Requirement for Space Separation between Buildings - Coursework Example

Introduction Fire safety and protection in buildings is one of the key aspects that must be taken into consideration when designing a building. In fact, the aspect of fire safety and protection is among the prescriptive design requirements in building regulations. These regulations provide building design approaches that ensure that acceptable fire safety and protection levels are achieved, and it is the responsibility of those conducting building work to adhere to the requirements of these building regulations. This paper discusses the British building regulations, particularly those related to, among others, the allowable protected areas, space separation, and construction of external wall. These regulations are outlined in the Approved Document B (ADB, BS9999, BR 187 etc). According to Read, FRICS, & MSFSE (1991), this document is meant to outline the requirements for various common building situations, and how to comply with those requirements. It is, however, important to note that the solutions outlined in the Approved Document are not obligatory and one can use other solutions to meet the relevant building requirements. Requirement for Space Separation and External Fire spread The requirements for external fire spread as outlined in part B4 of the Building Regulations, as per the standard guidance for England and Wales (ADB, BS9999, BR 187 etc) include the following: i. The external walls of the building shall have sufficient resistance to stop the fire from spreading to other buildings and over the walls, putting into consideration the position, use, and height of the building (HM Government, 2010). ii. The roof shall have enough resistance to stop the fire from spreading from one building to another and over the roof, also putting into consideration the position, use, and height of the building (HM Government, 2010). External walls Part B4 of the ADB outlines the requirements for external walls of a building in order to have enough capacity to stop the fire from spreading to adjacent buildings. These requirements are very much related to the requirements for space separation which delineate the amount of protected area on the wall (HM Government, 2010). The amount of unprotected area on the wall is dependent on the distance of the wall from the relevant boundary. This implies that all or part of the wall can have no resistance to fire except for parts that are load bearing (HM Government, 2010). The relevant duration of fire resistance is dictated by size, use, and height of the building. However, if the distance between the wall and the relevant boundary is at least 1000mm, a reduced fire resistance standard is allowed and the wall only requires fire resistance from outside (Stationery Office, 2010). Requirements are also stipulated to limit fire susceptibility of the external walls of buildings that are less than 1000mm from the relevant boundary. This is meant to minimize the susceptibility of surface to combustion from external sources as well as minimize the spread of fire up the external wall. In order to minimize the chances of fire spreading from a building to another adjacent building beyond the relevant boundary and vice versa, the following requirements of part B4 of the Approved Document should be met (HM Government, 2010): The external walls of the building should be built such that the risk of fires from generated from external sources and the spread of fires on the surfaces of the walls is not limited by making provision for them to have low rates of heat release. The overall size of the unprotected areas in the inside of the building should be limited in order to limit the amount of thermal radiation that can be transmitted through the wall, taking into consideration the distance between the relevant boundary and the wall. The roof should be constructed in such a way that the chances of fire spreading from an external source are minimized. According to the ADB, separation between buildings and the construction of external walls to avoid the external spread of fire are very much related. The possibly of spreading of fire between buildings depend on the following situations: Separation distance between buildings Fire protection provided by the facing sides of the buildings Intensity and size of fire in the concerned building Risk presented to people in other adjacent buildings Space Separation Requirements on space separation stipulate the extent of unprotected areas required on the walls of buildings that will not provide sufficient protection against the fire spread to adjacent buildings. These provisions are based on the following assumptions: 1. That the requirements enable a logical space separation standard to be specified 