i’m building stairs with a larger than i normally build run = about 14″run with 6″ rise. at what ratio do i become concerned that a 2×12 will have too deep a cut to make a strong stringer?…..i understand that generally you need to leave at least 3 1/2″ on the back, but i just can’t seem to figure out a formula for determining how much will be left with a given rise/run.
also, when i run into this (a rise/run that is too big for 2×12), i generally build them from laminated plywood….but in this case, it’s for an exterior deck and i’m not sure what material to use other than treated lumber.
if i haven’t confused everyone….help would be appreciated.
Replies
Merlvern,
Strange as it may sound, your stairs will likely have more meat left in the stringers than normal stairs, since the unit rise is the controlling factor for notch depth.
You always need to look at the effective span and the effective depth together to determine suitability. If your 6:14 stairs are going up 9' in a straight run, your span will be about 20', which is too long. But they are probably a lot shorter than that.
Bill
thanks,yeah,....i already mocked it up and found i would be fine, but is there some formula for figuring this out?
Yes.
Let me guess ? but that's gonna cost you.
there is a formula.. but i always just draw it in CAD and then measure.. before CAD i used to draw it to scale on graph paper..
it's pretty eays to see what you're going to get
thanks for the reply,any idea on the exterior material for a stringer with a notch to big for lumber?
for exterior work you might want to consider Pressure treated LVL'sMike Smith Rhode Island : Design / Build / Repair / Restore
didn't know there was such a thing.....thanks very much!
http://www.shalla.net/
"A wink is good as a nod to a blind man."
great! thanks
Remember the 1st rise on the stringer cut may not be 6" it will be less to account for the thickness of th 2 X 12.
Inexperience carpenters will cut the stringer exactly at 6", not taken in consideration that the total height from FINISHED floor to floor. Its highly unlightly that your rise will be exactly 6" to make ALL the steps even, unless you install a landing with adjusted height.
Around here. about 20% of the stairs 1st rise does not match the rest. It shows you that the Building Inspector is not doing his job.
http://www.blocklayer.com/Stairs/StairsEng.aspx
this site has a great free run & rise calculator... plus about 10 other free calculators... i use it and print out a cut sheet for every stringer i cut...
p