Insulating 1/2 story of cape, old questions, need guidance
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kushwood



Joined: 30 Sep 2005
Posts: 6

PostPosted: Thu Jan 02, 2020 9:28 pm    Post subject: Insulating 1/2 story of cape, old questions, need guidance Reply with quote

I've read through conversations in the Forum about insulating attic spaces to try to find some guidance for our small story and a half cape (1830s-50s) in NH. This feels like an old tale. 

We don't need the 1/2 second floor for living, but we do need some storage space.

The half story (height at center is about 6'6"), accessed by a central steep, narrow-stepped flight of stairs next to the center chimney, is 'conditioned' space from the 1920s/30s/40s with finished flooring and heating vent The 33" high knee walls and ceiling slope were outfitted with rock wool and finished with fiber board. Whoever did this work (1950s?) attached a thorough 2x4 interior structure to the old roof planks, rafters and purlins. Five foot long windows with aluminum storms are at each gable end of the 1/2 story. 

The energy audit advisor (through NH Saves) recommended that the eaves get blown in borated cellulose behind the kneewalls that are lined with rockwool. We're okay with that.

We were told to remove the ceiling slope fiberboard and rock wool (which we did) to prep for insulating. The energy audit advisor and the insulation co. rep recommend spraying roof deck with closed cell foam. An alternative had been discused (polyiso with some air space between it and the roof deck) but they said that would only trap moisture.  We re-roofed about 20 years ago; there is 1/2" strapping between the old planks and plywood sheathing, shingles and a ridgeline vent. The roof decking seem very dry.

I'm not eager to have spray foam insulation on the old roof planks with knots and cracks. In winter we keep the door to the upstairs closed, close the doors to the less lived-in side of the cape and close off those hot air registers. We could build an insulated "trap" door to the upstairs. The finished fir floor up there sits on top of two layers of wide board flooring. In order to lay down insulation on that plane over our living space, we'd have to rip up the 3 layers of flooring.
 
Do we leave the roof deck exposed? It may have been foolish to remove the old ugly fiberboard (& rockwool and mouse), but it is done. Any suggestions?
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