Small Project Design

BI(h)OME (by Kevin Daly Architects)

Quick Links

Who we are

AIA Small Project Design (SPD) Knowledge Community supports, celebrates, and promotes small projects by engaging designers and the public.

Expand all | Collapse all

Width of stacked stairs to basement

  • 1.  Width of stacked stairs to basement

    Posted 07-17-2018 14:15
    So, this has come up twice recently - designing new homes where we have a 3 levels (basement, 1st, 2nd). Small homes, where every inch matters, so ideally we have code minimum 3' wide stairs. If we have a 3' stair from level 1 to level 2, the stair from level 1 to the basement gets shortchanged where it intersects the foundation wall, since the foundation wall is thicker than the stud wall above.

    How do you resolve this? In my mind:

    1) The stair from Level 1 to Level 2 ends up at ~3'-6" wide. Does this mean it also needs a 3'-6" landing if it doglegs halfway up?

    2) Or, the stair can't be at the edge of the house, it has to be internal.

    3) Or, the stair to the basement is narrower than 36", which isn't supported by code.


    David Sisson AIA
    Providence RI
    Call for Nominations

  • 2.  RE: Width of stacked stairs to basement

    Posted 07-18-2018 17:55
    David: How about thickening your frame wall at stair only to 8”.
    Chip Chambers, AIA

    Sent from my iPhone

    Call for Nominations

  • 3.  RE: Width of stacked stairs to basement

    Posted 07-18-2018 18:00
    Comes up all the time.  We work with a lot of old houses, with 18" wide stone basement walls, and 24"+/- wide stairs to the basements.  We make sure not to touch these too much, but obviously the client has to be comfortable with that sort of basement access.  In new work, just keep the stair internal is the easy answer.  But designs with stairs to the exterior seem to work in many situations. We have learned for some of the old houses, and designed locally thin foundation walls, less concrete or concrete block with more rebar at the stair.  Your notion to have a 3'-6" flight up over a 3'-0" flight down is the most usual solution.  And then there is the furring & insulation of the basement wall, which makes it even more problematic.

    Christopher Pickell AIA
    Pickell Architecture, LLC
    Flemington NJ

    Call for Nominations

  • 4.  RE: Width of stacked stairs to basement

    Posted 07-18-2018 18:03
    We furr out the basement wall and add framing to the wall above to align the finished surfaces. Extra framing a small price to pay for simplifying the stairwell, imo.

    Michael Byrd AIA
    CORE10 Architecture, Inc.
    Saint Louis MO

    Call for Nominations

  • 5.  RE: Width of stacked stairs to basement

    Posted 07-18-2018 18:27
    You could alter the thickness of the basement wall where necessary (with adequate structural compensation of course)-  for example switch from 8" concrete to 4" with additional reinforcing

    Bruce Ward, Architect
    (315) 824-1094
    7122 Springhill Rd.
    Hamilton, NY 13346

             _ \ <, _                             
    ...... ( • ) /  ( • )

    Call for Nominations

  • 6.  RE: Width of stacked stairs to basement

    Posted 07-18-2018 18:47
    Yes I would suggest you make the Stairs that 3’-6” wide (or 3’-4” wide depending on your foundation wall). Even in a small home the 3’-0” wide Stair is very narrow. The wider Stair feels better, gives one better communication room from level to level, and is easier of removing items up and down.
    The 4” or 6” to the L. Level can become a shelf.

    Call for Nominations

  • 7.  RE: Width of stacked stairs to basement

    Posted 07-18-2018 19:21

    Any three could work depending on the project.  I've actually used all 3 conditions in separate projects.  The basement stairs are allowed to be narrower if they are not the primary exit (walk-out basement) or if they are existing and unchanged.  Talk to the building inspector or code official to get their take on it.  Sometimes they have unique solutions!


    Suzie Van Cleave, AIA



    4421 N Oakland Ave #200                 O 414.204.8917 

    Milwaukee, WI 53211                        C 847.778.1625




    Call for Nominations

  • 8.  RE: Width of stacked stairs to basement

    Posted 07-18-2018 20:26
    David -

    Clearly, option 3 is not really an option, is it?

    I would strongly suggest option 1, since 3 ft wide stairs are really too narrow - can't get furniture upstairs, for example.

