My hot attic - conclusion

[CJT]

Do you have a credible cite for that? I suspect it's an urban myth.

[Travis Jordan]

Sounds like twstanley put his finger on it; the most likely source of the problem is heat gain from the garage, most likely due to the lack of adequate flooring insulation in the bonus room. Heat gain from the attic through insulated (R-6 or better) ductwork isn't significant. I doubt that power venting the attic will do anything to change the situation.

[Joseph Meehan]

Well if I said it would start a fire, I would call it an urban legend. I may have miss worded it. How about "Insulating under the roof may raise the temperature of the roof to the point it may reduce its life" :-)

[Joseph Meehan]

Bingo! The problem is the heat coming into the room and a lot of it is coming in from the garage.

[CJT]

What little actual information I've been able to find suggests any temperature rise is on the order of a few degrees -- far less than the difference between shady and exposed areas.

[Bob]

Does the heat pump use attic air for its cooling air? If so, exhausting its output air though a gable vent, or using a vent for its input air might solve your problem, and increase its efficiency.

Bob