Aspects of Building Regulations - Coursework Example

Word Count: 3050 Building Regulations Assignment Student Name: Institution: Date: Contents List of Figures and Tables 2 Figures 2 Tables 3 PART A 4 Introduction 4 Functional requirements of external fire spread & space separation 4 Where space separation needs to be considered 6 Boundaries 6 Allowable Unprotected Areas (UPAs) 7 Methods of Calculating UPAs 7 Method 1: 7 Method 2: 8 Method 3: Enclosing rectangle (geometric method) 9 Method 4: Aggregate notional (protractor method) 9 PART 2 11 Introduction 11 Calculations to determine allowable UPAs 12 Scenario 1: No internal compartmentation + 100% UPA 13 Scenario 2: Compartment floor + 100% UPA 15 Scenario 4: Compartmentation floor + only Glazing UPA 19 Alternative Solutions that can be used to increase the allowable UPA 20 Conclusion 21 References 22 List of Figures and Tables Figures Figure 1 – Wall surface provisions for recreation or assembly building of more than one storey 5 Figure 2 – Determining a notional area using a protractor 10 Figure 3 – Site floor plan plates showing the location of JB Firth and Maudland buildings 11 Figure 4: (a) - No internal compartmentation + 100% UPA 13 (b) - Compartment floor +100% UPA 15 (c) - No internal compartmentation + only glazing UPA 17 (d) - Compartmentation floor + only Glazing UPA 19 Tables Table 1 - Permitted amount of unprotected areas in small residential flats or other residential purposes 7 Table 2 - Unprotected areas permitted in compartments or small buildings 8 PART A Introduction The building regulations in part B4 provide the guidelines for external fire spread with regard to the height of the building, its intended use and the position of the building relative to other surrounding buildings. The possibilities of fire spread to adjacent buildings depends on the distance separating the two buildings, the fire protection measures provided on the external surfaces of the building, the intensity of fire and the risk it poses to the occupants of the building. The requirements cover on the provisions for external walls and the roof; separation distance, fire spread over these parts of the building, and across the boundary to other surrounding buildings beyond the boundary. The main aspects of external fire spread covered in this part include; the requirements of part B4 of ADB, and a review of the standard guidance with regard to consideration of space separation, methods to asses space separations and allowable unprotected areas, boundary distances, site boundaries and relevant boundaries. Functional requirements of external fire spread & space separation The external walls of a building should be built with appropriate standards of fire resistance to prevent ignition, combustibility and spread of fire over the walls and through the boundary of separation to other closer buildings. The materials used are required to be of limited combustibility. If the boundary of separation is 1000 mm, then a wall with reduced standards is acceptable, and if it is < 1000 mm, then measures need to be taken to restrict the combustion of the walls and spread of fire. The fire resistance performance standards of the structural elements used in the construction of walls are provided in appendix A, Table 1A of ADB. The factors that affect these standards include; the density of fire load, the height between the top floor and ground level, type of occupancy, and whether the building has basements. Sometimes, portal frames are used in single storey commercial and industrial buildings where fire resistance may not be needed. The guide recommends that the external walls of such buildings have to be fire resistance if they are close to the relevant boundary to avoid the spread of fire to nearby buildings. If the separation distance to the boundary for any building other than recreation or assembly building of more than one storey is >1000 mm, no provision is indicated. If the purpose of the building is recreation or assembly and is more than one storey, with public access to the part of the building, then a class 0 surface is to be provided as indicated in the figure below: Figure 1: Wall surface provisions for recreation or assembly building of more than one storey. The separation distance is considered from the building to a boundary to enable the calculation of the percentage of unprotected area. The provisions provided under space separation are based on a number of assumptions. These assumptions are that: the size of fire depends on the building compartmentation; the fire intensity relates to the use of the building; the highest life risk is represented by recreation, assembly, and residential purpose groups; there is a building with similar elevation on the other side of the building in context located the same distance from the relevant boundary; and that any amount of radiation passing through a fire resistant wall is negligible. Buildings with a smaller distance of separation or more unprotected area is desired