LSF - Light Steel Framing
The word steel refers to raw material used in the structure, the steel. The inclusion of light indicates that steel elements are underweight since they are produced from steel sheet with reduced thickness. In order to focus that characteristic many publications utilize the term light gauge (gauge is a unit of measurement, now almost into disuse, which defines the thickness of metal sheet). Others describe steel as cold formed steel, being this molded steel or cold shaped, as reference to sheet molding process through mechanic processes at room temperature, such as bending or lining up. The word light reminds as well that during construction is not necessary the use of equipment and heavy machinery. Also emphasizes flexibility, given that it allows any type of interior and exterior finish.
Moreover, the building self-weight is low, not only because its structure is light but also because light steel framing (LSF) is especially meant for low-rise buildings, in contrast with heavy structures of large apartment buildings. Despite light galvanized steel elements are used, to non-structural purposes, in larger buildings, the expression light steel framing is especially utilized in reference to residential buildings up to two or three levels, i.e., light buildings. The word light is also employed to remind the ease with which materials are applied in works of rehabilitation of old buildings, whose structures, although heavy, have low seismic resistance.
Framing is the word used in English to define a structural skeleton composed by several individual elements connected together, starting to work conjointly, to shape and support the building and its content. The term also refers to the processes used to interconnect the structural element already mentioned, being them in wood, iron or galvanized steel. Given its hard to translate to Portuguese (the closest term would be framework) one has chosen to say structures.
Thus, light steel framing can be translated as light steel structures.
This is probably the aspect that the future user will quickly think when examine the possibility of constructing a building with a steel structure. The fact of using lightweight materials, in contrast with concrete weight, can lead many to question the resistance of that kind of constructions. However, such doubt is unfounded, considering the resistance of the structure is ensured by metal. In this sense a house in light steel framing system doesn’t defer of any other brickwork house. The structural strength of any ordinary house is ensured by the use of iron rods built-in cement pillars and lintels. However, in the first case, are used profiles and beams of galvanized steel, with spacing of 60 centimeters or less. Taking by chance a normal size housing, having a ground floor and an upper floor, totaling 150 m2 for example, are used about 1000 meters of profiles or vertical amount, 380 meters of floor joists, channels of 600 meters besides hundreds of other essential metallic elements.
This represents over 8 tons of metal elements of high resistance joined by thousands of structural screws. However, in this example, the house would be much lighter than a common one, since it’s not necessary the whole weight of cement or brick. Meaning that, practically all the weight of a LSF construction is derived from its structural metallic skeleton.
The house becomes a flexible structure, adapting to minimum variation of ground, not opening cracks on the walls and without presenting a risk of falling columns or plates, in the event of a violent earthquake. This also contributes to the low weight of the entire building and uniform load distribution, reducing the points of concentration of forces and tensions. This advantage of light steel framing has boosted residential building construction with a steel structure in the United States of America, especially in California, in South Korea or in Japan, given that these are areas of the planet that are at serious seismic risk.
One of the most valued qualities in a house and perhaps the least successful is thermal insulation. Materials should give housing a complete shield against temperature and humidity experienced outside. In these aspects, a house with LSF structure is completely isolated from the exterior by expanded polystyrene plates, OSB and/or cement plate, several centimeters of mineral wool and plasterboard. Characteristics of both polystyrene and mineral wool give the building a thermal protection impossible to achieve in a common construction.
With all of these materials, the interior of a LSF construction is considered a climate controlled environment. This represents an energy saving that will become increasingly significant over the years. Because of this, usually dwellings of this kind are equipped with air condition or heat recovery from fireplaces since it requires low energy consumption to provide the necessary comfort to residents.
In most modern buildings is necessary to take into account the sound produced in other areas of the house or even the noise from outside. It is often thought that the only way to avoid the propagation of noise is to increase the width of the walls. However, this problem could be solved if it were used materials that reveal to be poor conductors of sound, unlike what happens with brick and cement.
The mineral wools used in the interior cavity of walls, are effective not only for its structure but also for its density being considered by laboratory tests as having high power of acoustic insulation. However, other materials also act as a shield noise baffle. In the interior walls, the use of plasterboard helps to reduce the sound transmission. In exterior walls, besides the plaster on one side must also be taken with OSB and/or cement plate and with expanded polystyrene. The mineral wools are also placed in space between floor joists (up to 250 mm section), minimizing a lot air noise, advantage that is not possible to obtain in a conventional construction.
For these reasons, a house with a metallic structure has a different sonority than a common one. The sound produced within a division is reflected by the walls and transmitted by them preventing several times more noise propagation than a brick wall. This effect causes a different sound, giving sensation of hollow wall when hitting on walls, because the sound of the impact is not fully transferred to the other side.
Impact noises or percussion on the floors can be minimized or even eliminated by the application of high density mineral wool, or other appropriate materials, directly under OSB coating the slab structure and finally applying the final pavement.
