Walls of masonry and concrete bricks/blocks
FIRE PERFORMANCE DATA
6.3 Compartment walls Dry lined studwork walls
Main application in respect to this Design Guide:
Provide horizontal fire separation between compartments within a building as required by Table 2.2 of the Design Guide. These compartment walls may be required to separate special risks from the rest of the building, to reduce the area at risk and to prevent fire spreading to adjacent properties within a multi-user complex.
They may also be used for the construction of protected stairways, shafts or corridors within buildings.
FUNCTION OF COMPARTMENT WALLS
• To maintain the integrity of the wall for the duration specified in Table 2.2 of the Design Guide.
• To restrict the rise in temperature on the unexposed face to those levels required to prevent fire spread for the duration specified in Table 2.2 of the Design Guide.
• The construction shall not make a significant contribution to the growth or intensity of the fire.
• To restrict the passage of smoke for the same duration as integrity.
• To be not capable of spreading flame on their surface.
• To withstand the loading and deflection to be experienced in use and during fire exposure whilst maintaining the requirements above.
• To be able to accept the services described in Data sheets 6.7 and 6.9 without detriment to the fire separation provided, e.g. integrity, temperature rise and smoke restriction. To achieve the smoke restriction all penetrations shall be fully sealed.
• To maintain the separating performance over the lifetime of the building, or for a shorter duration if allowed for in the fire safety management plan, in respect of realistic impact and/or ambient conditions.
Studwork walls are made up of a number of components, namely the stud framework, board linings (single or multiple), board fixings and in many situations an insulating infill. These all make a contribution and these components are considered separately in this guide.
BEFORE READING
Construction design and data sheets 6
EVIDENCE OF FIRE PERFORMANCE:
In the absence of a Loss Prevention Standard (LPS) covering compartment walls of studwork construction, they shall comply with all of the following:
• Fire resistance performance*. The wall may be loadbearing or non-loadbearing in use. The wall shall comply with the requirements given in relevant codes and standards needed to provide the fire separation specified in Table 2.2 of the Design Guide at the height at which it is to be installed. There are three components to fire resistance, loadbearing capacity, integrity and insulation and the contribution of the components to these are considered individually.
Alternatively, compliance with test evidence generated in accordance with BS 476: Part 2119 or EN 1365 Part 127a (walls), preferably supported by a field of application report identifying any structural changes needed to provide the performance at the required height.
• Temperature rise (insulation). The studwork wall should restrict the temperature rise on the unexposed face.
• Smoke resistance. The studwork wall will be impermeable and any gaps within the wall or between the compartment wall and any wall built-up to it shall be sealed with an appropriate linear gap seal (see Data sheet 6.7.2).
• Surface spread of flame. The surface of the wall shall have a surface spread of flame of Class 1 to BS 476: Part 71dand be rated Class 0 as defined in England and Wales Building Regulations, Approved Document B29; or other national regulations. Alternatively the product shall be designated as being of limited combustibility.
• Loading and deflection resistance. The studwork construction shall be supported by calculations or design information from recognised codes or standards (e.g. Eurocode 618) indicating that it can withstand the anticipated loading and deflections in use and during fire exposure without producing gaps through which smoke and fire could spread.
Shall conform to calculations and design criteria in recognised codes and standards.
• Contribution to fire load. The construction shall not make a significant contribution to the fire load.
• Ability to accommodate services. Evidence shall be available to substantiate that the penetration by services (which should be kept to a minimum in compartment walls) will not impair the achievement of any of the above performance requirements.
• Distortion generation. Evidence should be provided to show that any distortion which may be induced in the surrounding construction as a result of installing the chosen studwork system has been taken into account.
• Durability. Evidence shall be available to show that the materials used in the construction of the wall are not going to be adversely affected by the ambient conditions, and any impacts and abuse, reasonably foreseeable during the anticipated life of the building.
6 Design Guide for the Fire Protection of Buildings
1. STUDS
There are only two commonly used materials for studs, namely timber or lightweight folded or rolled steel, the latter of which is normally galvanised.
This section of the data sheet compares the relative behaviour of these two materials in respect of their contribution to fire protection when used as components for commercially available dry lining systems. (See Figures 1 and 2). Timber studs are normally able to be used for constructions with fire resistance rating between 30 and 90 minutes. Lightweight steel studs are nominally used over the range 30 to 240 minutes.
1.1 Timber studs
1.2 Lightweight metal studs 1.1 TIMBER STUDS
For comparison purposes it is assumed that the timber studs are made of softwood with a nominal density of 450kg/m3when dry.
