SPECIFICATION & ENGINEERING GUIDE For Light Steel Frame Construction
www.lsf-association.co.uk VERSION 1 - DEC 2020
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Specification & Engineering Guide
Benefits of light steel frame construction Utilising Light Steel Frame (LSF) structures as the offsite manufacturing product of choice has many benefits when compared to other construction methods and building technologies. LSF has a high strength to weight ratio, making systems the lightest material for a load-bearing frame whilst still maintaining a robust structure. The main benefits of utilising light steel frame construction are as follows: Established and certified • Proven and versatile technology with an established supply chain • Third party certified to industry standards, i.e. BS EN etc. • Fully compatible with BIM modelling Quality • Quality product manufactured in factory-controlled environments • Accuracy of design, manufacture, and installation • A robust product which can create long spans, large openings and concrete floors Excellent performance characteristics • Fire, thermal, acoustic, air tightness, weathertightness and lower embodied carbon • Reduced risk from fire/arson in the construction phase • Lighter construction means reduced foundation materials and costs Sustainability • A high percentage of the steel used is recycled with end-of-life potential for re-use • Contributing to BREEAM Excellent with A and A+ products • Minimum disturbance to the locality during construction with fewer deliveries Speed of build • Reduced programme times and prelims • Reduced labour on site • Early access for follow-on trades
In summary LSF… • • • •
is manufactured in factory-controlled conditions for superior quality provides speed in construction ensuring faster delivery is a safer form of construction improving onsite health and safety reduces site labour requirement increasing resource efficiency
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Contents
Introduction .................................................................................................................... 4 Design Opportunities .............................................................................................. 5 Performance in Construction ...........................................................................6 Performance in Use .................................................................................................. 7 Sustainability and LSF ........................................................................................... 8 Light Steel Infill Walling Systems ............................................................. 10 Light Steel Oversail Walling Systems ...................................................... 11 Load-bearing systems .......................................................................................... 13 Walling ............................................................................................................................... 14 Flooring................................................................................................................................ 15 Roofs ......................................................................................................................................16 Interfaces .......................................................................................................................... 17 Other LSF Elements ............................................................................................... 18 Elements used in conjunction with LSF .............................................. 19 Components for Modular Construction ...............................................20 Hybrid Construction ............................................................................................... 21 Innovative Offsite Housing Systems ...................................................... 22
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Specification & Engineering Guide
Introduction The Light Steel Frame Association (LSFA) was established to influence legislation, regulation and to support the overall objectives and growth of the sector. LSFA works closely with its members to raise awareness of the benefits of using steel framing systems (SFS) and provide access to industry contacts, technical expertise and market intelligence. LSFA members comprise manufacturers, supply chain partners, installers, consultants and clients all working together towards the common goal of growing the specification and use of LSF technology. Light steel frame (LSF) is an established method of construction with over 30 years history of use in the UK. LSF systems hold an excellent track record of in use performance with the solution being used in many different applications, with LSF structures forming a significant portion of the offsite construction sector. There are various types of LSF systems which generally fall into two categories: Load-bearing frames Load-bearing frames which replace the inner skin of a traditionally built structure. Typically built up to a maximum of 15 storeys high.
Steel components Steel components which are installed within a concrete or steel frame host structure. These systems are often referred to as SFS and include ‘infill’ sections/panels which are set between the host frame members and ‘oversail’ sections/panels where the system is fixed to the face of the structure.
These systems can be built as a through-wall system with lining boards factory applied, panelised systems with external sheathing board and insulation, or steel sticks for erecting independently on the construction site. Light steel frame can also provide the structure of a volumetric modular building or be used in conjunction with other building products to create a hybrid structure. Sectors covered by LSF include - residential, commercial bedspace (which includes care homes, hotels and student accommodation), education, healthcare, and commercial.
Ayrshire Metals
There is often a misconception within design circles that the use of offsite construction limits architectural flare and leads to uninspiring box-like structures. This is far from the case as can be seen from the wide range of structures in differing architectural forms which members of the LSFA have produced. To maximise the benefits of offsite construction, early identification of the type of offsite system to be used leads to more cost-efficient construction, and the benefits of using LSF noted in this Guide clearly demonstrate why LSF is the preferred product. This Guide gives a high-level overview of the system and is not intended to provide the technical answers, but to signpost to other sources of technical information to assist in the design and development of steel frame projects.
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Design opportunities Utilising light steel frame as the principle structural component in a building creates many design opportunities providing the build system is selected early in the design process. Engaging the manufacturers design team early ensures that their knowledge and expertise in the use of the system permeates through the design process.
