Double Stud Wall Framing for Passive House

Out at our Passive House, we are framing double wall exterior walls. Check it out as we walk thru the details

[@JL-hn6hi]

The interior comfort level with double stud is A+, in my experience. Love it.

[@stevenbaczekarchitect9431]

Agreed - great acoustical solution too

[@mrmike6996]

My son has been building double stud walls for a few years now. Outside wall is 2x4 16” on center and that wall is spray foamed. 2” gap and than inside wall again 2x4 16” OC but of set 8” with exterior wall and that gets Rockwool insulation. Now for a question I have for you. Have you had drywall screw heads start showing up over time? First 3 houses he did, so he came to me and asked way that might be happening. I thought about it for a bit and figured out that the inside stud wall was twisting because nothing on the back side stopping it from twisting. Put blocking half way on wall and next 4 houses and no problems so far

[@hodesto]

Great content Steve. Are the numbers crunched to see what more cost effective putting added insulation on the outside or as you did in that house. A double studded wall. I like the double studded approach. Wish big red can show some cost comparison.

[@danielstover3029]

Hello Steven! When you have the opportunity, would you please expand your explanation of the possibility of a double negative of a thicker a 24" double wall in a cold climate. You commented something about making the exterior side of the wall colder and the possibility of greater issues. Your content is greatly appreciated and I have watched all of your videos. Thanks for sharing! Always liked and subscribed... 👍👍👍👍👍

[@r.j.bedore9884]

Yeah, he did talk about it in the video, but I think he assumed prior knowledge on the part of viewers for some of it, so I will try and explain. As he said in the video, the temperature of the wall changes as you move through a cross section of the wall. In a cold climate heating scenario, the inside surface of the wall will be roughly equal to the indoor air temperature, while the outside surface of the wall will be equal to the outdoor air temperature. At every point in the wall's thickness the temperature will be somewhere between those two temperatures depending on the R-value of the material that portion of the wall is made of. Here's the part he glossed over. As you may or may not be aware, the amount of moisture air can keep suspended in itself in the form of water vapor depends on the temperature of the air. Warmer air can hold more moisture, so as the warm air cools down it can reach a point at which it can no longer keep that amount of moisture suspended and some of the moisture gets rejected from the air in the form of condensation. The temperature at which this condensation formation occurs is known as the dew point (and if I remember correctly it changes depending on both the relative humidity of the air, and the atmospheric pressure). You can see this happen when water vapor from the air condenses on the outside of a cold glass. Since the temperature of the wall gets colder as you move through the wall from the inside to the outside, there can be a point in the wall where the temperature of the wall material drops below the dew point, causing condensation to occur. If this point occurs outside of your water and air barrier that's applied to your sheathing, it isn't usually a problem. However, if this dew point temperature occurs on the inner side of your sheathing you can have condensation occur inside your wall cavity which can lead to mold and rot issues if your wall assembly isn't able to dry out at a faster rate than it is getting wet from the condensation. This is where making that double wall thicker in a cold climate can become an issue, since as you add more insulation inboard of the sheathing, the colder that sheathing will end up being and you can end up moving that spot in the wall where the dew point occurs from outside of your sheathing to the inside of the sheathing. This is why building codes in cold climates are starting to require a certain amount of exterior insulation, since adding insulation on the outside of the sheathing will move it to a warmer location along that temperature gradient inside the wall assembly and reduce the likelihood of condensation forming inside the wall cavity. Basically he is saying that by adding too much interior insulation you can end up with condensation issues inside your wall assembly, so you need to be mindful of that and if at a certain point you feel like you still need more insulation, you are better off adding it to the outside of your sheathing instead. I hope this explanation helps, even if it comes a year after you asked.

[@danielstover3029]

@@r.j.bedore9884 Thank you! 😁👍

[@garyjones101]

Thanks for the detailed explanation!

