Deck stairs. Deck Details:

Building Tall Stairs
For A Second-Floor Deck

Part 1 of 2

In This Article:

After some careful planning and CAD design:

  • A part of the original deck railing is removed.
  • The deck platform is extended.
  • New supporting posts are installed for the extension and the stair stringers.
  • The stringers and treads are installed.
Related Articles:
Skill Level: 3-4 (Intermediate to Advanced) Time Taken: About 3 Days

By , Editor


House with high deck and no exterior stairs. The owners of this house in Northern Michigan wanted to be able to reach their deck without going through the house.


The deck surface is just over 10 feet above the ground.

Note pavement below the deck. This complicated the digging of the post holes.


After some discussions with the homeowners, we decided that this corner of the deck would be the best location for the stairs.


A view of the underside. Note how the deck joists rest on a double-2x10 "beam" that is bolted to the posts.


I began by removing a short section of handrail spindles.


I marked the rim joist where I planned to cut. This is the left edge of the fourth joist (red arrow).

There will be a new joist fastened to the side of this one.


I cut the 2x8 rim joist with a reciprocating saw.


Then I hammered and pried off the 4-foot piece of rim joist.

Note how the deck board above has been pried up so the nails would pull out of the rim joist.


I needed to remove the corner newel post, so I pried the handrail boards away from the post.


Then I cut the nails with a reciprocating saw and the post fell right out.


I installed the first extended 2x8 joist. I clamped this board to the outside joist and also to the deck board above, to pull it up tight against the original deck surface.


Then I installed another extendo-joist next to the fourth original joist.


As you can see, the new joist extends behind the "beam".

But getting this joist into place wasn't easy... the bottom of the 2x8 hit the beam. The old joists had shrunk a bit, so I had to trim about 1/8" from a short stretch of the bottom of this new joist.


I inserted the middle two joists, but did not attach them.

I also added a filler strip to the outside of the first joist.


I started attaching the new rim joist, but there was a small problem. The double joist on the left was twisted.

Since I had no helpers on this job, I clamped a scrap of 2x4 (red arrow) to a joist to support the weight of the rim joist.


Fixing Twisted Lumber:

I intentionally installed this rim joist on a slight angle.

Since the middle joists were not attached yet, they sagged a bit. This allowed the rim joist to sag downward as the right-hand end rested on my temporary support block. Luckily, the sag was just enough, so the rim joist was perfectly aligned with the side of warped double-joists.

Then I drove 6 deck screws into the left hand end of the rim joist, to connect it to the double-joist.


I raised the right-hand end of the rim joist by squeezing the mis-aligned joists with a Quick-Grip clamp.

This caused the twisted double-joist to straighten out. Since the "lever arm" is 4 feet long, it's easy to twist another joist (or two) into compliance.


I fastened the middle two joists. First I drove screws through the rim joist into the ends of the middle joists, then I clamped them to the existing joists and fastened them with 3" deck screws and 10d galvanized nails.


Supporting Structure:

I set the deck support posts into place and clamped them to the deck joists.


Then I adjusted them until they were plumb.


Post Holes -
Cutting Through Asphalt:

I used a can of landscape spray paint to mark the centerlines of the posts, and the hole to be cut in the driveway.


I used a circular saw with a diamond blade to cut the asphalt driveway.


I used a rotary hammer to chip away a corner of the asphalt. I also tried a pick-ax, but it sprayed too much debris in my face.


Then I used a huge 4-foot long pry bar to lift the chipped-out corner. The blacktop just popped right out.

But... on some of the holes, I had to chip away the asphalt with my rotary hammer and a chisel tip bit. It's basically a mini-jackhammer. With an emphasis on mini.


I dug the post holes over 4 feet deep with post-hole diggers. I also used a shovel and a pointed pry bar for loosening the packed soil.

When the digging was complete, I compacted the soil in the bottom of the hole, using a cast iron tamper. A chunk of 4x4 also works.


I nailed a post anchor to the bottom of the post. These are 10d galvanized nails specially made for attaching framing connectors.


I set the 14-foot-long post in the hole.

This was kinda awkward, since I had to slide the post through the proper space between the deck joists.


At the top I clamped the post to the joists.

Note that the post was too long (it only needed to be as high as the deck joists). This was okay, since cutting off a piece of excess post is much easier than trying to estimate the post length beforehand.


Down below, I clamped a bar clamp to the post while the post anchor was resting on the bottom of the hole.

Then I lifted the post slightly and supported the clamp on a pair of 2x4's. This kept the post anchor a couple of inches above the bottom of the hole, which is necessary for the concrete to properly surround the curved metal tabs.


I screwed the cross-boards to the post. I kept knocking the posts out-of-plumb, but I'll have plenty of opportunity to re-plumb the posts after I pour concrete into the holes.


I poured concrete in the post holes, making sure the concrete almost reached the bottom of the wood post. I used one 80 pound bag of Quick-Crete for two posts.



I cut the stringers. Since I started with a simple QuickCad drawing, I was able to easily get accurate stringer dimensions. I would never approach stair construction without CAD software.

Cutting stair stringers is a subject for an entire article. You can read this article about cutting short deck stair stringers. These 16-foot long stringers used the same layout and design techniques... there are just more notches.

Download a Stair Stringer Spreadsheet at



I added this extra piece of 2x8 (red arrow) below the joists. The top of the stair stringers will rest against this board.


To support this "back board", I screwed some 2x4 blocks behind the joist.


I set the outer stringers in place to help lay out the location of the two bottom posts.

