housed-stringer exterior stairs

1 Professional Deck Builder • January/February 2007

Housed-Stringer Exterior Stairs

A simple site-built jig made it easy to build this elegant outdoor staircase

by Andy Engel


Iprefer to build stairs using housedstringers, which means that the

ends of the treads and risers arewedged and glued into mortisesrouted into the stringers. While thisapproach sounds like a lot of work, it doesn’t take much longer thancrafting a decent set of notched-stringer stairs. What you get for theextra effort is a stronger stair — sinceyou haven’t notched away half thestringer — and one that’s practicallyseamless.

While I first used this technique tobuild interior stairs, I particularlylike it for exterior ones. The tight,glued joints at the stringer tend tokeep out water, and I pitch the stairsabout 1⁄ 8 inch per foot of run to pre-vent water from puddling. Stairsbuilt this way stand up to theweather without the cupping andcracking common to most porch ordeck stairs. And because each riseracts as a beam supporting the treadabove, I’ve never felt the need formore than two stringers. I’ve builtporch stairs that were 8 feet wideusing just two housed stringers.

Preparing the StockYou can use any rot-resistant materialfor exterior stairs. For the projectshown on these pages, I chose rela-tively cheap pressure-treated 2x12s forthe treads, since they would be paintedto match my client’s painted porchfloor. The stringers (which would alsobe painted) are treated 2x10s; becausethey remain mostly intact, they’reactually much stronger than notched

2x12s. I used 4/4 meranti — a fairly rot-resistant tropical hardwood that’sreadily available in my area — for therisers, in part because PT stock isn’tavailable in the 1x8 or 1x10 sizes that I needed. In addition, merantirisers clear-finished with a Penofinpenetrating oil finish (707/462-3023,www.penofin.com) would nicelymatch the meranti porch railing thatI’d already made for the deck.

When I’m building a set of stairs, Iselect the best stock I can, checkingfor knots, digs, and pitch pockets,and cutting out as many defects aspossible. I pay close attention to thebows and crowns in all the stringer,riser, and tread stock. In every case,any crown faces up. Additionally,when I lay out the stringers, I makesure that the bows in them will faceeach other. That way, the bows moreor less cancel each other out, result-ing in a straight, square stair.

After cutting the treads and risersto length, I rip them to width. Tostraighten the edges, I like to rip bothsides of the stock. These treads are 11inches wide, which, with a 11⁄ 4-inchoverhang, gives me a run of 93⁄ 4inches. (This run does not conformto the International ResidentialCode’s minimum run of 10 inches, soit may not be legal in your area. Itdoes satisfy the Connecticut Supplementto the IRC, which allows a minimumrun of 9 inches, and a maximum riseof 81⁄4 inches for residential stairs.)

After ripping the treads, I bullnosethem with a 3⁄ 8-inch roundover bit.This bullnose perfectly matches the

radius left at the front of the mortiseby the 3⁄ 4-inch-diameter bit I use tohog out the mortises. I rip the risersto the stair rise of 71⁄ 2 inches, exceptfor the bottom one, which has to beone tread thickness — 11⁄ 2 inches —narrower.

Laying Out the StringersThere are two main differencesbetween laying out housed-stringerstairs and notched-stringer stairs.Unlike notched stringers, housedstringers are laid out from the bot-tom edge of the stringer. And insteadof marking the bottom of the treadand the back of the riser, the layoutmarks you make for housed stringersrepresent the top of the tread and thefront of the riser (Figure 1).

I set stair gauges on my framingsquare exactly as if I were going tonotch the stringers, with one gaugeon the 9 3⁄ 4-inch run and one on the71⁄ 2-inch rise. Working from the bot-tom, I lay the square on the stringer,mark the run line, then remove thegauges and shift the square forwardalong this line by about 2 inches.Holding the square exactly on thisline, I reset the gauges, then lay outthe first riser and tread.

As I move the square down thestringer to lay out the rest of the treadsand risers, I align the original 93⁄4-inchrun length on the square with the riserline I’ve just marked; if I’m moving upthe stringer, the original 71⁄2-inch riserheight on the square lines up with thetread I’ve just marked.

When all the treads and risers arelaid out, I mark the top and bottomcuts. The top cut is one riser thick-ness behind the face of the top riser. Ilike to make the bottom plumb cutabout half the thickness of the newelbeyond the bottom tread nosing.

