Design Considerations
60Pages

Design Considerations A guide to designing with Sto facade systems

I know the price of success: dedication, hard work, and an unremitting devotion to the things you want to see happen Frank Lloyd Wright, 1867–1959

Introduction: A Brief History of the Wall Building components have changed and evolved over the centuries, but the basic elements have remained the same: walls, floors and roofs. This brochure is all about the wall element. The physical properties of walls have remained fairly constant throughout time. Their principal functions were to protect from the elements and act as a defence against other humans. Buildings evolved from simple timber structures incorporating wattle and daub, into sophisticated stone structures, with defence their primary concern. Moving forward in time, buildings...

The Design Considerations brochure attempts to address the main issues that may arise when specifying Sto facade systems and also explain some the origins of the technical requirements. Sto has tried and tested products and systems to meet the requirements of various organisations, be it the NHBC, Building Regulations or TRADA. If you require further advice or information, please contact Sto Technical Services. Typical External Wall Insulation system applied to masonry. cavity was far cheaper than a solid, double thickness brickwork wall. Whatever the reasons, good thermal performance was...

Wall Construction Methods Framed structures There are a number of key factors to consider when specifying a cladding system for a framed structure. Building Regulations require insulation or sheathing to be separated from the external wall cladding in framed structures. They must be separated by a drained and/or vented cavity with a breather membrane on the inside of the cavity. If the free cavity is over 50mm wide the breather membrane is not required. Insulated carrier systems can be used as the backing for render onto framed buildings. Direct application of insulated cladding to the...

Render onto carrier board The guidelines change slightly when render is applied to a carrier board before being fixed to a framed structure. It is possible to fix the carrier board to timber battens on the sheathing to create a cavity. If the battens are placed vertically, it is straightforward to ventilate this cavity and drain it at the base. The thermal insulation required fits within the frame studs, or further inboard of the frame, such as behind the cavity. Sto have NHBC approved details for the StoRend Flex system onto StoVentec render carrier boards. A 35mm wide cavity is created...

Ventilation performance of cavities A fully ventilated cavity provides the most reliable means of removing moisture within the cavity. The air movement removes moisture vapour that has migrated from the internal environment. It also encourages evaporation of any water and promotes drying of the cavity. A vented cavity will have less capacity than a ventilated cavity to remove excess moisture. Its performance depends on two main areas: • the vapour resistance of all materials to the cold side of the cavity, and • the size of the openings between the cavity and the external environment Larger...

Cavity widths – TRADA recommendations The Timber Research & Development Association (TRADA) is a centre of excellence for the specification and use of timber products. They recommend that timber framed buildings have a ventilated cavity between the insulated/sheathed timber fame and the exterior render cladding. TRADA offer two recommendations for cavity widths depending on the system: • Backed systems (where deleterious material cannot fill the void) – A cavity of 25mm minimum • Unbacked systems (i.e. traditional render onto metal lath without a breather membrane) – A cavity of 50mm TRADA...

Thermal Performance All building materials have the ability to transfer heat, some more so than others. There are two main material categories when considering heat transference: • Heat conductors are materials with high thermal conductivity that allow heat to pass through with little resistance, such as metals. • Thermal insulators are materials with low thermal conductivity that are resistant to heat transference. Most non-metal materials are thermal insulators to some degree. Expanded Polystyrene and mineral wool products are both good examples of thermal insulators. Measuring Thermal...

Condensation Risk Depending on the climatic conditions, there is calculable movement of moisture within the building envelope. It is important to understand and predict how the wall construction will behave in terms of moisture vapour movement. Failure to do so could risk condensation within the wall, known as ‘interstitial condensation’. In order to calculate the condensation risk, the vapour resistivity of each material layer within the wall must be known. By using this information and assuming environmental conditions for the site1, you can predict the risk of condensation2. Air can hold...

Thermal Bridging Thermal bridging is a phenomenon where heat can be lost through material ‘bridges’. Where components with higher thermal conductivity penetrate or partially penetrate the insulating layer of the building, heat can be lost. Examples of thermal bridging can be seen in concrete lintels or edge beams. Both can penetrate the inner leaf of a cavity wall, bypassing the insulation in the cavity. Even mortar joints within a brickwork facade will create a thermal bridge, allowing greater heat losses. Buildings are often complex structures that have to perform numerous functions. When...

The solution: External Wall Insulation Systems Internal Wall Insulation Interior Cavity Wall Insulation Interior External Wall Insulation Interior The temperature at which condensation would normally start to form within the wall construction or on internal surfaces. Thermally insulating the exterior of the structural fabric of the wall makes good technical sense on a number of levels. The building is figuratively wrapped in a thick, well insulated and protective blanket. The worst effects of thermal bridging are nullified and the detailing to achieve high thermal performance is greatly...