How can I convert a closed stringer staircase to an open stringer staircase?

Question

Currently I have a closed stringer staircase against a wall in my home, and my plan is to convert it into an open stringer staircase. I have looked underneath the staircase and there is no central stringer, just three triangle bits against the join between the treads and risers.

How feasible is this conversion and would it be a case of simply cutting the tops of the stringer in line with the treads, or a case of adding a central stringer maybe?

Just to aid my question I have attached a pic from underneath and how it looks above

Answer 1

It depends on how the particular stair was constructed. Although the absence of a central stringer is evidence that the treads are capable of spanning without the support of a riser, it is not proof that they are adequate for the span. Likewise, the absence of a central stringer does not mean that the stair is laterally stable without risers.

Even assuming the stair is constructed to withstand the removal of the risers, the feasibility of 'simply cutting the tops of the stringer' has a lot to do with what constitutes feasibility. Risers stiffen. Bouncing treads or squeaky steps are not consistent with the intent. What performed well before, may not perform well after modification.

In addition, aesthetics probably plays a role and might even be the driving motivation. Just having open risers is unlikely to be enough, they need to look good, and the ease with which the desired results can be obtained is probably also a consideration. Sawing and cutting and patching a closed riser stair to the point of an aesthetically satisfactory open riser stair is likely to be extremely labor intensive. Particularly given that errors are part and parcel of the learn as you go method one must use when tackling a problem without a straight-forward solution.

So sure, it might be feasible. That doesn't necessarily make it cheaper or easier or more cost effective than simply replacing the existing stair with something close to what you actually envision. Cutting out the risers doesn't change the basic fact that it's a construction project where quality of fit and finish matter.

Answer 2

The problem you have is that on a staircase designed with open stringers, the tread sits on top of the full thickness of the stringer, and often sticks out a bit over. In a closed stringer setup, the tread is wedged in a dado (a groove) cut into the inside face of the stringer. Generally the groove is about half the thickness of the stringer.

If you cut off the sections of stringer over each tread, you make the stringer less rigid, both vertically and laterally. You also weaken the lateral compression that helps hold the staircase together.

Unless you can get an engineer (or very experienced builder) to affirm that the stair will be strong and stable enough after surgery, I would strongly urge you not to do it.

As an alternative, you might be able to insert a properly constructed open stringer inside the two existing stringers, sister (attach laterally) the new and old stringers, then trim the old. This would depend on whether you have sufficient access to the inside areas, and whether you can get adequate support on the top and bottom edges of the new stringers.

Answer 3

You will need to completely redo the stairs to convert to an open stringer. If you were to cut the stringer flush to the top of the stairs you will not have enough structural support left to safely support the stairs. From the pictures you provided, there would be about 2-3 inches of material left from the cut. Do you really only want that much material to support 12 feet of stairs?

Answer 4

What if you temporarily supported the stairway from underneath (use 1x10s or 2x10s against the bottom of the stairs, supported by vertical 4x4s) then cut out and remove the outside stringer completely. You could then use the bottoms and backs of the existing treads and risers as a template to cut a new heavy-duty stringer. Then you could replace the treads one by one. Make sure your finished width from new banister to wall meets or exceeds local code clearance requirements.

Buy hardware at your local mom-and-pop shop when you can, and buy American made products whenever possible.