    R311.7.6 says, "The width perpendicular to the direction of travel shall be not less than the width of the flight served." Not the depth in the direction of travel. 
    At the end of the paragraph it says, "Where the stairway has a straight run, the depth in the direction of travel shall be not less than 36". " 

    Emphasis added.

    If you find that last sentence somewhat ambiguous, so do I. You are asking about a stairway with a return leg. If that is the best location for the stair and you don't like option 2, ask your building official.

    Judith Wasserman AIA

    Bressack and Wasserman Architects
    751 Southampton Drive
    Palo Alto CA 94303 
    ph: 650 321-2871  
    fx:  650 321-1987

    Call for Nominations

  • 9.  RE: Width of stacked stairs to basement

    Posted 07-19-2018 00:38
    You could align the inside of the framing to the inside of the foundation wall and then place rigid insulation on the outside of the basement wall.  This will align the stair to the upstairs and to the basement.  Then it's a matter of beautifully flashing / sloping the outside top of the foundation wall.  I think that it's elegant for the foundation to stand proud of the material above.

    Call for Nominations

  • 10.  RE: Width of stacked stairs to basement

    Posted 07-19-2018 11:52
    I've always felt that the code (both res code and IBC) don't do a good job with describing safe access / egress to service and mechanical areas. We all know that a mechanical platform - even one that approaches the size of a mezzanine or room - could be accessed with a ladder or ships ladder.

    In my case - the basement is storage / mechanical only. If it was a finished basement, then I'm certain I'd need a 3' ++ stair, but if it's just service, would it really need 3'? I suppose this is a local inspector issue. I've seen plenty of older homes that 'resolve' this issue by having a narrow stair to the basement. But this isn't supported in code.

    This wouldn't be such an issue for me, and I'd resolve it with a wider stair above, if this wasn't such a tiny home. The added 6ish inches really matters for the home.

    Thanks for all the nuggets of advice.

    David Sisson AIA
    David Sisson
    Providence RI

    Call for Nominations

  • 11.  RE: Width of stacked stairs to basement

    Posted 07-19-2018 12:11
    I have encountered this situation many times David. Yes you are right, the basement stair cannot be narrower than 36" so it will be wider than the stair from level 1 to 2.  That also means the basement landing will be wider.  The only way to get around this is to locate the stair internally as you mentioned.

    Sheila Swalling AIA
    Swalling Walk Architects, LLC
    Olympia WA

    Call for Nominations

  • 12.  RE: Width of stacked stairs to basement

    Posted 07-23-2018 09:58
    ​Cur a wall section  and start from there.

    David DeFilippo AIA
    Tsoi/Kobus & Associates, Inc.
    Boston MA

    Call for Nominations

  • 13.  RE: Width of stacked stairs to basement

    Posted 07-24-2018 18:03
    Increase the width of your exterior wall (frame)to 8” at the stair only. Then everything stacks cleanly above the concrete foundation wall.
    Chip Chambers, AIA

    Sent from my iPhone

    Call for Nominations

  • 14.  RE: Width of stacked stairs to basement

    Posted 08-19-2018 11:07
    Hello, Folks 

    Ah, stairs, what fun.

    And, it gets better when I try to allow 4" or so along the cellar wall, for insulation now or later.  When possible, I tend to go with dogleg stairs; my pitch includes the line, "Kids WILL fall down the stairs; this dogleg layout simply cuts the distance in half."

    Usually, beyond-Code sizes of stairs to the cellar don't concern me a whole lot, because the hatchway, if designed properly, takes care of large objects (pianos, water heaters).

    On a recent job, we had space for the landing to the cellar to be a dogleg, with a gap for several inches of insulation on the cellar wall.  But they framed the landing to the wall, w/ insulation studwall above.

    However, on the same job, I was able to do my favorite dogleg.  The new house, on a '50s - '60s foundation beefed-up (Zoning issues), was well-behind the current front-yard setback-line.  So, the dogleg's landing is cantilevered out several feet, for an 8x8-foot interior landing up to the 2nd floor.  This gives small kids a place to build a blanket-"fort" (w/in sight of the kitchen), or for a mini-library, often done so well in some Victorian houses, or a wee home office, or ???.  It has a nice large window.

    And of course, the movers smile when they see that big landing.

    Bonus round; the landing's roof ("woof!") continues sideways, over the front door, for an attractive, sculptural entry (not built quite as drawn).

    Enjoy "Architekkin' "!

    Call for Nominations