Wet Area

Design

This section deals with floors and walls, layout of fixtures and their special arrangement. Water supply and drainage are part of sanitary-plumbing system.

Floor

Floor of wet area deserves special mention due to its constant exposure to water. The floor should be designed to prevent the accumulation of water on the surface which in turn can create unhealthy or hazardous conditions. In order to minimize the harmful effect of water, the floor is divided into wet and dry zone. The wet zone floor requires adequate slope for drainage and dry area is fairly levelled.

Waterproofing System

Waterproofing membranes are applied on the floors and walls in order to make the wet area watertight. It varies significantly from waterproofing of basement or roof. Wet area unit is a relatively small internal component of building. Hence waterproofing in this part is not subjected to hydrostatic pressure and harmful UV ray from sun unlike the cases of basement and roof respectively. However, it contains numerous pipe penetrations, projections and structural joints to meet the functional and aesthetic requirements. The waterproofing should be able to cover these discontinuities and make the unit perform as a monolithic structure. There are mainly three types of waterproofing systems:

Liquid applied membrane (LAM): asphalt, bitumen, PVC, PE, EPDM etc.
Preformed membrane: modified bitumen, acrylic, epoxy, PUR etc.
Integral systems: admixture, screed, crystalline waterproofing etc.

Detailing of Waterproofing

Continuity of waterproofing suffers at the pipe penetrations and structural joints between floor and wall. These are weak points vulnerable to seepage and may result in rising damp. Moreover the walls adjacent to fixtures such as shower also require waterproofing due to the fact that these fixtures are source of splashing and seepage of adjacent walls and floors.

Plumbing Layout

Plumbing layout has significant influence on wet area maintainability due to two main reasons. Firstly, an efficient layout reduces discontinuities in the structure and hence in waterproofing and secondly it provides an easy access for inspection and cleaning of both the fixture and the adjacent floor or wall.

Fixture and Fittings

Sanitary fixtures and fittings irrespective of their appearance should fulfil the basic criteria of convenience to the user and the maintenance personnel in terms of minimum dimension, zoning and spacing. It should ensure a controlled water flow and must not contribute to defects like leakage, seepage, splashing, difficult access etc in order to keep the wet area hygienically clean and dry.

Finishes on Floor, Wall and Ceiling

Wall and floor finish is a multi-component system and the success of design decision depends on the compatibility of all of these components namely, substrate, bedding, tiles, grout and movement joints. Tiles can be either natural stones such as granite or marble and artificial homogeneous or ceramic tiles. Selection of tiles involves both durability and aesthetic criteria. For e.g. granite is stronger, less permeable, and highly resistant to chemicals as compared to marble. Still marble is selected abundantly due to its beautiful veins. Paint in wet area is applied in ceiling and wall above 1800mm. It needs to serve both as decorative and protective coating. A typical paint system comprises of primer or sealer, texture (optional), undercoat and topcoat. In wet areas, the paint is exposed to constant moist condition and is highly susceptible to peeling, flaking, blistering, biological attack and efflorescence. Hence it should have higher water resistance.

Grading for Design of Floor

Factor	Grading criteria	Grade
Wet & dry zoning	Two zones are separated by a kerb of 75mm cast along with floor.	5
	Wet zone is lowered by at least 150 mm from the dry zone. Note: To maintain a minimum screed depth of 20mm around any embedded pipe, the drop may be considerably high in cases where the layout requires soil pipe to be embedded in the screed.	4
	No segregation. Entire toilet is wet.	1

Gradient	Direction of slope towards the outlet and across the pedestrian traffic flow. Minimum fall in shower / wash area: 1:60 and for rest is 1:80.	Yes: 5 No: 1
Concrete Slab	Structural design as per SS CP 65 to address strength, integrity, porosity etc. Requirement of water tightness as per SS CP 82. Incorporation of movement joint with proper detailing as per SS CP 68.	Yes: 5 No: 1
Screed	Screed provides protection to the waterproofing membrane and constructs the slope for drainage. Adequate thickness to embed the service pipes by at least 20mm. For thicker screed, coarse aggregates of smaller size should be used. The movement joint in structural slab should be carried through screed.	Yes: 5 No: 1

