Construction Technology

Question 1

What is the cost of steel?

Answer 1

Recent increases seen
Recent experience on a mezzanine structure in existing warehouse, 25 tonnes at £4-4.5k / tonne inclusive of the British Steel increase in 2022

Question 2

Which of the Approved Documents are you familiar with?

Answer 2

• Part B - Fire safety
• Part F - Ventilation
• Part L - Conservation of fuel and power
• Part O - Overheating

Question 3

What are the recent changes to the building regulations (2022)?

Answer 3

• Changes have come in as part of proposed transition over next 2 years with the Future Buildings Standard due in 2025
• Part L - associated with carbon emissions and energy efficiency. 27% reduction for non-domestic buildings
• Part F - relating to improved ventilation systems following covid, to reduce transmission of airborne infection , CO2 monitors
• New Part O - relating to overheating

Question 4

What systems can be considered regarding Part F changes?

Answer 4

• Where ventilation systems recirculate air between more than one space, there should be a mode to reduce risk of transmission of airborne infection
• Systems capable of 100% outdoor air (less energy efficient)
• Incorporating UV-C Germicidal irradiation system (in HVAC)
• Systems designed to incorporate HEPA filters

Negligible cost difference in changes

Question 5

You mentioned you read AECOM Building Regulations cost model review. What did you learn from this?

Answer 5

• Updates to the building regulations F, L and O
• Anticipated the improvements will impact outer London buildings more so due to higher regulations already stipulated by GLA
• New guidance due in the Future Build Standard in 2025
• Costs of interventions such as triple glazing now only £20-30m2 more than double when in same frame (increase by £50 / 100m2 when different frame)
• Gas to heat pumps adding ~£50m/2 on construction costs
• Upgrade to out of town office to meet Part L update with heat pump ~£32 / m2”

Question 6

What is the size of a facing brick and typical block?

Answer 6

• Brick - 215mm x 102.5mm x 65mm (60 bricks in sqm)
• Block - 440mm x 215mm x 100mm (or 140mm) (10 per sqm approx)

Question 7

Describe a traditional cavity wall construction.

Answer 7

Cavity walls are formed by an outer and inner skin, typically of brickwork and blockwork, connected by wall ties but separated by a cavity filled with insulation. As well as for thermal purposes, the cavity prevents moisture transmitting from the outer skin to the inner skin -any moisture reaching the cavity from the outside will run down the internal face of the outer skin and be directed to weep holes by cavity trays.

Cavity trays are installed where there are penetrations across the cavity, such as above window and door openings, as the downward flow of moisture would be interrupted at these. A vapour control layer is typically installed to the external face of the inner skin, between the inner skin and the cavity insulation, to prevent warm, moist air from inside the building penetrating through and causing condensation within the cavity.

Question 8

On Eddington you discussed value engineering opportunities with the brick framing. Can you explain?

Answer 8

Elements of the design included rotated brickwork and projected brickwork for architectural interest. This increased as a proportion across the building as the design developed.

Due to the additional labour required compared to a traditional brick bond, the cost saw an increase from £200m2 to circa £260 - 323m2

Savings of 65k due to a reduction in the projected brickwork by 150m2

Question 9

What is a roof build up?

Answer 9

Pitched - Roof joist with ridge and barge board, Breathable Membrane / Roof felt, battens, tiles

Flat - Decking (slab / timber ), vapour control layer, insulation, waterproofing layer, finish e.g. chippings

Green - Structural support, roofing membrane, Root barrier, Insulation, drainage, aeration and root barrier, soil, vegetation.

Question 10

Name some different types of roof construction.

Answer 10

• Single ply membrane
• Built-up
• Pitched tiled roof
• Green roof - Extensive, semi-intensive and intensive

Question 11

What is curtain walling?

