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Deck and house on frost line piers - do deck stairs need as well?

cyberwombat

cyberwombat

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Jul 13, 2022
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42
Location
Arizona
Have pier and beam 30" down, building a deck and I know deck piers need to match. Unsure about the stairs to deck though. I'd like to simply pour a concrete pad. This post says no. Most of the IRC just talks about the deck itself and not deck stairs so not sure where that fits in. I see info about it being positively attached but not much else. On IRC 2018.
 
We have seen it done both ways, post at the bottom of the run attached to the stringer and notched around the step and we have seen the post piers at the bottom which if your following code you follow the frost line depth. However the diameter of the pier will in most cases be less than the deck support posts pier diameters, that is determined by tributary load area.

The bottom of the stairs can move with frost heave as well as your proposed concrete slab at the bottom step. Also be aware that if the stairs stringer spans are lengthy you'll need additional stringer support which again will required post piers at the frost line depth.
 
I have been inconsistent with this as a plan reviewer and inspector. It always was dependent on what my supervisor wanted. Worked for a few different 3rd party inspection companies and they all had different opinions on this. Maybe the code will make this plain one day.
 
For replacement of existing steps that don't have frost piers, no we never required it when I worked up north. If, however, they are long stairs that require support in the middle, the supports will be to frost depth. I have been on the fence with this but ultimately never required frost depth footings for the bottom of your typical exterior stairway. It is not a load-bearing issue, it's a frost heave issue, otherwise, we would require footings for the bottom of the interior stairs too.
 
Ok. Am gonna go chat w the plan examiners. Id hate to put 4 posts just for the stair stringers when my small deck only needs two!
 
The bottom of the stairs could be argued that they are not a permanent support of the structure (deck) and therefore be supported at grade and required to extend below frost depth. In Montana the good contractors will place 6" of 3/4 washed gravel and then pour a pad/landing that the bottom stringers will bear on.

R403.1.4.1 Frost protection.
Except where otherwise protected from frost, foundation walls, piers and other permanent supports of buildings and structures shall be protected from frost by one or more of the following methods:

1. Extended below the frost line specified in Table R301.2.(1).

4. Erected on solid rock.

Footings shall not bear on frozen soil unless the frozen condition is permanent.

Exceptions:

1. Protection of free-standing accessory structures with an area of 600 square feet (56 m2) or less, of light-frame construction, with an eave height of 10 feet (3048 mm) or less shall not be required.

2. Protection of free-standing accessory structures with an area of 400 square feet (37 m2) or less, of other than light-frame construction, with an eave height of 10 feet (3048 mm) or less shall not be required.

3. Decks not supported by a dwelling need not be provided with footings that extend below the frost line.
 
SCBO1 said:
I would take that code section number to mean a self supported deck not using the house wall ledger.

Would anyone agree with that?
Click to expand...
yes...But the funny part is CT screws that up by amending this...

Exceptions:
  1. Protection of free-standing accessory structures with an area of 600 square feet (56 m2) or less, of light-frame construction, with an eave height of 10 feet (3048 mm) or less shall not be required.
  2. Protection of freestanding accessory structures with an area of 400 square feet (37 m2) or less, of other than light-frame construction, with an eave height of 10 feet (3048 mm) or less shall not be required.
  3. Decks and ramps not supported by a dwelling need not be provided with footings that extend below
    the frost line.
  4. The footing for the grade level termination of stairs or ramps attached to decks or landings, whether the deck or landing is supported by a dwelling or not, shall only be required to be placed at least 12 inches (305 mm) below the undisturbed ground surface in accordance with Section R403.1.4.
 
The code does not define what a wood deck is. So, are wood exterior stairways a deck or only when attached to a deck? Are we supposed to use the wood deck section to build exterior wood stairways and landings? Where is the stringer span sizing table? Will we ever know?
 
Good constructors know... If you find one let them know that Ambers want to partner up and discuss some business ideas.
 
It makes sense to me that the stairs also should be frost protected to minimize differential movement. However, that is not standard practice in my area, and we have significant frost, and there is no history of problems with this. I guess there is enough play in the stair/deck connection that a little differential movement is not creating problems.
 
In most cases that frost heave on the deck stairs is very possible even if the stringers land on a concrete pad. The concrete pad will move creating an issue with the stairs. Here in the mid-west that could be in the first year after the deck was built or it may never be an issue.

Since stairs are one of the major areas of accidents in the home, I've tried to follow the code regarding stair construction requirements. If the pad moves and the stairs are landing on the pad they are going to move so it's important to have the post set below frost. The pads going to move if there's any frost issues but if the post are set below frost the stairs should remain where they are intended to be. The bottom step to pad will always be an issue with frost heave so we try to make work.

Not setting the post in a pier subjects the deck stairs to up and down movement. Like they say "watch that last step, it's a doozy!"
 
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