are recommended to have smaller sizes of compartments. This is to reduce fire spread from one compartment to another. Where space separation needs to be considered ADB provides requirements for space separation of external walls based on the building purpose and the amount of unprotected area. These requirements are shown in Table 1 and Table 2 of this report. For external walls that lie within 1000 mm from the relevant boundary or coincident with the boundary, will have to meet the requirements for separation if fire resistance is considered on the rest of the wall from both sides, or if the external parts of the wall of a large uncompartmented building are >30 m above the ground level. If the distance from the wall to the relevant boundary is 1000 mm or more, then the provisions given for space separation will be considered if the extent of the unprotested area fall within the methods provided for the calculation of acceptable unprotected area in ADB or if there is any part of the wall inside the building that is fire resistance. Roofs that are pitched at angles >70o to the horizontal require a consideration of space separation. BR187 recommends consideration of space separation between two buildings if the incident intensity of radiation exceeds 0.3 cal cm-2s-1. In BS 9999, space separation should be considered where the total thermal radiation intensity from all unprotected areas is 12.6 kW/m2. As can be noted, there is a difference between the three provisions. However, a suitable criterion for space separation is applied based on the conditions at the construction site. Boundaries There are three boundaries to be considered; site boundary, relevant boundary and notional boundary. These boundaries are used in the calculation of space separation requirements. A site boundary is the boundary at the site of construction. A relevant boundary means a boundary that is parallel, coincides with, or lies not >80o to the walls of a building (HM Government, 2013, p.97). A notional boundary is an assumed boundary that exists between buildings on the same site. They exist where: one or both of the buildings are for residential, assembly or recreation purposes; or more than one buildings managed by different organizations are put up on the same site. Notional boundary is situated where one of the buildings comply with the requirements of space separation. Allowable Unprotected Areas (UPAs) An unprotected area is an area on the external wall surface with combustible surface materials covering > 1 mm thickness of the external wall surface, or part of an external wall with fire resistance lower than the amount provided in table A2 of ADB. The area with combustible materials should amount to 50% of the actual area of the external wall material for the area to be considered as unprotected. This excludes wall surface materials with class 0 rating and parts of external walls within a stairway situated in a protected shaft. If the classification is “s3, d2”, then the limit for smoke production or flaming particles is not provided. Methods of Calculating UPAs There are four methods provided to help in determination of the size of UPAs. Method 1: This method is applicable for small residential buildings that belong to block of flats, or for other residential purposes, but not for institutional type buildings. The rules to determine the maximum unprotected area are as stated below: a) The height of the building should not exceed 3 storeys or exceed 24m in length. Basements are not counted as part of building height. b) The provisions for space separation have to be met by all sides of the building if the distance between the relevant boundary and distance of the side of the building, and the amount of unprotected area fall within the limits provided in the table below: Table 1: Permitted amount of unprotected areas in small residential flats or other residential purposes. Minimum distance between the relevant boundary and the sides of the building (m) Maximum amount of unprotected area (m2) 1 5.6 2 12 3 18 4 24 5 30 6 No limit c) All the parts of the side of the building which happen to be excess of the maximum protected area have to be fire resisting. Method 2: This method of calculation is intended for a compartment and building for any other use and the distance from the relevant boundary to all the sides of the building is greater than or equal to 1000 mm. The rules should be followed to determine the maximum amount of unprotected area. a) The height of the compartment or building should not exceed 10m. However, for an open-sided car park, the height limitation is not considered. b) All the sides of the building will meet the provisions given for space separation if the distance from the relevant boundary to the sides of the building or the amount of unprotected area are within the limits provided in the table below: Table 2: Unprotected areas permitted in compartments or small buildings Minimum distance between relevant boundary and the sides of the building (m) Max. total percent (%) of unprotected area Building purpose groups Office, residential, recreation and assembly Industrial, storage, Shop and commercial, and other non-residential Not applicable 1 4 1 2 8 2.5 5 20 5 10 40 7.5 15 60 10 20 80 12.5 25 100 Total % of un-protected area = (total unprotected area/Area of the rectangle that encloses all the unprotected areas) x 100%. Method 3: Enclosing rectangle (geometric method) In the geometric (enclosing rectangles) method provided in BR187, the building elevation is viewed and the unprotected area is marked using a rectangle. The minimum boundary distance is provided in Table 1 of the BR187 document based on the area of the rectangle and the amount of unprotected area. This process is repeated for all the building elevations to obtain a trace on the whole plan. The boundaries that fall out of the trace are discounted. The assumption in this method is that, the external enclosure lie in a single plane, while setting back large parts will give an overestimated distance. For more complicated plan shapes where enclosing rectangle method cannot be applied, the protractor method is applied. Method 4: Aggregate notional (protractor method) In this method, a building is viewed from a number of points on the boundary, then calculations of effective visible unprotected areas is performed. The notional or effective area is smallest at the furthest unprotected area from the boundary. The notional area is obtained by multiplying the actual area by distance-dependent factors. These factors are obtained by putting a protractor (as shown in figure 2) of same scale as the plan viewing which zones fall under unprotected areas, and their corresponding factors. It should be noted that the sum of aggregate notional areas do not exceed a fixed area. Figure 2: Determining a notional area using a protractor PART 2 Introduction In this part, detailed calculations of how allowable unprotected areas (UPA) should be determined for the elevation of the JB Firth building that faces the Maudland building have been presented, with emphasis on buildings on the same site. J.B Firth is a 5-storey building that is an extension of Maudland building. The building is used to house schools of Pharmacy and Pharmaceutical Sciences and Forensic and Investigative Sciences, and accommodation for staff. It is assumed that JB Firth is yet to be constructed at the proposed site. Below is the site plan floor plates of the buildings. The purpose group of the building is assumed to be office, residential or recreation/assembly. Figure 3: Site floor plan plates showing the location of JB Firth and Maudland buildings Calculations to determine allowable UPAs To determine unprotected area, the first consideration is to establish what part or sections of the building constitutes an area that can be categorized as “unprotected area” in regard to space separation. Parts of external wall that will contribute to spread of fire must be considered, including doors and windows that do not meet the require fire resisting properties. Combustible elements used in the construction of any parts of the building need also to be considered, as they sometimes ignite during a fire. The next consideration is to decide the building elevation to be used in the calculation of the unprotected areas. If no compartments are divided up in the building, then all the unprotected areas have to be considered. The area of the largest compartment must be considered for fire spread. Areas that open to the enclosures of stairways and form a protected shaft are not taken into account. Buildings with a lower fire load density are assumed to radiate at a relatively lower intensity as opposed to buildings with a higher fire load density. The method used in the calculation of UPA is the rectangle method. UPA was determined by considering four scenarios. Scenario 1: No internal compartmentation + 100% UPA In this scenario, we shall consider the building as uncompartmented as shown in the figure 3(a) below: Figure 4(a): No internal compartmentation Step 1: Establishing unprotected areas Unprotected areas are areas are parts of external walls with inadequate fire resistance duration that is recommended in the Building Regulations. It is assumed that the reference boundary is parallel to the relevant boundary with Maudland building and coincide with the face of external wall. Step 2: Determining the percentage unprotected area A rectangle marking the proposed unprotected areas is projected. In this scenario, the building is uncompartmented. Area enclosing unprotected area: Area of rectangle enclosing unprotected areas = (19.8m x 29m) = 574.2 m2 From table 1 in BR187, the smallest enclosing rectangle = (21m x 30m) = 630 m2 Amount of unprotected area = (19.8m x 29m) = 574.2 m2 Expressing this area as a percentage of the area of enclosing rectangle obtained in BR187, we have; % of unprotected area = (574.2/ 574.2)* 100% = 100% Step 3: Determining the minimum distance from the boundary We can