What is sunken slab?| Applications | Advantages | Disadvantages

sunken slab- cross section



What is Sunken Slab?

Sunken Slab is a slab which is provided below the standard floor level in bathrooms, laundry areas and toilets where drainage system is provided.

These types of slabs are generally constructed in area’s which is vulnerable to dampness at 20-30 cm depth from standard floor level.

This extra depth is used install drainage lines like pipes and utility ducts.

Sunken slab’s are constructed to hide or conceal all the drainage lines like pipes, Which are laid below the standard floor.

Bricks, coal, sand or other lightweight materials are filled between the space of standard floor and sunken slab in order to protect the pipes and other drainage lines.

Application of sunken slab

1. Sunken slab are suitable for damp areas like toilet, bathroom.

2.These slabs are used in architectural designs, where there is a sanitary system requirements.

3. These are used in mid-landing of the staircase to get sufficient headroom below the landing.

4. Providing sunken slab in areas where beam is designed as an inverted which is faced downwards in order to make it look plain surface, like in porch slab areas.

5. Drainage lines can be concealed inside the slab.


1. These slabs helps in conceal all the plumbing pipes and gives plain surface to attain architectural design.

2. Low maintenance and plumbing pipes which are concealed below last longer.

3. Due to its extra depth ,these slabs Helps in preventing water splashing  

4. Helps in reducing the noise of drainage lines during usage.

5. Drainage lines can be concealed inside the slab.


1. Decrease in slab’s height

2. Experienced or skilled labours are required

3. Sunken slab requires brickbat work and waterproofing which time consuming process.

Also read: What is fiber reinforced concrete?| Types of Fibers | Properties |Uses

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