Hardie Board > WRB > plank boards > closed cell spray foam?
My house was originally built in the 1960s here in Massachusetts. I found newspaper articles about JFK’s campaign in some of the walls, but that’s besides the point.
The house has been resided with Hardie cement horizontal lap boards and here’s the current layout, from exterior to interior:
2×4 construction, new windows recently installed
Hardie Board > Hardie WRB > wood plank boards with gaps > old insulation + paper > maybe a vapor barrier > drywall
I’d like to make the house less drafty and more energy efficient. I got a quote to rip out the drywall and old insulation, spray closed cell foam to a value of R-21, and install new drywall.
1- is an air gap needed between spray foam and the back of the plank boards?
2- will the spray foam get in between the plank boards, expand, and cause problems? Should I have felt paper installed in the bays first?
3- is a vapor barrier needed before installing new drywall?
4- what type of spray foam is least harmful health-wise?
5- any other options you’d suggest?
Appreciate your advice here.
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