2. That the fire size will be dependent on the building’s compartmentation so that fire may involve an entire compartment without affecting other compartments 3. That the fire intensity is associated with the use of the building, but that it can be moderated using a sprinkler system 4. That residential buildings as well as Assembly and Recreation buildings pose higher risk compared to other uses 5. That the amount of radiation passing through part of the wall that is resistant to fire may be discounted 6. That there is an adjacent building that has the same elevation as that of the building concerned and that the second building is situated equal distance from the common boundary. Space separation requirements do not apply to the roof section of the building unless the roof it inclined at an angle not less than 70o to the horizontal. In situations where an increased amount of unprotected area or a reduced separation distance is required, it would be appropriate to create compartments of small sizes. Boundaries Below are some of the key ADB provisions related to boundaries Making use of the distance to a boundary when measuring separation distance instead of using the distance to another building makes it possible determine the amount of unprotected areas, irrespective of whether there is an adjacent building and irrespective of the site of that building or the amount of unprotected areas it has. A wall that makes an angle of not more than 80o with the relevant boundary is considered as facing the boundary. The distance to the relevant boundary is the only distance normally considered. However, in situations where the site boundary links up with a space, such as a road, then part of the linking space can be considered as falling within the relevant boundary. It is assumed that a notional boundary exists where both or one of the buildings in question are in the Residential or Assembly and Recreation Purpose category, and where two or more buildings are built in the same site but are to be used by different organizations. Fire resistance and unprotected areas Provisions related to fire resistance and unprotected areas include the following: Any section of the wall whose fire resistance level is less than the stipulated amount is treated as unprotected area Any section of the wall of a stairway in a protected shaft is ignored when determining the amount of unprotected area An external wall is treated as unprotected area if it has the stipulated level of fire resistance but its external cladding is made of flammable material whose thickness is more than 1mm Very small unprotected areas on a protected wall may be ignored when calculating the amount of unprotected area as they are deemed to pose insignificant risk of fire spread. In a situation where the side of the building has canopies, then so long as the edges of the canopies are not less than 2m from the relevant boundary, separation distance can be measured from the wall instead of the edge of canopies. When determining the amount of unprotected area, sections of the external wall that are at least 30m above the ground can be ignored. Methods of assessing space separation and allowable unprotected areas Part B4 of the ADB presents two methods of determining space separation and the acceptable unprotected area on an external wall whose distance from the relevant boundary is not less than 1000mm or 1m (BSI British Standards, 2008). The first method is used in small buildings mainly used for residential purposes, while the second method is applicable in other buildings where the first method cannot be used. The key intention of determining the allowable unprotected area on the external walls of a building is to ensure that the distance from the boundary to the wall of the building is at least half the distance at which the intensity of the total radiation emanating from the unprotected areas that would be 12.6kw/m2 (HM Government, 2010). This is based on the assumption that the intensity of radiation at every unprotected are is (BSI British Standards, 2008): i. 84kw/m2 for residential, office, or recreation and assembly purpose groups ii. 168kw/m2 for non-residential buildings such as shops and other related buildings Each of the two methods for determining the amount of unprotected area has some applicable rules. For method 1, the following rules are applicable (HM Government, 2010): The building should not have a length of 24m and should not be more 3 storey hight Any part of the building in excess of the allowable unprotected area should be resistant to fire (HM Government, 2010). The side of the building will meet space separation provisions if the distance of the wall from the relevant boundary and the amount of unprotected area as within the stipulated limits (HM