Design programmes differ for each type of LSF system and working with the manufacturers designer and structural engineer enables the scheme to be value engineered and unnecessary cost can be eliminated. In load-bearing structures, engagement of the LSF designers and engineers at concept stage and prior to planning permission being granted is highly beneficial. This allows load-bearing lines to be identified from floor to floor to ensure efficient transfer of loads from the roof through the steel frame to the substructure. This reduces both the amount of steel required and reduces/ avoids the requirement for introducing other elements such as hot rolled steel to transfer the load.
When specifying LSF, a critical part of the design process is identifying any unusual features or plant/equipment that will add load to the structure. These items such as balconies, green/brown roofs, rooftop plant etc. can all be included but the structure should be designed to accommodate these elements from the outset. Once the system is selected the focus should be to ensure architectural design freeze is achieved as soon as possible, using BIM modelling technology so that potential impact from late changes to the design can be avoided. Early engagement of the LSF manufacturer/supplier maximises the benefits of using light steel frame.
The LSFA collaborate with the Steel Construction Institute (SCI) who are a trusted, independent source of information and engineering expertise globally for over 30 years, and remain the leading, independent provider of technical expertise and disseminator of best practice to the steel construction sector. Throughout this Guide you will find links through to Useful Documents published by the SCI and other leading industry organisations.
USEFUL DOCUMENTS Steel Construction Institute (SCI) Technical Information Sheets: ED027 - Best Practice for Light Steel Framing: Design and Construction ED028 - Best Practice for Light Steel Framing: Pre-Start Requirements ED029 - Best Practice for Light Steel Framing: Installation ED030 - Best Practice for Light Steel Framing: Follow-On Trades
Royal Sutton, Birmingham - Fusion
For further Information on the benefits of LSF construction go to: www.lsf-association.co.uk/library/lsfa-specification-and-engineering-guide/benefits-of-lsf-construction
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Performance in Construction Damage to a structure during construction through moisture or fire leads to potential losses/delays to contract and expensive remediation works or even complete loss of structure. A key advantage of LSF when compared to timber frame structures is fire performance and protection from weather during the construction process. Health and Safety Executive (HSE) Document HSG 168 - Fire safety in construction, provides excellent advice on the steps to be taken to reduce the risk from fire. The document highlights the three elements required to start a fire, and notes that removing one of the three negates that risk. Constructing in light steel frame has limited combustible materials (generally floorboards only) compared to timber systems therefore reducing the fuel for the fire and limiting risk of damage. This risk is reduced further when concrete or screed on steel deck is used rather than a timber deck.
The following should be noted with regards to the performance of a LSF structure during construction: Moisture Unaffected by short term exposure to moisture and no shrinkage, greatly reducing costly and unsightly re-work.
Dimensional stability Movement with steel is minimal compared to other materials and therefore predictable.
Accuracy Manufactured and installed to higher tolerance than traditional methods of construction, meaning other components are likely to fit first time and without the need for adjustment.
Non-combustible No risk of steel contributing to fire load during, or after construction.
USEFUL DOCUMENTS Health and Safety Executive Document HSG 168 - Fire safety in construction
For further Information on performance in construction go to: www.lsf-association.co.uk/library/lsfa-specification-and-engineering-guide/performance-in-construction
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Performance in Use LSF structures fully comply with the requirements of the Building Regulations and leading warranty providers. Performance covers structural, fire, acoustics, thermal, air-tightness, weather-tightness, shrinkage, programme and accuracy. Performance of LSF is assessed through rigorous testing and it should be noted that a tested ‘system approach’ is preferred rather than a tested product.
When meeting the Building Regulations steel frame is more than ABLE
A
B
L
STRUCTURE – LSF structures, with their well understood section properties are capable of being optimally engineered to ensure highly efficient material use with a reduction in materials of up to 50%. In addition to high strength to weight ratio, LSF systems with widely distributed points of connection, are also ideally suited to design to avoid the risk of disproportionate collapse.
FIRE – LSF frames are non-combustible and will not contribute to spread of fire during construction. Fire performance of LSF systems is based on extensive testing. LSF walls and cassette floors are protected using plasterboard for up to two hours. Composite metal deck/concrete floors have an inherent fire rating, with ratings of upwards of two hours achievable.
