FBE 03 Building Construction Science Lecture 3 Floor

FBE 03: Building Construction & Science Lecture 3 Floor System

Introduction • This chapter will consider the functional requirements of floors, both ground floors and upper floors • How the functional requirements are affected by the location of the floor

• primary function of all floors in a building is to provide support to the occupants of the building, along with any furniture and equipment • ground floors and upper floors • there are some distinct differences related to the location of the floor

Floor: Functional requirement • • • Strength and stability Fire resistance Sound insulation Thermal insulation Damp penetration

Strength and stability • loads being carried by the floor need to be supported without causing excessive deflection • Ground floor loads directly onto the ground beneath • upper floors will need to bear their loads onto supporting walls or beams ü deflection will be maximised at mid-span

Fire resistance • for upper floors • horizontal barriers to curb the spread of fire vertically throughout the building • Providing greater protection of people and property during a fire-related accident

Sound insulation • reduce sound transmission between storeys • normally only a requirement for upper floors • incorporate sound insulation materials within the construction of the upper floor

Thermal insulation • Heat loss through the floor • necessary to incorporate thermal insulation materials within the construction of the ground floor • Effective thermal insulation will bring energy saving

Damp penetration • Dampness may penetrate from the moist ground beneath the floor into the building • Require a damp proof barrier • Damage to surface finishes • Damage to equipment, or electrical failure

Solid floor construction • Benefits of floor construction on well-compacted hard material called hardcore: ü a level, horizontal surface on which to place the floor slab; ü a firm, dry working surface on which to place the concrete for the floor slab; ü it reduces the rise of ground moisture by virtue of the large voids between the pieces of hardcore which eliminate capillary paths; ü it provides additional support to the floor above should the ground beneath suffer settlement or subsidence.

Solid floor construction • Hardcore consists of: ü broken bricks; ü Stones; ü concrete or ü rubble ü laid to a minimum thickness of 100 mm ü a layer of ash or sand v Hardcore must not contain materials that are soft or can crumble easily and must not contain deleterious material that will either rot or corrode, leaving voids or react with the concrete

Solid floor construction • three positions in which the dpm may be located ü sandwiched between the blinding above the hardcore and the concrete slab; ü sandwiched between the top of the concrete slab and the screed; ü sandwiched between the surface of the slab and the floor finish.

Solid ground floor with dpm below the floor slab

Solid ground floor with dpm above the floor slab

Suspended floor construction • Suspended floors do not bear directly onto the ground but bear onto supports that will themselves indirectly bear onto the ground • often utilised on sloping sites to reduce the amount of fill materials • Types of suspended slab: ü Suspended timber ground floor ü Suspended concrete ground floor

Suspended timber ground floor • timber is warmer to the touch than concrete • provide increased thermal comfort to the user • comprises small timber beams or joists which span between points • joists are sized according to the loads that are to be carried and the distances that are to be spanned

Suspended timber ground floor • ventilation is provided by air bricks within the external walls • ventilation helps to remove the damp air beneath the floor construction and replace it with drier air from outside • A limitation of air ventilation is allowed to prevent thermal insulation value of the floor will be detrimentally affected • cross flow of air within the void beneath the timber floor is maintained by building the sleeper walls in a honeycomb bond, which consists of a stretcher bond with voids of half brick width

Honeycomb bonding to sleeper walls

Suspended concrete ground floor • This form of construction overcomes three problems: ü dry rot in timber floors; ü excessive fill beneath floors of buildings situated on steeply sloping sites; ü variable loadbearing capacity soil beneath the floor.

Suspended concrete ground floor • constructed from in situ concrete, similar to a solid floor or from precast concrete components. • depth of fill required • floor bearing directly onto the ground may not be considered suitable ü span between loadbearing walls

Suspended concrete ground floor • in situ concrete suspended ground floor: ü incorporate sufficient steel reinforcement in its lower section to enable it to effectively carry the loads bearing ü require support until it has hardened sufficiently to carry its own weight ü necessary to place fill materials onto the ground to provide a firm, dry, level horizontal surface onto which the slab may be cast ü Supported by the loadbearing walls

Suspended concrete ground floor • precast concrete suspended ground floor: ü precast concrete joists ü In-filled with concrete blocks and topped with a screed ü joists are generally an inverted T shape and are pre-stressed to reduce their size and weight ü No beneath support is required ü No fill beneath of the floor is required

Precast concrete suspended floor

Upper floors • Upper floor construction in houses is based on similar principles to that of suspended ground floor construction • difference being that the spans between loadbearing supports are generally greater with upper floor construction, so the joists need to be larger in size

Upper floors • Support: ü ends of the joist will need to be supported by loadbearing walls ü support is provided by the external cavity walls the end of the joist will bear onto the internal leaf. ü joists are to be built in to the supporting wall, their ends need to be treated with preservative

Support to the joists at an external wall

Support to the joists at an internal wall

Support to the joists by the use of a joist hanger

Upper floor • four types of joist used for this framing: ü The common joist – This is a full length joist spanning between wall supports without interruption. ü The trimmed joist – This is similar to the common joist but has been cut short to form the opening. It spans in the same direction as the common joist and one end is supported by a wall and the other end is supported by the trimmer joist.

ü The trimmer joist – This joist forms the side edge of the opening and supports the cut ends of the trimmed joists. It spans at right angles to the common and trimmed joists. ü The trimming joist – This forms the front and rear edges of the opening and supports the ends of the trimmer joist. It spans in the same direction as the common and trimmed joists and, similar to the common joist, it spans between walls supports without interruption.

Common joist

• framing to openings, various joints are used between the joists: ü The housed joint ü The bevelled housed joint ü The tusked tenon joint

Housed joint

Bevelled housed joint

Tusked tenon joint