Can I furr out the exterior side of house wall studs?

Question

I have a house built around 1910 with dimensional 2x4's spaced 16" apart. There are enough different issues going on that it makes sense to strip the exterior down to the studs and rebuild the exterior in a more modern way with at least basic insulation and air sealing. We are in New England, zone 5A. Because batt insulation isn't ideal for dimensional 4" studs, I'm wondering about the possibility of furring out the exterior side of the studs by 1.5" to 5.5" in order to use batts meant for nominal 2x6 studs. I'd be adding sheating, replacing windows, and attaching something like Hardie Plank siding.

Is this ever done? My searches only come up with info for doing the interior of walls.

If so, and done right, can I consider the new outside surface of the studs for nail penetration considerations when attaching siding and sheathing, or do I still need to penetrate the original 2x4?

Any guidance and consideration here would help a ton.

Answer 1

Interior is usually nicer since no weather is involved, and insides are more often changed.

Vapour barrier goes on the inside warm wall(drywall, vapour barrier, insulation, outside sheeting). I think the poly type is better for draft stopping.

So the vapour barrier(going around the studs) and the weather makes exterior work a bit more frustrating, but can be done/is done if siding replacement is in the works and inside is nice.

1.5 inch furring attached to the 2x4s well, should hold nails/screws well enough.

Answer 2

There are methods to add insulation to the outside of a house without having to add an extra wall on the outside, including an EIFS system

However, I wonder why you would want to go to a lot of extra work if you are stripping the house to the studs from the outside. You might consider having closed cell foam injected into the walls from the outside that only takes holes drilled in the outside sheeting.

I had a house built in the 1950's that had zero insulation in the older part of the house on the outside walls. I was replacing the siding anyway and once I stripped it down I found that the exterior was boarded with one by material (3/4" boards) rather than plywood or OSB. Consequently, it was fairly easy to pry off the one by boards and install batt insulation in the walls before replacing the boards, adding exterior vapor barrier, and then the siding.

I would recommend trying to get the maximum R-Value into the existing walls first before attempting to add an entire exterior wall system onto the existing house.

Injected closed cell insulation in the existing walls and then if you still want to go maximum add an EIFS layer on the outside on top of that.

Keep in mind heat rises and most heat in a house is lost through the ceiling to the roof. Make sure your attic insulation is maxed out also.

The saying is "add as much insulation as you can afford because it will eventually pay for itself".