Starting at the back-of-the-tread/bottom-of-the-riser intersections, I usea square to transfer index marks to the


Run Rise

71⁄ 2" original rise

71⁄ 2"

93⁄ 4"

A. Set stair gauges on square (93⁄ 4" for the run and 71⁄ 2" for the rise) and mark run line

2 x 10 stringer

B. Remove stair gauges. Shift square forward along run line by about 2", moving tread/riser layout further into stringer. Reset gauges.

93⁄ 4" original run

C. Lay out treads and risers using original rise/run measurements to index framing square. If necessary, shift layout one way or the other to accommodate any wood defects.

Crown

Figure 1. After laying out thestringers, the author makes a plywood jig to guide thepattern routing bit he will use to cut the mortises forthe treads and risers.

Laying Out Housed Stringers


Illustration continued on page 4


second stringer. When laying out thesecond stringer, be sure that thosesame tread and riser intersectionsalign with the index marks. You mayhave to fudge one or two by as much as 1⁄8 inch, but as long as you staywithin that tolerance, the stringerswill be consistent and your stair willbe square. Fudging the layout in thisway may require you to plane some ofthe treads for an exact fit.

Because more than half the stringerwill be visible to anyone walking upthe stairs, I pay attention to knotsand the like. Simply shifting the lay-out 6 inches one way or the other can

place wood defects behind the treadsand risers, making a piece of #2 mate-rial look like #1.

Cutting the MortisesYou don’t need a lot of specializedtools to build a set of housed-stringerstairs.

To cut tread and riser housings, I usemy old 21⁄2-hp Bosch plunge router(anything smaller would be straining)with a pattern routing bit (I use a CMT811.690.11B) guided by a jig I makefrom plywood scraps. I use a Kregpocket screw guide to help me fasteneverything together (Kreg Tool Co.,

800/447-8638, www.kregtool.com).The jig and a pattern routing bit is

the key to building housed-stringerstairs. To match the 1-inch depth ofthe available pattern routing bits, Imake my jig 1 inch thick by gluing uptwo 16-inch-by-20-inch thicknesses ofvoid-free 1⁄ 2-inch plywood.

I mark the cutouts in the jig severalinches longer than any stair layout I’llever make, since they have to be longenough for the mortises to extendthrough the bottom of the stringer,and any extra opening beyond thebottom of the stringer helps in clear-ing chips. It’s okay to make the jig

D. Align jig with tread/riser layout lines, clamp to stringer

4° angle

20"

16"

11⁄ 2"11⁄ 4"3⁄ 4"

10"

Clamp

Tread/riser layout lines

Site-built jig

14"

1"- thick plywood jig (2 layersof 1⁄ 2" plywood glued up)

Laying Out Housed Stringers continued

larger, but don’t make it any smaller,or the clamps used to hold the jig inplace will get in the way of the router.

When I cut out the opening, Iplunge cut with a circular saw andfinish up with either a jigsaw or handsaw (Figure 2). Since this jig willguide the router bit, any flaws in thecuts will show up in the mortises, so Icut carefully.

Rout in a clockwise direction. I clampthe jig to the stringer so that the topof the tread and the front of the riseralign with the layout marks. Thetread nosing, of course, sticks outpast the riser mark. Using a 3⁄ 4-inch-diameter pattern routing bit, I cut1⁄ 2-inch-deep mortises in two passes,making sure that the bit is loweredenough that the bearing rides on thejig. (If the bearing doesn’t ride on the jig, the bit will cut into it.) Tominimize any chance of nicking thejig, I lower the bit into the jig be-yond the stringer before starting therouter (Figure 3).

With such a large bit buried in atough southern yellow pine stringer,feed direction is critical. I move therouter clockwise so that I don’t jamthe router by climb cutting, and Istop when necessary to clear chips.To avoid tear-out where the back ofthe tread meets the front of the riser,the routing passes are made working

from the top to the bottom of theright stringer and in the oppositedirection on the left stringer.

After cutting the mortises, I makethe top and bottom cuts in eachstringer with a circular saw.