FIRE PERFORMANCE DATA
• Fire resistance (integrity). Whilst not having a direct implication on the integrity of the studwork wall, softwood studs demonstrate little deflection or expansion when heated and therefore make an ideal support to board joints etc. (✩✩✩✩✩)
• Temperature rise (insulation). Softwood is naturally insulating and as a consequence there is no conductivity between the front and rear faces of a studwork wall at stud positions. Even when gaps become exploited due to shrinkage of boards the lack of conductivity of the stud material will prevent an undue temperature rise on the unexposed face.
(✩✩✩✩✩)
• Smoke resistance. This property is not directly applicable to a structural member but timber is an impermeable material and therefore smoke should not be able to exploit any joints in the lining. The timber studwork would during the late stages of a fire contribute a small volume of smoke, but again this would be insignificant in respect of the total volume of hot smoke that would be exploiting any gap in the linings at this stage of the fire. (✩✩✩✩)
• Surface spread of flame. Not an applicable criterion for studs which are hidden below the surface of the linings.
• Loading and deflection resistance. Timber is relatively stable at high temperatures, although drying out as a prelude to burning, will cause a stud to shrink on its heated face whilst the unaffected section remains large, this will not induce significant distortion. Distortion may become a problem when the residual cross-sectional area reduces and is not strong enough to resist the shrinkage. Timber studs do not have an expansion problem under fire because the natural insulation characteristics of wood means that the stud does not experience a significant rise in temperature. Any applied loading shall be in accordance with either test or assessment evidence which takes into account the expected degradation of the assembly and char rates of the
Construction design and data sheets 6
timber used. The cross-sectional areas of studs are typically small and hence they are not usually found in loadbearing applications. In instances where they are loadbearing, bending moment deflection and bearing load calculations should be carried out. In loadbearing applications timber sheeting is usually applied across the studs on bracing and the outer skin of the fire protective lining is applied over this bracing. Again test or assessment evidence of performance of such design enhancements should be provided. (✩✩✩)
• Contribution to fire load. Timber is a combustible material, but the volume of timber used within 10m2 of studwork walling is only approximately 50kg. This itself is not released until there is a failure of the lining which is quite a long way into the fully developed fire phase.
(✩✩✩✩)
• Distortion generation. Timber is relatively stable at high temperatures, although drying out as a prelude to burning, will cause a stud to shrink on its heated face whilst the unaffected section remains large, this will not induce significant distortion. Distortion may become a problem when the residual cross-sectional area reduces and is not strong enough to resist the shrinkage. Timber studs do not have an expansion problem under fire because the natural insulation characteristics of wood means that the stud does not experience a significant rise in temperature. As a consequence there will not be any restrained distortion induced deflections as a result of heating a timber stud frame. (✩✩✩✩)
• Durability. Timber in the dry conditions experienced in many modern commercial buildings is unlikely to suffer and decay. Similarly the conditions in these buildings are such that insect infestation would not be anticipated and even less likely inside the frames protected by linings.
Wood, when properly sized is strong enough to resist most anticipated impacts. There are many timber framed buildings hundreds of years old still in an excellent state of preservation. (✩✩✩✩)
1.2 LIGHTWEIGHT METAL STUDS
For comparison purposes it is assumed that these are of lightweight cold formed steel ‘c’ shaped or ‘z’ shaped studs.
FIRE PERFORMANCE DATA
• Fire resistance (integrity). As for timber studs, the stud itself does not make a direct contribution to integrity. It should be noted however that steel does expand and does suffer differential distortion when heated.
This distortion may cause joints to open prematurely thereby causing a reduction in the potential protection afforded by the boards. (✩✩✩)
• Temperature rise (insulation). Steel is a conductive material and will readily transfer heat from the rear face of the exposed board to the board on the unexposed face. This will be made worse as board shrinkage occurs and the face of the stud is directly exposed to the heat.
With longer duration periods of fire resistance it is common to use additional board fillets affixed to the studs which increase the degree of insulation they provide. (✩✩)
6 Design Guide for the Fire Protection of Buildings
• Smoke resistance. Steel is non-permeable and therefore will not directly be the cause of cold smoke permeating from one side of the construction to the other, but distortion may cause gaps to open when the stud gets hot and the resistance to warm or hot smoke may be reduced. (✩✩✩)
• Surface spread of flame. This is not an applicable property as the metal stud is inside the lining.
