Design and Specification

Question 1

What are the U-Values for an existing and new roof?

Answer 1

In Part L2B, the threshold for a refurbished roof is between 0.35 and a new flat roof is 0.18.
For a new pitched roof, a u value is 0.16-0.18 dependent whether the insulation is on the ceiling (0.16) or between rafters (0.18)

Question 2

Talk me through how you specified the new roof lights?

Answer 2

I determined the size of the aperture and the upstand detail. Was the rooflight going to be flat or would we install a dome.

Question 3

What would you consider when specifying Roof Lights?

Answer 3

1) Part A - Structure - To install a rooflight, the roof structure will generally need to be altered to create the opening. The roof will have to be able to carry the load (weight) of the new rooflight. If the roof can not do this then it will need to be strengthened.
2) Part L - Energy Efficiency - Any rooflight that is installed will need to prove that it has sufficient insulation against heat loss i.e. is energy efficient.
Part B - Fire Safety - If the rooflight is in close proximity to a boundary, the fire performance of the rooflight will need to be considered.

Question 4

What does Part L say in relation to Rooflights?

Answer 4

Part L provides a table showing the building type as well as the percentage of windows/doors that can be used on an exposed wall. In the same table is also makes reference to rooflights as a percentage of the area of a roof. 20% apprears to be the maximum opening areas in an extension for a rooflight.

Question 5

What are some of the standards/code of practice which govern the industry?

Answer 5

British Standards (BS) ,

International Standard (ISO) – Quality management standards,

NHBC (National House Building Council) Standards.

BBA (British Board of Agrement)

Question 6

How would you go about specifying a new roof?

Answer 6

1) Clients Objectives
2) Carry out research and site inspections
3) Find out more information – site surveys, trial holes etc.
4) Statutory Compliance
5) Approved installer/manufacturers guarantee/Buildability and suitability
6) Design details

Question 7

What did you specify for a roof deck at Weald of Kent Science Block?

Answer 7

I specified 18mm WBP Ply fixed to the joists with staggered joints with 3mm between joints. Insulation on roof deck – 130mm to achieve 0.18 u value rating for roof using tapered insulation. The roof structure was designed by a Structural Engineer and this was formed from 450mm centres C24 timber joists.

Question 8

What did you specify for Weald of Kent Roof Replacement?

Answer 8

I specified a 3 layer mineral felt system with 130mm tapered insulation to meet Part L. This required for the flat roof to have a minimum u-value between 018-0.35. This was achieved by installing 120mm tapered insulation. Timbers were installed and unexposed edge to keep insulation in place i.e. perimeter and internal gutters. Metal lined Vapour Control Layer installed to warm side of insulation.

Question 9

You mentioned you requested a contractor to replace a flashing detail to RBS Bournemouth. What mortar did you specify? What flashing detail was this for? Do you know the recommended flashing heights?

Answer 9

Flashing was the stepped flashing above a soaker and this should be dressed up 75mm from the tiles, tucked in by 25mm and lapped by no less than 100mm.

Question 10

How far should lead flashing be set into a chase?

Answer 10

25mm.

Question 11

What is the statutory guidance used when replacing roofs?

Answer 11

Under Part L it states that a Major Renovation is considered to be being undertaken where more than 25% of the surface area of the building envelope undergoes renovation.

The replacement of an existing layer means either stripping down elements to the structure or replacing the waterproof membrane on a flat roof.

Question 12

What roof repairs did you recommend and why did you recommend them at Merstham?

Answer 12

At Merstham Primary School, the school had damp patches on the lathe and plaster ceilings. I traced the cause to the base of the pitch of the roofs into the lead valleys. I recommended the replacement of the section of lead valley to provide the client for longevity as accessing the valley was quite difficult and could be quite disruptive if the school was occupied. The code of lead used was 4 as recommended by the lead sheet association.

Question 13

How did you price the costs for roof repairs and prepare budgets?

Answer 13

I use rates from previous projects and assessed the complexities and access arrangements to determine whether the rates need be increased and apply these to the square meterage of the roof.

Question 14

When specifying the roof for the school in Tonbridge, what was the build up?

Answer 14

The deck was concrete, so the deck was primed, VCL installed, aluminium foil tape compatible with VCL, Insultation, 3 layer mineral felt membrane (underlay, primer and torch on felt).

Question 15

How did you address the ponding on the roof?

Answer 15

Check you drains, remove any blockages using a specialist contractor.

Question 16

How would you calculate the number of outlets required on the roof?

Answer 16

Part H provides details on drainage. Notes: Area (m2) = length (m) x width (m). Total flow rate = rainfall intensity x area (m2). Regardless of the size of roof area, there must always be a minimum of two outlets. A civils engineer should be consulted when designing a new roof.

Question 17

When designing the toilet specification, what did you have to consider?

Answer 17

Size and height of WC pans for each Key Stage. KS1 have lower pans, 355mm and KS2 400mm. The number of toilet provisions required were 1 for every 20 pupils and 1 for every 25 staff as per BB 103 (Area guidelines for mainstream schools). All works in schools undertaken in accordance with BB103.

Question 18

What other Building Bulletins have you used?

