Correcting Stair Riser Height in Place

An old stair stringer with incorrect riser dimensions needs fixing, on site. Here's a long discussion about how to do it. July 30, 2009

I have an enclosed staircase with a knee wall and banister on the right side. The stringers, 5 treads, and 6 risers, installed in 1965, were not cut correctly. I need to cut 1/4 inch off four of the treads from each stringer. Each of the trim skirts have been and will be removed. Drywall is attached to the bottom side of the stringers to make up a ceiling underneath the staircase, making it impossible to use a circular saw to cut the treads. Currently, new stringers are not an option. I am looking for suggestions as to what type of tool I might use to finely cut the stringer treads, thus lowering the riser height, in such a tight space? I'm considering a Bosch 1640vs flush cut saw, a router, or an osculating multi-function type saw.

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Forum Responses
(Architectural Woodworking Forum)
From contributor R:
I have to do things like that all the time when I do stairs. The Bosch will work, but a Sawszall is better with long blade and a slower speed (the Bosch is tougher to get into the corners, unlike the flexible blade of the Sawzall). Remove the skirts, as you said, then any damage to the drywall will be covered by the new ones. What I finally did was get a left and a right sided circular saw to cut most of the way through and then finish with the Sawzall and a good sharp chisel. You won't get them perfect. Shims and PL Premium Urethane adhesive used somewhat generously will take up any space when you level the new treads and risers. Also, stay off the stairs for at least 8 to 10 hours afterward to allow the adhesive to harden up. 24 hours is even better. Oh, and a large bottle of Advil for afterward.

From contributor A:
The much easier method would be to route the underside of the treads. Good luck on accurately cutting all of those stringers with any tool.

From contributor R:
If you mark your lines, take your time and cut on the line as far as you can with a circular saw, then finish with the Sawszall, you can accomplish what you need to do pretty accurately. When you install your new treads and risers you will shim and glue anyway, so any imperfections in your cut will be removed. If you can, talk to your supplier and get a tongue and groove tread/riser combination. Rip your risers to their proper height. That will also make your job much easier for the installation.

I have done a considerable amount of stairs over the years and they are never level or consistent. I always have to do some type of modification to the stringers to get the stairs to go together correctly. A lot of times that means doing exactly what you have to do.

A Fein Multimaster with e-cut blade will let you get into the corners of the stringers easier than a Sawszall, if you have access to one.

From contributor B:
You could make a template of the existing treads with cardboard, cut down to where they need to be, and then make a template out of wood. I would probably make a full length template to make sure all my calculations were correct and I could test it out before cutting. A top bearing bit will work, but that will take a few passes since you probably will not find a bit that will cut 1.5" deep. A template guide will work too, but then you will have to make sure to add the appropriate offset to your template cut. Use a chisel to fix the round at the end. Just an idea.

From contributor M:
Are you sure about the 1/4" off of the 4 treads? Current code allows for 3/8" variance between all risers in a flight of stairs. Doing the math on what you describe (based on your post), you should be within the allowed variance? Most of the time it's the first step (starting step) that is higher or lower than the rest. I use a story pole to check for what the actual riser dimension should be (overall height from finished floor surface to finished floor surface divided by number of risers - example: 45" overall rise divided by 6 would equate to 7.5"). A pair of dividers in conjunction with the story pole is the most accurate way to figure out the riser dimension, especially when the overall height is not easily divided mathematically (or for those of us that don't use calculators on the jobsite or are mathematically challenged!). To correct a riser height issue - say the first step is 1" higher, then typically you would be cutting 1" off the first rough stringer rise dimension, then probably 7/8" off the next and so on over several to taper the correction and stay within the 3/8" allowance.

As far as the actual cutting of the rough stringers, I've done it two different ways.

1. Just as contributor R said, basically, except I use my cordless Makita 6.5" circular saw and a simple cutting jig made from 2 pieces of 1/4" MDF that I can screw directly to the rough stringer exactly on the cut line, then I finish/clean up the corner with my Fein saw. Only disadvantage is I have to make a plunge cut cutting from the back to front on one of the rough stringers because of blade to saw base orientation. Having a jig for the saw to ride on is pretty accurate, way more than the freehand method used to cut the rough stringers originally.

2. Overcut with cordless saw/Sawszall/Fein (freehand) then add 6/4 poplar blocking (3.5" - 4" X needed length). I use PL poly construction adhesive and my 15 gauge nail gun with 2.5" nails. Just be sure to scrape/brush off/vacuum rough stringers where blocking will be attached. I used to go back and add screws the next day but after many, many stair re-do's using this technique, I rely on just the PL and nails.

