Converting attic to bedroom – Insulation and Venting Questions for Ceiling and Floor
Greetings. I’m Spillers, a new member here and had a question about insulation.
I’m in a 1929-built craftsman home in climate zone 3A (Warm-Humid) and desire to enclose the attic to add additional bedrooms and a bathroom. The attic currently has blow-in cellulose on the attic floor and no insulation in the rafter bays or on top of the roof sheathing. The attic is currently vented by Gable Vents (there are no soffit or ridge vents); the roof is a 3-tab asphalt shingle with multiple hips. The rafters are 1 3/4″ wide by 6 1/4″ deep.
I’ve edited my question after reading your article on cathedral ceilings, here: How to Build an Insulated Cathedral Ceiling – GreenBuildingAdvisor
Question 1.
Is it a good idea to use a mixture of a vented (baffles) assembly where I have soffit-to-ridge ventilation between the rafter bays and an unvented (closed-cell SPF) assembly where I have hips that prevent soffit-to-ridge ventilation?
__I do not have the option of installing insulation on top of the roof sheathing at this time.
Question 2.
Should I spray the entire attic ceiling with closed-cell SPF, or, at least, a 1-2″ layer of closed-cell SPF against the underside of the roof sheathing and then apply batt insulation?
__ Or, is my climate too warm for this “hot roof” effect?
Question 3.
In choosing any of the foregoing options, would I need to install a smart vapor retarder such as MemBrain between the insulation and final wood-finished ceiling (I intend to use wood and not gypsum to finish out the interior second-floor ceiling and walls.
Question 4.
What do I do about the space between the ceiling of the first level and the new floor of the second level?
__I am going to remove the blown-in cellulose insulation during construction. I’ve thought about creating a gap between the first floor ceiling drywall by placing a 2×4 block on the top plates of the load-bearing walls and then installing new floor joists – resulting in a 1 1/2″ gap between the new floor joists and the lower-level drywall ceiling.
__Should I have the cellulose insulation blown between the first and second floors? Or, should I install a layer of Rockwool’s Safe-N-Sound or like product to keep the sound levels low from second-to-first floor.
__ __ __ In either case, would I be creating an unwanted moisture trap between floors or would the space be able to dry out sufficiently?
Thanks,
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Unless there is an existing code compliant stairway, I think it is a bad idea.
Generally making the room down stairs for a safe stairway makes a big mess out of what was a good floor plan.
My guess is by the time you lose some ceiling height to get R38 insulation on the roof line and the fact that joists are almost certainly under sized for uses as living space means you lose another 3 inches of head room. The number of square feet with 7.5 feet of head room is getting pretty small.
The existing windows are likely to small to meet egress requirements.
Did I say I hate half story houses mostly because they are almost impossible to air seal?
Walta