Government, 2010). For method 2, below are the rules for determining the allowable unprotected area (HM Government, 2010): The compartment or building in question should not be more than 10m high except for the car park that is open sided. Any part of the external wall of the building that is in excess of the maximum unprotected area should be resistant to fire. The sides of the building will meet the space separation requirements if the amount of protected area, and the distance between the relevant boundary and the side of the building is within the stipulated limits. PAR B How Allowable Unprotected Areas (UPA) is Determined An unprotected area is described as any part of an external wall of a building that does not achieve the required duration of fire resistance. There are two main methods of calculating allowable unprotected areas (UPA) of a building. These include enclosing rectangle method and simple geometry method. The methods are obtained from the Fire Research Technical Paper No. 5, 1963 and are useable for buildings located more than 1.0 m from the relevant boundary (Read, FRICS, & MSFSE, 1991). In this particular situation, however, the enclosing rectangle method will be used. Enclosing Rectangle Method First scenario From the first scenario shown in the figure above, the rectangle enclosing the unprotected areas has the following dimensions: Height (h) = 19.8m Width (w) = 29m From the table showing the permitted unprotected percentages, the enclosing rectangle has the dimensions: Height (h) = 21m Width (w) = 30m Therefore, the area of enclosing rectangle = (21m x 30m) = 630m2 From the figure above, it is shown that the entire elevation of the building is completely unprotected. Therefore, the unprotected area is calculated as follows: (19.8m x 29m) = 574.2m2 Therefore, unprotected percentage, also described as unprotected areas as percentage of area of enclosing rectangle is given by: 574.2m2 as percentage of 630m2 = (574.2m2/630m2) x 100 = 96.4%. We use 100% column on the table showing the permitted unprotected percentages. Therefore, 100% of the area of enclosing rectangle = (100/100) x 630m2 = 630m2 This implies that the allowable unprotected areas (UPA) for the building based on the first scenario indicated above is 630m2 Second scenario From the second scenario shown in the figure above, one compartment of the building is considered. In this scenario, the rectangle enclosing the unprotected areas of the compartment has the following dimensions: Height (h) = 3m Width (w) = 29 – (0.6 x 2) = 27.8m From table showing the permitted unprotected percentages, enclosing rectangle = 3m x 30m Area of enclosing rectangle = (3m x 30) = 90m2 The total unprotected area on the compartment is calculated as follows: 10(2.15m x 3m) + (3m x 3.3m) = 74.4m2 Therefore, unprotected percentage, also described as unprotected area as percentage of enclosing rectangle, is given by: 74.4m2 as percentage of 90m2 (74.4m2/90m2) x 100% = 82.7%. We use 80% column in the table showing the permitted unprotected percentages. Therefore, 80% of the area of enclosing rectangle = (80/100) x 90m2 = 0.8 x 90 = 72m2 This implies that the allowable unprotected areas (UPA) for the building based on the second scenario indicated above is 72m2 Third Scenario From the third scenario shown in the figure above, the entire elevation of the building is considered. In this scenario, the rectangle enclosing all the unprotected areas of the wall has the following dimensions: Height (h) = 19.8 – (1.2 x 2) = 17.4m Width (w) = 29 – (0.6 x 2) = 27.8m From the table showing the permitted unprotected percentages, the enclosing rectangle has the dimensions: Height (h) = 18m Width (w) = 30m Area of enclosing rectangle = (18m x 30m) = 540m2 The unprotected area is calculated as follows: 30(2.15m x 3m) + 10(2m x 3m) + 3(3m x 3.3m) + (3m x 3.1m) 193.5m2 + 60m2 + 29.7m2 + 9.3m2 = 292.5m2 Therefore, unprotected percentage, also described as unprotected areas as percentage of enclosing rectangle is given by: 292.5m2 as percentage of 540m2 = (292.5m2/540m2) x 100 = 54.2%. We use 50% column on the table showing the permitted unprotected percentages. Therefore, 50% of the area of enclosing rectangle = (50/100) x 540m2 = 270m2 This implies that the allowable unprotected areas (UPA) for the building based on the third scenario shown above is 270m2 Fourth scenario From the fourth scenario shown in the figure above, the unprotected areas to be considered is curved out by the red dotted line. In this scenario, the smallest rectangle enclosing all the unprotected areas of the wall has the following dimensions: Height (h) = (1.8 x 2) + (3 x 3) = 12.6m Width (w) = (2.15 x 10) + (0.3 x 9) = 24.2m From the table showing the permitted unprotected percentages, the enclosing rectangle