Thursday, July 1, 2010

New Stairs for Old,..New Stairs for Old...

STAIR MATH!!

So its our 3 yr house-iversery today and I'm feeling a bit bummed cause we haven't really done anything on the house for a while.


So I hit on the idea to finally redo the stairs off of our back porch. In order to get the deck 'normalized' I need to rebuild the stairs with code compliant guard rails, width and rise-run which it is not compliant with now.



As you can see the back stairs are a bit wonky being supported by a tacked in place post and that weird cross beam.




The ugly bottom of the stairs. You can just see under that ramp the two anchor bolts that I need to use for the 2by4 'kicker'




Here's a shot looking up at the underside of the deck. That 2by12 with the notch taken out of it is going to be a problem. The house movers cut that notch so they could get a beam in there to support the deck-house. The deck has 2by6 joists as you can see which are not deep enough for the stringer or carriage to land on. I'll probably have to remove this and the horizontal board and reinstall a fresh pressure treated 2by12 bolted to the framing.




To figure the total rise and run I used a plumb bob and my laser level. Yay for laser levels they save a lot of time...but they don't work in bright direct sunlight...
The plumb line seen here represents the edge of the deck or the start of the run. The level is clamped at the height of the finished landing or the top edge of our fancy retaining wall. I used the laser level to determine this so no need for the magically straight and long piece of framing lumber. Right now the exterior ground is a couple of inches lower than this level but when finished-landscaped it will be even with it.
So I can measure up from the top of the level to the top of the deck boards to get the total rise.


Then I marked on the level where the plumb line landed. From there I could measure to the outer edge of the retaining wall to get the total run.



Annnnd here is what I found. A total rise of 81" and a total run of 99 1/4" So here's where the math comes in.

Stair Math: The cities code for stair cases is the minimum individual run for the stair case can be 9" and the maximum individual rise can be up to 8". I've got to figure out how to fit a stairway that does not exceed those numbers into the given constraints of total rise-run.

If I guess that I am going to need 10 risers I get (total rise)/(number of steps)= 81"/10= 8 1/10" individual rise...that's too high a riser by 1/10th of an inch! I don't want to risk an anal inspector so I'll have to make 11 risers work. That gives me an individual rise of 81"/11= 7 4/11". 4/11"? geez that sounds convenient! Dang. The math for the individual run works out better thank goodness... individual run = (total run)/# of risers= (99 1/4")/11=9 1/44" individual run. I think I can fudge the landing 1/4" so I can use an even 9".

Here's what I don't understand. The stair building section in my Taunton deck book says that the total # of treads will either be = to the number of risers or 1< # of risers depending on how the stringers are attached to the deck framing. Cept it doesn't really explain that at least not to me? So hopefully I'll have 11 treads and 11 risers right?

So it looks like I can make it a code compliant stairway without intruding into the side yard! It'll be steepish but we had a similar layout for the back stair on our last house and it wasn't too bad.

Here's a shot looking up the stairway. The distance between the guard rails needs to be at least 36" but this was built with only 35". What I'm wondering here is, if I even need the guard rail on the right side. If I can delete it than I can make the stairs wider and I won't have to mess with that short little return section. If the stairs are going to go within say 1" of the finished house siding why do I need a guardrail there?

I could bolt a handrail to the siding though..if I need two handrails?

So, once someone confirms my math I figure I'll need 3 12' 2byb12's for the stringers and using a 1" nosing my treads will be 10" deep. For the treads I'll have to use a 1by8 and a 1by3 with a 1/4" of spacing in between to get the 10" actual...that'll look weird.

I still don't have any idea about what type of guard rail I'll need but I figure I'll use 3 4by4 posts, one on each end and one in the middle to support it.

Does anybody have any ideas on easy guardrail designs? I plan to build the entire thing out of brown pressure treated wood. (hope they make 1by3's in pressure treated.)

Any helpful input would be greatly appreciated.

2 comments:

Anonymous said...

I always forget if you are supposed to count the ground floor or upper floor as one of the steps. So if it were me - I'd be making a full size pattern of the stringer out of cardboard box pieces and duct tape and holding it in place to check that all is well - much easier (and cheaper) to correct any errors in cardboard!

Cheryl
Orlando

Ayse said...

The difference in number of risers on the stringers is in whether you have your stringers form the rise of the last step or not -- this actually can happen at either end of the stair, because if you had a concrete bottom step it would have to be taken into the calculation of rise and run for code. Basically, depending on how your deck was framed you might end the stringers 6-7" under the top of the deck and have the edge of the deck be the riser. That kind of framing doesn't happen on decks as tall as yours.