May 2011: Conditioned Attics

Conditioned Attics

The decision to create a conditioned attic space can be a viable solution with regards to much of the housing stock and existing configurations we find within our mixed humid climate.  The four points referenced in the Guidelines (4.6.1) should always be considered. Sometimes the driving force is the mere fact that the space contains: a furnace, air handler, or large amounts of duct work that are presently outside of the existing pressure and thermal boundary. It was recently found in two test houses (Knoxville, TN) where one attic was conditioned and one was not, that the unconditioned/vented attic experienced average daily temperature swings of 40-55 degrees during the summer and 25-30 degrees during the winter. No matter how well sealed or insulated the duct work is, it cannot overcome these kinds of temperature differentials.

The approach should not be simply to foam the entire attic space. Sectioning off the space to create a newly dedicated, abbreviated, conditioned zone and leave the accompanying unconditioned flats or wings left as they are should be evaluated. Obviously erecting a fire proof wall or envelope, satisfying make up air, and addressing all code issues should be figured into the cost/equation. A recent meeting with a county code official revealed they all generally take the position to defer to the manufacture guidelines and specifications for compatible ignition barriers and coverings. Relevant permits for: erecting a wall, changing out to solid fuel appliance, or providing acceptable make up air after reconfiguring a space may apply and the onus is upon the contractor to be aware of Virginia Construction Code (section 108). Often times because of the existing pressure and thermal boundary is: very convoluted, extensively floored, has not been sealed, and is hard to navigate that conditioning becomes the obvious and only feasible strategy.

When conditioning an attic it is paramount that it is completely isolated from the outside and other unconditioned areas. Properly identifying the newly reconfigured pressure/thermal boundary and insuring that it satisfies the three guideline requirements is essential in justifying and actualizing the added retrofit cost. Making sure that the foam does not simple wash over an existing batt on the flat, that end floored ceilings bays have been addressed and knee wall junctures have been blocked of are only a few of “checks” in the application process. Sealing major penetrations on the ceiling plane and insuring that any vertical chases are not connected via series leakage to horizontal chases would be critical in providing a quality installation. Blower doors with smoke sticks, zonal and pressure diagnostics can also provide valuable feedback about whether the newly conditioned space is disconnected from the outdoors.


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