All floors must have sufficient strength and stability in order to support various loads. Such as? People Furniture Equipment Machinery Partitions

Transcription

1

2 All floors must have sufficient strength and stability in order to support various loads Such as? People Furniture Equipment Machinery Partitions

3 Functional requirements of ground floors What are the functions of a concrete ground floor? 1. Carry loads 2. Prevent dampness penetrating the building 3. Provide thermal insulation 4. Prevent growth of vegetation 5. Provide suitable wearing surface

4 DPM should lap under dpc for full thickness of inner leaf. Dampness from underneath the floor due to capillary action is prevented by a layer of impervious material

5 Brian Callan 2004

6 Ensure proper seals around services Ensure adequate laps Homebond 2001

7

8 Sequencing Hardcore Blinding Damp-proof membrane DPM Insulation Concrete slab Wearing surface (screed) Finish (floor covering, tiles etc)

9

10 square mesh with 10mm bars at 200mm centres Building construction 1988

11 What are the functions of a screed? 1. To provide a suitable level surface to receive the floor finish. 2. To take out any irregularities in the concrete bed. 3. To accommodate any pipes or cables. 4. To provide insulation.

12 Radon details for a cavity wall/ground supported floor Homebond 2001

13 DPC Continuous radon membrane with all joints lapped & sealed Radon resisting sealing tape Perpend ventilator Pipe terminates outside and is capped Timber frame construction 100mm dia pipe to sump Homebond 2001

14 Typical radon sump location in a single storey dwelling. Homebond 2001

15 Cowl Pipe cranked at eaves Radon sump Fan location Hombound 2001

16 Alternative ridge vent 100mm dia pipe Radon sump Cowl Fan mounted close to outlet to minimise condensation Typically pipe may be located in a cupboard or hotpress Alternative option: vent stack carried Homebond 2001

17 Concrete floors incorporating timber Concrete floors lack the resilience of wood. This problem can be overcome by: a) Attaching a timber floor on to the concrete b) Building a timber floor into the concrete

18 Fixing a timber floor to a concrete floor. Building construction 1988

19 Brian Porter 1991

20 Brian Porter 1991 Building a timber floor into the concrete

21 Solid floors with timber finishes: Concrete floors may be covered with floorboards or wood block. Blocks cut from wood with a good resistance to wear are laid on a thoroughly dry, clean level screed. A thin layer of adhesive is spread over the surface of the screed and on to this the blocks are pressed. The blocks are normally laid in bonded patterns.

22 Building construction 1988

23

24 When is a suspended timber floor best used? Used where the depth of fill exeeds 900mm. 900mm

25 Underfloor Ventilation Why do we need ventilation? To avoid excessive build up of moist air in the underfloor space. To keep the moisture content of the timber floor members below 20% of their dry weight, to prevent fungal attack taking place.

26 Building construction 1988

27 There should be a ventilated air space measuring at least 75mm from the concrete to the underside of the wall plate & 150mm to the underside of the suspended timber floor Homebond 2001

28 Stepped DPC only over vent Wall plate DPC 150mm min from ground level Block sleeper wall Homebond 2001

29 Wall plate underside treated Sleeper wall 150mm gaps DPC Block sleeper wall Gaps left between blocks to allow air circulation 150mm Homebond 2001

30 Each external wall must have ventilation openings placed so that ventilating air will have a free path between opposite sides and to all parts of the underfloor void. The openings should be large enough to give an actual opening at least equivalent to 1500 mm for each metre run of wall Homebond 2001

31 Brian Porter 1986

32

33 Joists at right angles to fireplace opening Brian Porter 1991

34 Section through hearth Note: if flue walls are less than 200mm thick, a gap of at least 40mm is left as shown (50mm is usual) Brian Porter 1991

35 Hearth Homebond 2001

36

37 Functional Requirements of Upper Floors To carry the imposed loads without distortion. To provide adequate thermal insulation. To provide sound insulation.

38 Advantages and disadvantages of suspended timber upper floors Advan. Disadv. 1. Easily erected 2. Cheaper than concrete floors 1. Deeper joist required than a suspended ground floor 2. Prone to getting wet until the roof is finished.

39 Upper Floor Design In timber floors the joists are usually placed across the shortest span. The size of the joist will depend on the superimposed loads, and the span must comply with building regulations. A simple rule of thumb method for finding the approximate joist depth for an average floor is.

40 Depth of joist. = span in mm Example floor span of 3.6m. = = 200 mm deep joist The above assumes the joists have a thickness of 50mm are spaced at 400 centres (400 c/c)

41 Floor joist strapped to cavity wall Solid bridging Packing between joist and wall Homebond 2001

42 Single upper (intermediate) floors Code for joists: B Bridging T Trimmer TD- Trimmed TG - Trimming Michael Hannon 2003

43 Michael Hannon 2003

44 Trimmers (T) are supported by a wall or trimmings joists and provide a bearing for trimmed joists. Trimming Joists (TG) are supported by a wall and provide a bearing for trimmers. Trimmed joists are supported by trimmers, or by a trimmer and a wall, and provide joists filling between trimming joists or between a wall and a trimming joist.

