a decorate finish with hardwood etc...
• In our case the upper stair is going to be ( 10"- 3/4" ) which will give us 9 1/4" for our upper stair.
• Cut the height of the stair tread off the bottom of your bottom stair.  In this case I will use the common 1 1/8" stair tread height. (7 3/16" - 1 1/8") gives us 6 1/16.  that will be the size of the bottom stair.
• Then cut out enough room to slide a 2 X 4 under the front bottom of the stair on all 3 stringers.
• After that cut  two (2 X 4's) to match the bottom chord of the stairs.  I usually just trace them.  Then attach them to your two outside stringers.  This is so the decorative skirt board has something to sit on.

4. Attach your stringers. 

• Measure down off the upper floor your riser height and tread height and snap a chalk line or level across this mark.  In our case measure down  (7 3/16" + 1 1/8) or 8 5/16".  This is the line where you will attach your stringers to.
• After the previous line is made, make a center mark for your middle stringer.
• Attach the stringers with nails or screws.  I usually put in a couple of blocks between my stringers for extra support.
• Now cut a 2X4 at the size of your stairs.  In our case this is 36" and slide it in the notch we made at the bottom of the stringer mark the center and nail this off.  I also put a couple extra block in the bottom for extra support.

5.  Attach your kick plates and treads. 

• Cut all your tread and kick plates.  We will need 14 kick plates and treads.
• The kick plates as we discussed earlier are usually 3/4" X 8".  You will need to rip these to fit, especially the first one. 
  
• Since our stairs are 36" cut everything and that length.
• Glue your run and your rise with floor glue.  This ensures that the stairs will not squeak.
• Work your way up nailing the kick plates on before your treads.  Make sure to use either ring shank nails or screws.

That is how you build a basic simple set of stairs:  You will apply most of these techniques in the more advanced stairs.

Thank you for reading.  Jared