THERMAL – as steel is an extremely good conductor of heat, thermal bridging is a key consideration with LSF wall systems. All LSF systems use warm frame principles, whereby insulation is placed outside the frame, keeping the frame warm and eliminating the risk of interstitial condensation. Similar principles are applied at junctions to reduce linear thermal losses and maintain durability.
E
ACOUSTICS – LSF systems rely on isolating the structure of the building from the finishes, thus reducing the amount of acoustic energy transferred between different areas of the structure. Robust and reliable acoustic performance is achieved, using well established and tested principles, further aided by the dimensional accuracy inherent in LSF structures.
USEFUL DOCUMENTS SCI Publications including: P402 - LSF Residential Guide P302 - LSF Modular Residential P262 - Durability of Light Steel Framing in Residential Building P272 - Modular Architects Guide P348 - Building Design using Modules P367 - Energy efficient Housing using Light Steel Framing P370 - Sustainability of steel in housing P407 - BIM and 3D Modelling in Light Steel Construction P424 - Fire resistance of light steel framing P426 - Uninterrupted Height of Masonry Cladding to Light Steel Framing SCI Technical Information Sheets including: ED014 - Light Steel Module construction ED015 - Acoustic Performance ED016 - Fire Performance ED019 - Thermal Performance ED020 - Sustainability of light steel construction ED021 - Robustness ED022 - Durability
For further information on performance in use go to: www.lsf-association.co.uk/library/lsfa-specification-and-engineering-guide/performance-in-use
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Sustainability and LSF Steel construction provides the most sustainable and economic buildings, representing the most efficient use of resources. This longevity combined with the inherent value of an asset that can be recycled or reused at end of life means that steel is not a cost, it is an investment. Light steel sections are protected from corrosion by continuous hot-dip zinc coating, and the natural properties of steel prevents it from shrinking, warping or changing shape. Galvanised steel does not suffer from fungal or biological deterioration and is not susceptible to insect infestation.
Steel as a material is sustainable for a number of reasons: 1. Reduced Resource
The development of higher strength steels means that LSF structures are built using less steel. Less steel lowers upfront carbon, not just from the material itself, but also reductions in the transport weight, construction and foundation weight.
2. Durable and Long Lasting
Building with a material such as LSF that requires little or zero maintenance, and can meet design life requirements within three figures, meaning the utilisation of the resource is maxmised.
3. Well Suited to the Circular Economy The durability and adaptability of steel enables: • Modification and adaptation of existing buildings • Reuse of steel at the end of its initial use • Deconstruction and ‘remanufacturing’ of the steel for another purpose • Steel that is not reused in construction can be repurposed to form another steel product
EOS - Sir David Attenborough Building, University of Cambridge
4. Minimal Waste Many of the by-products of the steel manufacturing
process can be utilised in other processes or industries, significantly reducing wastage.
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LSF systems provide significant sustainability credentials including:
Thermal efficiency
Embodied carbon reduction
Reduced materials – load to weight ratio
Productivity/speed of build reduced, having a positive environmental impact
Reduced transportation
Reduced waste
Compatibility with renewable energy technologies
Hadley Group
Easily adapted/dismantled for re-use
Steel is the most recycled product on earth after water
End of life recyclability Hadley Group
USEFUL DOCUMENTS Steel for Life and BCSA Supplement: Steel Construction Carbon Credentials SCI Technical Information Sheet: ED020 – Sustainability of Light Steel Construction
For further information on LSF and sustainability go to: www.lsf-association.co.uk/library/lsfa-specification-and-engineering-guide/sustainability-and-lsf
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Specification & Engineering Guide
Light Steel Infill Walling Systems In multi-storey framed construction light steel external walling systems are used extensively to create a rapid dry building envelope on a range of building types and are an economic and efficient method of providing facade walls. There are two common types of walling systems – infill and oversail walls, also known as continuous walling.
Sigmat
Infill Walling is a term for external walls that are built between the floors of the primary structural frame of a building which provide support for the cladding system. Much lighter and thinner than conventional block work, light steel infill walls do not apply heavy line loads to floors. Infill walls do not support floor loads, but they resist wind loads applied to the facade. Light steel infill walls using vertical C section studs are prevalent within both steel and concrete-framed buildings and have largely replaced masonry or timber alternatives. The C section size and spacing selected depend on the structural requirements. The spacing is also selected to be compatible with the external facade materials. With layouts engineered to support windows and openings and additional studs around openings for lateral tie back for brick tie channels and brackets for facades. The panels which fit between the elements of the primary structural frame consist of a bottom track attached to the floor and a head track attached to the underside of the floor above and allowing for building deflection. Wall panels can be prefabricated as storey-high units offsite or site assembled from C sections that are delivered cut-to-length. So reducing noise and risk on-site as no cutting is required. Light steel infill walling systems can be used with a range of cladding types including ‘heavy’ cladding, such as brickwork, or ‘lightweight’ claddings such as insulated renders and rain-screens.
