Ground, First and Intermediate Floors PDF

Ground, first and intermediate floors Module Leader: Graham Terry An Introduction to Technology and Design Ground Floors Learning outcomes To gain an appreciation of types of domestic floor construction To investigate some problems with older forms of floor constru...

Ground, first and intermediate floors Module Leader: Graham Terry An Introduction to Technology and Design Ground Floors Learning outcomes To gain an appreciation of types of domestic floor construction To investigate some problems with older forms of floor construction Introduction to ‘U’ values and formula for calculations Topics for the session Ground floors Functions and stability Early timber floors Solid floors Suspended floors Insulation requirements. Ground Floors Definition A horizontal level surface designed to support the buildings occupants and their furniture and fittings, equipment or machinery Ground Floors Functional requirements Strength and stability Resistance to damp penetration Good thermal insulation Durability. Ground Floors (cont.) Floors are classed as solid or suspended Solid ground floors are those that gain their support from the earth Suspended are those floors that span between supports Ground Floors (cont.) Ground floors may be constructed from: Timber joist with timber floor Concrete with a sand & cement screed Concrete with floating timber floor Concrete beams & infill blocks & screed Precast concrete floor panels with a screed. Early Timber Floors 1890s Early Timber Floors 1890s Sleeper wall Arrows show direction of joists Kitchen (solid floor) Most Victorian and Edwardian houses have suspended timber floors apart from kitchens and sculleries which were likely to be solid floors. Joists, spaced 350-400mm apart, supported on external and intermediate sleeper walls  Early Timber Floors (Cont.) Joists built into external wall Air vent Bare earth 100 x 50mm joists supported on sleeper wall Problems: Damp, dry-rot + less seriously - draughts through plain-edged boards  Timber Floors 1930s Improvements in the construction of such floors introduced during 20th century consist of a oversite concrete, separate support by honey-combed sleeper walls which include damp proof courses and the provision of a large number of sleeved floor vents + T & G boards or boarding. Timber floors 1930s Modern Timber Floors Raised timber ground floors are fairly rare in new construction because they are considerably more expensive than their ground bearing concrete counterparts. Stability of a Suspended Timber Floor Depends on: Span Load being carried Depth of joist and its thickness Timber species Spacing of the joist Type and thickness of covering forming the floor Use and spacing of strutting. Early Concrete Floors 1890s Sleeper wall Arrows show Most Victorian and Edwardian direction of houses switch to ground bearing joists solid floors for their kitchens and sculleries Kitchen (solid floor) Concrete oversite concrete of between 100-125mm thick laid over prepared ground Early Concrete Floors 1890s to 1930s First Type of Solid Concrete Slab Floor – No Hardcore and so vulnerable to damp Progress to Hardcore Fill beneath the Floor Solid ground floor construction (1930s – 1960s) Solid ground floor construction Construction sequence Construction sequence Modern solid ground floor construction Modern solid ground floor construction (cont.) Suspended ground floor (cont.) Suspended ground floor (cont.) http://www.bing.com/videos/search?q= floor+insulation+youtube+UK&&view=det ail&mid=0871A0B595DBC2924E9A0871A0 B595DBC2924E9A&FORM=VRDGAR Suspended ground floor Floor is supported on the inner leaf of the external walls and on the internal walls. Inverted ‘T’ beams 150-200mm deep are factory produced. These support concrete blocks. The void beneath the floor should be ventilated, and there is normally no need for any separate concrete oversite. The void should be free from all organic material however. https://www.youtube.com/watch?v=YykxPXbDBsc Suspended ground floor (cont.) Suspended ground floor Precast concrete floor panels Light weight for its depth (225mm in depth same as standard blocks) High load bearing Up to 6 meters in length available by 1.2 meters wide Why suspended ground floors are used? If the nature of the ground requires piled foundations it may 1. not be suitable for ground bearing slabs. Reinforced concrete Unstable ground at shallow depths ground beam 2. Where the water table is high. 3. Where there are aggressive chemicals in the ground which may attack the hardcore or concrete slab. Why suspended ground floors are used? (cont.) 4. Where a large volume of hardcore is required below a ground bearing slab. This could cause the slab to settle as consolidation occurs. Maximum 600mm of hardcore 5. Where sloping sites may result in excessive and uneven depth of hardcore. Damp Proof Membranes to Floors To prevent moisture rising there is a need to provide some form of horizontal damp proofing in the slab Usually formed in polythene sheet Crucial that this is linked to dpc in external walls Common effect of omission is dampness Damp Proof Membrane Linked to DPC  Screeds Screeds are used to provide a level base for floor finishes Screeds need to be 75mm thick when laid onto floor insulation to achieve sufficient strength Mix proportions of screed should be at a ratio of 1:3 (cement to sharp sand) If bond is poor or screed is too thin it will crack with a tendency to curl at the edges of the slab Screed should be solid to walk