In researching high efficiency buildings, and deep energy retrofits, I am confused why in a tight building, it is still suggested to insulate the roof/ceiling more than the walls.

I understand that generally more insulation is required in the roof/attic than in the walls. My understanding for this is that buildings lose more energy through their roofs due to pressure gradients (hot air rising, creating increased pressure near the roof) and thermal gradients (air near the roof will be hotter, and therefore more insulation is required to limit increased energy loss due to larger temperature differential across the insulation.

I am confused why this rule of increased insulation in the ceiling still applies in very tight building envelopes (particularly ones with controlled air circulation/ventilation). In a very tight building (eg a REMOTE or PERSIST building ) there should be very little energy loss through the roof/ceiling due to pressure gradients (since there should be very little air leakage possible) and there should be very little energy loss due to thermal gradients, since the temperature near the ceiling should be very close to the temperature in the rest of the building (due controlled circulation of air throughout the building ). Can somebody please explain the factors that I have missed?

Thanks very much,

Matt (in Canada)