Answer 11

Curtain walling is a type of façade used for the external envelope of a building. It can be used as:

• Stick system, that is delivered to site as separate components and build on site
• Unitised system that is pre-fabricated off site and fixed to the frame on site
• Rain screen system that incorporates panels in front of the actual curtain walling to reduce wear and tear, reduce exposure to the elements and improve performance
• Structural glazing, this is a load bearing structure

Question 12

What is an EWS form?

Answer 12

External wall system - required to be submitted to the local Fire service on blocks 11m+ (5 storeys) - legally required from jan 2023
Required every 5 years

Question 13

What does a transfer slab do?

Answer 13

Transfers load from columns and walls above to structural members below. They can be used where there is a different grid between floors, for example below a repetitive structure that has a different grid to the floors below, such as hotel lobbies and bedroom floors.

Question 14

What are Post-tensioned concrete slabs?

Answer 14

A method of reinforcing concrete slabs with high strength steel cables known as tendons. Tendons are placed within ducts running in both directions and profiled at high and low points so the duct follows a shape that reflects the bending profile of the slab when loads are applied i.e. high points over columns and low points at mid-span. As the concrete cures the tendons are jacked at different stages. Anchors are at the end of each tendon to lock them after they have been jacked to the pre-determined tensile force, and they are then grouted.

Question 15

What are the benefits of Post-tensioned concrete slabs?

Answer 15

PT slabs allow for increased clear spans, therefore fewer columns are required and more architectural freedom is granted. Slabs are thinner, therefore reducing cost, weight and foundation requirements and reducing the building height. Significantly less conventional reinforcement is required. They do however require specialist skilled labour to handle and install the tendons.

Question 16

What are the pros and cons of choosing a precast concrete frame over insitu?

Answer 16

• Time -quicker to install, can be in manufacture whilst other works are ongoing, unaffected by labour shortages, not affected by the weather, however can be long lead-in times.
• Quality -greater quality given it is manufactured in factory controlled conditions, however care must be taken when delivering and handling the precast members to ensure they are not damaged
• Precast offers less flexibility as the client cannot introduce changes once the members are in manufacture
• Site constraints might affect the delivery and handling of precast concrete members and specialist lifting equipment will be required i.e. a crawler crane
• Cost -no formwork required for precast concrete, however there is the cost of specialist lifting equipment -ultimately the economy achieved by using precast concrete is partially offset by the transport and handling costs, therefore a lot depends on the location of the factory in relation to the works in order to minimise these. Precast may require specialist subcontractor involvement from an early stages and upfront costs i.e. advance payment or payment for materials off site.
• Typically requires specialist subcontractor involvement, which could lead to upfront costs i.e. advance payment (PCSA perhaps) / materials off site payments.

Question 17

Why does concrete need reinforcing?

Answer 17

• To increase tensile strength

Question 18

What is the difference between stick and unitised curtain walling?

Answer 18

Stick curtain walling is constructed on site of the different components -the steel framing is erected and glazing slotted in, whereas unitised curtain walling is prefabricated off site.

Stick curtain walling is used for smaller or more complex areas, whereas unitised is best suited to repetitive facades such as high rise buildings. Unitised has greater quality due to being manufactured in factory controlled conditions, avoids higher labour costs on site and is installed quicker than a stick system, however stick systems are cheaper. Stick systems require significant space for installation and material storage, and are therefore not always viable in city centre locations.

Question 19

What is curtain walling?

Answer 19

Curtain walling is a weatherproof, non-load bearing enclosure of glass or metal panels in a light metal framework that is fixed back to the structure of the building. Any loads imposed upon the curtain walling are transferred back to the structure.

Question 20

What is rainscreen cladding?

Answer 20

Rainscreen cladding is a double wall construction made up of a watertight, insulated backing layer and an outer skin of cladding panels, separated by a ventilated cavity. Water is able to penetrate into the cavity where it drains off, but the rainscreen outer skin is designed to provide protection from direct rain.

Question 21

What must happen before demolition can commence?

