This post will show you how to DIY build redwood deck stairs. I’m building replacement front and back decks on the Main House Fixer Upper here at One Hundred Acres Home. You can check out the build progress with the deck footings here, the deck framing here, the 2×6 redwood decking with hidden screw connectors here. Now it’s time to build the stairs. I’m building three, yes THREE, sets of custom deck stairs. Two sets on the back deck and one on the front. OK. let’s get started.
Foundation for Deck Stairs:
First, we need to place the concrete footing that will support the base of the stairs. But how do we determine where the stairs will land? Well, we need to take some measurements and do a little math. There are building code requirements that regulate how tall and wide each step needs to be. Typically, each step can be 7-3/4 inch max in height and needs a 10 inch minimum width. Check out this detailed and very helpful prescriptive deck guide. The stair information starts on page 20.
First, I measured the height I need to get from the top of the deck to the ground. Determine how many risers you’ll need by using a 7-3/4 inch maximum rise per step.
Once you have the number of risers figured out, determine how far horizontally you need the stair foundation to support the bottom of the stringers by multiplying the number of horizontal treads you need by the length of each tread.
I’ve found its best to draw this out. I use a computer drafting program called AutoCAD LT that will draw to scale so I can double check my layout and catch errors. They offer a 30 day free trial if you want to give it a go. But also do a Google search for a drafting program. I use AutoCAD in my day job so that was the most natural choice for me.
I draft up the stringer dimensions and use that to determine the exact placement of the stair foundation. Below is printout of a stair stringer design.
The foundation needs to run the width of the stairs. In my area, the foundation needs to extend 1 foot below grade. WE don’t have a freeze line. If you do, your foundation will need to extend below the frost line, likely 3 or 4 feet. Check your local building code.
Below is the formwork for the stair foundation at the back deck. Yes, it’s real janky, but it will do. Most of the foundation is buried so you won’t see it anyway.
Placed two number 4 rebar bars the long length towards the bottom of the footing. Two 5/8 inch diameter anchor bolts minimum are needed to hold a pressure-treated (PT) sill in place. More on that in the next section. Below is a photo at the other side of the back deck with the newly placed concrete footing. Rinse and repeat at all stair locations. Make sure the top of your footing is level! Otherwise, the stair stringers will be off.
Once the foundation has cured, re-measure your stinger and stair dimensions in case you need to fine-tune anything now that the concrete is set.
PT Sill at Stair Foundation:
Next, install a flat pressure treated (PT) or redwood sill to the stair foundation. The sill should be anchored to the foundation. Then the stringers will be connected to the sill.
Below is a progress photo at the back deck with the PT sill in place with two anchors. The outside stingers bear directly on the concrete. I screw through the side of those stringers to connect them to to sill plate. Interior stringers are notched at the base to bear on the concrete and the sill.
You can also see that the sill plate does not align with the very front of the foundation. Leave room for a finish board to cover the sill.
The stringers here are supported at the deck along a dropped beam. I use Simpson LSCZ, adjustable stringer connectors for a very sturdy connection. I want these decks to last!
Redwood Deck Stair Stringers:
Below is a photo of the stringers a the front deck. Their support at the deck is a little different here. The top step of the stringers is actually the top of the deck. So they align with the ends of the joists. I also added blocking between the joists and the Simpson LSCZ connectors for even more support.
Also, see how the side stringers extend past the sill plate and the interior stringers rest on top of it?
The photo above shows the sill plate anchors. I added more at this sill. Then, each singer has a Simpson A34 clip from the stringer to the sill plate to help hold them in place.
You can also see I added the rim at the top of the deck, that horizontal face board. Now the stairs flow into the top of the deck. This works great with 2×8 joists as the are 7-1/4 inches tall which is below the code maximum for a stair rise of 7 3/4 inches. It is a bit on the tall end for people that have trouble with stairs. But thankfully, the back deck stairs are lazy so there are options here.
Guardrail Posts at Stair Landing:
Lastly, we need posts at the bottom of the stairs to pick up the guardrail. Below is a photo of the posts at the back deck.
Here is a close up of the post base. It is a Simpson ABAZ post base. This can be installed with an epoxy anchor or a Simpson Titen HD concrete screw after the foundation is cured. So it’s easier to place exactly where you need it after the stringers and sill plate are in place.
The side bolt you see is connected to a hidden Simpson DTT2Z holdown at the inside of the first riser. This keeps the post from wiggling side to side.
One last thing I like to do is install Deck Joist Tape on the horizontal parts of the stingers to give some extra moisture protection. Then connect the risers to the stringers followed by the horizontal treads.
Brick Landing at Deck Stairs:
Last but not least, stairs need a proper solid landing to meet code in this area. We had some concrete bricks left over from the she shed brick floor. Plus I like the quaint look of brick. Below is a photo of my husband setting the bricks at the front deck over a layer of sand.
Below is the finished brick landing.
I installed a similar landing at the back deck you can see in the photo below.
*Spoilers* with the guardrail in the photo below. I’ll cover how to install that hog wire guardrail in the next post. Stay tuned!