over. Edge insulation is provided to prevent cold bridging to walls Screed Laying Screed laid onto concrete base Perimeter edge insulation visible Thermal insulation The main function of thermal insulation is to reduce the rate of heat loss through the external fabric of the building The reduction in the rate of heat loss will result in a lower total heat input into the building thus saving fuel and power  Thermal insulation Approved Document L of the Building Regulations is concerned with the conservation of fuel and power and applies to dwellings whose floor area exceeds 30m2 Think of U value as the rate of heat flow through a material. The lower the U-value, the better the insulation performance through the element or structure Heat losses from ground floors are greatest at the perimeter as the heat flow to the external air is possible at this position. https://youtu.be/6RVl5iAsWAY  Calculation of U-values The thermal transmittance or U-value is calculated using the following formula: U-value = 1 ---------------------------------- Total thermal resistance U = 1 (W/m2K) -- RT https://www.youtube.com/watch?v=jcKqYq_6qXM Calculation of U-values (cont.) The thermal resistance of a component is obtained either by: For a material: Thermal resistance = Thickness of the material ------------------------------------ Thermal conductivity R = t (W/m2K) -- λ For an air space or surface – use standard values from the table Thickness of insulation Thickness of insulation (cont.) Insulation What we have covered today To gain an appreciation of types of domestic floor construction and how methods have developed To understand the circumstances in which one type of floor might be more appropriate than another for ground floor construction Introduction to ‘U’ values and formula for calculations Upper floors Learning Outcomes To understand what are Victorian floors To understand what are Modern timber floors Size of floor joists Openings, restraint and services Space joists TJI joists To understand what are Concrete floors Beam and block Hollow core To understand what are Finishes To define what are Stairs Victorian floors Joist size Span in feet divided by 2, then add 2 inches A span of 12 feet therefore requires 8" joists Victorian floors (cont.) Modern timber joists with a timber floor Modern timber joists with a timber floor (cont.) Floor joists Most upper floors are constructed using a series of timber joists (rectangular in shape) covered with chipboard or floorboards Joists are usually spaced at 400mm, 450mm or 600mm centres Reasons for using timber Readily available Relatively cheap Easy to work (cut and shape) Fixings are used easily Repairs can be carried out.  All structural timber used in suspended floors must be stress graded to conform with current Building Regulations – Approved Document A and TRADA Fact Sheet No. 3. Use of structural The spacing and size of joist depends upon timber ⚫ Load ⚫ Span ⚫ Grade of timber used A 50 x 150mm timber joist can typically span 2.5 - 3m A 50 x 225mm timber joist can typically span 4 - 4.5m Size of floor joists Floor joists arrangement Restraining floor joists Restraining floor joists (cont.) Openings in timber floors  Strutting Strutting is used to limit twisting of the floor joist ⚫ Herringbone Joist span (m) Rows of Strutting Up to 2.5 None ⚫Solid 2.5 to 4.5 1 at centre span ⚫ Patent Metal Over 4.5 2 equal spaced Provision of Services Services can easily be incorporated into upper floors by the use of holes for cables and notches for pipes This should be kept to a minimum and must conform to the Building Regulations (also see the NHBC guidelines). Provision of Services (cont.) Modern joists Metal web joists (space joists) and 'I' beams have become more common These beams can span bigger distances than readily available joists, thus reducing the need for loadbearing partitions In addition the metal web joists don't require notching or drilling for pipes and cables. Space joists Space joists consist of parallel stress graded timber flanges joined together with engineered, galvanised steel webs Webs are fixed to flanges by nail plates top and bottom Sizes are compatible with solid joists with a choice of depth from 252mm to 418mm. Standard Truss Joist (TJI) 'I' shape in cross-section Manufactured at a low and uniform moisture content to avoid splitting, bowing and twisting They are much lighter than solid timber joists Available in lengths up to 20 m Increased floor rigidity by eliminating laps over beams and walls. Concrete floors Concrete floors are usually used in flats and maisonettes to provide good sound and fire resistance The Building Regulations Approved Document E gives information on the passage of sound. Beam and block floor Beam and block floor detail  Hollow core floor A 150 mm thick floor can span up to 7 m Finishes Most modern floors are covered with tongued and grooved (T & G) chipboard, however floorboards can still be used where the floor is to be varnished Modern ceilings tend to be formed in plasterboard and covered with a plaster skim finish. Sound and fire In the Building Regulations (AD E) it is a requirement to insulate the upper floors of houses against airborne sound Suitable construction is provided if there is a 100mm sound deadening quilt between the joists and a 15mm plasterboard ceiling More sophisticated construction is required for flats where there are also issues of impact sound and 1 hour fire protection to be considered (AD B) Houses Flats Any questions Floor Details 73 Any questions