I needed space saving stairs built in my tiny house to access the sleeping loft. My lofted bed was 6 feet tall. I looked up space saving stair designs and this alternating tread staircase concept fit the bill. I was able to build this staircase for little money and it turned out looking pretty nice.
What are alternating tread stairs?
Alternating tread stairs are typically built in tiny homes to save space. Alternating tread stairs are when the stepping ledge of the stairs alternates in a predetermined pattern. This pattern is left foot, right foot alternating up and down the stairs. The reason to build an alternating tread staircase is to save space but also keep the stairs safe and user friendly.
What is the point of alternating tread stairs?
Alternating tread stairs save space and improve safety of use. The alternating pattern can be created by cutting a notch in each step to allow more space for a foot to land. This allows the stairs to be steeper than normal to save space but also comfortable to walk on. Steeper stairs take up less space than less steep stairs.
How steep can alternating tread stairs be?
| Type of stair | Low egress stairs | Normal Stairs | Alternating Tread Stairs |
| Rise to run | .5 inch rise for 1 inch run | .7 inch rise to 1 inch run | 1.2 inch rise to 1 inch run |
| Pitch steepness | 26 degrees | 34 degrees | 50 degrees |
Alternating tread stairs can be 45 degrees and above in steepness. They can be more steep than normal because they notch cut in the stair allows more stepping space for the foot to land.
How do I build alternate tread stairs?
Step 1: Measure the Installation Site
Measure the height the stairs need to be. For me I knew the support pieces of the staircase had to reach 6 foot in height. This is also a good time to consider how wide you want the staircase to be. I wouldn’t recommend going any thinner width than 20 inches for the staircase.
Step 2: Build Materials List
Source the materials. I decided to use 2×10 lumber to be strong enough to support human weight safely. To build the staircase I just needed four 8ft 2x10s costing around $80 in March 2022 prices. I built this in early 2020 so prices were even lower. You will also need some nails for a pneumatic nail gun which I already had a box. Usually costs around $25 for a box. I also used 2×4 support pieces under each step to reinforce it so needed 2 2x4s costing $17. Total cost is $122
Step 3: Cut the Support Pieces
Start by cutting one side of both the support pieces at a 45 degree angle. Then lean the 2×10 pieces agains the edge of the loft with the 45 degree cut part on the ground. Mark the support pieces at 90 degrees where they meet up with the edge of the loft. Make the cut at 90 degrees and lean the pieces against the loft it see how it lines up. It may take some trial and error to get the right cuts that fits snuggly against the ground and loft.
Step 4: Nail to Ground
Nail the two support pieces to the ground and against the joist of the loft. Make sure the support pieces run completely parallel and equidistant before nailing. Since my staircase ran against a wall I was able to nail one of the support pieces into the studs of the wall.
Step 5: Calculate Treads Needed
Plan out and mark where the treads will be on the support pieces. I chose 9 treads because this would allow 7 inches of rise between each stair tread keeping the incline comfortable and safe. I wouldn’t recommend doing more than 7 inches of rise per step.
Step 6: Cut the Stair Treads
Cut the treads of the stairs. For me I needed 9 treads that are 20” wide each. The treads of the staircase and support pieces are made of 2×10 lumber.
Step 7: Nail the treads to Supports
Nail the stair treads in every 7 inches making sure the stair is level on all sides. Shoot the nails through the support pieces and into the ends of the treads. Also toenail the treads into the support pieces. Don’t hesitate to be liberal with the nails. When you nail in the treads you will notice the treads overlap each other making it hard to get entire foot on the stair. Don’t fret the next step handle this.
Step 8: Cut Notches for Alternating Tread Stairs
Cut the notches in the stairs. The bottom stair in the staircase will be left uncut because it doesn’t overlap another stair. If you are a righty your first step will most likely be your right foot. This means the first notch on the second stair from the bottom must be on the right side. Then alternate notches right and left until the top. Each notch is cut 10.5” wide and 5.5” deep. This will allow a large foot hold for the climber to step on. Use a circular saw to make the cuts.
Step 9: Support Pieces
Add 2×4 support pieces underneath each step. After cutting out the notches this will reduce the amount of surface area that is attached to the support pieces. This is why it is necessary to add these support pieces to reinforce.
Step 10: Sand
Sand everything! Make sure everything is smooth to the touch because this is a surface that will be walked on.
Step 11: Finishing Touches of Alternating Tread Stairs
Stain or paint and seal. I chose to stain my stairs a natural oak color that wasn’t too dark. This showed off the grain of the wood and matched the other wood elements of the house. After staining I wanted to add glow in the dark paint to the edges of the stairs and support pieces so it would be easier to climb or descend the stairs in the dark. I did this by taping off the stair and spray painting the edges. Finally I finished everything off by sealing the stain and spray paint in with 3 layers of oil based sealer.
Step 12: Railing
Add trim and railing if needed.
Conclusion: Alternating stairs save space, look cool and are comfortable to be climbed or descended. This can be built for not much money or time.
Are alternating tread stairs safe?
Yes they are safe. The increased pitch of the stair does not decrease the amount of tread for the foot to land on. This allows the user to ascend and descend safely at a steeper than normal pitch.
Are alternating tread stairs legal?
Yes alternating tread stairs are legal under international building codes.
What is the minimum width for alternating tread stairs?
The minimum width for alternating tread stairs is 20 inches. This is the minimum recommended for normal size and normal weight humans. For larger humans I would recommend wider stairs.
More resources: https://www.houszed.com/space-saving-staircase-ideas/
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