KEY BENEFITS • Light weight, speed and ease of installation are important constructional advantages • Rapid installation permits much earlier access for follow-on trades • Installation process is ‘dry’ so shrinkage and other drying-out problems are eliminated • Large windows, parapets and other architectural features can be incorporated
Preassembled frames offer site saving on install times of up to 30%.
• 120 minutes fire resistance can be achieved with certain boarding systems • Can achieve excellent acoustic performance when combined with facade elements • High levels of thermal performance can be achieved with proprietary insulation, as per system data • Complete infill panel systems are now available which have been tested from inside room to cavity and cavity to inside which offer system warranties and ‘golden thread’ assurance removing risk for client, developer, main contractor and insurer
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Light Steel Oversail Walling Systems As an economic and efficient method of providing external walling systems for steel and concrete framed buildings, light steel external oversail walls are designed to resist wind loading on facades and to support their own weight and that of attached lightweight cladding materials. Ayrshire Metals
Typically constructed from the outside of the building, continuous walling ‘oversails’ the edge of the primary structure with studs being fixed via cleats maximising floor area. The components used in oversail are similar to those used for infill walling. However, there are some significant differences that must be considered in design and construction. Oversail walls are placed externally to the primary structural frame rather than between the floors as in the case of infill walls. Oversail walling systems are particularly suited to situations where cladding materials are sensitive to differing movement of the main frame. Adequate base support must be provided to accommodate vertical loading from the cladding. Openings in the building facade and a variety of cladding options can be accommodated. The continuous external walling system consists of vertical light steel C sections and bracket connections to fix them to the primary frame. Allowance for movement of the primary frame must be incorporated into the connections, usually by use of slotted connections. Dead weight of masonry cladding must be supported directly by the primary structure or foundations. However, light steel external walling systems can generally provide horizontal support against wind through the inclusion of a proprietary system of brick tie channels and brick ties positively fixed back to the stud. In addition to structural requirements, the design of both infill and oversail external walling systems must also consider fire resistance, condensation risk, weathertightness, thermal insulation and acoustic performance, and must allow for interfaces at windows, patio doors and balconies.
USEFUL DOCUMENTS SCI Publications including: P402 - LSF Residential Guide P302 - LSF Modular Residential P262 - Durability of Light Steel Framing in Residential Building P272 - Modular Architects Guide P348 - Building Design using Modules P367 - Energy efficient Housing using Light Steel Framing P370 - Sustainability of steel in housing P407 - BIM and 3D Modelling in Light Steel Construction P424 - Fire resistance of light steel framing P426 - Uninterrupted Height of Masonry Cladding to Light Steel Framing SCI Technical Information Sheets including: ED014 - Light Steel Module construction ED015 - Acoustic Performance ED016 - Fire Performance ED017 - Design and Installation of Light Steel External Wall Systems ED019 - Thermal Performance ED020 - Sustainability of light steel construction ED021 - Robustness ED022 - Durability
www.lsf-association.co.uk/library/lsfa-specification-and-engineering-guide/infill-and-oversail-systems
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Specification & Engineering Guide
COMMERCIAL Kier - Reading Gateway
RESIDENTIAL Sigmat - Byron House Apartments
HEALTHCARE EOS - Sarah Swift Building, Uni of Lincoln
COMMERCIAL Fusion Building Systems Bleinham Care London
EDUCATION Fusion Building Systems University of Sussex
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Load-bearing systems LSF load-bearing structures have structural capability up to 15 storeys. Structures are generally formed as pre-panelised systems which are lighter and easier to erect than alternative building technologies. Structures are formed using wall and floor components as referenced in later sections of this document. Walls Walls in load-bearing systems can be formed as: • Open frame • Frame lined with external sheathing boards • Insulated frames • Fully through wall systems
Floors DACS - Tekla image
EOS - Gardiner Place development
Intermediate floors can be formed as: • Concrete Floor – site installed concrete slab flooring made up using concrete on composite metal decking • LSF Cassette Floor – factory formed LSF cassette floor panel with either OSB 3 or exterior grade plywood
Roofs Roofs in load-bearing systems can be formed as:
There are different requirements for load-bearing structures based on the overall height of the building relating to both disproportionate collapse and fire protection to load-bearing elements. When referring to fire performance buildings can be generally grouped as: • Structures up to 11m (two and three storey houses) • Structures up to 18m (structures up to six storeys) • Structures up to 30m (structures up to ten storeys) • Structures over 30m (structures over ten storeys) Supplied as pre-panelised components or site specific formed to the required size, elements are delivered to site direct from the manufacturing facility, which allows for easy installation on site, and easy access to restricted or hard to access sites, with one crane required to lift the components into place.
