HVAC Thermal imaging upstaird-downstairs temperatures

Published on January 4th, 2017 | by Henri


Balancing upstairs-downstairs temperatures

Q.  I am seeking advice about the best way to insulate our attic. We have a two story frame house. In the summer, the second floor is much hotter than the rest of the house, and in the winter the second floor is much colder than the rest. We just use the attic for storage, but I notice some moisture up there on the things that we are storing. After we bought the house, we laid down R-25 insulation and covered it partially with a plywood floor in the center, leaving the sides with insulation exposed. We also installed pull-down stairs.

We are looking at spray foam insulation on the underside of the roof as well as the floor (R-25 would be removed), but they want to cover the ridge vent and I have doubts about that.

Could you please offer advice about the best way to keep the second floor more comfortable and the proper way to insulate an attic?

A.  To even out the temperature between the two floors in winter, you should have an HVAC contractor balance your system, and if you also have central air-conditioning, balancing the system should also help with the summer differential.

The moisture you find in the attic in the winter would indicate that there is some convection of warm, moist air from the conditioned space below.
What is the insulation under the R-25 you added: fiberglass, cellulose or? Do you know how thick it is and its R-factor?

You may have enough insulation on the floor, but you should find out where are the convective paths and seal them.

If they are not obvious, such as around ceiling lights and fans, and cracks in the drywall on the ceiling and at the joints with the walls, the best way to locate these paths is through a blow-door test and infrared thermography.
Instead of foaming between the rafters and blocking the ridge vent, make sure that any existing soffit vents are open. If there are none or if they are not fully continuous, and therefore not equal in net free ventilation area (NFVA) to the exhaust capacity of the ridge vent, consider having this deficiency corrected.

If there is no overhang on your roof, there are venting systems that provide soffit ventilation at the eaves of the roof itself.

You may also want to consider stapling aluminum reflective foil to the bottom of the rafters to reduce the summer’s heat in the attic. A light-colored roof covering also helps.

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