At this step it was very important to make sure the stringers were parallel to the original deck.


I set a 4x4 in place and marked the center lines with landscape spray paint. Marking pavement to be cut out for deck stair support posts.


I attached some blocks of 2x8 to the backer-board. The tops of the stringers will be fastened to the sides of these blocks.


The holes for the lower handrail posts were dug.


Stair stringers installed between ground and high deck. The outer stringers were set in place against the top fastening blocks.


I clamped the top of the stringer to the 2x8 block and drove in a few 3" deck screws.


We adjusted the lower ends of the stringer until everything was level (not a simple task), then attached the ends of each stringer to a temporary support board.


We placed two 8-foot 4x4 posts in the holes (with metal anchors attached to the bottom ends) and secured them so the anchors were a couple of inches above the dirt.
  • We adjusted the posts until they were reasonably plumb.
  • We made sure the stringers were still in good parallel alignment with the main deck.
  • We poured concrete into the holes to surround the metal anchors.


After the concrete had hardened, I back-filled the holes part way.

I cut out another section of pavement so I could attach a 4x6 beam to the posts, to support the middle two stair stringers.


To properly support the middle two stringers, I fastened this piece of 4x6 (red arrow) to the posts, just below the outer stringers.

This was difficult to fasten because I could barely get my drill/driver into the hole to drive some lag screws through the post  into the 4x6 beam. I also added some metal angle brackets with galvanized nails for extra fastening power.


I dug two more holes and installed the middle support posts.

These are mainly needed to support the handrail, but they also stiffen the stair stringers substantially.

I could have just used short posts to attach the handrail to the stringers, but I wasn't sure if these 16-foot stringers would work without extra support in the middle. I figured they would be strong enough, but the building inspector said that the deflection had to be less than L/240. Since L (the length of the structural member) was 192 inches, that gave me an acceptable deflection more than 3/4 of an inch. While that might be acceptable with the building codes, I wanted the stairs to be less springy, so I opted to extend the handrail posts all the way into the ground.

Like the other posts, these go 4 feet deep to prevent the frost from heaving them during our frigid winters here in Northern Michigan.

I installed the middle stringers. Four stringers used to support stair treads.


These stringers are attached to the front 2x6 board, and also to the 4x6 beam.

I used some synthetic shims to support the middle stringers and get them to the right height.


At the middle posts, I added a pair of 2x6 cross-members underneath the stringers.


I used some small blocks of 4x4 (red arrow) to attach the middle stringers to the cross-members.


Tread Installation:

I fastened the treads to the stringers.

This procedure needs to be done starting at the bottom and working up, because the nose of each front board overlaps the screws in the board below, making it difficult to reach those fasteners.

Also, the back tread board needs to be installed before the front board.

I always pre-drill holes for the screws at the ends of the boards. While treated wood often won't split during construction (because it has so much moisture in it) as the lumber dries out the ends will split at the screw locations.

I installed all 34 tread boards (for 17 steps) in about an hour and a half.

These treads were 42 inches long. I needed the extra length so the opening between handrails would be at least 36 inches, which is required by the building code. This is a drawback of the wide handrail design used on this deck.


After the stair treads were installed, I built the handrail.

This topic is big enough for it's own article.


Some Final Details:

When I poured concrete around the deck posts, I had tacked some small pieces of expansion joint material to the post.

I'm not sure that this extra feature is necessary. I figure it falls into the category of "can't hurt, might help".

I should have nailed this expansion joint material more carefully, so the top edge was at the same level as the surrounding pavement. That allows the expansion joint to be employed as a guide to screed the concrete. But I was in too much of a hurry... I just tacked this stuff in place as the homeowner poured the concrete.

I used a sharp knife to cut the expansion joint back to ground level. It took repeated cuts to slice all the way through.


To supplement the strength of the deck screws, I drove 16d nails at major load-bearing connections.

Building inspectors (and building codes) require a certain size of nail for many structural connections.


The Finished Product:

The view from far away.


I was very pleased with the feeling of sturdiness in this stair project. Adding the middle support posts probably made a huge difference, and using 4 stringers helped too.

If I had employed only 3 stringers, the spacing would have been about 21 inches on center, which may let the stair treads flex noticeably under load. Regular deck boards should be supported at 16 inches on center, or less. With 4 stringers, the spacing was about 14" o.c., so the treads didn't flex at all.


One problem with modifying an old deck is the stark contrast between old and new materials.

A few days later I used a small 1200 PSI pressure washer to clean the surfaces of the old deck and handrail. After three hours of cleaning the old wood looked much newer.

Click here to read Part 2 about installing
the handrails for this deck.



Tools Used:

  • Cordless Drill/Driver
  • Basic Carpentry Tools
  • Circular Saw
  • Reciprocating Saw
  • Jig Saw
  • Heavy-Duty ½" Drill
  • Rotary Hammer
  • Miter Saw
  • Table Saw
  • Belt Sander
  • Bar Clamps

Materials Used:

  • Treated Lumber:
  • 4x4 x 14' (2)
  • 4x4 x 12' (2)
  • 4x4 x 8' (4)
  • 2x8 x 8' (7) (Joists, Beams)
  • 2x12 x 16' (4) (Stair Stringers)
  • 5/4x6 x 14' (8) (Stair Treads)
  • 5/4x6 x 8' (5) (Decking)
  • 3" Deck-Mate Screws (about 5 lb.)
  • 2½" Deck-Mate Screws (about 10 lb.)
  • 16d Galvanized Nails

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Copyright © 2005

Written November 13, 2005