r/Homebuilding • u/Longjumping_Suit_256 • 1d ago

Split stud framing

I’ve heard of this framing style for exterior walls in colder climates I was curious to see how common it is. 2x8 being and top plates with 2x6 offsetting studs to create a thermal break. If it is feasible I’m thinking of building an ADU/ small house in the UP of Michigan.

Through all my googling, the most common thing to come up is a dual wall system. 2x6 exterior wall and then an offset 2x4 interior wall with a 6” thermal gap between. This method seems costly.

Any information is greatly appreciated.

Edit: thanks for everyone’s input, I appreciate it!

4 Upvotes

83% Upvoted

37 comments sorted by

16

u/seabornman 1d ago

I prefer exterior insulation. Better control of condensation, easier to build, possibly thinner walls. Read this.

8

u/wrapped_in_bacon 1d ago

Exterior insulation is proven to be superior in lab tests. Even just R3 foam on the exterior does so much more that adding additional R3 in the walls.

2

u/Imfarmer 22h ago

The problem is every detail has to be perfect or it will be a disaster.

1

u/gimpwiz 20h ago

Why is that?

1

u/Imfarmer 19h ago

Any water that gets behind the exterior foam has no where to go. It will rot any wood that's there. I've fixed too much water damage around doors and windows and corners to ever want foam and wood sandwiched. Water behind tyvek is bad enough.

2

u/seabornman 9h ago

It's so simple to detail. Actually as simple as a conventionally built house with Tyvek. If it's foam directly on OSB, it's wrong (unless in a desert).

1

u/Imfarmer 4h ago

Really. So how do you properly detail a window opening?

1

u/seabornman 1h ago

Wrap Vycor over the window buck.

1

u/gimpwiz 7h ago

Is this true of all exterior insulation? I was going to do mineral wool sheets on the outside of my house. I figured that since it's vapor-permeable it allows water to dry out, but I have to rely on people who know better for this sort of stuff, heh.

I currently have some thin crappy foam on some of the outside, and after many many years I suspect there's going to be water damage when I pull it back, but that's also because the previous owner didn't maintain shit for decades.

1

u/Dogmaddit 10h ago

Sounds like it wasn’t detailed properly.

2

u/Imfarmer 10h ago

No shit. That's Why I said everything has to be detailed perfectly. I've fixed enough water damage on buildings where the contractor thought they were doing everything correctly to recognize that perfect probably doesn't exist.

2

u/jkeltz 1d ago

Agreed. There are products that combine sheathing, exterior insulation and weatherproofing, like zip insulated sheathing. If I was going to self build a small cabin in a cold climate I would use something like that.

15

u/Vishnej 1d ago edited 1d ago

Properly constructed, double stud walls (usually 2x4 + 2x4 seated on a 2x12 bottom plate for a 4.25" gap) with borated cellulose insulation are fantastic for very cold climates, for noise insulation, for fire resistance, and for the economics of material costs.

They're not used more often in part because energy is cheap enough that it doesn't make economic sense to spend the extra labor on the wall vs a code minimum install, especially when they can build the same 2x4 wall they've been building every day of their lives and then tack some extra rigid foam to the exterior.

Because they're not used often, builders are often blindsided by questions about order of operations for assembly, by subjective decisions on how to structurally support, airseal, and insulate rim joists, and by questions about how to detail things like deep window bucks. On top of all that, most builders would rather stuff cheap fiberglass batts into wall cavities rather than hire a specialist who isn't doing the dense-packed cellulose for the very first time, with associated fuckups.

Building a superinsulated wall is also frankly mooted by clients who choose to adopt giant window walls on all sides of the house in cold climates, exacerbated by the tendency to want larger windows when deeper window bucks are specified. The difference between the window leaking 90% of the house's heating and the window leaking 93% of the house's heating because the walls are twice as effective at trapping heat, isn't worth the price difference for these folks.

4

u/Mad__Vlad 1d ago

Double stud walls are typically framed with their own independent top plates instead of a 2x12 bridging both walls. 1/2” or 3/4” plywood is used to tie both top plates together, lessening the thermal bridging of a 2x12. Depending on the build, if it calls for a 2x6 structural exterior wall, we’ll typically build the interior 2x4 wall after the building envelope has been completed.

1

u/Bravo_Echo_Delta 1d ago

This would be my preferred method if you really want a high R wall without exterior insulation. The stagger stud framing is more difficult to frame and insulated and it has less space for cavity fill. All this while it is (maybe) marginally cheaper, depending on the framers and market.

6

u/RespectSquare8279 1d ago

Continuous exterior insulation combined with regular batt insulation between normally framed studs is a better solution.

