Construction Technology & Environmental Services Flashcards
What impact do the Building Regulations and British Standards have on the design, construction and refurbishment of buildings?
- The building regulations help ensure that new buildings, conversions, renovations and extensions (domestic or commercial) are going to be safe, healthy and high-performing.
- BSI defines a standard as ‘something that is generally accepted’. British Standard (BS) publications are technical specifications or practices that can be used as guidance for the production of a product, carrying out a process or providing a service.
Can you explain some of the recent regulatory changes to the Building Regulations or British Standards?
- Updates to Part F and Part L in June 2022.
- Part F – Increased ventilation (to balance changes to Part L).
- Part L – Uplift in U-values, requirement for continuous insulation (no gaps).
- Part O – Overheating (limiting solar gains and ability to quickly remove excess heat).
- Part S – Infrastructure for charging electric vehicles.
- Part T – Toilets.
What are G-values?
- A measure of the amount of heat let into a building through its windows.
- Measured between 0 and 1 (0 is nothing, 1 is everything).
What are U-values?
U-values measure the amount of heat loss / gain through a building element.
U-value = 1 / the sum of all R-values (thermal resistance) of the individual layers making up a building element (a lower U-value means greater resistance).
What are R-values?
R-values measure thermal resistance (a higher R-value means greater resistance).
What are L-values?
L-values measure how airtight windows are (the lower the better).
What British Standards are you aware of that influence the ways in which buildings are constructed?
- BS 8102:22 Code of Practice for Protection of Below Ground Structures Against Water Ingress.
- BS 9999 (fire safety in the design, management and use of buildings).
- BS 8215 (installation of damp proof courses in masonry construction).
- BS 3921 (compressive strength of bricks).
Can you give some examples of different types of construction?
- Foundations – strip, raft, pad, pile.
- Floors – suspended timber, suspended concrete, block and beam, ground bearing concrete slab
- Walls – solid, cavity, framed.
- Roofs – flat (warm/cold/inverted), pitched (dual/mono pitch, hipped).
What are the different types of foundations commonly used?
- Strip foundations – low-rise residential buildings.
- Pad foundations – heavy concentrated loads (columns sit on top of pad).
- Raft foundations – poor soils, used to spread load where individual column loads are heavy in poor soil conditions.
- Piled foundations – Low bearing capacity sub-soils – requirement to transmit load to low level in ground. Typically used for large or high-rise buildings.
What are the different types of piling and when would you use them?
Bored Piles (Replacement Piles)
- A hole is bored in the ground using a piling rig with flight auger. The void is then filled with reinforcement if required and concrete (either pre-cast or in-situ).
- Used in cohesive soils such as clay and where vibration and noise are to be kept to a minimum.
Precast Piles (Displacement Piles)
- Precast concrete piles are driven into the ground using a piling rig with a drop hammer, displacing the subsoil.
- Used in non-cohesive (sandy) soils and where vibration and noise is not an issue.
Secant Piles
- A permanent structural wall is formed of interlocking bored piles.
- Primarily female piles are bored and cast with spaces in between for the boring and casting of secondary male piles.
Sheet Piling
- Sheet piling can be used as temporary support in excavations but also to form permanent retaining walls.
- The sheet piles have interlocking joints and are available in a range of sizes and strengths, up to a typical maximum length of 18m.
How would you establish the load bearing walls within a property?
- Check to see if wall is solid masonry or lightweight partitioning.
- Check direction of joists (if perpendicular to walls, likely to be load beading).
- Check to see if there is contact between the tops of walls and ceiling joists.
- Central / spine walls are likely to be load bearing.
- Check positioning of walls in relation to upper floor walls and roof timbers e.g. struts that may be supported by load bearing walls.
What are the potential implications of using two different (abutting) floor constructions?
- Reduced ventilation to suspended timber floors if concrete floor is added.
- Increased likelihood of condensation within sub floor and subsequent rotting of timbers.
- Ducting should be provided within concrete floor to maintain cross ventilation.
- Using a combination of suspended concrete and timber floors would maintain provision for cross ventilation.
Can you explain the build-up to the external render system specified for 86 Victoria Street?
3no. coat system (NHL 3.5)
- Scratch coat (applied up to 10mm, flattened and keyed/scratched)
- Float coat (rubbed up with a normal float and finished with a devil float to provide a key for the top coat)
- Top / finishing coat
Was there any requirement for upgrading of the thermal performance of the external walls when re-rendering?
- Alterations were made internally to external walls to meet a minimum U-value of 0.26.
- Required when over 25% of the surface area of the external building envelope is renovated – classed as a major renovation.
What are the benefits of a silicone render and when would use specify its use?
- Highly durable.
- Low maintenance.
- Provides a level of breathability.
What are the different types of lime and when would you use them?
- Hydraulic lime – for use in exposed locations – sets fast, durable, less flexible and permeable than non-hydraulic lime.
- Non-hydraulic lime – for use in less exposed locations – sets slowly, less durable and more flexible and permeable than hydraulic lime.
What are the different grades of natural hydraulic lime (NHL)?
- NHL 2 – Internal plastering or pointing up soft masonry.
- NHL 3.5 – General bedding and pointing mortars.
- NHL 5 – Limecrete floors and exposed areas.
What is a castellated beam and when would you use one?
- A castellated beam is a beam that has a regular and repeating pattern of hexagonal or circular holes.
- The provide a high strength to weight ratio – deeper beams using less steel.
How is lateral restraint provided within roofs?
- Installing metal straps across rafters (minimum 3), hooked over internal blockwork leaf. Provides lateral restraint to gable walls.
- Ensure ceiling joists / rafter ties (resists roof spread) are fixed to rafter ends and collar ties (resists rafter separation) are installed, spanning between rafters.