• Concrete Roof – concrete slab flooring on composite metal decking • LSF Cassette Roof - LSF sections to form the structure • LSF Trussed Roof – warm pitched roof created using LSF trusses or with traditional trussed roof or trapezoidal profile roof deck and cold rolled purlins
Ways to improve Health and Safety on site When constructing load-bearing structures there are opportunities to build in elements to improve health and safety on site. These include: • Use of temporary cassettes to close openings within the floor • Incorporating the stairs with temporary handrails during the build for access to upper floors • Connection points for scaffolding and access systems such as hoists etc.
For further information on load-bearing structures go to: www.lsf-association.co.uk/library/lsfa-specification-and-engineering-guide/lsf-load-bearing-systems
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Walling Light steel frame components can be used as a direct replacement for structural walls as either fully load-bearing structures with external facades or as secondary components in load-bearing frames. These frames are formed from galvanised steel plate up to 4mm gauge as studs at a maximum of 600mm centres. LSF walls can also be used in volumetric modular construction as either primary components to form the box structure or as walls within a bed-stead type frame. [Refer to Section ‘Components for Modular Construction’ later in this guide for more detail] All wall types are lined internally to provide fire and acoustic performance and externally to accommodate facades and provide racking as required. LSF manufacturers and lining board providers have fully tested loadbearing walls to BS EN 1365-1.
Walls forming full load-bearing structures
Facades to LSF walls
Load-bearing structures are designed and installed to relevant codes and standards, to create full structures to which facades are then applied. LSF frames and components are combined to form external, separating and internal walls. Lift shafts and stairwell walls can also be formed along with those required to form shafts and risers.
LSF walls used in the applications noted can accommodate the following cladding types:
Infill and oversail walls Walls are used to replace a blockwork skin in steel or concrete frame host structures. This results in reduced load on the primary frame, whilst being robust enough to accommodate the external cladding. For infill walls components are typically fixed between the host structure main frame, whereas in oversail the components are fixed on the outside face of the frame.
• Masonry* • Brickslip systems • Insulated render • Metal rainscreen cladding • Terracotta rainscreen cladding • Timber rainscreen cladding * NOTE: LSF will not generally be designed to accommodate loads, other than lateral restraint for the masonry skin.
Sigmat
For more information about walling go to: www.lsf-association.co.uk/library/lsfa-specification-and-engineering-guide/lsf-walling
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Flooring LSF components are used to form structural floors in load-bearing structures. LSF floors can also be used in volumetric modular construction where floors are formed from a double deck system of a floor and ceiling combination. Refer to Section ‘Components for Modular Construction’ later in this guide for more details. Formed as either steel joisted floors or as composite concrete floors in ground floor applications if part of the LSF system, together with separating and intermediate floors. Joists are formed from galvanised steel plate up to 2.5mm gauge from joists at a maximum of 600mm centres. All floor types are underlined to provide fire and acoustic performance and overlaid with a floor finish. Loads that need to be accommodated vary when used in either domestic, commercial or communal areas. Corridor floors are often designed using a shallower depth as the span is reduced but increased loads need to be accommodated. Enhancements are required to the floor build-up such as floating floors and acoustic ceilings to achieve the acoustic performance. Refer to Section ‘Elements Used in Conjunction with LSF’ in this guide for more detail. LSF manufacturers and lining board providers have fully tested load-bearing floors to BS EN 1365-2.
When designing floors to be used in LSF structures it should be noted that: • Early identification of any elements that may add loads to the structure and any penetrations that may be required within structural elements to accommodate services etc. This early design input is essential to avoid cutting additional holes in to studs post installation. • When LSF structures are used to form ground floors the protection to the steel will need to be increased and the level of galvanisation may also need to be increased. Some warranty providers may require the steel to be kept a minimum of 150mm above external ground level. • Ground floor components should be kept warm, insulated and membranes incorporated in line with the requirements of a condensation risk analysis.