Grading for Waterproofing Selection

Factor	Grading criteria					Grade
Material selection	Liquid applied membrane (LAM):					5
	Pros	Easy application on both horizontal and vertical surface. Seamless for complex geometry and protrusions. Fast curing, reinforced and thick – very good puncture resistance. Built–in primer allows application for both substrate and screed. Better dry film thickness for hot application systems.
	Cons	Needs a well prepared dry substrate and protection until cured. High TVOC content.
	Integral:					2
	Pros	Excellent bonding & easy application.
	Cons	Needs sufficient thickness to render existing cracks and cannot accommodate movements of live cracks.
	Pre-formed:					1
	Cons	Flashing is not seamless especially over penetrations. Labour intensive, field fabricated product. Difficult to use on vertical surface – slippage may take place. Substrate priming and pressure rolling may be required.
Material property	Required material properties of suitable standards but not restricted to the following list should be considered: Permeability, water absorption. Adhesion to substrate, resistance to leakage at joint. Tensile strength, elongation to break and crack bridging. Resistance against perforation and laceration. Durable –minimum number of replacements during building’s useful life.					Yes: 5 No: 1
Feasibility of application	Selection is made considering feasibility requirements of application suitable for the particular situation (As presented in the following section).					5
	No such consideration is made.					1
Feasibility requirements for application: Generally, water based systems are more suitable than solvent based types for damp surface conditions.
Feasibility Requirements	Waterproofing systems
	Rubber based		Acrylic based	Polyurethane	Cementitious
Vertical surface finish	Stone & ceramic tile		Stone & ceramic tile	Stone & ceramic tile	Ceramic tile
Bond on damp screed	Moderate		Good	Good	Very good
Application	Brush, rollers or airless spray		Roller to work material into fibre glass reinforcement	Brush, squeegee/broom. Vertically by brush/ trowel.	brush or spray followed by trowelling
Curing method	Air drying		Air drying	Moisture cured	Moisture cured
Curing time	1 hour		48 hrs for total system	24 hr	1-2 hr
Time before flood test	72 hour			72 hr	24 hr
Ventilation for curing	Moderate		Moderate	Critical	Not important

Grading for Detailing of Waterproofing

Factor	Grading criteria	Grade
Joint details	To make the entire floor watertight and prevent rising dampness A min. upstand of 300mm of the waterproofing is required. The membrane should extend min. 100mm horizontally from flashing to achieve adequate lapping with subsequent membrane application. To negate any stress in membrane due to differential movement between structural members or in-fill materials, at the joint a reinforcing fibreglass mesh or an angle fillet or a bond breaker or a flexible sealant can be used. Details of waterproofing upturn at floor-wall joint	Yes: 5 No: 1
Penetration details	Floor traps and pipe penetrations affect continuity of membrane and increase seepage risk. Number of penetrations should be minimized by using common discharge stacks & cast-sleeve. Recommended details are: The membrane should be dressed up at pipe penetrations and down at least 50mm into the floor outlet. Use of reinforcing fibreglass mesh along with the upstand is a better solution. The membrane should extend min 100mm horizontally around the pipe and overlap with subsequent membrane applied to the entire floor. A slurry coat should be provided to accommodate embedded pipes. It protects the membrane against any damage during the installation of pipes. Pipe Penetration with Sleeve Pipe Penetration without sleeve	Yes: 5 No: 1
Detailing for fixture	Walls in shower/ bath area or behind fixtures such as basin are subjected to high amount of water splash. Detailing for these wet walls are: Waterproofing should be applied to at least 1500mm in width and 1800mm in height of the wall. If a basin or sink is within 75mm of the wall, the wall adjacent and behind to it should receive waterproofing for a min height of 300 mm. Detail of waterproofing for fixtures	Yes: 5 No: 1