• Loading and deflection resistance. Lightweight metal studs have such a small cross-sectional area that they are rarely used for loadbearing applications. As such the use of steel studs is generally restricted to non-loadbearing constructions and therefore this section is not applicable.
They are able to carry dead loads associated with the construction but being steel they go through a metallurgical phase change at around about 500oC which causes them to lose half of their strength. (✩)
• Contribution to fire load. Steel is non-combustible and will therefore make a zero contribution to the fire growth within the building.
(✩✩✩✩✩)
• Distortion generation. Steel has a high coefficient of expansion and therefore when it gets hot it is likely to be fairly disruptive to the construction. Steel when heated only on one face can induce quite significant distortions, which again have a disruptive influence on the linings and may reduce their potential protection. Steel studs, when adequately fixed can resist normal impacts, but in order to accommodate expansions they are sometimes less than perfectly fixed and may suffer impact damage. (✩✩)
• Durability. Most steel studs are galvanised therefore not expected to suffer any degradation due to rusting. especially in modern commercial environments. (✩✩✩✩✩)
2. LININGS FOR STUD PARTITIONS
This section considers the likely performance of the following common lining materials and their ability to meet the performance requirements outlined earlier;
2.1 Unreinforced gypsum plasterboard linings (normally used for 30 to 90 minute ratings)
2.2 Reinforced gypsum plasterboard linings
2.3 Calcium silicate board lining (normally used for 30 to 240 minutes) 2.4 Cement based board linings
2.5 Wood based board linings (normally used for 30 to 60 minute ratings) 2.6 Steel sheet linings (normally used for 30 to 240 minute integrity ratings*) Observations are made in respect of generic material and it is pointed out that individual manufacturers products may be better or worse than the analysis given and it is recommended that manufacturer’s product data is consulted for full details of the likely performance of proprietary products.
* Insulation is only likely to be satisfied for 5 to 10 minutes without the addition of cavity insulation.
Construction design and data sheets 6
2.1 UNREINFORCED GYPSUM PLASTERBOARD LININGS
Plasterboard, a gypsum core of various thicknesses from 9 to 19mm with a paper face auto-adhered to both faces is the most traditional of the applied facings. The paper provides the strength to the board in the cold state, but contributes nothing in the hot state.
FIRE PERFORMANCE DATA
• Fire resistance (integrity). Low propensity to crack but may do so;
normally considered good. (✩✩✩✩)
• Temperature rise (insulation). Gypsum has excellent resistance to temperature rise until all the water of crystallisation is driven off.
(✩✩✩✩✩)
• Smoke resistance. Unless damaged the boards are considered to be impermeable, although joints and edge details will need to be developed to meet this requirement. (✩✩✩✩)
• Surface spread of flame. Class 0 surface, core of limited combustibility.
(✩✩✩✩✩)
• Loading and deflection resistance. Only limited ability to withstand deflection and the individual project design details need to be reviewed if a system is to meet this requirement. Linings are non-load carrying.
(✩✩)
• Contribution to fire load. The contribution is limited to the facings which is effectively negligible. (✩✩✩✩✩)
• Ability to accommodate services. Normally rigid enough to accept sealants around single services but support will be needed to retain special closing devices and sealing systems. (✩✩✩)
• Distortion generation. Gypsum based products are inert and will not impose any deflection on the wall when heated. (✩✩✩✩✩)
• Durability. Not suitable for use in wet conditions, but generally durable in normal environments, although prone to impact damage.
(✩✩✩)
2.2 REINFORCED GYPSUM BASED BOARDS
Reinforced gypsum boards may or may not incorporate paper facings to each side.
FIRE PERFORMANCE DATA
• Fire resistance (integrity). The material is unlikely to crack when heated and has excellent integrity performance. (✩✩✩✩✩)
• Temperature rise (insulation). Gypsum based products have an excellent resistance to temperature rise until the water of crystallisation has been lost. (✩✩✩✩)
• Smoke resistance. Unless damaged the boards are considered impermeable although joints and edges may require special treatment.
(✩✩✩✩✩)
6 Design Guide for the Fire Protection of Buildings
• Surface spread of flame. Normally Class 0 or limited combustibility.
(✩✩✩✩✩)
• Loading and deflection resistance. The fibres incorporated in reinforced gypsum boards enable it to withstand deflection more than normal plasterboard. The material is, however, inert and it will not impose deflections on the framework. (✩✩)
• Contribution to fire load. The contribution to fire growth is nil for non-paper faced products and negligible for paper faced board.
