Types of floors and their construction

1. FLOORS

2. Definition
 A floor is a structure formed of beams, girders and other members
with proper covering, which divides a building horizontally into
stories.
 It can also be defined as the base or surface of a building on which
all activities in the building take place.
 Floors maybe stone, wood, metal, or any other material that can
support the expected load.

3. Functions of floors
Floors need to satisfy a number of functional requirements as listed below;
GROUND FLOORS
i. To withstand the loads that will be imposed upon them, with domestic buildings
they are normally confined to persons and furniture but in other classes such as
factories floors maybe subjected to much heavier loads and must be sufficient to
carry them.
ii. To prevent growth of vegetable matter inside the building by provision of
concrete over site.
iii. To prevent damp penetrating the building by inserting a damp proof membrane
in or below the floor. Suspended floors also require under floor ventilation to
prevent stagnant, moist accumulating below them.

4. iv. To meet certain prescribed thermal insulation standards by incorporating a layer
of insulating material to reduce the heat loss into ground below.
v. To be reasonably durable and so reduce the amount of maintenance or
replacement work to a minimum.
vi. To provide an acceptable surface finish which will meet the needs of users with
regard to appearance comfort safety cleanliness.

5. UPPER FLOORS
The functional requirements of upper floors include;
i. To support their own weight, ceiling and super imposed loads.
ii. To restrict the passage of fire, this is particularly important in high rise
buildings or where large amounts of combustible goods are stored.
iii. To restrict the transmission of sound from one floor.
iv. To posses an adequate standard of durability.
v. To bridge the specific span economically and be capable of fairly quick
erection.
vi. To accommodate services readily.
vii. To provide an adequate surface finish in the manner described for
ground floors.

6. Functional requirements of floors
 Strength;
The strength of a floor depends on the material used for the structure of the
floor such as concrete timber or steel. The floor must be strong enough to
support safely the dead load of the floor and finishes fixtures partitions and
services and anticipated imposed loads of occupants and furniture.Bs.6399:
Part 1 is the code of practice for dead and imposed loads for buildings
 Stability
A floor is designed and constructed to serve as a horizontal surface to support
people and their furniture. The floor should have adequate stiffness to remain
stable and horizontals under the dead load of the floor structure and such
partitions and other fixtures it supports and the anticipated static and live loads.
The floor should also support and accommodate services either in its depth or
below or above the floor without affecting the stability.

7.  Durability and freedom from maintenance
All floors should be durable for the expected life of the building and require little
maintenance or repair. The durability of floor finishes will depend on the nature of
materials used and the wear to which they are subjected to.
 Fire resistance
Suspended upper floors should be constructed to provide resistance to fire for a
period adequate for the escape of the occupants from the building. The notional
periods of resistance of fire range from ½-4 hours depending on the size and use of
the building set out in the building regulations.

8.  Resistance to passage of heat
A floor should provide resistance to transfer of heat where there is
normally a significant air temperature difference on the opposite sides
of the floor. This would include any building which was heated but
would not include some external buildings, such as garages.
 Resistance to passage of sound.
Upper floors that separate dwellings (party floors), or separate noisy
from quiet activities, should act as a barrier to the transmission of
sound. The comparatively low mass of timber floor will transmit
airborne sound more readily than a high mass concrete floor.

9. Floor construction
 SOLID GROUND FLOORS
With domestic buildings a choice has to be made between solid (ground supported)
and suspended ground floors. Solid floors are likely to prove cheaper on fairly level
sites, may reduce the quantity of walling, eliminate the need for under floor
ventilation and hence reduce heat loss through the floor. For these reasons majority
of ground floors are of solid construction comprising,
 Hardcore
Its used to raise the finished level of oversite concrete slab. It also reduces the
amount of moisture rising. Materials used for oversite should be hard and durable
and chemically inert for example gravel, tile rubber, clinker, quarry waste etc.

10.  Concrete slab
Concrete oversite should not be less than 100mm thick although its often 150 mm
thick. The mix of concrete should be 1:3:6 with a maximum size of coarse
aggregates of 38mm.
 Damp-proof membrane
It can be located below the floor screed and often insulation linking with the damp
proof course in adjoining walls. To provide satisfactory protection for applied
finishes a damp proof layer must be impermeable to water, continuous with the DPC
in adjoining walls and tough enough to remain undamaged when laying the screed.
 Floor screeds
These serve a umber of functions for example provide a smooth surface to provide
floor finish, accommodate service pipes and cables. Cement and sand screed is
usually used.