use the 100% column to determine the minimum distance from boundary. From table 1, Minimum distance from boundary = 16.5m In this scenario, the building is not sub-divided by compartment floors or compartment walls. This means that the height of the rectangle which encloses all the unprotected areas has to be considered. The unprotected area is 100%. Scenario 2: Compartment floor + 100% UPA In this scenario, we shall consider the building compartmented as shown in the figure 3(b) below: Figure 4(b): Compartment floor + 100% UPA Step 1: Establishing unprotected areas The building is divided horizontally by the compartment floor. The areas of unprotected area in all the compartments are not equal. Therefore, we are going to consider the compartment with the largest unprotected area. This will give the area of the enclosing rectangle with the greatest exposure hazard. Step 2: Determining the unprotected area Area of rectangle enclosing unprotected areas = (10.8m x 29m) = 313.2 m2 From table 1 in BR187, enclosing rectangle = (12m x 30m) = 360 m2 Amount of unprotected area = (10.8m x 29m) = 313.2 m2 Expressing this area as a percentage of the area of enclosing rectangle obtained in BR187, we have; % of unprotected area = (313.2/ 313.2)* 100% = 100% Step 3: Determining the minimum distance from the boundary We can use the 30% column to determine the minimum distance from boundary. From table 1, Minimum distance from boundary = 12.5m Scenario 3: No internal compartmentation + only glazing UPA Here, we shall consider the building compartmented as shown in the figure 3(b) below: Figure 4(c): No internal compartmentation + only glazing UPA Step 1: Establishing unprotected areas The building is can be viewed as one large compartment floor. We shall consider the glazing area of exposure. Step 2: Determining the percentage of unprotected area Area of rectangle enclosing unprotected areas = (18.6m x 27.8m) = 517.08 m2 From table 1 in BR187, enclosing rectangle = (18m x 30m) = 540 m2 Amount of unprotected area (glazing) = (12.6m x 3.3m) = 41.58 m2 Expressing this area as a percentage of the area of enclosing rectangle obtained in BR187, we have; % of unprotected area = (41.58/ 540)* 100% = 7.7 % Step 3: Determining the minimum distance from the boundary We can use the 20% column to determine the minimum distance from boundary. From Table 1, Minimum distance from boundary = 3.5m Scenario 4: Compartmentation floor + only Glazing UPA In this case, the building is divided into four compartments using one horizontal compartment floor and one vertical compartment wall. Figure 4(d): Compartmentation floor + only Glazing UPA Step 1: Establishing unprotected areas The building is divided horizontally by compartment floor. The areas of unprotected area in all the three compartments are not equal. Therefore, we are going to consider the compartment with the largest unprotected area. This will give the area of the enclosing rectangle with the greatest exposure hazard. Step 2: Determining the unprotected area In this scenario, we shall consider unprotected area of the largest enclosing rectangle. Area of rectangle enclosing unprotected areas = (12.6m x 24.5m) = 308.7 m2 From table 1 in BR187, enclosing rectangle = (15m x 27m) = 405 m2 Amount of unprotected area (glazing) = (12.6m x 3.3m) = 41.58 m2 Expressing this area as a percentage of the area of enclosing rectangle obtained in BR187, we have; % of unprotected area = (41.58/ 405)* 100% = 10.3 % Step 3: Determining the minimum distance from the boundary We can use the 20% column to determine the minimum distance from boundary. From table 1, Minimum distance from boundary = 3.0m Alternative Solutions that can be used to increase the allowable UPA Sometimes, it may be found that the amount of ‘unprotected area’ in relation to the area of the enclosing rectangle exceeds the permitted unprotected percentage for a given distance. In such cases, it is advisable to modify the design to ensure that a reasonable UPA is obtained. This is one way of increasing the allowable UPA. Another solution is to reduce the number of compartment floors and compartment walls on the storeys, and avoiding isolation of entrance and stairways, so that it becomes unprotected shaft. This way, the glazed area will be counted as ‘unprotected area’. Conclusion The space separation between two or more neighboring buildings is of important consideration to limit fire spread between the buildings or beyond the boundaries. If an external part of a building does not meet the requirements for fire resistance, then there is high risk of fire spread to other buildings. Obtaining the amount of unprotected area enables us to obtain the boundary distance. In determining this boundary distance, it is assumed that the more amount of unprotected areas or openings a building has, the further the separation distance from the boundary. The boundary distance required for a particular floor plan increases of the building is to have more compartments. References Read More