How to Frame Simple Stair Stringers
"Every stair-framing project has its own unique circumstances that always have to be considered—from simple to complex, interior to exterior, winders, landings, radius, type of finish materials, railings, etc. However, there are some consistent factors in framing stair stringers that are almost always the same. Most importantly: calculating the rise and the run, factoring in for tread and riser thickness, and making a drawing."
Understanding these simple techniques will set you on the road to framing perfect stairs every time and help you with a solid foundation in entering into more complex stair framing!
The simplest set of stair stringers to frame in my experience are a straight run from a deck. This is because deck stairs don't usually have the same sort of restrictions that interior stairs do. With interior stairs, you have to consider head height, drywall, skirt boards, and of course the precision of finish material that tie into them. That's why I believe, if you're an apprentice, it is probably best to start with a straight set of stair stringers off a deck. If you're a journeyman and haven't really done that many stairs, this will be great review!
The three most important things you will learn today are:
- How to calculate the rise and run.
- How to mark out the stair stringer.
- How to measure tread thickness cut off the bottom of the stringers.
The material we are using today, since we are building exterior stairs, will be pressure treated 2x12 material purchased from Dunn Lumber Company. They have the best and most consistent quality as far as I'm concerned. Stringer framing should always be cut from a 2x12, by the way. I have seen them cut from 2x10 and even 2x8 before for some ridiculous reason. DON'T DO IT!
Step 1: Measure for the Overall Rise
First we are going to measure the over all height, or rise, from finish surface to finish surface. It is critical you know where your finish surfaces are located because your measurement is based upon finish-to-finish!
You must also take the rise measurement from the deck finish decking to where the stringers are going to sit, if say, the ground is uneven, or sloped in some way. If the surface is sloped in a way that will cause your first riser to taper, find a spot centered on the stairs, or maybe where they are most traveled, to maximize comfort in use. Use your best judgment here! (Note: To know how far out from the deck to measure your rise, you must also know how many treads you have. The count can be found by taking a close but rough measurement where you think the stringers will land. Follow the steps below. Don't be discouraged if this takes a couple of tries to dial it in.) Using a level on a straight edge, just level out and measure down from finish decking material to whatever your finish is below. And that's it!
Step 2: Calculate Risers
Now comes the math. Remember it's very important to always find the most comfortable riser height that circumstances allow. Take your overall riser number, in our case 26 ¾", and divide by an average single stair riser height. I like to use 7"; it's a good benchmark for calculating. Take 26 ¾" and divide that by your phantom single stair riser. This will give you a number that will help decide how many risers you need. So 26 ¾" divided by 7" = 3.82 stair risers. Well! You can't have a fraction of a riser. It has to be a whole number, so let's round up to four risers. Now we can take the total rise measurement, divide that by 4 risers, and that will give you the exact height of each riser. Let's see what we get.
So 26 3/4" divided by 4 risers = 6.68 or 6 11/16 for each riser. That's pretty comfortable for walking up a staircase! By the way, if you calculated using 3 risers it would come out to almost 9". Yuck! Trying 5 risers gives approximately
5 5/16". Not so great either.
Step 3: Create a Drawing
Once the riser calculations are made, you'll want to draw your measurements on a scrap piece of plywood around the site. Write down your math calculations and then draw out the riser, tread, framing, and finish material to show how everything goes together. This will help minimize any mistakes and give you a drawing to refer back to.
Step 4: Calculate the Treads
It is important to know what size treads we will use, and how much we want the nose of the tread to overhang the riser. First, we must ask the question: How many treads do we have? We know we have 4 risers. Usually the first riser is the edge of the deck, so there is no need to lay that one out on the stringers, and stepping off the deck down to the first tread, means there is one less tread than the number of risers! So, in our example 4 risers means 3 treads. Note this is good to know because it tells us the distance out we are going, approximately 33".
There are a lot of different sizes of decking material ranging from 5 ½" down to 2 ½" nominal on average. So it's important to know what width of decking we are using including spacing to get perhaps a ½" to ¾" nosing overhang. I've seen too many stairs where this isn't taken into consideration and the look terrible! My advice is to avoid this by taking a little extra time for layout.
In our case, we are using 3 ½" wide material with nail width spacing at the riser and between each deck board. Mock up three deck boards and you should have approximately 11" to 11 ¼" total tread distance, depending on your spacing width. If we are going to have a ½" to ¾" nosing overhang, just simply subtract that out of the total tread distance, and that's the tread cut measurement. I like to use 10 ½" for my run cuts for 5/4" x 4" cedar decking because even if there is a bit of difference in spacing, or decking size, I'll still end up with a nosing overhang of at least ½". In our example we are using 5/4 cedar decking, so remember the thickness is approx 1".
The real secret of laying out your treads first is to avoid any ripping in your decking to make up for a weird distance at your riser. This not only looks bad, but it is also a major cost in extra time and grief.—another good reason to spend time laying it out!