Fusion Building Systems cassettes
For further information on LSF flooring go to: www.lsf-association.co.uk/library/lsfa-specification-and-engineering-guide/lsf-flooring
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Roofs LSF elements are used to form either flat roofs using steel joists following the principles of the separating floor or pitched roofs either with roof cassettes or steel rafters and purlins. Roofs formed in LSF should always be a warm roof and either a flat roof or a habitable space such as a room in a roof. Cold steel frame roofs are not to be used as there is a risk of condensation build-up if the steel frame is not kept warm and dry. To create a warm roof that meets these requirements the insulation should be placed on the outside of the frame. In addition vapour barriers and breather membranes may be required, the location of which should be assessed through a condensation risk analysis. Falls to flat roofs can be accommodated by laying the joists/deck to falls, but design of flat roof to falls is generally only suitable based on forming mono/duo pitched or gull wing roof types. Where the architecture of the building and subsequently the roof is angular then complications are encountered particularly when the roof is formed in roof cassettes. Terraces can be formed at roof level where setbacks in the verticality of the structure occur. As with all roof areas rainwater management needs to be addressed in the same manner as a traditional build. Loading to be applied on the roof should be assessed at the initial design stage, and any additional loads from plant, machinery etc. needs to be calculated to ensure the structure can accommodate it. Green and brown roofs can also be formed using LSF but the build-up and weight need to be identified. Timber roofs can also be used in conjunction with and accommodated by LSF structures which are formed up to wall plate as an alternative to LSF roofs.
EOS
For further information on LSF roofs go to: www.lsf-association.co.uk/library/lsfa-specification-and-engineering-guide/lsf-roofs
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Interfaces Key interfaces with other non-LSF elements are relevant to both load-bearing and non load-bearing systems. Interfaces need to be determined early in the design process to ensure requirements are captured and costed for. Interfaces with load-bearing structures Foundations Connections to different types of foundation require different approaches but typical suitable foundations are: • Slab • Strip footings • Pads • Beam and block floor • Concrete plank floor
Balconies Balconies can be Juliette, inset, cantilevered or propped and whilst they can be attached to the LSF structure the preference is for posted balconies. When detailing balconies, the following points should be considered: • When connecting balconies to LSF structures careful detailing is required to prevent cold bridging – this can be achieved through the use of proprietary connection brackets. • Inset balconies create issues with regards to wrapping any external posts required at the corner of the balcony, to maintain warm frame detailing. • Cantilever balconies create cold bridging issues at floor level. Thermal break connectors can be introduced to address this.
Brise soliel Brise soliel systems can be connected but the location and connection points must be plotted at the commencement of the design process.
EOS
General access during and post construction: Connections can be made to the LSF structure for the purpose of access during the construction phase through to end use. These connections include: • Scaffold connections • Edge protection system connections • Access towers • Mast climbers • Man-safe systems Locations of connections and loads imposed are to be determined during the structural design phase.
Interfaces in infill and oversail systems When designing these types of LSF components it is important that the interface with the host structure is considered, particularly in setting out. Setting out should ensure that the minimum bearing along the length of the support under the steel sections is in line with system parameters. In addition, the requirement for allowing for deflection at the head should be considered, with specific requirements needing to be addressed at ribbon windows. It is important to ensure the system considers and works to/maintains the tolerances required. Close attention to detail is required at the interface with the selected cladding systems to be used, particularly where rails and brackets are fixed to both the host structure and the LSF system.
For further information on LSF interfaces go to: www.lsf-association.co.uk/library/lsfa-specification-and-engineering-guide/lsf-interfaces
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Other LSF Elements In addition to the previously noted interfaces with the LSF structures there are other elements that are formed from LSF that can be integrated into the design. Again, it is essential that these are identified early as items that attach to or are loaded onto the structure will impact the structural design. Early engagement with the structural designers allow these to be assessed and incorporated at concept stage rather than an afterthought.
Pods (Bathroom/Kitchen/Utility)
Other items
Pods can be used to add a further fully fitted out offsite element to the build structure. These may be formed from light steel frame components but can also be formed from timber or glass reinforced plastic (GRP) etc.
Garages (integral) - where garages are incorporated into a dwelling this results in a semi-exposed wall.
When using pods as part of the design the size, weight and location of the pod needs to be determined early in the design process. It is also important to determine if the pod is to be loaded to its final position in the building or set away from the structural walls to allow drylining. Care should be taken, as the latter means that loads may be imposed in other locations during the build.