12. Floor Construction
 IN-SITU CONCRETE FLOORS
The principal types of reinforced in situ concrete floor construction are:
o Beam and slab
o Waffle grid slab
o Drop beam slab
o Flat slab
 Beam and slab
This system consists of beams framing into columns and supporting slabs spanning
between the beams Figure. It is a very traditional system. The relatively deep beams
provide a stiff floor capable of long spans, and able to resist lateral loads. However,
the complications of beam formwork, co-ordination of services, and overall depth of
floor have led to a decrease in the popularity of this type of floor.

14.  Ribbed floor
Ribbed floors consisting of equally spaced ribs are usually supported directly by columns.
They are either one-way spanning systems known as ribbed slab or a two-way ribbed
system known as a waffle slab. This form of construction is not very common because of
the formwork costs and the low fire rating. A 120-mm-thick slab with a minimum rib
thickness of 125 mm for continuous ribs is required to achieve a 2-hour fire rating. A rib
thickness of greater than 125 mm is usually required to accommodate tensile and shear
reinforcement. Ribbed slabs are suitable for medium to heavy loads, can span reasonable
distances, are very stiff and particularly suitable where the soffit is exposed.

16.  Hollow Pot Floors:
These are in essence a ribbed floor with permanent formwork in the
form of hollow clay or concrete pots. The main advantage of this type
of cast in-situ floor is that it has a flat soffit which is suitable for the
direct application of a plaster finish or an attached dry lining. The voids
in the pots can be utilised to house small diameter services within the
overall depth of the slab. The floors can be designed as one or two way
spanning slabs, the common being the one way spanning floor.

18. Drop slab floor
The floor construction consists of a floor slab which is thickened
between columns in the form of shallow but wide beam. A drop slab
floor is of about the same dead weight and cost as a comparable slab
and beam floor and ill have up to half the depth of floor construction
from top of slab to soffit of beams.

19. Flat slab
A simple reinforced concrete flat slab cast to act as a suspended floor is
not usually economical for spans over 5metres. To overcome this
problem beams can be incorporated into the designs to span in one or
two directions. Such beams usually span between columns which
transfer their loads to the foundations. The disadvantages of
introducing beams are greater overall depth of the floor construction
and the increased complexity of the form work and reinforcements. To
reduce the overall depth of the floor construction flat slabs can be used
where the beam is incorporated with the depth of the slab.

21.  Soffits and Beam fixing; concrete suspended floors can be designed to carry
loads other than the direct upper surface loadings. Services can be housed within
the voids created by the beams or ribs and suspended or attached ceiling can be
supported by the floor. services which run at right angles to the beams or ribs are
usually housed in cast-in holes. There are many types of fixings used in
conjunction with floor slabs, some are designed to be cast-in whilst others are
fitted after the concrete has cured. All fixings must be positioned and installed so
that they are not detrimental to the structural integrity of the floor

22. Pre cast concrete floors
Precast concrete floors are available in several basic formats and
provide alternative form of floor construction. Precast concrete is
an inherent structural material and works well for floors.
Advantages of precast concrete floors
 Elimination of the need for formwork except for normal
propping which is required with the same system.
 Curing time for concrete is eliminated there fore the floor is
available for use as a working platform at an earlier stage.
 Superior quality control of product is possible with factory
produced components.

23. Disadvantages of precast concrete floors
 Less flexible in design terms.
 Higher degree of site accuracy is required to ensure that the precast
concrete floor units can be accommodated without any alterations.
 Formation of large openings in the floor for ducts , shafts, and
stairwells usually have to be formed by casting an in-situ reinforced
concrete floor strip around the opening position.
 .

24. Types of precast concrete floors
 Hollow core floors
It consists of concrete elements cored along their length. They are
generally available 1200mm wide. Narrower units are also available
at 600mm or 750mm. Depths are 100-400mm, depending on span
and loading conditions, providing efficient flexible solutions across
all markets for most building types.

25. The photo view

26.  Beam and block
Beam and block uses inverted 'T' sections of beams 150-225mm deep.
The infill between the beams can be made up of dense, medium or lightweight
aggregate blocks or, where improved thermal performance is required, of expanded
polystyrene blocks. The latter provide insulated permanent formwork for a structural
concrete topping. Such construction is mainly used at ground floor level although it
is also suited to upper floor applications.

