AskCodeMan

In a single-family residence is a door leading from a conditioned space into a unconditioned ventilated attic required to be solid core or hollow care and insulated or uninsulated? Assuming required compliance with 2006 IRC and 2006 NEC and in either zone 2 or 3, what are the applicable codes?

Hi Arron,

The wording in the IRC is vague on the requirements for 'attic' insulation in that it specifies 'ceiling' R-value requirements with the implication that it is referring to 'ceiling/attic' insulation, when it is in reality referring to insulation separating the 'attic' from the thermal envelope of the structure.

If we keep in mind that the intent is to insulate (and thus separate) the 'attic' from thermal envelope of the structure, then it also can be presumed that the intent is that this insulation is applicable to all surfaces which adjoin the attic, i.e, attic access hatches, attic access door, attic-ceiling surfaces, and attic-wall surfaces.

If the surface adjoins the attic then the required attic insulation R-value applies to that surface.

Thus, in your example, there is a door in a wall which opens to the attic, and (presumably) the attic floor is the ceiling to a portion of the thermal envelope of the house, thus the attic floor (ceiling to the space below) will require R-30 insulation, likewise the wall (and its opening - the door) to that attic also requires the same R-30 insulation.

Treating the door insulation R-value as being the same as the wall insulation R-value is the same as requiring the an attic access opening cover to have the same insulation R-value as required for the rest of the ceiling with the attic space above it - and that is presumed and done all the time.

Along the same line of reasoning then I assume that a hollow core door would not suffice.

aaronm wrote:Along the same line of reasoning then I assume that a hollow core door would not suffice.

Hollow core or solid core would not matter.

That door is not like a door to the exterior, it is like an attic access hatch cover: whether made of plywood or gypsum board the attic access hatch cover is required to be insulated to the same as the rest of the ceiling ... thus you can think of that door as a hinged attic access hatch cover - and that it requires the same insulation as the wall that door is in, which requires the same insulation as the ceiling to the attic requires.

It was my understanding, from the IECC, that the attic is the exterior of the building envelope and thus the exterior of the house. Would that not make any door to that area an exterior door?

aaronm wrote:It was my understanding, from the IECC, that the attic is the exterior of the building envelope and thus the exterior of the house.

The attic is outside the thermal envelope of the house, however, the attic is not the same as "outdoors" with regards to the thermal envelope of the house as the attic requires a much higher insulation R-value than is required for the exterior walls - which do have the "outdoors" on their exterior side.

The air in the attic is considered to be "outdoor" air for many reasons, but the attic air and the outdoor air are not the same temperature and thus are treated differently with regards to the thermal envelope of the house.

Here is just one conflict regarding the attic air: 1) the attic air is considered to be the same as "outdoor" air for combustion make up air; 2) the attic air is not considered to be the same as "outdoor" air for exhausting exhaust fans. There are many such conflicts regarding the attic air and "outdoor" air.