45 Trimmers and trimming joists will be more heavily stressed than trimmed or bridging joist, due to load transference between members; therefore both trimmers and trimming joists must be thicker than the rest of the joists, usually by 25mm.

46 225 x 50mm joist 200 x 75 mm trimmer joist 200 x 50 mm trimmed joist 200 x 75 mm trimming joist Construction studies 1988

47 Steel joist hanger mostly used today Brian Porter 1991

48

49 Double joist Brian Porter 1991

50

51 As the span increases there is a tendency for the joists to twist which could cause damage to the ceiling. To prevent this twisting, strutting should be included if the span of the floor exceeds 2.5m. Folding wedges are inserted between the end joist and the wall, in line with the strutting.

52 Note: Deep thin beams are inclined to buckle under load Brian Porter 1991

53 Sound insulation Poor sound insulation is one of the main disadvantages of the method of constructing suspended timber first floors. A method of improving the sound insulation value is to apply a double layer of plaster board.

54 Sound insulation Construction studies 1988

55 Construction studies 1988

56 Dry sand Plywood platform Supporting batten screwed to joist

57 Insulated timber floor with light pugging Michael Hannon 2003

58 Insulated timber floor with heavy pugging Michael Hannon 2003

59 Alternative floating floor construction Michael Hannon 2003

60 1. Floorboards 2. Plasterboard 3. Metal channel rest on resilient slip 4. Clip 5. Additional layer of plasterboard 6. Insulation 7. Existing plaster ceiling

61 Concrete or Fire Resisting Floors An in-situ reinforced concrete floor is one in which concrete is cast in its final position. Since concrete is strong in compression but weak in tension, reinforcement is provided where tension occurs in the concrete. The thickness of the floor and the amount of reinforcing steel will depend on the span and the loads to be carried. The wet concrete has to be supported over the entire area by formwork and props. It is necessary to wait several days until the concrete has set and hardened before the floor can be loaded and formwork removed.

62 Suspended ceiling insulated

63 Framework lined with plasterboard

64 Thermal insulation The external wall of a building, along with the Roof, must prevent heat from inside escaping to The atmosphere. The reverse is also true, that they Should prevent the interior heating up excessively During hot weather.

65 The external wall is made up of a number of different materials which all transfer heat at varying rates. Heat is transferred by one or more of the following : Conduction, radiation or convection.

66 CONDUCTION: is the transfer of heat energy through a material without the molecules of the material changing their basic positions. construction studies 1988

67 RADIATION: is the transfer of heat energy by Electromagnetic waves. construction studies 1988

68 CONVECTION: is the transfer of heat energy through a material by the bodily movements of particles.this will happen in liquids and gasses but never in solids. construction studies 1988

69 Thermal insulation helps to prevent condensation. It also reduces expansion and contraction of the building.

70 The thermal transmittance or U-value of a wall is a measure of its ability to conduct heat. The higher the U-value, the greater the rate of heat loss through the wall U values are expressed in W/m 2 K (watts per square metre for 1 kelvin difference between the internal and external temperatures).

71 Bricks There are three categories of clay brick available: common, facing and engineering bricks. The standard brick measures: 215mm x 102.5mm X 65mm. The length of bricks is more than twice the width. This allows two bricks to be laid side by side with a 10mm mortar joint between them.

72 Pressed bricks have a depression called a frog on one or both faces. The frog reduces the weight.

73 Bonding In order to get the individual brick or blocks to work together as one unit they chould be built so that the vertical joints, called perpends, are staggered. By so doing the load the wall is carrying will be spread over a greater area thus providing better strength and stability.

74 Mortar

75 construction studies 1988

76 List four requirements of a good Spreads readily. quality mortar: Remains plastic while brick/blocks are being laid. Provides a good bond between the block and the mortar. Resists frost and aquires early strength.

77 Two admixtures used in mortars: Plasticisers: these trap air in the mix thereby impoving the workability of the mix. High Alumina cement may be used where early strength or resistance to chemical attack is required.

78 Concrete blocks Concrete blocks are is made from sand, fine aggregate and cement. They are manufactured in a similar fashion to concrete bricks. In order to obtain lightweight blocks manufacturers can use lightweight aggregates such as expanded clay, vermiculete, or furnance slag instead of the normal stone aggregate.