[@connormalloy1]

Great video, Steve. Thanks for sharing this one

[@tealkerberus748]

Puzzled why you'd go to that much effort for a 3" gap when you could add a whole lot more so easily - especially when the common studs aren't even offset from each other, so at every stud you literally only have that 3" gap. Upgrading even a little bit, to say a 6" gap, and having the common studs offset so they're not so close to each other, would give you a much better performance for zero extra effort.

[@afraidknot9473]

So…where’s the fire stop required in most areas?

[@scorpio6587]

Question: Would it make sense to stagger the inner and outer studs, potentially increasing the thermal break from three inches to 6.5 to 8.5 inches, in most stud locations? Or is this effect negated by something else? Great video.

[@stevenbaczekarchitect9431]

Maybe there is a slight benefit in terms of heat transfer........as for overall Whole Wall R Value - it won't change it

[@scorpio6587]

@@stevenbaczekarchitect9431 That makes sense. Thanks!

[@jamesryan7750]

Steve, I see some builders sheathe the inner wall on the air space side and tape (and may even call it a vapor barrier, a term I question). Wish I had used the double framing in mine. Instead, I framed a 2x6” wall, used dense pack cellulose, spay-foamed the stud edges, applies 4” of open cell styrofoam, then battens and a cedar rain screen. If I do a double frame, whether to use sheathing on the interior frame or exterior air space is an open question for me. Drywall again on the inside wall would be done again.

[@marcbellucci2469]

Great video, thanks! Hey, do you have a favorite type of house building method I.e. wood, metal, ICF, concrete or concrete block etc.?

[@aldoogie824]

For the recessed windows, are you doing nail on to a 2x that's connected to the sheathing? or are they blockstyle windows connected directly to the sheathing on the inside of the window buck you've designed? ( LOVED THIS VIDEO!!, amazing details!)

[@DragonTalkShow]

A lot of people naysay about putting OSB on the outside of a double stud because of its relatively low permeability. Do you see that being an issue at all or is that overblown? Will this walk use a vapor control membrane on the interior to slow moisture drive during heating seasons or is it fine without one?

[@granthmeek]

Love your video! QUESTION: to be clear, is the 3" thermal break filled with cellulose? Also, isn't he true weighted average R-value of the wall significantly reduced by the large window?

[@RogerWilsonTodd]

Steve, what factors should be considered when choosing between these two 12" double-stud walls: 2x4+5" gap+2x4 OR 2x6+3" gap+2x4?

[@brianhewlitt2989]

That was great coverage on dbl stud walls Steve! And glad you talked about how the "dew point" moves within the wall assembly and having to pay attention to potential condensate. I was wondering your view on offsetting the 2x6's and 2x4's centres (ie by 12")? Effectively that would produce greater depth of insul in the cavity between the two walls (ie., 6-1/2" of insul between the inside face of a 2x6 and the vap barr / drywall, and 8-1/2" of insul from the front face of a 2x4 to the exterior sheathing, respectively). Obviously most applicable on long running walls, but do you think that would add materially to the R-values, rather than simply a consistent 3" thermal break? Worth the bother?

[@RogerWilsonTodd]

Steve, what factors should be considered when choosing between double-stud and staggered-stud?

[@ianupton4027]

Curious what the “need” is for the 2X6 on the exterior wall? Would 2X4 interior and exterior be structurally sufficient? Potential for a larger thermal break where the stud section of the wall would have greater R value, not to mention less lumber.

[@stevenbaczekarchitect9431]

It is on Martha's Vineyard - 120 mph wind zone framed 24"OC

[@2brazy4ubitch]

@@stevenbaczekarchitect9431 Which is an interesting point. Double Stud is a really straightforward way to make reasonably good performance tall and/or very high wind and/or very heavy cladding situations work, because you don’t really need to care about the framing factor of the outer wall since no interior finishes are attached directly. Question - ever framed with structural sheathing to the inside for your primary air barrier, cavity (i.e. to the outside of the sheathing) filled with batts and then fluid applied + glass mat sheathing or just a textile WRB as the water-shedding plane?

