Written By: Dave Stevenson, with contributing writer Jim Whalen P. Eng.
Welcome again to the Plasti-Fab Insulspan SIPs’ blog. This time, I’d like to dive right into a subject that even the most knowledgeable building professionals seem to struggle with. Specifically; what is to be done regarding ventilation of SIP buildings? Does the indoor conditioned space of a SIP building require mechanical ventilation? And what about the exterior wall cladding and roof finish design? Should these be vented, as well?
These are all very good questions and ones that are brought up regularly by architects, HVAC system contractors, building envelope consultants, city building department officials, and most of all, by the builders themselves.
Let’s start with Heating, Ventilation and Air Conditioning (HVAC) requirements for buildings built with Insulspan SIPs. The short answer to the question whether these buildings require mechanical ventilation is ‘Yes’. Generally speaking, building envelopes built with SIPs have a higher thermal resistance and are much more air-tight than typical wood framed buildings. Because of the reduced air-leakage, an energy efficient SIP building requires some sort of mechanical ventilation to supplement natural ventilation. The controlled ventilation will exhaust contaminants from within the building and control indoor relative humidity.
It is therefore very important that HVAC contractors are aware of the higher R-values and increased air tightness, and take these into account when designing the HVAC systems. Proper design of the system will typically result in a smaller and more efficient furnace that can easily maintain required indoor air temperatures without short cycling, and in most energy efficient buildings will also include a heat recovery ventilator to provide the required ventilation. (Reference PIB 206 – HVAC System Requirements)
It should be noted that SIPs are not unlike any other air tight, energy efficient building system with regards to mechanical ventilation, and the decision to build with SIPs does not necessarily equate to additional cost due to ‘special’ HVAC requirements. It simply means that like any air tight, energy efficient building , the design of the HVAC system should suit the application for which it is intended.
Stay tuned for my next blog where we will move to the exterior of the building and discuss appropriate rain screen and venting applications for wall and roof claddings.