has the dimensions: Height (h) = 15m Width (w) = 27m Area of enclosing rectangle = (15m x 27m) = 405m2 The unprotected area is calculated as follows: 30(2.15m x 3m) = 193.5m2 Therefore, unprotected percentage, also described as unprotected areas as percentage of enclosing rectangle is given by: 292.5m2 as percentage of 405m2 = (292.5m2/405m2) x 100 = 72.2%. We use 70% column on the table showing the permitted unprotected percentages. Therefore, 70% of the area of enclosing rectangle = (70/100) x 405m2 = 283.5m2 This implies that the allowable unprotected areas (UPA) for the building based on the fourth scenario indicated above is 283.5m2 When calculating the allowable unprotected areas (UPA), the following are ignored (Read, FRICS, & MSFSE, 1991): A. An unprotected area that is not more than 0.1m² and not less than 1.5m from any other unprotected area in the same side of the building or compartment (unless that other falls within (B) below); B. One or more unprotected areas with an area not more than1m² and not less than 4m from any other unprotected area in the same side of the building or compartment (except any such area as is specified in (A) above); C. An unprotected area in any section of an external wall that forms part of a protected shaft; D. An unprotected area in the side of a building not divided into compartments, if the area is not less than 28m above any ground adjoining that side of the building HM Government 2010. Using a formula The other way of determining the allowable unprotected areas is through the use of the formula below. This method is used where the distance from the relevant boundary is indicated. Therefore, it cannot be used in the four scenarios provided above because the respective distances from the relevant boundaries have not been provided (Read, FRICS, & MSFSE, 1991). Below is the formula: u = Where d = distance from the relevant boundary, h = height of the enclosing rectangle, w = width of the enclosing rectangle, f = factor obtained from Table 2 in the appendix below In scenarios where the value of h or w is more than 140m, a value of 140m is used; and where u is equivalent to 1 or more, it shows 100% unprotected area. For example, considering the elevation of the JB Firth building where Height (h) = 19.8m and Width (w) = 29m, and assuming that the distance from the relevant boundary is 9m, then the allowable unprotected area is calculated as follows: u = Since w is greater h in this particular case, then f = w/d, Therefore f = 29/9 = 3.2 Hence from table 2 (in the appendix), f = 0.62 u = = = = 0.37 Therefore, the maximum protected area at a distance of 9m from the relevant boundary is 40% This area is equivalent to, 29m x 19.8m x 0.4 = 229.68m2 Alternative Methods/solutions for Increase the Allowable UPA The allowable unprotected areas of a building can be increased using various alternative methods or solutions. Some of these methods include the use of sprinkler systems, external walls of portal frame buildings, and use of canopies and open-sided car parks. a. External walls of portal frame buildings External walls of portal frame buildings do not have to be resistant to fire because they only support the roofs. More protection against fire, however, is required in buildings with framed entries close to the relevant boundary. Therefore, portal frame structures can minimize the transmission effect owing to the fire from roof claddings or rafters. b. Sprinkler system According to the BSI British Standards (2008), it is logical to presume that the extent and intensity of fire will be reduced drastically in a sprinkler system is installed in the entire building. This implies that the amount of unprotected area on a building can be increased if the sprinkler system is installed. With the presence of sprinkler, the amount of unprotected area on a building may be doubled (HM Government, 2010). c. Canopies and open-sided car parks The presence of canopies and open-sided car parks on the building ensures that there is sufficient ventilation for heat dissipation. Therefore, with the presence of canopies and open-sided car parks, the amount of unprotected area on a building may be increased. References HM Government 2010, The Building Regulations 2010, Approved Document B: Fire Safety. Buildings other than dwelling houses, HM Government, London. BSI British Standards, 2008, Code of practice for fire safety in the design, management and use of buildings (BS 9999:2008), The Stationery Office, London. Read, R, FRICS and MSFSE, 1991, External fire spread: building separation and boundary distances (BR187), Building Research Establishment, Garston, Watford. Stationery Office, 2010, The Building Regulations 2006, Approved Document B: Fire Safety, The Stationery Office, London. Appendix Read More