One word about the PL Premium Polyurethane Construction Adhesive - it's a bit expensive, but after using all the others, nothing comes close. It's basically bombproof! The extra $50-$100 bucks for a stair job amortized over the life of the stairs and peace of mind about no issues with squeaks, etc. is well worth it. The client is paying for it, not me. Just factor it into your bid. Word of caution - it's like working with roof mastic (aka Henry's) - it will get on everything including you. Always have plenty of disposable rags and naphtha or mineral spirits at hand!

I sister/scab onto both sides of the middle stringer. This technique allows you to level the treads and plumb the risers if you also cut back the front of the stringer. Most of the time all you have to do is push everything forward about a 1/4" and this extra cutting is not necessary. One thing affects another with stair work, so be careful here - I usually only do that when I can control the nosing at the landing so my tread depths/overhangs stay consistent. Most of the time the rough stringers are not in line with each other, so...?

Only use dry, well machined wood for this blocking, or what I've done lately is glue 3 pieces of 3/4" exterior grade plywood and cut new stringers and PL/nail them in place. I typically use 3 piece glueups for outer stringers and 2 piece glue ups on either side of the middle stringer. After everything is installed (lots of PL - as stated, it will take up any minor imperfections/bridge small gaps), it feels like you're walking on concrete stairs!

For the ultimate stair job and only when the client wants to fork out the extra dough, I will run pocket hole screws in the blocks/plywood stringers before I install them and then PL/screw the treads down from underneath. Need a right angle impact for that - works awesome, though - no face nailing through those beautiful solid 1" treads. Everything comes out super tight - you can even pre-finish treads if you're really good.

I disagree with contributor A - solid 1" treads are that thick because they are spanning across the rough stringers and will carry a fair amount of weight/stress. Routing out 1/4" on bottom side results in only 3/4" to do the same thing. In my experience there is too much deflection with 3/4" material when installed over rough stringers only.

From contributor A:
You are wrong about my post. The treads will be 3/4" only where they are supported by the stringers. They will remain 1" where they span the stringers. Structurally there is no difference whatsoever.

From contributor R:
Actually the wood is only as strong as its thinnest point, so where it is unsupported is irrelevant. Although 3/4" is fine.

The biggest problem with routing (thickness issue aside) is that if all three stringers aren't perfectly level with each other it will be almost impossible to get the rout depth to work. Also, cutting all those stopped dadoes is going to be a royal pain in the butt and if they are off, you can't get in to shim where needed. Easier to just cut the stringers to height. Once you set your story pole, all you need are a couple of levels and a sharp pencil to mark them out.

As I said in my prior post, a left and a right cut circular saw will get you close, then finish with the Fein Multimaster. If you don't have a need for them in the future, then rent them. Porter Cable makes a great 6 inch pair, the Saw Boss (only about 150.00 ea). All you have are 5 steps? Shouldn't take more than a half an hour to do. Mark one stringer to the proper height and then transfer the lines with the levels. The left and right saws allow you to get in tight to the wall.

From contributor M:
As contributor R said, "the wood is only as strong as its thinnest point." That was my thinking too. Not a personal attack, just a different opinion. Sounds like you've done it that way, so it can work. Just not what I would do.

What exactly is the riser issue? Looks like in the picture the tread nosings are pretty consistently spaced down from the top edge of the skirt boards - can't really tell unless you set a long straightedge across the tread nosings, then you'll see which are low and/or high. Remember, changing the overall slope angle will affect this tread nosing to skirt board top edge dimension.

From contributor R:
If you are going to be doing stairs as part of your job, this is a last resort, but in the case that you cannot re-cut the stringers in place and shims or scabbing on pieces will not resolve the issue, cut new stringers, cut off the teeth of the old stringers and sister the new ones onto the sides. And remember to use the PL urethane adhesive and screws. Just a thought for future reference. Adhesive is cheap compared to the cost of a callback, especially on stairs.

From the original questioner:
Thank you very, very much - I am going to apply contributor B's method. Clamp and nail a 1/4" plywood template to the outside of the stringers (skirts removed), 1/4" below the current tread, run a 2" flush trim router bit over the tread, removing the 1/4" necessary to correct to the consistent riser height. This still leaves the bottom step 1/4" high because it is currently 1/2" high. I think I can live with that.

Contributor R, I really like your last thought - sister up new stringers. If the router doesn't work, that is what I'm going to do! Perfect will do.

From contributor R:
As far as the extra 1/4", why not divide it over each stringer, especially if you are making a template?

From contributor A:
The stair tread is a thin beam. The thickness where it is supported is irrelevant. The only concern would be grain separation, but reducing 3/4"-1" would not cause this to happen. Think about a floor joist. You can notch the ends a minimum of 1/3 of its depth. That is only because of the grain sheer issue. If they are made out of steel you can almost get away with only leaving 1/3 of the depth. The ends of a beam are only in shear so depth does not matter.