Answer 21

The CDM Regulations demand a written a plan of work for demolition, even where a project is non-notifiable. This would typically include an asbestos refurbishment and demolition survey, utilities information i.e. disconnections, any structural hazards and risks, site constraints, historic use of the building, pre-construction information etc.

The building owner must give the Local Authority Building Control 6 weeks’ notice ahead of carrying out any demolition works via a Section 80 notice.

Question 22

What types of curtain walling are there?

Answer 22

• Stick system, that is delivered to site as separate components and build on site
• Unitised system that is pre-fabricated off site and fixed to the frame on site
• Rain screen system that incorporates panels in front of the actual curtain walling to reduce wear and tear, reduce exposure to the elements and improve performance
• Structural glazing, this is a load bearing structure

Question 23

What is a Air Source Heat Pump (ASHP)?

Answer 23

An air source heat pump is usually placed outdoors at the side or back of a property. It takes heat from the air and boosts it to a higher temperature using a heat pump. The pump needs electricity to run, but it should use less electrical energy than the heat it produces.

Question 24

What are the types of air conditioning systems available?

Answer 24

Fan Coil Units – these are local units that use water pipework and filters to condition and cool/ heat the air in a particular area which is recirculated using the rule of convection
Variable Air Volume unit – this is a series of ductwork linked to an air handling unit, it uses local controls and dampers to regulate the air supply to each area
Underfloor air conditioning – this uses a zone air conditioning unit that extracts air through the conditioning unit and recirculated it via underfloor ductwork and terminals.

Question 25

What does an air handling unit (AHU) do?

Answer 25

They supply, circulate and extract air from buildings. The air handling unit is generally located within plant space and is connected to the ductwork within the building to supply and extract air. 'Localised' air handling units that consist of only a fan and a heating or cooling element are referred to as fan coil units.

Question 26

What are fan coil units?

Answer 26

Four-pipe fan coil units have two hot water pipes (supply and return) and two cold water pipes (supply and return). The pipes are fed from central boilers and chillers. They are often placed in the suspended ceiling void, but can be wall mounted or free standing. They are more economic to install than ducted air handling units, but can be noisy and cause vibration given they are located within the occupied space as opposed to on the roof or within a plant room.

Question 27

What is MVHR?

Answer 27

Mechanical ventilation with heat recovery. Whole house (installed in loft space and ducted) or single room means of ventilation whereby moist, stale and polluted air is continuously extracted and passes over a heat exchange cell which recovers and retains the heat that would otherwise have been lost from the extracted air. This heat is then transferred to the incoming fresh air that the MVHR unit is supplying, resulting in minimal heat losses. MVHR is an ideal replacement for inefficient extractor fans.

Question 28

What are the different levels of fit-out / specification a client might want his building constructed to?

Answer 28

* Shell and core -structure, cladding, base plant, completed common areas and external works. * CAT A (developer's spec) -raised access floors, suspended ceilings, distribution of M&E services, internal finishes and partitions. * CAT B (tenant's spec) -kitchen fit-outs, furniture, installation of specialist facilities and lighting, final finishes and branding.

Question 29

What were your findings when you assessed the benefits of bathroom pods?

Answer 29

Despite the lengthy lead-in times there were clear programme benefits to using pods due to the repetition across the 180-bedrooms as only two different types were required, and it further reduced wet trades on site whilst giving quality assurance. I've looked at pods for other projects such as a residential development in Birmingham's Jewellery Quarter and they were not the most cost effective option due to the differing apartment types losing economy of scale, so it needs to be assessed on a project by project basis.

Question 30

What are Pad Foundations?

Answer 30

Pad foundations are a form of spread foundation formed by rectangular, square, or sometimes circular concrete ‘pads’ that support localised single-point loads such as structural columns, groups of columns or framed structures. This load is then spread by the pad to the bearing layer of soil or rock below. Pad foundations can also be used to support ground beams.

Question 31

What are Raft Foundations?

