Building technology

Question 1

What kind of loadings would a structural engineer take into account when carrying out a loading assessment?

Answer 1

• Dead load: load imposed by the structure itself.
• Live load: load imposed by occupants and objects in a structure.
• Environmental load: load imposed by rainfall, snow and wind.

Question 2

What considerations would you need to make when installing photovoltaic panels to property?

Answer 2

• Whether the existing power and infrastructure is sufficient.
• whether the structure of the building can take the new imposed load of the panels.

Question 3

How do solar PV systems work?

Answer 3

• The PV cell consists of one or two layers of a semi conducting material, usually silicon. When light shines on the cell it creates an
  electric field across the layers causing electricity to flow.
• The solar panels generate DC electricity from sunlight which is fed through an inverter to convert it into AC electricity.
• The inverter is connected to a consumer unit (fuse board) so the electricity can be used in your home.
• Any solar generated electricity which is not used in the home immediately will usually feedback to the grid (export).

Question 4

What should a fire door with a half-hour fire rating have? What part of the building regulations would you use to confirm?

Answer 4

• Three hinges.
• Intumescent strip on door or edge of frame.
• Self closing devise.
• If glazing panel present, it must be 6mm thick, wired glass to a max of 1.2m2 with 13mm x 13mm wood beads encased with non-combustible materials.
• Approved Document B - Fire Safety

Question 5

What is a syphonic drainage system?

Answer 5

• Drainage system is an alternative to the gravity drainage system. In
  syphonic drainage, water is sucked from the guttering in to the drain pipe so there is
  no need to have pipes set at a gradient and to rely on gravity to pull the water to the
  drain (a vacuum is created to achieve this).
• Syphonic drainage has the advantage that narrower down pipes can be used.

Question 6

What is composite cladding?

Answer 6

• Composite cladding is formed of a sandwich construction which comprises 2 outer layers of steel or aluminium sheet enclose an inner core of adhesive-bonded lightweight insulation.
• Insulation can comprise of the following:

1. Rigid polyurethane (PUR)
2. Polyisocyanurate (PIR)
3. Extruded polystyrene (EPS)
4. Phenolic foam
5. Mineral fibre

Question 7

What did you pre-purchase advise did you give to your client with regards to composite cladding?

Answer 7

• Advised the client that they should have the vendor confirm the specification of the cladding, including the material that makes up the insulation core and whether the panels are Loss Prevention Certification Board (LPCB) approved.
• Advised that the vendor may have access to this information is they are in possession of the H&S file for the property.
• Approached one of the main manufacturer’s (Kingspan) to see if they had record of the cladding purchased for the property.
• Advised that insurers consider that any risk containing non-LPS compliant panels represents a higher potential for fire spread, they will either restrict cover or offer cover on higher rates, perhaps with higher excesses. If panels of unknown origin are contained within an existing building an assumption may be made as to the type of insulant in order to set the premium accordingly. On this basis, insurance requirements could dictate the replacement of panels, the fitting of fire suppression systems, improved compartmentation and routine fire risk management procedures.

Question 8

Why should you be careful when specifying composite panels?

Answer 8

• Selecting composite cladding materials that comply in all respects with Building Regulations does not mean that building insurers will automatically accept a risk, nor does it mean that they will not inflate premiums. Building Regulations are aimed at ensuring the health of users and neighbours of the building (and of course visitors and emergency services), whereas insurers may seek higher standards of protection, fire suppression and or more reliance upon non-combustible materials.
• Insurer’s will likely want to see that the cladding is LPS Certified.

Question 9

What is the test that is conducted to certify composite cladding materials?

Answer 9

• LPS 1181 (fire growth) and LPS 1208 (fire resistance).
• LPS = Loss Prevention Standards
• LPS 1181 - Is a suite of robust large scale tests designed to determine the fire growth performance of cladding products. Has two parts; Part 1 (external wall and roofs) and Part 2 (internal wall and ceilings).
• LPS certification as tests are carried out are large scale and therefore mimic performance of panels once installed on a building - others will test performance of single panels etc.
• The standards were developed in consultation with a wide range of key stakeholders including the Associated of British Insurers and trade association representatives of the panel manufacturers.
• LPS standards can be downloaded via the REDBOOK LIVE website.
• There are two main LPS product grades:
• Grade EXT-A: Product that satisfies requirements of both fire resistance (LPS1208) and fire growth (LPS 1181 Part 1).
• Grade EXT-B: Product that satisfies fire growth (LPS 1181 Part 1) only.

Question 10

What is the difference between PIR and PUR isolation?

Answer 10

• The most significant difference between PIR foam and PUR foam is its resistance to high temperatures and fire. Whereas PUR foams start to degrade at temperatures of around 230-250°C, some PIR foams will only begin to degrade as temperatures rise towards 400°C.

Question 11

How would you identify a composite panel?

Answer 11

• Flat or micro-ribbed panels, usually 900-1200mm width, often (but not exclusively) laid horizontally.
• Top hat type vertical joint covers on side sheeting.
• Interlocking edges with concealed fixings.
• Shallow profiles with wide troughs and thinly ribbed liner panels.
• Spacer type primary fastenings. (These have a thread just below the head washer together with a separate thread to the main
  shank. The top thread supports the outer metal sheet and prevents crushing of the insulation.) It will be necessary to remove a
  primary faster for examination.

Question 12

What is the size of a standard brick? What is the standard size of a block?

Answer 12

Standard brick = 215mm x 102.5mm x 65mm

Standard block = 440mm x 215mm x 100mm

Question 13

Describe the typical build-up of a concrete floor slab.