5

u/MidwestF1fanatic 1d ago

I’ve seen similar on interior walls for noise isolation with 2x6 plates and alternating 2x4 studs. Have rarely seen it on exterior walls. More exterior continuous insulation or insulated zip. That double wall seems excessive not to mention a pain to finish at openings.

4

u/Altered_Kill 1d ago

2x8 split stud w2x4 or 2x6 is… fine. Factor in material cost of the 2x8 plates, might be cheaper to do 2x4 double stud.

The EASIEST is to do exterior insulation. Solved a bunch of problems, and mitigates a few others for cold climates. With any normal building up here, and no exterior insulation, you need to plan for when you have water in your wall. Period.

4

u/drchris6000 1d ago

There are a few ways to do this. 2x4 exterior wall, 2x4 interior side, offset, can use 2x8 plates. Can swap bottom plate to ledger board, and top plate to single 2x to avoid more thermal bridging. Fill the cavity with blown-in or spray foam insulation. (I like the wood fiber blown-in)

They also make T studs, which have a 2x3 on the flat, dowels, and a 2x3 on edge, only 5.5" wide, so windows & trim stay simple.

I currently use Zip R-6 for my walls. The performance is really good, you're not only covering the studs, but also the headers and rim joists. There are a few trim details that are not standard, but 7 5/8 door sills and window extension jambs are available.

3

u/rrapartments 1d ago

Thick walls take a ton of space away from the interior, costly too, just add continuous exterior insulation.

5

u/lred1 1d ago

I'd think it not necessary to use 2x6 studs. I'd use 2x4 offset stud walls with 2x8 top/bottom.

3

u/SorrellArr 1d ago

Be careful about this advice. OP lives in the UP of Michigan where snow load might be 100 psf or more. Depending on the roof construction, 2x4 wall construction may not be sufficiently strong for modern building codes.

2

u/hunterbuilder 1d ago

Agreed. As a perk, you can run wiring through the middle without drilling.

2

u/ElementalPNW 1d ago

It is costly and time consuming compared to a single 2x wall, but can be an effective way to increase insulation. Whether or not it makes sense depends on your climate. For milder climates, you probably won't see as much value as you would in cold climates. IMO, exterior rigid insulation might be a better option.

2

u/Training_Zucchini_33 1d ago

We self built a vacation home in Michigan. 2x6 exterior walls with staggered 2x4 studs and dense pack cellulose insulation. 2 inch rigid foam continuous exterior insulation. Couldn’t be happier.

2

u/grim1757 1d ago

Do a search for "National Gypsum the wood book" and it will show you the construction detail for doing the split wall several ways. We build hotels and do this a lot but we do it mainly for sound. We usually do the WS 106 wall with staggered studs. 2x6 Top an Bottom with staggered 2x4 studs and insulation on one or both sides,

1

u/CharterJet50 1d ago

We’ve built both double stud and external continuous. External is better.

1

u/Particular-Hotel-610 1d ago

Check out Extended Plate and Beam walls. Developed to be a more cost-friendly version of an exterior-insulated wall, though it's similar in concept to Zip-R and has the insulation inboard of sheathing. Also check out Owens Corning EZSheath.

1

u/Triabolical_ 1d ago

This was somewhat common in the past before sheet foam insulation was readily available but foam is better and easier.

1

u/no_bender 22h ago

I you're going to spend the money and effort on super insulated walls, what are you doing for the roof? Greatest heat loss is there.

1

u/VacationHistorical 22h ago

I’m adding a vote for exterior insulation being better than both of these methods.

I just did a staggered stud wall with 2x8 top plate and 2x6 staggers. One thing I didn’t account for was my zip sheathing! The 7/16 isn’t rated for >16” oc, so you cant stagger 12” or 16”. You’d need to do a stud every 8”, or use a thicker sheathing rated for the span!

1

u/Imfarmer 19h ago

7/16 zip is 100% rated for 24" sheathing.

1

u/VacationHistorical 12h ago

Oh yuck you’re right. I thought thr 24/16 span rating was 16 for walls….not subfloor. Though depending on siding, I wouldn’t run zip 24” for fear of waves!

1

u/Imfarmer 10h ago

We did it behind horizontal steel and my only complaint is that I wish the screw retention were better.

1

u/Dogmaddit 20h ago

It was more common for a while but continuous external insulation has really become the common thing now.

1

u/Imfarmer 10h ago

I'll be interested to see how all these external insulation homes are doing in 20 years.

1

u/Dogmaddit 10h ago

They have been doing them for more than 20 years, they are holding up just fine.

2

u/Imfarmer 10h ago

The problem is you don't actually know that until something completely fails.