Bay and oriel windows – these elements are formed using LSF sections within the wall build up to create projections from the structural frame. As with all LSF components these should be designed to be within a warm dry environment.
Parapets Parapet walls are generally formed in one of two ways and are to be covered by specific engineering design: • Parapet supported by wind posts Generally formed of hot rolled sections formed in an ‘L’ shape with the bottom leg fixed to the roof cassettes. The posts are set at centres determined by the engineer and infilled between with cold rolled steel panels. • Parapet supported by buttress panels Either rectangular or triangular in shape and fixed to the roof cassette and parapet wall panels. If buttress panels are specified, they can present challenges around weatherproofing and maintaining the warm frame principles.
EOS
There is also an option for upper floor panels to be extended to form the parapet.
For further information on other LSF elements go to: www.lsf-association.co.uk/library/lsfa-specification-and-engineering-guide/other-lsf-elements
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Elements used in conjunction with LSF When forming LSF structures other components/elements are required to create the finished structure. These elements need to be considered at the early design stage: Substructure
Acoustic enhancements
LSF structures can be built on various substructures but can also be used on podiums and transfer slabs including under-crofts. Loads imposed from the LSF structure can be accommodated by the substructure below.
LSF floors/ceilings do not always provide the acoustic performance required, particularly when used as separating floors. Floating floors and acoustic ceilings can be added to the build up to enhance acoustic performance.
When LSF components are in contact with the substructure a DPC must be used to protect the underside of the steel frame.
MEP installation
Communal areas/Access LSF walls are used to form communal areas, lift shafts and stairwell walls. These walls are formed as outlined before but will also need additional components to accommodate lifts and stairs in the structure. In lifts, channels for attaching the doors and restraints to the lift car are built into the lift shaft walls. In stairs, additional fixing points are required for the stair risers, landings, handrails and balustrades.
Full MEP installation can be included within the LSF design, with the option for service holes to be included in the steel components. Early engagement of the MEP Designer/Consultant to identify the service runs means that the service runs can be accommodated at concept stage.
Applied to the exterior of the structure Components such as canopies can be fixed through the external façade and solar panels/PV’s may be added to the roof. The LSF structure can accommodate these provided they are identified at the onset of design.
NOTE: Free standing hot rolled steel (HRS) frame or concrete lift shafts can also be used as an alternative to LSF lift shafts.
Intelligent Steel
For further information on elements used in conjunction with LSF go to: www.lsf-association.co.uk/library/library/lsfa-specification-and-engineering-guide/elements-used-in-conjunction-with-lsf
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Components for Modular Construction LSF provides an engineered solution and components that are used to form the volumetric box. This document is not intended to cover the entire volumetric modular solution. Modular construction (aka volumetric construction) significantly reduces time on site, but it may not be the right choice for every project. The pro’s and con’s of modular construction must be understood so that the designer can establish whether this is the correct solution for the project.
BENEFITS Significant time saving on-site
Cost effective solution
Work carried out on-site is more about connecting the plumbing/electrics of each module together and installing the façade.
Significant savings can be made due to the repetitive nature of the build along with the reduced on-site requirements (e.g. length of time you need to have a crane on-site) and shorter timeframe required to insure the build stage.
Reduced safety risks The majority of work is carried out at floor level within factory conditions.
Reduced overall build time As the building frame, fabric and in some circumstances the contents can be installed while demolition/groundworks are being carried out, overall construction time can be significantly reduced.
Benefits of LSF See page 5 of this guide.
CONSIDERATIONS • Final design is required before modules can be constructed. • Using a podium structure – great for putting a modular building on top of a retail unit or shopping centre. • Cranes are always required for all modular projects. • Site access – is there room to lift (via a crane) the modules to the footprint of the building.
Ayrshire Metals
• As with all LSF systems, early discussions with a modular manufacturer is crucial to the success and cost-effectiveness of the build.
For further information on components for modular construction go to: www.lsf-association.co.uk/library/library/lsfa-specification-and-engineering-guide/components-for-modular-construction
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Hybrid Construction For the purposes of this guide we define hybrid construction as systems that include a combination of hot rolled and cold rolled steel. This is generally in areas where additional hot rolled elements are required to enhance the performance of the structure. LSF is a supremely efficient load-bearing solution and in lower rise structures where there is a full alignment of load paths from roof to substructure, a fully cold rolled structure can be highly efficient. However, in higher structures and those where set-backs and insets are formed, it is rare that the structure of a building would be formed purely from LSF. In reality most of these structures exhibit varying degrees of a hybrid approach:
Hot rolled steel (HRS) Hot rolled steel (HRS) is present in varying proportions in every LSF building. HRS is used to break up areas of large span, with LSF doing the work in between. HRS is also introduced to cater for areas of more concentrated load, such as from stairs, lift shafts or to provide cantilevered support for balconies. External structural features, outside the line of the warm frame, are also most commonly formed in HRS.
