Understanding plumbing duct and its construction process are really important as there are many things involved.
Once upon a time when plumbing ducts of a building were kept exposed. If I looked at a building, I would see, drainage and water supply pipes run outside of the building.
This types of plumbing ducts are still seen somewhere in some types of buildings.
But in most of the modern residential building, plumbing ducts are covered. Nowadays, if you look at a modern residential building you won’t see any pipes run outside the building.
If you are completely new to building construction, let me introduce you plumbing ducts.
What is a Plumbing Duct?
The mechanism of a plumbing system in a building is to supply fresh water to the building and remove the wastewater from the building.
For this purpose, we use various stacks in a plumbing system of a building. The commonly used stacks for removing waste water from the building are waste stacks, soil stack, and vent stack.
We also use a separate stack for supplying fresh water to the building.
These stacks are run along the building, either outside of the building or inside of the building (if there is any void inside the building).
If these stacks are installed here and there along the building, that will look ought and you will face many problems to properly install the sanitary system in the building. It will also increase the cost.
To overcome these problems a combination of stacks is installed in an organized way. This combination of stacks is called Plumbing duct or Sanitary duct.
So what stacks are combined in a sanitary duct?
Stacks in a Plumbing Duct
Typically a sanitary duct contains a soil stack, a waste stack, a vent stack, a rainwater stack and a water supply stack.
If you don’t know about the stacks read the post “Understanding Soil, Waste and Vent Stack of a Sanitary System in a Building“.
It is not necessary that every duct of a building should have a rainwater stack. But it is necessary that every duct should have at least a soil stack, a waste stack, a vent stack and a water supply stack.
How duct is constructed
As I told before, ducts are normally covered by masonry walls in modern buildings. When an architect makes plans of a building, he places ducts in an organized way around the building.
In a high rise building, if you don’t properly plan to construct ducts, you’ll face problems later.
I will show you an effective way to construct ducts.
This has been a practice of workers to construct slab of duct portion later.
But it is better to construct the slab of duct portion at the time of constructing floor slab.
If you don’t construct the slab of duct portion during floor slab casting, you can’t build walls of duct during making masonry walls of the floor.
More than that you need to wait to cast that duct portion till the outer scaffolding is made. You also need to make the duct’s wall after installing the plumbing stacks. If you are on tight project schedule then this strategy is just not good for you. This strategy will delay your project handover.
But if you cast the slab of duct portion at the time of floor slab casting, you can make the outer masonry wall of ducts at the time of making floor’s walls. You don’t have to wait to make those walls till the outer scaffolding is made.
In that case, you only need to left just one wall of the duct unbuilt. After installing plumbing stacks, you can build that wall.
More than that you can also install the plumbing stack from the floor. You don’t have to wait for outer scaffolding.
Step By Step Procedure for Constructing Plumbing Ducts
I often follow the procedures below to construct plumbing ducts. You can try these procedures. It will save you times and hassles.
Step 1: Study the Drawings
Study the plumbing and architectural drawings simultaneously to know if there is any possibility to displace the duct or if there is any mismatch.
This is a common issue. I often find a duct is placed somewhere in the plumbing drawing. But the same duct is placed somewhere in the architectural drawing.
If you found the same thing, consult with architect and plumbing designer.
Once solved you can proceed to step 2.
Step2: Construct The Duct While Constructing floor slab
This is a common practice of workers to cast a slab without the duct portion.
It is just not a good practice.
If you cast the duct portion while casting floor slab, it will save you from many hassles later.
Step 3: Make The Duct Wall While Making Floor Walls
Make outer three walls of the duct while making floor walls. You just need to leave one wall to install plumbing stacks.
Step 4: Install Plumbing Stacks in The Duct
While plumbing work is started on the project, plan to install plumbing stacks in the duct and fix those stacks with the wall by clamps.
Step5: Cast The Slab of Duct Portion with Concrete
As you know, there is an opening along the duct in every floor. Although you have fixed stacks with the wall by clamps, there is a possibility to bend the stacks. So, duct opening must be cast.
Another benefit of casting the duct opening is, if any stack is licked somehow, you will know, on which floor that happens.
If you don’t cast the duct opening, you will face hard time to find out the leakage portion of the stack.
Step 6: Complete Masonry Wall Making of The Duct
Do you remember we left a wall of the duct in step 3?
Now, it’s time to make that masonry wall.
As we made the outer three walls of the duct before, we now need to make only one wall which we can make from the building’s floor.
In step 3, if you made the inner wall instead of outer three walls of the duct, you now need to make outer scaffolding to make those outer masonry walls. But now, you have been able to complete your ductwork without making any scaffolding work at outside the building.
Step 7: Make Masonry Walls of The Duct on The Roof
It is always a question – how long the duct wall should be above the roof?
The general formula is – the duct walls on the roof should be longer than the man height.
We normally make the duct wall 6’-8” high from the roof.
Step 8: Make an RCC Slab on The Top of The Duct
After completing the duct wall making, we just put a 2 inches thick RCC slab on the top of the duct wall.
Including the slab thickness, the duct wall height will be 7 feet from the roof.
After putting the slab, we just make some holes all around the duct wall for air circulation.
It seems that making a plumbing duct is a lot of works. But it isn’t.
You just need to keep few things in mind to make the process easy. Those things are – casting slab of duct portion during main floor slab casting, making outer wall of duct instead of inner wall during floor’s wall making, and after installing plumbing stacks make the inner wall of the duct.
After all these work, just finish the duct wall making above the roof. That’s it.
How do you make plumbing ducts of a building? Please share your experience in the comments below…