I am in the beginning stages of renovating my 200+ yr old farmhouse. This is a post and beam house that has been in my family since 1834 and I am the 6th generation to call it home. It sits on a 250 acre dairy farm in Central New York that I help my father run. Since it has quite a family history I want to make sure any “improvements” that are made are made right. I plan on gutting the entire house in phases as there is not any insulation in the house and the electric is 1950’s era that is in need of an update. My main question is to get an opinion on my plans for my attic and wall assemblies.

First the attic, it is a 35′ x 25’walk up attic with full 2×8 joists running 20″ on center with a lathe and plaster ceiling below. I plan on removing the existing attic floor, removing all electric, cleaning the joist cavities, dense packing cellulose, then reinstalling removed floor. To add Rvalue, below the lathe and plaster I plan to add 4″ of polyiso then add 2×4 to attach drywall and also to provide a cavity to run electric. So the assembly would look like –

-attic floor
-8″ cellulose/8″ floor joist
-lathe and plaster
-4″ polyiso rigid – 2 layers offsetting seams
-2×4
-gypsum drywall

Which will give me an approximate R Value of 53.5

My walls currently consist of 8″ posts, in the corners and midpoints of the exterior walls. The wall assembly from the outside in is – cedar shakes, original wooden clapboard siding, full 4×4 studs 16″ OC, and lathe and plaster. My plan is to make a double stud wall and dense pack with cellulose that will look like this –

-cedar shakes
-wood clapboard siding
-4″ cellulose/ full 4″x4″ outer stud
-1/2″ plywood sheathing, taped for air and vapor control
-3.5″ cellulose/finished 2″x4″ inner stud – Also thinking about substituting closed cell spray foam for the cellulose to increase r value
-gypsum drywall

This layout should give me an approximate wall Rvalue of 27 (not counting windows) with all cellulose and 36, if I substitute closed cell spray foam on the inner half of the double stud wall.

If anyone has any thoughts or suggestions I’d appreciate hearing them as I keep 2nd guessing myself as to whether these assemblies will give me a house that will last another 200 years and be energy efficient.

Thanks
Ed