Construction Technology
Key principles of buildings:
- Buildings should be safe for occupation and day to day use and occasional use.
- The building needs to be suitable for the purpose (commercial or residential).
Regulation and enforcement:
- Administered locally.
- Local authority building control
- Approved inspectors
- Privatised building control.
- Commercial focus.
Gaining approval for plans to be approved:
It’s a written application to the LABC or to an approved inspector which included the construction
details (extension), materials information, calculations and specifications. This application must show
that they comply to the regulations set out to the council.
Building notice:
- A written notice to show that you intend to carry out building work.
- Full plans of the building work are not required.
- More responsibility to comply
- Tends to be minor work for example, adding a shed.
Full plans submission:
- An application that includes full details of the proposed building works are submitted for
approval before the work is carried out.
- This requires comprehensive checking.
- There is flexibility so they can add to the conditions.
- This includes minor to major works.
- Always for non-residential reasons.
Compliance process – what an inspector will do:
- examine calculations and documentation.
- Impose restrictions and conditions
- Offers advice on how to improve the building work.
- Visits the site to inspects the methods used and materials.
- The inspector will issue and compliance certificate.
Structure:
Loading: strength and stability of elements, robustness of connections and durability.
Ground movement: suitable foundations for location, performance and construction type.
Disproportionate collapse: To prevent a disproportionate collapse in case of an accident.
Fire safety:
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- B1 – means of warning and escape. (Audible and visual alarms)
- B2 – internal fire spread linings. (How does fire spread through the building).
- B3 – internal fire spread structure. (Compartments between buildings)
- B4 – external fire spread. (Spread to other buildings)
- B5 – access and facilities for the fire service. (Water provision, firefighting stairs and access
for fire engines)
Site preparation and resistance to contamination:
- C1: site preparation and resistance to contamination (ground contamination, old foundations
or chemical degradation). Health and safety – lead, asbestos, radon and methane. Ground
source pathogens and clinical waste.
- C2: resistance to moisture: Rising damp, penetrating damp, weatherproofing, interstitial
condensation, moisture between layers of building fabric.
Toxic substances:
- Cavity wall installation – leeching of urea formaldehyde gas, hazardous to health, sick
building syndrome (ventilation, monitoring and air quality management).
Resistance to the passage of sound:
- Protection against sound from other/ adjoining buildings. (Terraced, apartments, new build,
conversions) (adjoining offices, industry, retail and leisure).
Ventilation:
- Dwellings, non-dwellings and alterations.
- Ventilation systems will be based in the kitchen and bathroom.
- Passive vs active systems – air bricks and mechanical extract.
- Alternative approach CIBSE complaint system (standard setter and using computer
information to create the best ventilation system for the dwelling).
Sanitation, hot water safety and water efficiency:
- G1- Provision requirements for dwellings and non-dwellings.
- G2 – dwellings only – facilities, hot and cold-water system, foul waste connection.
Drainage and waste disposal:
- Foul water drainage: WCs, kitchen sinks, straight to treatment works.
- Wastewater treatment: Septic tanks, cesspools
- Rainwater drainage: potential for recovery or harvesting.
Combustion appliances and fuel storage:
- Gas, heating oil – protection from fumes, carbon monoxide protection.
- Environmental protection – bunded tanks, protected enclosures and testing.
Protection from falling, collision and impact:
- Stairs, ladders and ramps – dimensions and construction.
- Protection from falling – balustrades and handrails, barriers (roof edges).
- Vehicle barriers and loading bays – crush protection and auto safety stops.
Conservation of fuel and power:
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- L1A: new dwellings, L1B: existing dwellings, L2A: new non-dwellings,
L2B: existing non-dwellings
Access to and use of buildings:
- Much wider than just for a disability. Many people need aids who aren’t disabled (elderly)
Electrical safety – dwelling:
- P1: design and installation – stops people having a go, imposes legal standards, approved
installers can self-certify to regulations.
Security:
- Relevant security where windows and doors are accessible - distance above ground level
externally and a change of use is included.
Internal data infrastructure:
- New builds and refurbishment work.
- Ductwork and containment for copper and fibre.
- Satellite and wireless performance.
Regulation 7 – materials and workmanship:
- Contains: selection, handling, storage and management of building material.