Step 5: Mark Out the Stringers
For lay out you will use your framing square with stops that clamp onto the edge, commonly called stair gages. Our rise cut distance is 6 11/16" and our run cut distance is 10 ½". Simply clamp the stops on the framing square to these measurements and this becomes our layout tool. Next, crown the 2x12 joists and layout on the crown side. Start at one end and mark out each spacing until there are the total number of risers and treads needed. In our case, step off three risers and three treads. Then mark off the cheek cut at the top and the seat cut at the bottom. That's it for now.
Step 6: Cut the Pattern Stringer
It's best to make the first cuts at the cheek and seat, so we can test the stringer against the deck to verify that everything is working out before cutting out the whole pattern stringer. Once it's tested and verified, then all final cuts can be made. (Note: Remember at this point we haven't yet cut off the thickness of the tread from the seat cut of the stringer. I'll show you why that's important in a minute!)
When making cuts, I like to use a fine tooth finish blade in my worm drive and finish the inside corner cuts with a good jigsaw. This will make my cuts clean and smooth without any edge tear out. I've found it provides a more exacting cut for marrying up edges or finishes in the building process.
Step 7: Lay Out and Verify the First Stringer
Before marrying up the first stringer to the deck, we must lay out the locations of the stringers and mark a horizontal line where the first tread cut meets the deck rim. Important: the horizontal line to be marked is the framing surface of the top stringer tread. So, measure down 6 11/16" from the framing of deck, then layout the locations of the stringers making sure they are 16" or less, center to center. Also, I like to use doublers at each side of my stair framing to give something solid to tie in railings, decking, and fasciae, etc. Note that the width of your staircase and location of your post tie in will accommodate railing to railing code.
Once the layout is done, you mock up the first stringer to the deck and something seems weird. When we try to line it up with our horizontal line, the stringer seems off. Well, lets try moving the stringer up a bit to get our cheek cut to sister up nicely to the rim. By doing so it looks a lot better, but the top of the stringer is above our horizontal line by approximately 1", the thickness of our decking.
Why? Because we haven't yet cut the tread thickness off the bottom off the stringer. Doing so will drop the stringer to match up with the line. Look at it this way, if we add a tread at the first bottom step without cutting off that thickness from the stringer bottom, we will end up with our first riser 1" higher and our last riser at the top 1" shorter!
Now measure the thickness of the decking (in our case it's 1") and cut that off the seat cut from the bottom of the pattern stringer. Try it again and see how well the stringer fits now. Now finish all the cuts on the pattern stringer and test it again. This time we can use a 2-foot level on our tread cuts to see where we are. Everything should look great!
Also, another thing to verify is if the cheek cut at the top of the stringer should be cut or modified in some way. I like to add fascia to my deck rims that are usually the same thickness as the riser material. If this is the case, then there is no need to do anything. But, say the framing rim is the finish surface. Then the riser thickness should be cut off the cheek cut, because again, like the treads, adding riser material to the stringers but not the rim will make the top tread wider than it should be. The trick to all of this is to get in the habit of always thinking of the finish look, material, and layout.
Now is also a good time to cut out a 2x4 sized keyway at the bottom seat cut on the pattern stringer. You can cut this in wherever you want, but just be sure it locks the stringers from sliding outward. I have found that it also helps in tying everything together and gives a great way to attach the stairs to a surface, like a concrete patio.
Go ahead and use the pattern to mark out all the rest of the stringers, make all the cuts, and that's it! Now is a great time to use the pattern piece to mark out for cutting any fascia pieces, because it's easier to do that now than later.
We are almost ready for install! However if you have a surface that is sloped in some way, remember the bottom of each stringer will need a custom cut. Each installation has its unique qualities that a good carpenter will adjust to, as needed, to ensure a quality product!
Step 8: Install the Stair Stringers
It is pretty simple at this point because all the layout has been done, but there are some final things to think about here as well. First, I like to use a good outdoor screw for all my deck framing because they are strong and will pull joints together. And as always, if a mistake is made things can be taken apart pretty easily. Before installation, sister together two stringers to make two doublers, one for each side of the stairs.
Second, if you find that you're framing a long run, you need to install extra support down the back of each stringer to minimize deflection. I call these a strong back, and they are simply a 2x4 sister secured to the side of the stringer along the back. Now is a good time to install these before stringer installation.
Next install the stringers, keyway, and even the fascias. You may also need to install a ledger below the deck stringer to secure the stringers to. Use straps and hangers as needed. Finally, check the stairs for square before securing the stringers at the bottom. That's it for framing a simple stair run!
You have just walked through a simple but detailed procedure for framing perfect stairs every time. As I said before, not all stairs are so simple, but they all have consistent qualities. Understanding how to calculate the rise and run, marking out the stringers, and understanding why it's important to cut the thickness of the tread from the bottom of the stringers are without a doubt the most common mistakes. Master these and you will up your carpentry game!
