Cellulose between ceiling and floor above – GreenBuildingAdvisor

1908 Foursquare style 3-story house in ND.  DIY renovating the house to preserve it for another 100 years and serve as a short term rental and a place for multi-generation families to vacation together. 

The south side of the house has an open deck on the 1st floor and an enclosed 9’x30′ ‘Sunporch’ on the 2nd and a ‘Hutch’ on the 3rd floor. Both the 2nd and 3rd floor have always been a 3-season area without electricity. The original build had the 2nd floor as a balcony but was built over soon after. 

The 2nd floor framing was in poor condition and was recently reframed with 2×8 floor joists insulated from above with fiberglass bats before the subfloor was installed. The walls are framed for large windows on all 3 sides. This side of the house has a lake out front and having this much glass will make for some fun parties looking out over the lake. This room adjoins 2 bedrooms, each with their own patio door. 

The space above the ceiling of the 2nd floor is not insulated. This space is easily accessible right now from the exterior south side and I’d like to add insulation. It won’t be expensive and will make the space more usable in the colder months. I’ll be adding a visor to shade the south windows and the opportunity to easily insulate will be over. 

The framing of the 3rd floor flooring to the 2nd floor ceiling is: 

— 1×4 tongue and groove boards (3rd floor flooring running N-S)

— Purlins running E-W and shimmed to provide a slope to the south for the floor.

— 2×8 joists N-S

— Beadboard ceiling of the 2nd floor E-W.

At the E and W end of the framing there are air gaps where the purlins sit on top of the 2×8 joists. 

I’m planning on blowing cellulose insulation above the beadboard and am wondering if there are downsides to consider. 

1) How deep I should go. Fill the cavity or leave some air gap to the bottom of the floor above?

2) I assume anything spilled in the 3rd floor will leak down onto the insulation. There is a slope to the floor. It should be able to dry out.

3) With foot traffic on the 3rd floor and a beadboard ceiling on the 2nd floor, will there be a continuous dusting of cellulose coming through the gaps in the beadboard? 

4) To limit the contact of cellulose to the beadboard, I could lay down cardboard strips. Is this really necessary? There would still be a small gap next to the joists. 

Appreciate reading this far and any insights to share. 

Tim