- Generic to many trades.
Air tightness test – door blower test.
- This is done on a nearly completed building. Checks must be done before the test, for
example, ventilation systems have to temporarily be sealed and all interior doors must be
open.
- A frame covered with an airtight membrane is fitted in to the front door frame. The fan is
fitted into the sheet (membrane) negative pressure builds up inside the sheet, then the
membrane will bulge inwards. The fan will blow the indoor air out of the structure to produce
negative pressure of 50 pascals (unit for pressure) in the interior. The fan then pumps outdoor
air into the structure to produce positive pressure of 50 pascals in the interior.
- The air tightness test determines the N50 value which is the structures air change rate through
leaks.
N50 = Loss of heated air through leakage (m3/h) / heated indoor air volume (m3).
N50 air change rate limits – building with natural ventilation = 3.0/h and building with air
treatment system = 1.5/h.
- If these values are exceeded, this means there is a leak. An individual will fill the structure
with theatrical smoke then a positive pressure will be established then the individual will be
able to recognise from outside where the smoke is escaping from therefore finding the leak. A
thermal anemometer will be able to recognise the speed of air (where the draught is coming
from). This draught will then be sealed and will be checked again by the anemometer to
ensure the speed of air is 0.
- A portable smoke machine can check component connections. If the smoke is forced out
through any leaks by positive pressure this can cause toxic mould in the walls.
Site assessment and improvements:
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- A brownfield site is a previously owned piece of land that has previously been built on with
demolition issues and no longer in use services.
- Greenfield sites are pieces of land used for agricultural use and have never been built on and
have predictable ground conditions.
- Features of building on a brownfield site: disturbed ground (poor loadbearing), contaminated,
additional project costs and existing features (roads, foundations and services).
- Poor loadbearing issues: The ground is disturbed from the lack of compaction, old
foundations, services and infilled ponds. The material from the ground will be from refuse
dumps, organic materials and old building materials.
- Poor infill materials: these can include the roofing slates, tarmac and bricks from the old,
demolished building and site waste. Site clearance will be required as there will be old
vegetation grown.
- Voids and lack of compaction: the density of the ground is reduced. The CBR (Californian
bearing ratio) measures how hard the surface is. They measure this by measuring the pressure
required to penetrate a soil sample with a plunger of the area. An additional load may
compact the ground causing an unforeseen and unpredictable settlement causing voids which
may be at surface or deep level.
- Avoiding the poor ground: Avoid ground that may be below infill, to bedrock or that have had
previous high-rise buildings on. A pile foundation may have to be used as these transfers
loads to a lower level of subsoil which will have a higher bearing capacity.
- Mitigating the poor ground: Raft foundations are built as they are good for patchy ground as it
spreads the weight of the structure through the whole ground floor area so this will
accommodate the areas of the weight which have a poor bearing capacity. Raft foundations
are constructed in the form of a continuous slab using reinforced concrete therefore many
houses can be built on a large area which also avoids overstressing soils. Raft foundations are
prone to edge erosion. They need special measurements for some of the concentrated loads.
- To improve the quality of the ground before the construction work takes place these
techniques can be used: grouting, soil mixing, soil compaction, vibro-replacement (vibro
stone columns), geo textiles and lime/ cement stabilisation.
Grouting – The injection of pumpable materials into a soil or rock to change its characteristics.
Soil mixing – It improves weak soils with high moisture content. It involves mixing wetter soils
with a dry cementitious binder to create soilcrete which increases the bearing capacity and
decreases the settlement.
Soil compaction – It increases soil density and decreases the air volume without producing a
decrease in water content. It improves shear strength, stiffness, bearing capacity and stability,
reducing settlement and frost heave.
Vibro-replacement – Uses a crane-suspended downhole vibrator to construct stone colums
through the weaker soils which improves there load bearings and settlement capacitites.
Geotextiles – These are made by using synthetic fibres which creates a flexible and porous fabric
capable of providing strength and stability.
Lime/ cement stabilisation – A binder will be added to reduce the moisture and improve stability.
Foundation selection:
- Deep foundations – bypass the contamination and piles
- Shallow foundations – above the contamination, raft and mini-piles.
DOMESTIC FOUNDATION TYPES:
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