Grading for Design of Piping Layout

Factor	Grading criteria						Grade
Wet wall (layout)	No. of wet wall		Plumbing	W/P discontinuity		Maintenance
	1 (minimum)		Simple	Minimum		Very easy	5
	2 (moderate)		Moderate	Moderate		Easy	3
	> 2 (large)		Complex	High		Difficult	1
Planning for penetration	Well planned layout and detailed working drawing. E.g. the pipes to be cast with the floor slab along with details such as gradients of horizontal pipes, joints and connections. It reduces chance of hacking or porous infill of cold joints.						5
	Decisions are taken at later stage.						1
No of floor / wall penetration	Extent				System design
	Minimum				One trap per 3 bath/shower or wash area. One trap per 10 toilet fixture. One trap per 10 wash basin. 2 more penetrations for common stacks (drainage & vent).		5
	Moderate				As above + additional 2-3 penetrations.		3
	High				Many penetrations due to haphazard and inefficient layout.		1
	Example of multiple fixture connected to a single trap
Accessibility for piping	Access	Characteristics of piping
	Very easy	Continuous pipes, joints, bends and traps are exposed or covered with removable fitting. Sufficient space for maintenance. E.g. walk in ducts.					5
	Easy	Continuous pipes are embedded in architectural elements. Joints, bends and traps are exposed or covered with removable fittings with sufficient space for maintenance.					4
	Moderate	Pipes and fixtures are mounted to the surfaces. In this case, the wall can prevent full access, increasing the risk of damage of both wall finishes and plumbing.					3
	Difficult	Pipes are embedded in the architectural elements. Pipes are covered with removable fittings but no sufficient space for maintenance.					2
	Very difficult	Pipes are embedded to the structural elements (slab, beam or column). The access is very difficult and costly since hacking of structural element needs special tools.					1
Accessibility for walls	Pipe position	Characteristics of wall
	No exposed pipe	There is no barrier to wall cleaning.					5
	Min gap of 150mm between pipes and wall	Easy access for wall cleaning.					3
	Others	Accessibility for maintenance is difficult.					1

Grading for Design of Fixture and Fittings

Factor	Grading criteria					Grade
General quality	Fixture and fittings made of impervious good quality material with smooth finishing. Design (forms) should not be over-decorative so that it becomes difficult to clean the fine grooves or corners. Material should not get stain from normal cleaning agent or hard water.					Yes: 5 No: 1
Basin selection	Water may seep through the adjacent walls of a lavatory or can be splashed out on the floor. To prevent these two, adequate size and detailing of basin is required. A min length of 500mm and width 400 of mm is suggested.
	Size	Mounting /Type			Remarks
	³ min size	Preformed counter top or vanity top with flashback of min 100mm high.			Flashback resists seepage. The apron edge prevents overflow of water to the outside of the lavatory.	5
	-do-	On pedestal -away from wall			Free-standing units. No seepage. There is little risk of splashing on the floor.	4
	-do-	Fixed to wall with flashback			Little risk of water splashing.	4
	-do-	Preformed but no flashback			Risk of seepage through the wall.	4
	-do-	Adjacent to wall			Risk of seepage and splashing.	3
	Smaller	Away from wall			Risk of splashing on floor.	2
	-do-	Adjacent to wall			High risk of seepage and splashing.	1
Basin layout	A min C/C distance of 800 mm. A min of 500 mm between the centerline of lavatory and adjacent wall.					Yes: 5 No: 1
WC & urinal selection	Wall hung: easy cleaning of floor with no obstructions.					5
	Floor mounted: some difficulty in cleaning the floor and wall behind the fixture.					3

