Friday, February 22, 2013

Thermal and Moisture in Metal Panels

When metal panels are designed well, they provide features that will service a building for many years to come. Whether the project is retrofit or new construction, the success of the design is dependent on the metal assembly. The installation of metal panels should specifically require the design of “control layers” in order to provide properly performing building envelope.  The four main control layers are:  Water control layer, air control layer, thermal control layer and vapor control layer.  Some products may actually provide more than one of these control layers. However, this can get confusing and this is why there is a great deal of information provided for you. There are publications from ASHRAE, the International Code Council, the National Institute of Building Sciences (Whole Building Design Guide) and the U.S Department of Energy. All of these publications provide guidance on this topic.  It is always a good idea to consult an expert and manufacturer when preparing for a project. 
Here is about more info on control layers.  Insulation provides thermal control layer which reduces heat loss or gain through the building envelope.  Air and vapor will control layers often one in the same.  The use of air barrier, depending on the weather, vapor barrier or vapor retarder may be needed.  What is vapor?  It’s basically the function of a vapor barrier which is simply the control of water vapor diffusion to reduce the occurrence of intensity of condensation.  What an air barrier system does is control air flow and thereby controls convective vapor transport.  The benefits that the control of air flow provides are: Increased comfort, reduced energy consumption, control of odor and sound transmission. 

Here are a couple of examples of control layers in metal wall panel assemblies. The first example is structural insulated panels or SIPs.  Basically these ones are structural insulated panel systems where the metal skin and insulation are laminated together to create a rigid panel. The benefit of these panels is that they combine control layers together. The more noticeable benefit would be that it combines water and the thermal control layers together. However, the performance of these panels is dependent upon the seal in the panel joints and flashing at their terminations. The second example is Rainscreen assemblies which are multi-component systems where the metal cladding and insulation are installed as separate layers.  The metal cladding and insulation is separated by drainage and ventilation cavity similar to the behind a brick veneer.  The rainscreen system provides significant benefits such as control of the flashings and transitions.  Because the insulation and metal cladding separated, it becomes easier to provide continuous R-value and tie in the water, vapor and air control layers at detail transitions. 

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