Assembling the StairBefore putting the stair together, I cutwedges from 9-inch-long scrap risermaterial with a miter saw. The wedgesare beveled at 4 degrees, which is doneby setting the chop saw to 2 degrees,then flipping the stock end-for-end ateach cut. I eyeball the cuts so that thesharp ends of the wedges measure

about 3⁄16 inch, and cut two for eachtread and riser (Figure 4, page 6). Aword of caution: Don’t cut too manywedges from each piece of stock; tokeep your fingers intact, throw awayat least 3 inches of each block.

Next I set the stringers upside downon horses, and firmly seat the top andbottom treads in their mortises withtheir crowns facing up. Then I checkthat the back of each tread aligns withthe riser cut above (“above” and“below” in this case refer to the orien-tation of the stair once it’s installed). Ifthe tread’s too wide, I plane it down tofit. With the tread seated and the

Figure 2. Because the site-built jig will guide the router, it’s im-portant to cut the template carefully. Here, a carpenter makes the first plunge cuts with a circular saw (left) and then finishesup with a jigsaw (above).

Figure 3. Using aplunge router with a 3⁄ 4-inch-diameterpattern routing bit, the carpenter cuts 1⁄ 2-inch-deep mor-tises in two passes.The jig is clamped tothe stringer so thatthe top of the treadand the front of theriser align with thelayout marks.


6

stringers bar-clamped together, I drivehome a heavily glued wedge on eachside, stopping when the end of thewedge starts to splinter (Figure 5). Ifthe wedge has intruded into the risermortise below, I chop off the intrusionwith a chisel. For glue, I prefer to useTitebond III (Franklin International,800/669-4583, www.titebond.com),which is rated for outdoor use, but PL400 (OSI Sealants, 800/999-8920,www.stickwithpl.com) or a polyure-thane glue would work, too.

After I’ve set the top and bottomtreads, I check for square by measur-ing the stair’s diagonals. If the treadsare squarely cut, the stair should bedead on. If it’s off a bit, I adjust thestringers to get the diagonals even.Then I set and wedge the rest of thetreads, cutting back any wedgesthat extend beyond their tread with ahandsaw.

Gluing sequence is important. Whenplacing the risers, I make sure thatany crown faces the tread above.First, I run a bead of glue along a risertop, then quickly seat it in its mor-tises so that it contacts the treadabove. This smears the glue around,and helps prevent drips.

Figure 4. Cut from 9-inch-long scrap riser material,the wedges are beveledat 4 degrees, which isdone by setting the sawto 2 degrees and flippingthe stock end-for-end ateach cut. The carpentereyeballs the cuts so thatthe sharp ends of thewedges measure about3⁄ 16 inch.

Figure 5. With the tread seated and the stringersbar-clamped together, the carpenter drives home a heavily glued wedge on each side.

Professional Deck Builder • January/February 2007


Then I pull the riser away from thetread below and run a bead of gluealong the back of that tread beforesliding the riser back into position(Figure 6). Finally, I liberally applyglue to a pair of wedges and smackhome a wedge on each side of theriser, occasionally tapping the riser tokeep it seated against the tread above.

Screws complete the assembly. Using aKreg jig, I drill three pocket screwholes into the top of each riser. ACQ-rated 15⁄ 8-inch deck screws drivenhere pull the tread and riser snuglytogether, and help ensure a soundglue joint. Using the Kreg pocketscrew bit (any countersink bit wouldwork, but this one’s handy), I thenpredrill for 21⁄ 2-inch stainless steelscrews into the back of the treadbelow (Figure 7). As soon as the lastriser is in, I flip the stairs over so thatI can scrape off any glue drips.

Setting the stairs is a piece of cake.Two or three guys can move theminto position, and half a dozen screwsinto the top riser secures them. ❖

This article was reprinted with the per-mission of JLC The Journal of LightConstruction.


Figure 7. Using a Kreg jig, the carpenter drills three pocket screwholes into the top of the riser, then uses ACQ-rated 15⁄8-inch deckscrews to pull the tread and riser together (left). Next he predrills(above) before driving 21⁄2-inch stainless steel screws througheach riser into the back of the tread below.

Figure 6. To set a riser,the carpenter runs abead of glue along itstop, then seats it in itsmortises so that it con-tacts the tread aboveand smears the gluearound, which helpsprevent drips (right).Then he runs a bead ofglue along the back ofthe tread before drivinghome wedges on eachside of the riser (below).


housed-stringer exterior stairs

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