Lots of detail. Read closely.
Background & set up: 2 story house construction completed in Spring 2006 in Dallas/Fort-Worth metro. Radiant barrier (Kool-ply) roof decking installed. 8 inches or so of blown-in, loose-fill fiberglass insulation in attic including over several raised-box ceilings, and blown-in cellulose in walls. Tyvek installed over OSB board shielding. Two 13-seer Rudd heat pumps installed: model UPMD-048JAZ with coil RCHJ-48A2GG24XI, and UBHK-21J14SFA with coil RCHJ-36A2GG21XI. (The heat pumps were originally designed as 12 seer but upgradeable to 13 seer.) The bigger heat pump is for about 2,000 sq/ft downstairs and the smaller unit for about 1,000 sq/ft upstairs. Both units use digital, programmable Honeywell thermostats for dual-zone A/C.
In the floorplan, the ceiling over the entryway, dining/family room area is the same height as the second floor and is open to the landing/loft on the second floor leading to a hallway that connects to three bedrooms and two bathrooms upstairs. Roughly 1,000 sq/ft (downstairs & loft) under that ceiling, and there are several IC-rated recessed lighting fixtures in that ceiling. There are two registers in the ceiling over the dining/family room opposite of the loft and a return near the floor. Over or on the loft, there are also two registers, a return, a thermostat, an insulated side-door to the attic over the downstairs-kitchen, and a pull-down attic stairway. In the winter, the lower return is used, and in the summer the return above the loft is used. Both air handlers are in the attic space above the loft. There is a custom-made fiberglass-batt insulator over the pull-down attic stairway. There is also attic decking around the stairway above the loft particularly underneath the air handlers. Some of this decking is Kool-ply with the RB surface facing down towards the insulation underneath it. Some of the insulation underneath this decking was blown-in cellulose before the ceiling drywall was installed on the 6” or 9”(?) joists. A little bit of the decking was added after drywall and before the loose-fill attic insulation was blown in; so, it MAY not have any insulation at all underneath. Some of the decking was added after all insulation was installed; so the insulation is somewhat compressed and thus have a lower R-value.
The main downstairs area does not heat up as well as I’d like in the winter. It maintains 68 degrees ok, but if the thermostat is set higher than 68, the heat from the 2 main registers seems to stay high nearer to the ceiling towards the loft which gets too warm. Making this loft zone so warm also affects an upstairs bedroom and bathroom in that bed & bath in that zone do not get the benefit of the warmth from the two main registers.
In the summer, the house seems to cool well enough around 78 degrees although the loft tends to be warmer. The warmer loft has the effect of making an upstairs bedroom and bath in its zone significantly cooler because of the zone turning on to cool the loft where the thermostat is.
1. What effect does the Kool-ply used as attic decking have on cooling or heating where the RB surface is facing down? 1.a. Is the effect different with or without loose fiberglass underneath it? 1.b. Whether the fiberglass is touching the RB or not? 1.c. Is it better to use wood without Kool-ply surface as attic decking in this case?
2. What can be done so that the warm air from the main registers in the high ceiling fills in toward the main floor and not warm up the loft as much?
3. I am considering adding fiberglass batt roles over the blown-in insulation in the attic. How can I add more insulation AND still have decking to walk on without compressing the insulation?
4. What is a standard minimum of how many inches of blown-in fiberglass insulation should cover the wood sides and corners of the raised-box ceilings?
I’ve got more questions, but I’ll start with those for now.