Sealing the ceiling - what to use?

[American Locomotive]

A family member has owned an 1800s farm house for the past 20, and at some point way in the past, the previous owners stripped the plaster and wood lath off the ceiling in the living room to expose the old giant hand-cut floor boards of the attic. You can see all the old rusty nail holes in the beams where the lath once was nailed in to. It's certainly quite the aesthetic, however there are large gaps between the boards, usually around 1/2".

The attic is not insulated, and is not conditioned. There is 3-4" of foam board insulation covering the entire floor in the attic, so the living room has some insulation, but it's certainly not forming an air-tight seal against the boards. We're working to try and reduce their utility costs, and I think the first step is to properly seal the attic floor/living room ceiling, as it's basically a giant draft leak right into the unconditioned attic.

Because the floor boards are exposed in the living room, using spray foam really isn't an option. The existing foam board insulation has a black face, so it blends in against the dark wood floor boards.

So what do you think would be best to seal the ceiling/floor to reduce drafts into the attic? Should I just get some black tyvek tape and tape all the seams? Put a huge piece of black plastic sheet over the entire attic?

The plan is to put at least R50 worth of insulation over whatever we use to seal the floor.

 

[Rusted Nut]

You could get some 1/8” plywood, paint to match the floor boards, and install over floor boards in attic. Then cover with insulation.

 

[larry4406]

At the day job we use a product called Thermoply to create air barriers on vertical walls at chases or attic knee wall framing.

There is green for air barrier and red for air barrier and structural.

It’s a 4x8’ sheet product about 3/16” thick. Like a slick compressed cardboard. It is easily installed with staples, screws, etc.

It readily curls on it self so somewhat easy to get into tight spaces (attics) for later unfurling. It accepts Tyvek tape, spray foam, etc.

Perhaps use it as the top side underlayment, fully taped off, prior to attic blow.

Thermo Ply | OX Engineered Products

 

[fitter30]

Don't think you want plastic. Have a heated/ cooled space and the other side is unheated/ cooled think the attic side might condensed at certain times.