Can I Attach Stair Stringers To Siding?
You can attach stair stringers to some
types of siding, but it won't work with all siding. Again, it would all
depend upon the type of construction, waterproofing and stair stringers
that were going to be used.
The picture above provides you with an excellent example of what could happen if a wood stair stringer was attached next to a wall with flat siding (T-1-11 of some type of tongue and groove or shiplap siding).
The biggest problem you're going to have with exterior wood that ends up touching another section of the building, including wood, without the correct waterproofing would be any type of moisture that could get trapped for long periods of time in between the two of them.
So realistically, the key to whether or not you can attach your stair stringer to any type of siding would depend more on how the stairway and building would be waterproofed than anything else.
If the stairway can be built safely and structurally sound, then it wouldn't be a bad idea to keep it at least three quarters of an inch away from the building.