Answer 31

Raft foundations are used where ground conditions are poor, such as soft clay, for low rise buildings so that the building essentially floats on the poor ground. They consist of a reinforced concrete slab (2 layers of mesh), which tends to be thickened at the perimeter (sometimes beneath major internal walls). Raft foundations are generally an economic foundation type as they're quick to construct and combine the cost of the foundations and ground floor slab.

Question 32

What is the purpose of blinding?

Answer 32

* To 'seal' the hardcore, preventing concrete running down between the stone (prevents wastage) and allowing moisture to penetrate up into the concrete * To protect a damp proof membrane from being damaged by the hardcore * To provide a sturdy, level base for the placement of reinforcement

Question 33

Pile foundation catagries?

Answer 33

* Piles may be classified by their basic design function (end-bearing, friction or a combination) or by their method of construction (displacement (driven) or replacement (bored)). * End-bearing piles develop most of their friction at the toe of the pile, bearing on a hard layer. The pile transmits load directly to firm strata, and also receives lateral restraint from subsoil. * Friction (or floating) piles develop most of the pile-bearing capacity by shear stresses along the sides of the pile, and are suitable where harder layers are too deep. The pile transmits the load to surrounding soil by friction between the surface of the pile and soil, which in effect lowers the bulb of pressure.

Question 34

What is CFA piling?

Answer 34

Continuous flight auger piling. This is the process of auger boring down to the required level, then simultaneously pouring concrete into the void as the auger is reversed and the spoil extracted. When the auger is fully removed reinforcing cages are inserted into the fluid concrete. It is typically used in city centre areas and nearby to existing buildings due to low vibration and noise.

Question 35

What is Secant piling?

Answer 35

Secant pile walls are formed by constructing reinforced concrete piles that interlock, and are often used as a cost-effective solution when short-term water retention is required. Secant piles are reinforced with either steel rebar or steel beams.

Question 36

How does secant piling works?

Answer 36

Typically, primary (female) piles are cast in situ, leaving space in between them. This is followed by secondary (male) piles being cut into the primary piles to form a continuous wall,

Question 37

What types of pile testing are there?

Answer 37

None Working pile – or proof piles, still result in being part of the end product but tested with additional loads of up to 50% to understand the depth of pile needed to sufficiently support the intended loads to enable reduction in safety margin Preliminary pile – sacrificial, essentially where overloaded to point of failure

Question 38

steel frame types

Answer 38

- Skeleton steel - column and beam steels connected, usually multi storey * Wall bearing steel - erection of masonry walls on the perimter and interior of building and anchored to masonry walls * Long span - used for wide spans e.g. >12m. Include trusses, Girders, Arches, Rigid frames

Question 39

When would you advise pad over strip foundations?

Answer 39

* Where the load required is single point i.e. from a column, as opposed to if the load was continuous or / too heavy for the soil conditions. A domestic house may use either, depending on ground conditions / cost / load etc.

Question 40

what are the sub-elements of piles?

Answer 40

- Mat (m2) - Rig (item) - Moving rig (nr) - Pile (length & diameter) (nr) - Pile casings (nr) - Disposal of excavated (m3) - Cutting off tops (nr) - Pile cap (nr) - Pile test (item)

Question 41

What forces do buildings need to withstand?

Answer 41

Dead / static loads Dynamic Loads Wind loads Snow / rain loads Settlement loads

Question 42

What is primary steel vs secondary steel?

Answer 42

Primary steel referrs to the components that help the buildings stand e.g. columns, beams and rafters secondary steel refers to giving support to external components such as the roof / cladding

Question 43

What are G & U Values?

Answer 43

G - Solar heat Gain through glazing U - Heat loss through a construction material (0.1 low, 1.0 high) From Part L updates external walls has gone from U value of 0.28 W/m2K to 0.18W/m2K

Question 44

What are the key factors do you need to consider and the key drivers behind cost increases as buildings increase in height?