What are the telltale signs of roof spread to a traditional purlin and rafter roof and what are the general causes?
- Sagging of the ridge.
- Pushing out of brickwork and wallplate to the top of external walls.
- Separation of inner walls from external walls.
- Generally caused by poor design / triangulation of roof structure or overloading of the roof (e.g. replacing slates with concrete tiles)
What was the roof structure construction of the house 21 The Horseshoe, York?
Timber purlin and rafter construction with a slate finish.
Can you explain the differences between a kingpost and queen post truss roof?
Queen post uses two supporting posts and can span longer distances than king post (one central supporting post)
Can you advise of the implications of having 2 different ground floor types in the same building?
Reduced provision for ventilation (potentially cutting off cross ventilation).
How can cross ventilation to suspended floors be maintained when solid floors are introduced?
Ensure ducting is included within new concrete floors, providing a clear passage from the front to rear of the property.
What are the requirements for sub-floor ventilation?
NHBC requirement of air bricks within 450mm of each end of a wall at no more than 2m centres.
A minimum void of 150mm should be provided below suspended timber or concrete walls.
How do you maintain solid walls to preclude damp?
- Regular maintenance of pointing / render.
- Regular pruning of nearby vegetation to prevent contact with walls.
- Ensure ground levels are a minimum of 150mm below DPC.
- Avoid using impervious (cementitious materials).
Can you explain the key features of a 1930s house please?
- Often semi-detached.
- Hipped roof with gable projection or flat roof to front bay.
- Bay windows (often at GF and FF).
- Archway to front entrance, with door set back.
How did you establish the imposed loads on the walls?
Took measurements of walls and multiplied the areas by the loads of different materials.
How would you identify a solid wall?
- Use of headers within brick bonds.
- Thickness of wall (typically 9 inches for solid brick walls).
Name some bonds of brickwork use for solid walls.
- Flemish bond.
- English bond.
- Garden wall bond.
- English garden wall bond.
- Rat trap bond.
How would you identify a cavity wall?
- Stretcher bond brickwork.
- Features within walls such as weep holes.
- Snapped headers sometimes used to give a more traditional look.
What are the nominal sizes of a brick and block?
- Brick – 215 x 102.5 x 65mm
- Block – 215 x 100 x 440mm
Can you describe the construction of a typical steel portal frame?
- Columns fixed to pad with base plate
- Rafters
- Purlins
- Eaves and ridge/apex haunch
- Longitudinal and diagonal bracing
- Cladding to walls and roof
Can you describe the construction of a typical internal stud partition wall?
- Timber top plate and sole plate
- Timber studs with noggins in between
- Insulation as required between studs
- Plasterboard
- Skim finish
Can you describe the construction of a typical suspended timber ground floor?
- Oversite.
- Sleeper walls.
- Wall plate to the top of sleeper walls with a DPC between the wall plate and brickwork.
- Floor joist.
- Floorboards / covering.
Why did you recommend that collar ties be installed within the top one third of the rafters at 21 The Horseshoe?
The lower the height of the ties, the less restraint to the top of the rafters.
At what position should rafter ties be installed?
Within the bottom third of a roof structure to ensure adequate restraint to spreading of rafters.
Can you please explain the different between built-up and composite roofing systems?
- Built-up or double skin systems are assembled on site and are made up of a number of components, including liner sheet, vapour control layer, insulation and top sheet. Spacer bars are installed at regular intervals, which the top sheets are mechanically fixed to.
- Composite roofing systems are pre-assembled and consist of two metal skins bonded to an insulating core.
How can you ascertain whether a metal roofing or cladding system is built-up or composite?
- By looking to the underside of top sheets to see if the insulation is a rigid or a wool type material.
- Reviewing any identification markings on panels.
- By tapping or pressing on the panels – hollow sound and some ‘give’ to ridges indicates a built-up system.
- Gaps between ridge of sheet and insulation if built-up system.
- Reviewing any specifications.
Can you describe where 30min and 1hr fire resistance may be required within a building?
- 60 minutes between individual dwellings
- 30 minutes to means of escape routes
What are the nominal wall tie spacings?
- 450mm vertically.
- 900mm horizontally.
- Within 225mm horizontally of an opening.
- Within 225mm horizontally (parallel to the top of a wall).
- No more than 300 vertically to the top of gable walls.
- No more than 300 vertically around openings.
What are the nominal spacings for lintels and weep holes?
At least two weep holes per opening, not more than 450mm apart.
At 5 Calcaria Court you recommended that the existing coping stones were replaced. Why did you recommend that larger stones were provided and what is the purpose of a drip detail?
- The existing coping stones did not project by a sufficient amount. NHBC standards recommend a minimum projection of 45mm for copings to parapet walls to balconies.
- The projection can be less for metal or GRP copings with performed drip details, provided the coping drains away from the wall.
- A drip detail prevents water backtracking underneath the coping stones and should also be provided no less than 30mm away from the external face of the wall.
What is the difference between copings and cappings?
- Coping - Construction that protects the top of a wall, balustrade, or parapet and sheds rainwater clear of the surfaces beneath.
- Capping - Construction that protects the top of a wall, but does not shed rainwater clear of the surfaces of the wall beneath.
What are some of the common failures of coping installations?
- No damp proof course (DPC) provided below copings
- DPCs that are provided are unsupported and/or insufficient width to cover across the whole parapet
- Cavity trays beneath coping non-existent or poorly installed
- No weep holes
- Poor pointing between coping
- Pressed metal copings used, with over-reliance on mastic or fixings with no gaskets. Often installed without any DPC below
- Non-proprietary systems being used without third party accreditation
