McDowell’s criticism of Searle’s account

7.6.4 This can be achieved through additional boarding or a wet finish. When boarding, the ceiling should be underdrawn with chicken wire and then battened out and boarded. If providing a wet finish, the ceiling should be underdrawn with metal lathing to prevent the plaster from becoming detached.

Fig 7.18: Upgrading with additional boarding

Diagram 1

Fig 7.19: Upgrading with additional wet plaster finish

7.6.5 Care should be taken where chimneys and gas flue blocks are present in the converted loft space. A minimum separation of 40mm should be allowed between the outer surface of the chimney and structural timbers such as floor joists and roof trusses. This dimension can be reduced to 25mm for gas flue blocks.

7.6.6 Any new steelwork provided in the loft conversion should achieve 30-minute fire resistance. This can be achieved through intumescent paint or by being encased in plasterboard ‘boxing’.

7.7 ADDITIONAL INFORMATION

7.7.1 Where an air circulation system is present in the dwelling the following guidance should be met to avoid the possibility of the system allowing smoke or fire to spread into the protected stairway:

• Transfer grilles should not be fitted in any wall, door or ceiling enclosed in the protected stair.

• Any duct passing through the enclosure to a protected stair or entrance hall should be of rigid steel construction and all joints between the ductwork and the enclosure should be fire-stopped.

• Ventilation ducts supplying or extracting air directly to or from the protected stair should not serve other areas as well.

• Any system of mechanical ventilation which recirculates air and which serves both the stair and other areas should be designed to shut down on the detection of smoke within the system.

• A room thermostat for a deducted warm air heating system should be mounted in the living room, at a height between 1370mm and 1830mm, and its maximum setting should not exceed 27°C.

7.7.2 For dwellings of three or more storeys, 30-minute fire-resistant loft hatches/roof void access panels may be required. Please see the following guidance:

• Loft hatches formed within the protected stair need not be fire-resisting.

• Where the stairs provide access to a single habitable room a loft hatch/roof void access panel formed within the room need not be fire-resisting.

• Where the stairs provide access to more than one habitable room, loft hatches/roof void access panels formed within the habitable rooms should achieve 30-minute fire resistance.

En suite

Bedroom

Room in roof - single room Room in roof - more than one room

Standard stud partition - typically 12.5mm plasterboard and quilt insulation Standard loft

hatch or roof void access panel

Fire resisting loft hatch or roof void access

Panel - secured

1. Rigid board (PUR/PIR)

PUR insulation products are made by reacting a liquid polyol component with a liquid polymeric isocyanate, Methylene Diphenyl di-Isocyanate (MDI), component in the presence of a blowing agent and other additives.

The blowing agent evaporates during this exothermic reaction and a rigid closed-cell low-density insulation product is created.

PIR differs from PUR in that it is produced using an excess of the MDI component. The resultant PIR insulation products exhibit increased fire performance and reduced combustibility and higher working temperature limits.

2. Extruded polystyrene

Extruded polystyrene is produced from structured, closed-cell foam. It is cured for 90 days, which means that there will be no further movement of the foam, ensuring that it will retain its final structural and thermal values.

3. Mineral wool (glass/stone)

Mineral wool insulation is available in rolls or batts/

slabs and is man-made from a range of materials including recycled glass and vitreous (silicate) fibres.

8.1 There are a wide variety of insulation materials on the market being produced by numerous manufacturers. Below are the seven main types

of insulation available, with a brief description of the generic product.

Fig 8.2 Fig 8.1

4. Multi-foil

Multi-foil insulation is made up of multi-layered reflective films, only a few microns thick. These layers, which are separated by wadding and foam etc., are sewn together to form a thin insulating blanket.

5. Expanded polystyrene

Expanded polystyrene is produced by expansion of beads containing pentane as a blowing agent.

The expanded beads are then re-expanded in a mould to produce large blocks from which board products are cut or shaped and mouldings manufactured; these are used in, for example, suspended beam and concrete floors.

Grey, low lambda products have a 20 per cent improved thermal performance over traditional white EPS.

6. In situ applied PUR/PIR

In-situ applied PUR/PIR insulation products are made from a similar reaction to rigid PUR/PIR board but are applied by approved installers directly to the surface to be insulated. A rigid closed-cell, low-density insulation product is created in situ.

7. Phenolic foams

Phenolic foams offer a range of thermal conductivity performance. The closed-cell type offers the lowest thermal conductivity available from any insulation material resulting from a closed-cell structure, extremely small cell diameter and low thermal conductivity gas permanently encapsulated in cells.

Phenolic foam can be up to 50 per cent more thermally efficient than other common insulation materials; this higher thermal efficiency allows reduced insulation thicknesses to be used, thereby saving valuable space.

Fig 8.4

Fig 8.5

Fig 8.6

Fig 8.7

8.2 A selection of the above products can be purchased with plasterboard laminated onto them. This is known as ‘plasterboard thermal laminate’. Plasterboards can be laminated with expanded polystyrene, extruded polystyrene and phenolic foam insulants to provide thermal insulation and a plasterboard lining in one fixing operation to the underside of rafters. Certain plasterboard thermal laminates also contain a vapour check to further maximise their usage in loft conversion projects.

8.3 As well as the above insulation products, many others are available and they are listed below:

• Expanded clay aggregate.

• Cellulose loose fill or batts.

• Aerogel.

• Perlite beads.

• Cork board.

• Hemp batts.

• Extruded polyethylene.

• Vacuum insulated panel (VIP).

• Sheep's wool batts and rolls.

• Exfoliated vermiculite.

• Strawboard.

• Wood fibreboard.

• Flax batts and rolls.

8.4 MULTI-FOIL INSULATION

Introduction

8.4.1 Multi-foil insulation systems arrived in the mid 1990s when the product started to be used for insulating loft conversions. While the claims made for very high levels of insulation were almost universally greeted with scepticism within the profession, many did ultimately choose to accept multi-foil insulation systems on the basis of ‘certification’ provided by a reputable testing organisation. Over time, however, the testing that formed the basis of this original acceptance has been more widely scrutinised,