SCOTTISH EXECUTIVE

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Building Regulations: Technical Standards

ROOFS AND ROOFLIGHTS

(D6.7) The requirements of D6.7 will be met by -

a. a roof covering or rooflight of a designation or description shown in the following table in relation to its distance from any boundary -

Table to (D6.7): Minimum boundary distances for roof coverings and rooflights

this table -
‘Yes’ means acceptable
‘No’ means not acceptable

Notes:

[1] For this purpose glass (wired or unwired) not less than 4mm thick can be regarded as having an AA designation. Thinner glass is subject to a minimum boundary distance of 6m unless it is over a substantially open area such as a loading bay or covered way. For designation refer to BS476: Part 3: 1958.

[2] For this purpose thermoplastic sheet as described in (E6.1)b.1. exceptions A, B, C and D of at least Class 1 when tested in accordance with BS476: Part 7: 1971 or 1987 can be regarded as having an AA designation.

[3] Acceptable only in the buildings listed in Note [4], in a part of the roof not more than 3m2 in area and at least 1.5m from any similar part, the remainder of the roof being of an acceptable designation related to its boundary distance.

[4] Acceptable only in -

a. a detached house; or

b. a building of purpose group 2, above a compartment of not more than 1500m3.

or

b. a roof covering or rooflight of plastics materials which does not satisfy the provision of para-graph a. above but is not less than 6m from any boundary and complies with (E6.1)b.1.i.-ii., except -

the boundary distance restriction does not apply to a plastics material in an open canopy or over a substantially open area such as a loading bay or in the roof of a detached swimming pool enclosure.

Note: A roof covering or rooflight which is exposed within the building will be subject also to the requirements of E6.1.

SINGLE STOREY BUILDING, OR COMPARTMENT OF SINGLE STOREY BUILDING, OF PURPOSE GROUP 4 (SHOPS AND COMMERCIAL)

(D7.2) The requirements of D7.2 will be met by a natural system of automatic smoke exhaust where

a. The height from the floor to the roof vent must not be less than 4.5m and not more than 13.5m.

b. The underside of the roof must be divided into not less than 2 smoke reservoirs which must be not more than 2000 m2 each, in plan area.

c. smoke reservoirs must be separated by suitable fixed smoke curtains:

i. The distance measured at right angles to the smoke curtains must not be more than 60m.

ii. A smoke reservoir must be at least 1.5m deep measured from the lowest point of the underside of the roof, or measured from the underside of high level plant or ductwork within the smoke reservoir in a building where there is no suspended ceiling, other than an openwork ceiling below the smoke reservoir; or in a building with an imperforate suspended ceiling, the smoke curtain must project from the underside of the roof to at least 1.5m below the ceiling.

iii. Where there is an openwork ceiling the free area of the ceiling must not be less than 25% of the plan area of the smoke reservoir, or 1.4 times the free area of the roof mounted fire ventilator above or 3.0 times this area when the height from floor to roof vent is more than 12m, whichever free area is the greater, and be evenly distributed.

iv. Where the smoke reservoir includes a suspended ceiling, other than an openwork ceiling, the free area of the ventilator opening in the suspended ceiling, or any ventilator grille in the ceiling, must not be less than 1.4 times that of the roof mounted fire ventilator above in the case of a ventilator opening or 2.0 times for any ventilator grille. Where the height from floor to roof vent is more than 12m the open ventilator must be 3.0 times that of the fire ventilator above or in the case of any ventilator grille 3.5 times.

v. No service pipe or duct must reduce the free area of the roof vent or any ceiling opening. Any duct which passes through a smoke curtain must have the same fire resistance as the smoke curtain.

vi. The structure which supports the smoke curtain must have the same fire resistance as the smoke curtain.

vii Fixed smoke curtains should comply with BS7346: Part 3: 1990.

d. Each smoke reservoir must be provided with one or more suitable roof ventilators activated by a thermal link, and a roof ventilator in every smoke reservoir must, via a frangible bulb activated valve or fusible plug, control a centrally positioned roof ventilator in another smoke reservoir to provide inlet air. The roof ventilator must be activated at the same time as the sprinkler installation. In addition there must be a manual override facility for the use of the fire brigade, to open the roof ventilation system in each smoke reservoir. Where there is more than 1 roof ventilator serving a smoke reservoir they should be evenly spaced out. Roof ventilators should comply with BS7346: Part 1: 1990.

e. The vent area for each smoke reservoir is as shown in the table to (D7.2).

Table to (D7.2)

Note:

1. To centre line of roof vent if the ventilator is other than horizontal.

2. A fresh air inlet is also considered to be provided by an open emergency exit door.

ENCLOSED SHOPPING CENTRES WITH MALLS

(D7.5) The requirements of D7.5 will be met by a mechanical system of automatic smoke exhaust where:

a. the design is based on the principles of the Building Research Establishment Report, BR368, "Design Methodologies for Smoke and Heat Exhaust Ventilation" (BRE, 1999);

b. smoke is only allowed to flow into one reservoir;

c. if a perforated or otherwise partly open ceiling is provided below each reservoir it must have an open area of at least 25% of its total area, the open area being distributed in such a manner as to prevent an unbalanced air flow to the reservoir;

d. the fans must be fitted at their outlets with shutters (where appropriate), provided for weather protection purposes which must open on the activation of a fan or fans;

e. the elements of the smoke exhaust system (including fans, ducts and reservoir screens), must be based on the calculated design temperatures, but rated to a minimum of 300°C for 30 minutes, in accordance with BS7346 1990;

f. a frontage having a fire resistance not less than 30 minutes for integrity only is provided between a shop and the mall adjacent to any part of the mall not protected by a reservoir;

g. there must be spare fan capacity in each smoke reservoir, equivalent to the largest single fan, which will operate automatically upon the failure of one of the fans, or which runs concurrently with the fans;

h. the system in the mall must operate upon operation of the sprinklers in the mall or a shop, or detection of smoke in the mall, or (following a suitable grace period, see E10.2) upon detection in a shop;

i. the system in a shop must operate upon operation of the sprinklers in the shop, or the operation of more than one smoke detector (or one smoke detector with a grace period of four minutes) in the shop;

j. any ducts forming part of the smoke exhaust system which pass through a separating or compartment wall or floor (excluding the roof) and on through the neighbouring compartment(s), must have the same fire resistance rating as the wall or floor through which they penetrate;

k. any ducts forming part of the smoke exhaust system, where they are immersed or exposed to a smoke layer in a smoke reservoir, must have the same temperature-time performance rating as the fans drawing smoky gases through those ducts;

l. the structure supporting the fans must have a period of fire resistance of not less than 60 minutes for load bearing capacity and integrity when both sides are exposed;

m. simple manual overriding controls of all smoke exhaust and air input systems (both in the mall and in shops with their own systems) must be provided at the main control panel within the fire control room; and

n. smoke exhaust system must be independently connected to its power source by mineral insulated cables or by cables which meet the requirements of Code A category as specified in BS6387: 1994 or by cables protected from damage to an equal standard.

o. an automatically switched standby power supply is connected to all mall and shop smoke exhaust fans capable of simultaneously operating :

i) in the event of a fire in the mall the fans in any two adjoining reservoirs; or

ii) in the event of a fire in a shop with fans, the fans in the shop and any adjoining reservoirs.

 

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