WC & urinal layout	WC & urinal: a minimum of 400 mm between the centreline of fixture and adjacent wall or modesty board. Urinal without partition or modesty board : a min. C/C distance of 750 mm.					Yes: 5 No: 1
Bath selection	Preformed shower tray Made of extremely hard and impervious materials such as vitreous china or acrylic. If it is mounted correctly, there is minimum risk of water seepage through the tray to structural concrete.					5
	Cast-in situ shower tray (made of concrete with tiled finishes). Water tightness relies on quality of pointing and finishing of joints. However can never be as watertight as monolithic preformed units.					3
	Pre-formed bathtub made of impervious material like steel or acrylic with provision of all pipe penetrations.					5
Shower layout	Shower or wash area is a wet zone and ideally be separated from the common toilet area (dry zone) to minimize water from affecting the entire floor.
	Area is enclosed: Water runoff is being controlled and restrained within the shower area. No risk of water splashing out, giving rise to easy maintenance.					5
	Separated by sunken floor or kerb (min.75 mm): Though the area is not enclosed totally, the level difference in floor prevents water flowing laterally to the dry zone.					3
	No segregation with dry zone: Splashing or flow of water to the dry zone. The entire toilet becomes wet.					1
Bathtub layout	Enclosure		Mounting	Remarks
	Yes		Away from wall	Low possibility of water running outside the bath area and almost no risk of seepage through the wall.		5
	No		Away from wall	No seepage through adjacent wall, but measure is required to control splashing away from tub.		4
	Yes		Fixed to wall	Water runoff is controlled and restrained within the enclosure. But seepage through wall may take place.		3
	No		Fixed to wall	There is risk of having water seepage through the adjacent wall and wetting the floor around the tub.		1
Piping material selection	Plastic materials (e.g. cPVC, PVC, etc) High durability, cost effective installation, labour and equipment due its lightweight.					5
	Cast iron (CI): Corrosion and water leakage are abundant.					1

Grading for Design of Floor and Wall Tiles

Factor	Grading criteria	Grade
Movement joint location	Movement joints absorb the stresses in tiling and the substrate due to shrinkage, deflection and moisture. So tiling should be divided into bays at: At all expansion joint and structural joint. Where tile work meets restraining surface. Points of stress concentration. Over junction of different background material, supporting wall and beam. On all cold joints and saw cut control joints.	Yes: 5 No: 1
Movement joint details	For various locations of movement joints, the details should follow the guidelines provided by SS CP 68. In general the requirements are: The joints location and width in tiles and substrate should be consistent. The maximum recommended spacing for internal wall and floor is 5 to 6m. Minimum joint width: 3-5mm (5mm is better) for wall and 5mm for floor.	Yes: 5 No: 1
Tiles selection	The tiles are constantly exposed to water, cleaning agents and foot traffic. The following properties should be considered while selecting a tile: permeability: resistance against water absorption; slip resistance (both dry and wet); impact and abrasion resistance; resistance against chemical, dirt and stain.
	Homogeneous artificial tiles	5
	Ceramic tiles	4
	Natural granite	3
	Natural marble	2
Bedding material selection	A good selection of bedding can prevent consequences such as debonding, cracking and efflorescence. There are main three categories of bedding: cementitious with liquid latex, organic and epoxy based. It should have adequate adhesive strength, open time and resistance to deformability. As a bonding material between the base and tiles substrates, it should be compatible to both. The compatibility chart is as follows:	Yes: 5 No: 1
Grout selection	Grouting improves the aesthetic appearance of tiled surface by covering the unevenness of the joints and acts as a sealer to prevent water seepage. It is very important for the grout to be compatible with the tiles, poses resilience and compressibility. The grading as per desirable properties:
	Polymer modified grouts Good workability, low shrinkage, good adhesion to the sides of the joints and higher durability.	5
	White cement / mixed with pigment to suit tile colour Low cost, but less durable.	3
	Note: the term durability depends on resistance to water, heat, cleaning agents, chemicals, mould growth, bacteria, and high-pressure water cleaning.

Grading for Selection of Paint

Factor	Grading criteria	Grade
Paint property	Selection of paint considers the following parameters: Substrate, environment, application method, feasibility of surface preparation, overcoating interval, appearance.	All: 5 Most: 3 None: 1
Water resistance	Water based emulsion paint: High water vapour permeability and low water resistance. E.g. vinyl, acrylic, butadiene-styrene, alkyd and multi-coloured lacquers.	5
	Cement based paint system/ water repellent coatings: Provides good surface protection by sealing and filling the porous areas.	3
	Skim coat: Offers minimum protection	1

Grading for Design Consideration of Ancillary Facilities

Factor	Grading criteria	Grade
Coordination among professions	Two way communication: The requirements of sanitary-plumbing and HVAC are explained to designers/contractors of concerned professions. Wet area design incorporates requirements of other professional.	5
	One way communication – poor coordination.	3
	No communication and coordination	1