Speed of Construction
Given that materials used in LSF construction are usually more expensive than those used in conventional construction, is precisely this characteristic that makes this constructive solution accessible and competitive. Clearly time and labor are deeply connected with the final cost of the construction.
It is a product of high mechanic resistance, ecologically friendly, enduring, versatile, and with qualities absolutely uniform, that definitely change its concept of structural panels.
OSB is a structural panel of wood strips perpendicularly oriented, in several layers, which increases its mechanic resistance and stiffness. These strips are connected with resin applied under high temperature and pressure. Through this highly automated engineering process, the panels are permanently controlled and tested to verify its levels according to strict quality standards.
Galvanized Steel Profiles
Metallic profiles used in Light Steel Framing constructions are manufactured from galvanized steel sheets covered with zinc by the continuous process of hot dip galvanization, which acquire their final shape through an industrial process of shaping or cold molding that can be in form of U, C, omega and L. This process aims to ensure the durability of the elements for hundreds of years.
Plasterboard are plates that are filled inside with plaster and outside with cardboard. According to UNE 102.023, PGL, when subjected to an impact of 2.5J, shows no rupture or cracking and the mark left can’t have a diameter greater than 20 mm. Concerning to acoustic insulation the mass value of PGL provides to the different constructive systems a behavior like mass-absorber-mass which gives them levels of performance above average when compared with conventional materials in terms of acoustic behavior. The high density and low thickness of plate causes the membrane effect towards the sound emitting source. The associated insulation plate, properly sized and performed, the SCPGL, allows conditioning solutions and acoustic insulation highly effective;
It’s defined as External Thermal Insulation Composite Systems (ETICS). Currently, exterior thermal insulation is recognized, in an undeniable way, as a high quality technical solution, because it allows:
• Reduction of thermal bridges, which translates into a smaller thermal insulation thickness to achieve the same surrounding global thermal transmission coefficient;
• Decreased risk of condensation;
• Increased thermal inertia inside buildings, since most of walls mass is inside of thermal insulation. This fact translates into improved thermal comfort of winter by increasing the useful solar gains, and also of summer due to the ability to regulate indoor temperature.
• Energy saving due to reduced need for heating and cooling of indoor environment.
• Decreased thickness of outer walls, increasing the habitable area.
• Reduce the weight of walls and permanent loads in the structure.
• Increased protection conferred to the rough walls towards solicitation of atmospheric agents (e.g., thermic shock, liquid water, solar radiation).
• Decreased temperature gradient that is subjected to the inner layers of the walls.
• Improved walls impermeability.
• Possibility of changing the appearance of the facades and placing at work without disturbing the occupants of buildings, which makes this insulation technique particularly suitable for rehabilitation of degraded facades.
• Wide range of finishing solutions;
• Energy savings and indoor comfort.
Sandwich Panel is extremely resistance and with high capacity of thermal insulation, thermal panel in polyurethane rigid foam, allows a greater energy preservation in buildings.
In Portugal, where the sun is present a great part of the year, this panel offers comfort conditions in indoor environments. The panel is composed by two sides in pre-painted steel – a flat plate and a trapezoidal, which are positioned in a special press. The polyurethane foam is distributed in plate by a modern equipment of continuous scattering, which ensures precise control of density in all panel extension.
Extruded polystyrene is a material similar to plastic, lightweight, used as thermal insulation. Its appearance is a rigid foam. It presents in several colors, being blue the most used. Commercially is known as roofmate, when is sold in plates. Widely used in civil construction industry, for its insulating properties, at the level of sound and temperature.
Mineral Rock Wool
Mineral rock wool is an insulating product formed by a woof of fibers of petrous materials that form a felt that keeps the air between them in static state. This fibers formation allows us to obtain very light products that for its unique configuration offer high levels of heat, noise and fire protection.
Rock wool is internationally recognized as acoustic insulation for its flexible structure and thermal by keeping the air in a motionless state. It is also incombustible due to its inorganic origin. Mineral rock wool is used in a wide range of applications where one can observe its excellent performance.
By volume the largest market segment for the use of mineral wool is in insulation for residential, industrial or commercial construction. Mineral wool adapts perfectly to new needs of modern architecture that seeks increasingly lighter solutions and easy placement that comply with principles of mechanic strength. To achieve this goal the market needs protective, lightweight and lasting coatings.
Phenolic compact, built by thermosetting resins, reinforced with cellulose fibers and manufactured under highly temperatures and pressures, gives steering plates the following characteristics:
• High durability and resistance to the elements;
• Low coefficient of expansion;
• Easy to clean (e.g., graffiti);
• Lack of maintenance;
• Resistance to vandalism;
• Easy to install;
• Easy to read;
• Good integration in the landscape;
• Wide range of colors.