79 construction studies 1988

80 construction studies 1988

81 construction studies 1988

82 Jointing & Pointing: In brickwork or blockwork the joints may be finished in either of two ways: JOINTING: The freshly exuded mortar holding the bricks or blocks is shaped with the point or side of a trowel. A special jointing tool can also be used. POINTING: The mortar is recessed during laying and allowed to set. After the wall is finished a new layer of mortar can be inserted and finished using a trowel or special tool. A number of different types can be produced as follows:

83 External Walls: Solid Walls: this type of wall is solid and dense throughout its thickness and contains no cavity. It can be constructed from a variety of materials such as brick, block, mass concrete and stone. The penetration of dampness to the inner surface may be a problem with this type of wall. This will cause damage to the decoration and may cause rot in timbers adjoining the wall.

84 Condensation is caused when warm moist air comes in contact with a cold surface and usually occurs on the inner surface of solid walls. When outside temperatures are low, a solid wall acts as a cold bridge to the inner surface and condensation will occur when saturated air comes in contact with this surface.

85 construction studies 1988

86 This problem may be particular severe in kitchens and bathroom where the air is usually in contact with water and being warm, supports a large amount of water vapour. Condensation developing within the structure of the wall is termed Interstitial Condensation

87 construction studies 1988

88 There are a number of methods of overcoming these problems. Increasing the wall thickness will help prevent the penetration of dampness. Providing an additional surface on the inner side of the wall will help to counteract condensation and heat loss.

89 Drylining construction studies 1988

90 Cavity Wall: this type of wall consists of an inner and outer leaf of brick or block with a cavity in the centre. It possesses two important advantages over the solid wall by providing better resistance to the penetration of rain and giving a greater degree of thermal resistance than a corresponding thickness of a solid wall of the same material.

91

92 Advantages of cavity walls Prevent moisture penetrating to the inner wall. Provide good thermal insulation. Inner leaf may be constructed of alternative materials such as timber or thermal blocks Greater sound insulation than a solid single leaf construction.

93 Disadvantages of cavity walls Greater care and accuracy required during construction. Damp-proof courses must be included to all openings. More expensive than a solid single-leaf wall.

94 Buildings using cavity wall construction, where each leaf is usually 100mm in thickness, are deficient in structural stability unless wall ties are used to tie both leaves together. Ties must be designed so as not to permit the passage of dampness across the cavity and must be strong enough to develop mutual stiffness in both leaves, thereby reducing the tendency of the individual leaves to buckle.

95 construction studies 1988

96

97

98 construction studies 1988

99 construction studies 1988

100

101

102 Problem Areas Keep cavities clean by the use of boards of cavity laths and/or daily cleaning of wall ties. Provide temporary openings at base of wall.

103 Board across cavity Cavity lath

104 Mortar filling to cavity too high: build up of mortar droppings. Cavity should be kept clean for between 150mm & 225mm below dpc level.

105 Projecting DPC catches mortar: ensure that DPC does not project into cavity at ground floor level.

106 Sloping wall ties act as a bridge across the cavity

107 Mortar droppings on wall ties allows penetration of dampness

108 Build up of mortar on trays/lintels over heads. Keep cavities clean as work progresses.

109 Build up of mortar on joists, purlins, projections or similar. Avoid such projection. Note: treat timber ends with coloured preservative.

110 PRESTRESSED CONCRETE LINTEL This is a concrete beam and can be most easily defined as precompressed concrete. This means that a compressive stress is put into the beam before it begins its working life and is positioned in areas where tensile stresses will develop under working load.

111 The usual methods of prestressing is to use tensioned steel tendons incorporated permanently in the concrete member. The tendons are usually in the form of hightensile wires, strands or bars, used singly or made up into cables. Using tendons there are two basic methods called: 1. Pre-tensioning 2. Post-tensioning

112 In pre-tensioning high-tensile steel wire or strands are streched to the required tension and anchored to bulkheads. When the concrete has achieved sufficient compressive strength, the steel is released for the abutments, transferring the force to the concrete through the bond that now exists between the steel and the concrete.

113 construction studies 1988

114 construction studies 1988

115 Where the span is short, a mild steel angle iron may be used. construction studies 1988

116

117 T/3 max vertical chase Horizontal chase T/6 max Maximum depth of vertical chase to be one third of wall thickness. Maximum depth of horizontal chase to be one sixth of HomeBound 2001 wall thickness.

118 Openings in cavity walls

119 construction studies 1988

120 construction studies 1988

121 construction studies 1988

122 HomeBond 2001

123 A damp-proof course must be inserted over reinforced concrete lintels where openings occur, under window sill and at jambs to openings.

124 HomeBound 2001

125

126 Provide DPC to bottom, back and ends of sills HomeBond 2001

127

128

129 Cavity closer block HomeBond 2001

130 Parapet walls This is the part of the external wall that projects above roof level. It forms a gutter at the bottom of a pitched roof. The height of the parapet wall above roof level should not exceed six times its width.

131 Michael Hasnnon 2003