Attic insulation in old house

[John]

Hi Everyone.

I'm about to add fiberglass bat insulation to my very old post-beam house. There's about 6 inches up there now, and I'd like to add much more (live in NH). My question is about whether to let the insulation touch the underside of the roof decking. I don't have soffit-ridge venting, so there's no worries about blocking airflow. I've got gable end vents up near the peaks on the gables. I've read to keep insulation away from the underside of the roof deck, as it can lead to moisture problems. One builder I know pointed out that you put insulation right up against walls in wall cavities, so why not?

What's the proper way to do this? I'd like to stuff as much as I can up there.

John B.

[Bob]

I would leave room for air circulation. Condensation is more likely to get into an attic than a wall.

[Sev]

Is the attic used as living space? I assume not, if it's vented to the outside through gable vents. In that case, the attic floor should really be the upper edge of your thermal envelope- though I can see where this might involve tearing up floorboards. If you were to do this, make sure vapor barrier is down, toward heated living space If it is used as living space, then I think your envelope should exclude those vents; ie have insulation cross from one side to other of your roof (supported in some fashion), excluding vented peak area. Make sure eaves allow air entry, and therefore do not fill ventilation space under roof decking as you were suggesting- in fact, it might be necessary to install baffles to insure adequate airflow. If you have knee walls, run insulation down them, then along floor to eaves(might have to lift some floorboards here), insuring a continuous thermal envelope, but again making sure to allow air inflow under eaves and up under roof decking.