If it takes you more than 1 hour to dado the backs on a table saw with a chisel for clean up, I would be amazed. Take them off, dado them, glue and nail them back down. Sistering stringers like that would be a full day's expedition at best. Cutting them with a saw will work, but another big waste of time. You will need lots of PL construction adhesive to even make it work.

The dado method is fast, accurate and changes nothing, so you could probably get away without the adhesive (I use it anyway). 2 hours out the door.

From contributor M:
Just a word of caution - have a death grip on the router, as that is a lot of diagonal/end grain to trim off. Also, in my experience, a lot of the time the rough stringers are bowed/twisted/warped out of plumb, which makes it that much more difficult to trim with a router. The cut will be clean but it will be perpendicular to the stringer face, which, if it is not plumb, will result in an out of level tread cut.

Sounds like you're as anal as I am and you want perfection like I do. The best way is to re-cut new stringers out of plywood or something dry and stable (I've used 8/4 poplar but now prefer laminated plywood). Using green lumber is why there is almost always a downward slope to the tread cuts after it has dried out, along with the warping issues. It does take extra time (most non-perfectionists would never even consider) but the results are near perfection. Just do some real careful layout on one piece as a master and template all the others off that - I usually trace/rough cut with a jig saw/glue/clamp or screw to master/flush trim with router setup. Set outer stringers first, plumbing with lots of PL and shims. It can be tricky getting a good reference point, so think that through before you commit to the PL. Use a straightedge/level to line all 3 or 4 up when installing the middle ones. Keep weight off new stringers as much as possible during installation - shims and screws at critical points will help. Don't forget the first riser height will be 1" less than rest when using 1" tread material - that's where an accurately laid out story pole comes in handy. Show rough stringer and finished tread locations, otherwise it can get confusing. My mentor, Lon Schleining, has a great article in Fine Homebuilding about making a story pole - check it out.

One last thought - there should be a law that only allows finish carpenters to cut and install the rough stringers for stairs! Only stair guys who've had to deal with poorly cut stringers will appreciate that.

From contributor R:
Amen to that. One time I convinced the builder to let me frame the stairs after the framer screwed them up (last step 3/4" taller than all the others, as well as out of code winders). I ripped it all out, reframed it perfectly level and square. The frame was so sloppy that when the drywall was hung, it actually sagged at the middle of the house. My stairs were on a foundation wall on one side. Imagine the vocabulary that came out of my mouth when I went to finish the stairs and found the house settled 3/8" in 3 feet. Had to use lots more shims and pl... It used to be that the stair builder would come to the house and frame the stairwell. The framers weren't allowed anywhere near it. Then the stairs would be built in the shop and delivered to the house when it was ready.

From contributor M:
I only used the router technique once - used 1/2" MDF screwed to the inside face of stringers to layout line and used top bearing flush trim bit - it's a monster bit that I use for radius template work. It's basically the spiral cutter out of the PC door planer (2.5" cutting length) with a top bearing added on. Slow down the RPMs to the point you're not getting a lot of vibration in the router - remember to eat your Wheaties that morning so you can have that death grip. Don't push too hard, as the tooth can have a fracture/crack right at the tread/riser cut parallel with the grain orientation. Most of the time I have to fix 1-3 by scabbing on plywood gussets. Often it happens when removing existing treads, so be careful how you pry them off.

Contributor R, I'm on the west coast in So Cal. If they used to have the stair guy come out during the framing stage, that was way before my time. I've only seen closed/routed stringer and skirt stairs on some 100 year old houses that I've worked on over the years. I think that's referred to as the "good ole days."

From contributor R:
Same here. Guys were doing the routed stringers until the late 70's early 80's here in the northeast. But I don't think a stair builder has had anything to do with actually framing the stairwell since the late 1800's.

From contributor K:
Trying to cut a 1/4" with a Sawszall is hard to do. I would cut as much away as I could with a Skilsaw and then (get ready) use a hewing axe and a slick. My guess is most have never used either, but a sharp hewing axe and slick, and I mean shave-the- hair-on-your-arm sharp, will remove wood faster in this situation than any other means I can think of. I mostly build stairs and a slick works very efficiently cleaning up pocket cuts, shoulder cuts, etc.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor C:
I think contributor M has it right. 3/8" between risers is a maximum variation in height between adjacent treads. I think I would leave it alone.

Comment from contributor E:
Regarding the comments made about having 3/8 of a difference from any two threads, I've always thought and worked believing you were allowed 3/16 max difference from one thread to the next. If your differences between all the threads over the whole stairs added up to more than 3/8 then the stairs could fail. So if you had 1/16 difference on each rise over seven rises the stairs could fail. Anyway, take your time marking the stringers level and plumb. As someone said earlier don't be afraid of the circular saw, worst case you cut too much and need to shim the thread. Building a stair can be very satisfying but trying to fix someone else’s mistakes can be frustrating. Just go for it.