Concrete Concrete, in the form of composite metal deck intermediate floors is a very common companion. In addition, concrete is by far the most common foundation layer for LSF systems.
Timber Timber – duo-pitch, cold roofs are frequently formed in timber trusses supported on LSF walls. And on occasion CLT, or glulam timber components, which rely on steel to create their joints, are also integrated with LSF components forming external walls – where timber is no longer permitted in buildings >18m. In reality there is spectrum between LSF and HRS, with simple low-rise structures (houses) being potentially 100% LSF, with higher and more complex structures having a greater proportion of HRS, with eventually higher structures having all load-bearing via HRS, with LSF purely acting as infill within the primary structure.
Ayrshire Metals - Reliance House, Liverpool1
For further information on LSF and hybrid construction go to: www.lsf-association.co.uk/library/lsfa-specification-and-engineering-guide/lsf-and-hybrid-construction
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Specification & Engineering Guide
Innovative Offsite Housing Systems One of the main advantages of light steel framing for residential projects is its versatility and the range of building types for which it can be used. Applications for LSF systems range from low-rise housing to multi-storey, multi-occupancy developments. The wide range of applications is in addition to the associated benefits of modern offsite methods of construction: rapid speed of build, high quality and performance, excellent safety and cost-effectiveness.
KEY BENEFITS
Advantages to the Construction Industry
• A packaged construction system in which all structural components are designed, delivered and installed by one supplier
Light steel framing systems augment the construction industry with a broad spectrum of benefits from offering predictability of costs and programme to reducing risk and enhancing building safety. The versatility of steel offers architects the freedom to achieve their most ambitious visions. Building owners value its adaptability and the benefits that steel framing solutions provide, such as the light open and airy spaces which are ideal for reconfiguring or extending with minimal disruption.
• Offsite manufacture minimises on-site deliveries. A house can be constructed from as little as 12 wall panels and up to four houses or large apartments can be delivered per lorry. • ‘Just in time’ delivery protocols reduce the need for on-site storage • LSF reduces loading on the foundations and any supporting structure • High-quality in terms of geometrical accuracy and freedom from any long-term movements due to creep and shrinkage • Good sustainability rating based on a range of environmental criteria. LSF systems can be designed for low U-values and scores A+ or A under the BRE Green Guide. • All steel components can be reused or recycled • Building extensions can be made easily to meet future requirements • Integrated BIM models are used by all construction partners
But to maximise the advantages of using LSF systems these considerations must be factored into the construction process: • Identify that LSF will be used at concept stage, and do not change track once detailed design commences • Engage early with the system manufacturers engineers and technical team • Ensure layouts wherever possible allow efficient transfer of loads from the roof to substructure • Determine if any additional elements are to be incorporated which will impose loads on the LSF structure.
For further information about offsite housing systems go to: www.lsf-association.co.uk/library/lsfa-specification-and-engineering-guide/innovative-offsite-lsf-housing-systems
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RESIDENTIAL Ayrshire Metals - Sandgate Pavilions
RESIDENTIAL Intelligent Steel Brent House, Wembley
RESIDENTIAL Fusion Building Systems Addlestone
RESIDENTIAL EOS - Pennine Close
You can contact the LSFA and our members:
Interested to find out more about the benefits of light steel frame construction? The Light Steel Frame Association is the representative body for LSF manufacturers, fabricators, structural building contractors and supply chain members including erectors, installers, designers, structural engineers and consultants. The Association works with members to raise awareness of the performance, productivity and sustainability benefits of steel. As the construction industry looks to raise the bar to meet the proposed new Building Regulations banning the use of combustible materials, the light steel frame industry is witnessing unparalleled demand for panelised and volumetric modular systems, together with ‘through the wall’ solutions which are delivered to site complete with wall linings and sheathing boards. For more information on the Light Steel Frame Association and members go to:
www.lsf-association.co.uk info@lsf-association.co.uk 01743 290 030
LSF_Association #LSFDesign Light Steel Frame Association
Contributors to this Guide include:
www.lsf-association.co.uk