(✩✩✩✩✩)
• Ability to accommodate services. Stronger than unreinforced gypsum boards and some service penetration closing devices may be fixed directly to the lining. (✩✩✩✩).
• Distortion generation. As for reinforced plasterboard. (✩✩✩✩✩)
• Durability. More resistance to impact damage but otherwise similar to unreinforced gypsum plasterboard. (✩✩✩)
2.3. CALCIUM SILICATE BOARD LININGS
These are monolithic boards designed to provide fire protection to elements of structure. Boards range from 4mm to more than 20mm in thickness but those most commonly used for stud walls are between 6 and 15mm.
FIRE PERFORMANCE DATA
• Fire resistance (integrity). Normally good, especially for low density boards with a low propensity to crack when heated. (✩✩✩✩✩)
• Temperature rise (insulation). Generally more conductive than some other barrier materials and may need to be used in conjunction with insulation to achieve ratings. (✩✩✩)
• Smoke resistance. Unless damaged they are considered impermeable although joints and edges may require special treatment. (✩✩✩✩✩)
• Surface spread of flame. Normally Class 0 or limited combustibility.
(✩✩✩✩✩)
• Loading and deflection resistance. Only limited ability to withstand deflection and design details will need to be given to meet this requirement. (✩✩)
• Contribution to fire load. There is no contribution from calcium silicate. (✩✩✩✩✩)
• Ability to accommodate services. Rigid enough to accept sealants around services and stiff enough to take pipe collars and penetration sealing systems. (✩✩✩✩)
• Distortion generation. The expansion and/or contraction can induce distortion in thin studs. (✩✩✩)
• Durability. Generally considered inert although some are susceptible to water and subsequent freezing which should be used only in frost free areas. Low density products are prone to some impact damage.
(✩✩✩)
Construction design and data sheets 6
2.4. CEMENT BASED BOARD LININGS
These are a fairly modern invention to produce a high strength board which is also capable of resisting fire. Such boards are normally between 10 and 20mm thick.
FIRE PERFORMANCE DATA
• Fire resistance (integrity). Normally good but high density cement boards can crack and bow significantly leading to a loss of integrity, particularly at joints between boards. (✩✩✩)
• Temperature rise (insulation). The lower density boards are moderately insulating, but as the density increases so does the conductivity and some cement boards rely heavily on insulation infills if they are to satisfy insulation. (✩✩)
• Smoke resistance. The boards are impermeable and exhibit good smoke resistance with respect to cold smoke but the distortion may result in a loss of hot smoke resistance at joints. (✩✩✩✩)
• Surface spread of flame. Normally Class 0 or with limited combustibility. (✩✩✩✩✩)
• Loading and deflection resistance. The higher density of these boards results in a strong board which is able to resist deflection but due to the propensity to distort it could induce deflection. (✩✩✩)
• Contribution to fire load. The contribution is low to negligible.
(✩✩✩✩✩)
• Ability to accommodate services. As for calcium silicate boards.
(✩✩✩✩)
• Distortion generation. Cement boards do have a tendency to distort when heated which due to the strength of the boards can induce deflection in studs. (✩✩✩)
• Durability. These boards have a high impact resistance and good resistance to ambient conditions. (✩✩✩✩✩)
2.5. WOOD BASED BOARD LININGS
These are generally restricted by their cost and difficulty in achieving the regulatory levels of surface spread of flame. This section covers linings of chipboard, plywood or MDF (medium density fibreboard) or waferboard.
Any other form of wood based product will need to be checked against the manufacturer’s claims. Wood based boards will normally be between 10 and 25mm thick for stud wall applications.
FIRE PERFORMANCE DATA
• Fire resistance (integrity). Timber burns away at a predictable rate which in the case of board materials is normally between 0.7 and 1mm/min. It is possible to select linings with adequate burn-through resistance to meet any normal requirement but weight will prohibit its use at periods in excess of 60 minutes. Well selected insulation can extend the period of integrity. (✩✩✩✩)
6 Design Guide for the Fire Protection of Buildings
• Temperature rise (insulation). Timber exhibits excellent insulation characteristics up until a few minutes before burn through. (✩✩✩✩✩)
• Smoke resistance. Timber boards are impermeable and will provide good resistance to smoke spread but in the latter stages of a fire the construction will produce some smoke. (✩✩✩✩)
• Surface spread of flame. In its normal state timber has a Class 3 surface spread of flame (✩). Needs to be surface coated, manufactured with
• Surface spread of flame. In its normal state timber has a Class 3 surface spread of flame (✩). Needs to be surface coated, manufactured with