Answer 44

* Increased frame size, and therefore foundation size, to deal with the additional wind loads. Wind loads increase disproportionately with height. * Efficiency is reduced as the net to gross ratio reduces with increased height. This is due to larger core areas being needed to serve a greater number of floors i.e. increased riser sizes, number of lifts. * Wall to floor ratio tends to be worse for taller buildings, which can also lead to increased levels of solar gain therefore affecting the services strategy. * It is important to take advantage of repetition, particularly for the façade -unitised curtain walling. * Whilst the number of lifts will be increased, they will also need to be larger and faster for high rise buildings, therefore the direct cost of lifts will increase. * Reduced productivity due to distances to the work face from welfare facilities and materials. * Intermediate plant floor may be required above a certain number of storeys, further reducing efficiency.

Question 45

What would you include under hard landscaping?

Answer 45

o Hard materials i.e. Paving / Underlays / Guttering / Drainage / Fencing / Ponds

Question 46

How does your knowledge of construction technology assist you in your role as QS?

Answer 46

* Allows a greater degree of accuracy and understanding when estimating, cost planning and measuring bills of quantities * Helps provide advice to clients in respect of value engineering * Assists in valuing the works

Question 47

What benefits might there be to using a composite slab in place of a traditional slab for upper floors?

Answer 47

The metal deck acts as permanent formwork for the concrete, and they are lighter as the corrugated profile of the metal means there is less concrete.

Question 48

Metframe / Fusion light gauge steel superstructure.

Answer 48

Metframe is a pre-panelised system used to provide the load-bearing structure for low to medium rise buildings. Studs are used in the same manner as SFS, except they are bolted together off site to form panels. The system offers significant programme savings as it typically takes less than 2 weeks per storey to construct. Panels are craned into position, and stairs and lift shafts are installed floor by floor, removing the need for scaffold access. Pods and plasterboard packs are also craned in floor by floor.

Question 49

What are the sub-elements of upper floors?

Answer 49

- In-situ concrete m3 (horizontal) - Power floating m2 - Formwork m2 - soffits, sides, sides to openings / columns - Reinforcement (post tensioned members) nr

Question 50

What is in costs for soft / hard landscaping?

Answer 50

Soft - top soil - compost - planting Hard - subbase - gravel / paving - metal edging - kerbs

Question 51

What was the external wall build up on one of your projects?

Answer 51

Metsec framing partition (cavity) Brickwork Insulation Blockwork lining Vapour control layer Plasterboard included for sub contractor prelims and overheads in rates

Question 52

Describe the brick slip system on SFS

Answer 52

The Corium brick slip system was reviewed, where vertical steel members (SFS) are installed at 600mm centres, then profiled aluminium sheeting is fixed to the SFS. The corium brick slips are then 'clipped' into the profiled sheeting. Once clipped in, mortar is applied to the joints. Installation of brick slips tends to be up to 3 times quicker than traditional brickwork.

Question 53

What is cold bridging?

Answer 53

Cold bridging is when colder air penetrates through an external wall, for example, and meets warmer air that then causes condensation.

Question 54

How can issues related to fire performance be overcome on a steel frame building

Answer 54

Intumescent Paint, boxing in

Question 55

What are the different levels of fit-out / specification a client might want the building constructed to?

Answer 55

* Shell and core -structure, cladding, base plant, completed common areas and external works. * CAT A (developer's spec) -raised access floors, suspended ceilings, distribution of M&E services, internal finishes and partitions. * CAT B (tenant's spec) -kitchen fit-outs, furniture, installation of specialist facilities and lighting, final finishes and branding.

Question 56

What are the different levels of fit-out / specification a client might want the building constructed to?

Answer 56

* Shell and core -structure, cladding, base plant, completed common areas and external works. * CAT A (developer's spec) -raised access floors, suspended ceilings, distribution of M&E services, internal finishes and partitions. * CAT B (tenant's spec) -kitchen fit-outs, furniture, installation of specialist facilities and lighting, final finishes and branding.