Answer 13

• Subgrade / formation level: The earth that the slab is built upon – this is compacted to provide a uniform finish.
• Subbase: Hardcore which provides a working platform for construction. Could use MOT Type 1 / 2.
• Blinding layer: Closes off rough spots in the subbase.
• DPM: Stops moisture ingress, protects against sulphate attack. Polythene sheeting used (required as part of building regs).
• Concrete slab: Usually strengthened with steel rebar mesh - increases tensile strength.
• Wearing surface: Concrete screed / epoxy floor finish.

Question 14

What are the main types of portal frame structure?

Answer 14

Question 15

What is a composite, in-situ cast concrete floor?

Answer 15

Question 16

What is a hollow clay pot floor?

Answer 16

• Common during post war years from the 50s to early 80s.
• Originally used to construct fireproof floors in multi-storey buildings. Also found to form inner leaf of masonry cavity walls in 60s high rise buildings.
• Floor is composed of hollow clay pots that span the floor with spacer tiles that set the width of the concrete ribs. The hollow clay pots form permanent formwork as concrete is then poured over the spacer tiles to form the concrete ribs in situ. A structural topping is then poured on top of the entire hollow clay pot floor surface.
• There are two types of clay pot floor:

1. Ribbed slabs whereby the concrete topping contributes to the structural strength of the floor.
2. Ribbed slabs whereby the concrete topping does not contribute to the structural strength of the floor, simply a screed with reduced strength compared to concrete cast for structural ribs.

Question 17

Review the reverse - hollow clay pot floor

Answer 17

Question 18

Sketch a typical warm roof detail

Answer 18

Question 19

Draw a sketch of a cold roof detail

Answer 19

Question 20

Draw an inverted roof

Answer 20

Question 21

What are the advantages of an inverted roof?

Answer 21

• Waterproofing membrane is protected from UV damage, thermal stress and impact damage.
• Can be walked on safely – allows access to plant room on office buildings / useable space on residential terraces.

Question 22

What are the advantages and disadvantages of pre-cast concrete framed buildings?

Answer 22

Advantages:

• pre-cast = cast in factory and ready made components e.g. beams, columns
• advantages:
o Since precast is manufactured in a controlled casting environment it is easier to control the mix, placement, and curing
o Quality can be controlled and monitored much more easily
o Since a precaster can buy materials for multiple projects, quantity discounts can lower costs
o Weather is eliminated as a factor-you can cast in any weather and get the same results, which allows you to perfect mixes and methods
o Less labor is required and that labor can be less skilled
o On site, precast can be installed immediately, there is no waiting for it to gain strength and the modularity of precast products makes installation go quickly
o Repeatability-it’s easy to make many copies of the same precast product; by maximizing repetition, you can get plenty of value from a mold and a set-up

Disadvantages:

o Limited design flexibility
o Connections can be difficult
o Cranes are required
o Transportation problematic

Question 23

What are the advantages / disadvantages of in-situ cast concrete framed buildings?

Answer 23

• insitu = pouring concrete on site over formwork or in reinforcement
• Advantages:
o High level of strength means suitable for foundations and floors
o High degree of insulation – no gaps
o Versatile – can be moulded to suit
• Disadvantages
o Labour
o Weather a factor
o Quality control more variable

Question 24

How are cladding panels attached to a warehouse portal frame?

Answer 24

• Aluminium side rails span between the portal frame columns and are fixed in place by bolts or rivets.
• Cladding panels are then bolted / riveted into the side rails.

Question 25

Tell me about pre and post tensioned concrete

Answer 25

Pre-tension = steel first tensioned in a frame and concrete cast around
o Advantages = speed, done in factory, avoid expensive falseworks
• Post-tensioning = concrete cast around tendons in sleeve and then tightens as concrete develops sufficient hardening
o less concrete needed, faster, beams are bonded in grout and less likely to corrode

Question 26

What remedial options did you recommend for the asbestos warehouse roof in Bermondsey?

Answer 26

• Cleaning of the existing roof - closed box system.
• Removal and replacement.
• Oversheeting.

Question 27

What are the issues with composite cladding?

Answer 27

• Difficult to extinguish a fire as the combustible cores can catch fire and then are protected by the external panel skin. This means that fire fighters or sprinkler systems have little effect.
• This internal spread of fire means that the cladding can breach the buildings compartmentalisation such as concrete floors and spread to successive floors in the building.
• Lack of fire resistance of panel fixings can lead to sudden collapse or delamination of the panels, exposing the combustible insultation directly to the fire.
• When the plastic core burns this leads to toxic, dense black smoke.

Question 28

What certification would you look for to confirm that a composite panel did not pose a risk to a property? What other certification / technical details would you look for with regards to combustibility?

Answer 28

• In the UK building systems should be LPCB approved: the relevant standard is LPS 1181 Part 1 & 2 and LPS 1208.
• Complying with the criteria set out in the approved document B paragraphs 12.5 to 12.9.
• Ensuring the cladding system as a whole (rather than individual components) meets the criteria set out in BS 8414 Fire performance of external cladding systems, and satisfying the performance requirements set out in BR 135 Fire Performance of external thermal insulation for walls of multi-storey buildings.

Question 29

What is ACM cladding? Why is it notorious with regards to fire safety in buildings? What statutory instrument governs its’ use?

Answer 29

• Aluminium composite cladding.
• Aluminium composite cladding with a polyethylene core (Reynobond PE ACM) was though to be in part responsible for the Grenfell Tower Fire on 14 June 2017.
• Approved Document B - ‘The external envelope of a building should not contribute to undue fire spread from one part of a building to another part. This intention can be met by constructing external walls so that both of the following are satisfied. a. The risk of ignition by an external source to the outside surface of the building and spread of fire over the outside surface is restricted. b. The materials used to construct external walls, and attachments to them, and how they are assembled do not contribute to the rate of fire spread up the outside of the building.’