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06-30-2012, 08:21 AM   #1
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## Stair Calculations

I'm building a new set of exterior entrance basement stairs to replace a rotted out set. The total run/area to cover is 65 inches, and the height is 72 inches. Very steep, but it's all I have to work with.

Doing the math, I get 10 risers, 7.2 inches rise height, and 9 treads of 7.22 inches.
Since a 1x8 or 2x8 is 7.25" cut, can I round these both up to 7.25" (essentially making a perfect 1/2 square)?

Is a railing also required? It could only go part way up due to bilco doors folding over the stairs.

Also, the area under the stairs occasionally gets a little standing water, is there anything I can put under the bottom of the stringers to protect them?

06-30-2012, 08:31 AM   #2
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Depends on what your building codes allow. I would make the treads wider if you can as 7.25" is very narrow and a wider step makes for more comfort when you use them.

 06-30-2012, 08:45 AM #3 Stairguy     Join Date: Apr 2010 Location: New Bedford, MA Posts: 737 Rewards Points: 508 An 8" rise and an 8-1/8" run would be better...that's 9 risers and 8 treads

 06-30-2012, 08:48 AM #4 I have gas!     Join Date: Mar 2007 Location: Massachusetts Posts: 1,975 Rewards Points: 1,374 Can you post a picture? Maybe our collective mind can come up with a better solution to give you tread depth that is closer to code. __________________ I tear things down and build them up.
 06-30-2012, 08:49 AM #5 Member   Join Date: Jun 2011 Location: Plattsburgh, NY Posts: 249 Rewards Points: 162 I could also do 8 risers and 7 treads... 9" rise height and 9.29" run. So a 1x10 riser would need 1/4" cut off, and a 2x10 tread would have a 1.04" overhang. Is that too much? I can get a picture later today but the broken stairs are still in the way. It's just an exterior basement entrance, made of concrete. I'm not sure if this is subject to standard staircase code, it may qualify as an emergency or utility exit, since it's an unfinished basement, that has another staircase from the house. Last edited by matt151617; 06-30-2012 at 08:53 AM.
 06-30-2012, 08:50 AM #6 Civil Engineer   Join Date: Mar 2009 Location: Boston Posts: 5,688 Rewards Points: 4,956 Typical code minimum is 11 inches for tread. Codes vary a little from place to place. I don't think you can build a code compliant staircase given the geometry you describe, which raises a number of difficult questions, such as future saleability of the house. I would discuss the issue with your building inspector, perhaps replacement of an existing staircase allows grandfathered geometry.
06-30-2012, 10:31 AM   #7
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Quote:
 Originally Posted by matt151617 exterior entrance basement stairs The total run/area to cover is 65 inches, and the height is 72 inches. Very steep, but it's all I have to work with.
Get a shovel (or backhoe). Do it right.

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