27.  Lattice girder
Lattice girder is found as part of a composite construction and is generally available
in widths of up to 2400mm. It consists of a reinforced concrete slab with
projecting steel 'lattice-girders'. This design ensures an effective mechanical bond
between the precast element and the applied concrete topping. Such floors are
particularly suited to car parking lots.

28.  Double Tees
Named for its shape, double-tees are used primarily as floor and roof deck
components for any type of structure, including parking structures and all types of
buildings. They are made either:
 Pre-topped using a flange thickness of 4 in., which creates the wearing surface in
parking structures; or
 Field- topped with a 2-in. flange, on which a cast-in-place concrete composite
topping of 2 to 4 in. is added in the field. For roof construction, there is typically
no need to add topping on the 2 in. flange.

29. Advantages of using concrete
floors
Disadvantages of using concrete
floors
Inherent sound insulation quality Problematic if incorrectly ordered
for span
Semi skilled site labor can lay
floors and screed if detailed
Requires large support wall lintels
Full design calculation provided as
part of the package
Moulding of components can be
expensive
No special site storage, often
delivered and crane hosted to
position
Alteration may require approved
structural backup
Availability of raw materials Difficult to correct faults on site
Low time to erect Service integration requires setting
out and preplanning

30. Timber Floors
Timber floors are approximately half the cost of similar reinforced
concrete floors. However, they are very poor at fire resistance and
sound insulation.
Timber floors comprise of different parts which include,
 Girders
 Joists
 Strutting
 Floor boards or planks
 Sheathing

31. Floor Joists
 The depth of joists depends on the imposed loads and the span of the
room.
 The spacing of the joists is usually between 400mm to 600mm
measured centre to centre from each member. Where girders are not
used it is common practice for the floor joists to be laid such that
they span the least width of the room from external load bearing
walls to internal wall partitions.

32. • The maximum economic span for timber joists is 4metres.
• Where the least span of the room is greater than 4metres girders are used and in
this case the joists are placed either on top of the girders or attached to the girders.

33. Floor Girders
 These are wooden pieces placed such that they span a shorter length
or dimension of the room. They are an un optional component of
timber floors and they are mainly used in wide spans.
 Girders receive loads from joists and transmit them to columns or
any other load bearers of the room. In other wards they are the
equivalent of beams within reinforced concrete floors. The size and
spacing of the girders depends on the loads to be supported and they
rest on the wall plate or attached to the side of the beam.

34. Floor Strutting
 Strutting refers to the pieces of timber fixed between all joists at
right angles to prevent the joists from shrinking and warping which
would result into cracking if any plaster is cast on the frame. The
strutting also provides extra supporting base on the floor boards
though it might be left out in some timber floor frame. It is placed in
line or may be scattered.

35. Floor Boards
 These are pieces of timber which form up the platform or the floor
decking and they enable the floor to serve its purpose and ease
movement, cut sound and aid vision to some extent.
 The floor boards are placed adjacent to each other and perpendicular
to the joists to increase strength.

36. Sheathing or wearing course
 This is a layer which can be made out of cement screed (1 inch to 2 inches) to
that is applied to seal off the floor and provide sound insulation, water
proofing and a smooth floor surface.
 The sheathing also helps to preserve the beauty of timber and help in making
the cleaning of the timber floor easier.

37. Advantage of using timber floors
 The floor is flexible. It is easy to alter the design.
 The floor accepts nail fixing.
 On sloping sites the floor reduces the need of filling to make up the
ground to the required floor level
 It is lighter than most of the other construction materials, hence
reducing the overall loads of the structure.

38. Disadvantages of using timber floors
 It’s a more expensive form of construction. This is in terms of floor
finishes
 It’s susceptible to dry rot and draught.
 It’s colder than the other forms of flooring
 Timber can easily be attacked by fungi and insects if not well
treated.

39. Floor Finishes
The type of floor finish to be applied will depend upon a number of
factors such as type of base, room usage, degree of comfort required,
maintenance problems, cost, appearance safety and individual
preference.
Floor finishes can be under three main categories:
 In-situ floor finishes – these are finishes which are prepared on site
and cast into place. Examples are in-situ concrete floors, terrazzo.
 Applied floor finishes - those finishes which are supplied in tile
form or sheet form and are laid on to a suitably prepared base.
 Timber floor finishes - boards sheets and blocks of timber laid on
or attached to suitable structural frame or base.

40. REFERENCES
 Building Construction Theory by Mutebi Ronald
 Building Construction Handbook by R. Chudley and R. Greeno
 www.theconstructor.org