In this post, I’ll show you a step-by-step process to calculate the required shuttering quantity for a staircase.
The calculation process of the staircase’s shuttering materials is almost the same as the calculation process of the slab’s shuttering materials. Yet there is a little difference.
However, let’s see…
How To Calculate The Shuttering Materials For A Staircase
Step-1: Calculate Sheathing Materials
Generally, wooden lumber is used as sheathing material. The size of the lumber is normally 1″ × 6″.
With that, let’s calculate sheathing for a waist slab.
For that, get the plan of the staircase. It’ll look like the image below:
This is an example of a staircase’s plan.
Also, get the section of the staircase. It’ll look like this:
With that:
Calculate the inclined length of the waist slab using the Pythagorean theorem:
= √{(5′)2+(7½′)2}
= 9 feet.
Now, Calculate sheathing materials for the waist slab.
In our example, the width of the waist slab is 4 feet.
But sheathing should extend 6 inches beyond each side of the waist slab to support stringer bracing blocks.
So, the sheathing width for the waist slab will be,
= 4′ + 6″ + 6″
= 5′
And, the area of sheathing is,
= Width of sheathing × Length of sheathing
= 5′ × 9′ [The length of sheathing is equal to the inclined length of the waist slab]
= 45 sq.ft.
As we are using one-inch thick lumber, the quantity of required wood will be,
= 45 sq.ft. × 1″
= 3.73 cubic feet. [1″ = 0.083′]
This is for one waist slab.
But we have two waist slabs. So the required wood for both waist slabs is,
= 2 × 3.73
= 7.46 cubic feet.
Next, Calculate sheathing for the landing slab.
From the image:
The width of the slab is 4 feet. If sheathing extends 6 inches beyond both sides of the landing to support stringer bracing blocks, it will be:
= 4′ + 6″ + 6″
= 5′
Similarly, the length will be:
= (8′-6″) + 6″ + 6″
= 9½′
So, the sheathing area for the landing is,
= 5′ × 9½′
= 47.5 sq.ft.
And, for 1″ thick lumber, the quantity of required wood is,
= 47.5 sq.ft. × 1″
= 3.94 cubic feet. [1″ = 0.083′]
So, The total quantity of lumber for sheathing for our example staircase is,
= 7.46 + 3.94
= 11.40 cubic feet.
Say, 12 cubic feet.
Step-2: Calculate Joists
Joists are used below the sheathing to support them. These also help to adjust the level of the staircase.
Normally, 2″ × 4″ wooden batten are used at Two feet centers for this purpose.
With that,
First, Calculate joists for the waist slab.
The formula is,
= Number of joists × Length of a joist
The number of joists is,
= Width of sheathing for the waist slab ÷ Distance between joists
= 5′ ÷ 2′
= 2½
Say, 3 nos.
And, the length of a joist is equal to the length of the waist slab which is 9 feet (see above).
So, the required quantity of joists are,
= 3 × 9′
= 27 running feet.
For two waist slabs, we need,
= 2 × 27
= 54 running feet.
Next, Calculate joists for the landing slab. The formula is,
= Number of joists × Length of a joist
Here,
The number of joists is,
= Length of the landing ÷ distance between joists
= 8½′ ÷ 2′
= 4.25
Say, 5 nos.
And, the length of a joist for the landing is somehow equal to the width of the landing which is 4 feet.
So, the required joists are,
= 5 × 4′
= 20 running feet.
And, the total required joists for our example staircase is,
= Joists for the waist slab + joists for landing
= 54 + 20
= 74 running feet.
Step-3: Calculate Supports
Supports are used below joists at 2 feet centers. You can use bamboo or wooden post (4″×4″) for this purpose.
The formula for calculating supports is,
= (Length of joists ÷ distance between supports) × length of a post.
Here,
- The length of joists is 74 running feet (we calculated this above).
- Distance between supports is 2 feet. And,
- Length of support varies as the height of the waist slab is not constant. That’s why, we will take half of the floor height which is 5 feet (a floor height is normally 10 feet).
So, the required post for supports is,
= (74′ ÷ 2′) × 5′
= 185 Running feet.
Step-4: Calculate Stringer
Stringer is used on both sides of the steps.
The height of the stringer is normally one foot.
So, the area of stringers for a waist slab is,
= 2 × Length of a waist slab × Height of the stringer
= 2 × 9′ × 1′ [we calculated the length of a waist slab above]
= 18 Square feet.
For both waist slabs,
= 2 × 18
= 36 square feet.
Normally, 1” thick lumber is used for stringers.
Therefore, the required quantity of wood for this is,
= 36 × 1” [1” = 0.083′]
= 2.98
Say, 3 cubic feet.
Step-5: Calculate Riser’s Face
The area of riser faces is,
= Number of riser × Height of a riser × Width of a step
Here,
The number of risers is,
= Floor height ÷ Riser height
= 10’ ÷ 6”
= 20 nos.
From the above formula,
= 20 × 6” × 4’
= 40 square feet. [6” = ½’]
Normally, 1” thick lumber is used for the riser’s face.
Therefore, the lumber quantity is,
= 40 sq.ft × 1”
= 3.32 cubic feet. [1”=0.083’]
Say, 4 feet.
These are somehow the required shuttering materials for a staircase.
Now…
Step-6: Summarize The Shuttering Materials For The Staircase
- 1” × 6” lumber = 19 cubic feet (Sheathing = 12 cubic feet, Stringer = 3 cubic feet, Riser = 4 cubic feet).
- 2” × 4” wooden batten = 74 running feet
- 4” × 4” wooden batten = 185 running feet
Conclusion
There is no hard and fast rule for calculating shuttering materials for a staircase. And there is no rule that which shuttering materials you’ll use for a staircase’s formwork. Most of the time you can use materials that are available in your project. I’ve just tried to give you an idea of how to calculate shuttering materials for a staircase.
Your Turn:
Which materials do you use mostly as sheathing for a staircase?
Please let me know in the comments below…
[Editor’s Note: This post was originally published in Aug 2021 and has been updated for accuracy and comprehensiveness.]