Answer 18

• BB101 – Ventilation, indoor air quality and thermal comfort in Schools - Suggestion for clean air in classrooms to increase oxygen levels and reduce CO2 levels.
• BB103 - Area Guidelines for Mainstream Schools - Guidance on classroom sizes.
• Output Specification for Schools.
• The School Premises Regulations 2012
• BS 8300 - gives practical guidance on how the requirements of Part M can be incorporated into the built environment.
• BS 6465 - Covers space for toilet design and provision of welfare

Question 19

What was the build-up for the new car park to St Marys in Carshalton?

Answer 19

The build-up required scraping back the binding course to the base. Installing new subbase and base to extension of car park. MOT 1 Hardcore and 70mm base course, 50mm binder and 30mm surface course.

Question 20

What brickwork repairs did you specify for Gainsborough primary school?

Answer 20

Yellow and red stock bricks. Samples were requested as part of the specification using 1m x 1m sample boards with the specified mortar repairs. These allowed the quality to be checked of the workmanship.

Question 21

What mortar mix did you specify?

Answer 21

3 part builders sand and 1 part NHL 3.5.

Question 22

Do you know the types of lime used in mortar?

Answer 22

Natural hydraulic lime (powder form) Non-hydraulic lime made from pure limestone and tends to be in form of a putty (sets slower).

Question 23

How would you specify render on a project?

Answer 23

Render should be applied in two coats with a thickness of at least 20mm. It should have a scraped or textured finish. The strength of the mortar should be compatible with the strength of the bricks or blocks. The joints in the wall is to be rendered should be scraped back by 10mm. The mix for render is one part cement, one part lime and six parts sharp sand. Guidance is provided in BS 5262. Premixed renders should be used in accordance with manufacturer’s instructions.

Question 24

Can you name some alternative products to render?

Answer 24

Cork render. It is a readily available material. Lightweight, flexible and breathable. It is environmentally friendly, it absorbs carbon. Plus is comes with a 15 year guarantee and does not crack like render.

Question 25

When specifying the external tiling repairs to the pathway, what factors did you consider in you design? What is a Pendulum Test Value?

Answer 25

Slip resistance, foot traffic, is the area level? Will vehicles ever be required to drive over the new paving. Determine what subbase is required and thickness of the tile. A pendulum test value is a value to determine slip resistance. A value of 36 is required on dry level floors as advised by the HSE. Each increase of degree will cause the PTV to rise by 1.75 and this value is rounded up.

Question 26

What factors did you consider when designing the replacement cladding at the fire station? Talk me through the specification? How tall was the building?

Answer 26

Non-combustible cladding must be used 6 or more stories or 18 metres in height (whatever is reached first.

What are the considerations for cladding:

1) Is there is a significant amount of cladding on the building (deemed as approximately one quarter of the whole elevation)?
2) Is there are ACM, MCM or HPL panels on the building?
3) Are there balconies which stack vertically above each other and either both the balustrades and decking are constructed with combustible materials (e.g. timber), is the decking is constructed with combustible materials and the balconies are directly linked by combustible materials?

Question 27

What is the definition of Preliminaries?

Answer 27

Preliminaries address and communicate to the contractor items that are not directly related to any measured works. The information provided will enable the contractor to ascertain his or her price for, among other things, management of the building project, site establishment, security, safety, environmental protection and common user mechanical plant, as well as the employer’s completion and post-completion requirements.

Question 28

What is the difference between preliminaries and schedule of works?

Answer 28

They are separate to the schedule of works. The are the costs that are required to support the safe carrying out of works. This may include plant/site staff/ parking/ management/ access / administration costs / insurances/ bonds.

Question 29

Can you explain the difference between the prelims document and prelims costs?

Answer 29

Provides a description of a project that allows the contractor to assess costs which are separate to the package of works. They include:

• Summary - description of project and parties.
• Pre-construction information
• Planning conditions
• Party wall requirements

Prelims Costs: Prelims are the cost of the site-specific overheads of any given project. They are the costs that are directly related to the running of the project.

• Administration costs
• Plant
• Site staff
• Facilities
• Parking
• Licences

Question 30

What is the NBS specification?

Answer 30

National Building Specification. NBS Chorus is the latest edition - Libraries of pre-written specification clauses, guidance and manufacturer product information.

Question 31

Can you name the Different RIBA Stages?

Answer 31

Stages 0-7. (Strategic Definition - 0, Preparation and Briefing - 1, Concept Design - 2, Spatial Coordination - 3, Technical Design – 4, Manufacturing and Construction - 5, Handover – 6, Use -7.

Question 32

What code of practice governs design and specification for Fire?

Answer 32

Ones that are notable are BS9999/Approved document B - Both provide guidance on fire design.

Question 33

Whar are recommnedations on travel distances in Approved Document B?

Answer 33

Part B - Travel distances - Depends on the number of exits and what floor you are on. 18m single exit, multiple exits 45m.

Question 34

What is the recommendation on the width of staircases in Part B?

Answer 34

Width of staircase is dependent on the number of people (occupants) using the stairs and it goes up in 60 - 750mm, 110-850, 220-1050 and then 220+ requires 5mm per person

Question 35

What is the recommendation on the number of exits in Approved Document B?

Answer 35

The number of exits is dependant of the number of people using the building 60-1, 600-2, >600-3.

Question 36

What guidance does approved document K provide in relation to handrails?

Answer 36

Part K requires stairs wider than 2m to have a central handrail.

The height of the handrails have to be installed between 900-1100mm above FFL.