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Baldwin Bros House: All Spray Foam? All Batts? Or Both?

yokamal | Posted in Energy Efficiency and Durability on

I sometimes refer to this project (in Seattle) as the Baldwin Brothers house. I used to say The Fabulous Baker Boys, but no one knew what I was talking about:).

The original home (Alec Baldwin) is a 1951 stick built single story with crawlspace foundation, lumber sub-floor (on 2×10 joists OC 16), lumber wall sheathing (on 2×4 OC 16 with asphalt paper and cedar shingles), and roof sheathing (on 2×4 OC 24 rafters).

There is a 2002 2-story addition (Stephen Baldwin) and garage on slab that aligned with the construction standards of that time (TGIs in the crawls, 2×6 walls, 2×4 rafters with OSB sheathing, and fiberglass everywhere).

Except for a new cathedral ceiling where we added skylights, and the walls of the older home where we removed the drywall, we’ve been careful to leave the remaining drywall in place and have no code requirement to retrofit to R30 in the crawl or R49 in the attic. We’ve added so many windows/doors/beams that only 45-50% of the square footage of the 2×4 walls are cavities.

The options in front of me are:

Option #1
– 4″ ccSPF in the crawl + rim/band joists to where the mud plate meets the foundation (vented crawlspace)
– 4″ ccSPF in the attic rafters from the ridge to to where the joists sit on the top plate (encapsulated attic)
– 3″ ccSPF in the wall cavities (assume vapor in with interior wall assembly of 1/2″ air space, 1/2″ interior CDX shearwall, and 5/8″ Type X with latex paint)
– Cons: While one vendor has priced me 20%-30% less than the others if I go all foam, it’s still expensive at $1.70/bf. Less R-value than code in the attic for a 2×4 assembly. In the future I will aspire to cross strap and add mineral wool for additional R-value and a thermal barrier.
-Pros: When I look at all that old lumber, I like idea of the added shear that ccSPF would bring to the assemblies. I’d like to reduce the ACH for an old home. Clear access to the attic floor for more DIY lighting and in-ceiling sound projects in the future.

Option #2
-2″ ccSPF in the crawl + R21 Rockwool batts
-Rockwool batts or dense cellulose in the walls
-R49 blown in cellulose in the attics, w/air sealing, and new baffles and roof  jacks
– Pros: 1/2 the cost and 2x the R-value (which is a big one).
– Cons: Not the same level of encapsulation, and air sealing. Cost of adding additional ventilation to the attics.

My heart is pushing me to Option 1, but my brain to Option 2. I’d appreciate any feedback from this hive mind on my mental model?

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  1. walta100 | | #1

    This seems like a silly time and place to ask for advice.

    If you care about the environment and or your operating costs then limit your windows to 15% of the walls area and keep the flat ceiling and cover it with a thick blanket of cheap fluffy insulation. It seems that ship has sailed.

    Back to your question in my opinion it just doesn’t matter what you but, in your walls, given the amount of glass you have. Let’s guess you splurged and bought dual pain windows filled with argon that maybe have a R value of 4 or so when you average 50% R4 with R13= R8.5 or you average 50% R4 with R20 = R12 the numbers are so low it is almost meaningless.

    Since you seem to like the spray foam you might as well get it but understand the next owner will not pay a nickel more for the house with or without the spray foam and you can't save enough fuel recover the price of the foam.


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