[@andreycham4797]

​@@2brazy4ubitch this is how they do it in north Europe

[@jonathanmilton9753]

Can you add exterior insulation to this wall to stop the problem of the sheathing getting cold?

[@roberthorkman9795]

Whats inspection say when it comes to electrical? I know fire caulking is only necessary in vertical penetrations but if all that wall was able to breathe??

[@garethreid6308]

Informative as ever Steve. But I have a question. Lets assume the same thickness of insulation is included in 2 different wall configurations. Along with the same interior and exterior finishing layers. Number 1 wall is the double wall as shown here. Number 2 wall is a standard 2x4 wall with 3.5" of insulation within it and the remaining thickness of insulation is applies to the exterior. Is there any advantage to No1 over No2? To my mind Number 2 has a better thermal break and a lot less lumber so will also be cheaper. Also as a potential owner builder with little framing experience I think No2 would be easier to build. Or if I did get framers in at least I'm only paying for one 2x4 frame to be built? Whats your thoughts? TIA

[@T_157-40]

Like it but could you use Zip R9 with 2” closed cell foam, then 4” RockWool in cavity, A vapor barrier, then the 3” of cellulose? Can this eliminate condensation and have higher rated insulation over long term.

[@billmongiello4885]

what do nyou do about fire blocking between the studs...actually there is an open space from floor to ceiling, between the two walls which would allow fire to go straick from floor to ceiling...what am i missing

[@JoshuaRes]

That space will be full of dense pack cellulose treated with a fire retardant.

[@natej6671]

So while the insulation info is good, what about that large opening without an appropriate sized header and no cripples?

[@ridgehackett8391]

Is there any reason that you couldn't offset the 2x4s from the 2x6?

[@patrickday4206]

It will be quiet inside

[@kirkellis4329]

If the inner wall was the 2x6 load bearing wall, the roof/ceiling spans would be a foot shorter. If it was zip-sheathed and then the outer non-load bearing wall unsheathed and supporting just the cladding, you would still have the same thickness of cellulose, but shorter spans for roof/ceiling, as well as "innie" windows, so why not do it that way ? The only downside I see is that you have no cavity to run wiring/plumbing between the two walls. On he plus side, you would eliminate the thermal bridging around the windows and doors because you don't need 12" wide jambs.

[@GodsProvidence]

The devil’s in the details, I guess … please comment more on making a durable low maintenance wall, especially with respect to moisture transfer. If we build a double stud wall are we signing up for finicky interior vapor barriers and fine tuned mechanical ventilation? Is there a way to avoid the infamous “cold sheathing problem” altogether, like flashing the inside of the sheathing with closed cell foam?

[@JoshuaRes]

Insulate on the exterior. You need long fasteners and other details, but you keep the sheathing above the dew point.

[@josephbooth1055]

Why dont you offset the inner and outer walls so the thermal break is more than 2 times the space.

[@oakcreekbuilders547]

Once the bridge is broken it’s broken. It doesn’t matter if it’s 3” or offset in half because the cellulose won’t bridge

[@TomLap-qd6xc]

What wall rafter connection can be made if you want a conditioned attic?

[@WILSON.1]

What's an estimated return on investment based on the savings in hvac costs vs the extra cost of the double framing?

[@JoshuaRes]

What’s the cost of extra comfort in the space? It’s not just energy savings, it’s a consistent temperature through the space and no outside noise.

[@WILSON.1]

@@JoshuaRes I suppose that matters in certain environments.

[@JoshuaRes]

@@WILSON.1it’s often the most impactful way to sell an upgrade like this. Definitely higher cost to build, but there are benefits beyond energy savings.

[@markcollins457]

You should wear a microphone.

[@DYI]

a 1.5 inch wide stud every 24 inches only is 6% of the total area so pretty negligible to have to have the R value of 6 (R value of solid wood)