A Complete Guide to Insulating Vaulted Ceilings | Unvented AND Vented Solutions

[@SommerBros]

Glad you mentioned workmanship as a key element for a successful assembly. Our favourite strategy is a scissor truss with a continuous ventilation baffle, (usually MSL wood fibre because it is easy to work with, affordable and vapour open) that runs from soffit to ridge. At the interior a monolithic air/vapour membrane, Intello or Majrex with fibreglass dense pack (or loose fill depending on slope). throughout the truss cavities and a 2.5” deep service cavity. We find this to be an economical system that allows for any roofing material or ceiling finish to be used and avoids foam all together.

[@ASIRIDesigns]

That is an excellent strategy, I assume you try to get a scissor truss profile with a raised heel?

[@SommerBros]

@@ASIRIDesigns yes, definitely a raised heel. Typically 12” minimum.

[@RileyLabrecque]

I always research people who post comments like these; hoping that they are local to me; alas~ I wish there was a directory of builders who spend a lot of their free time watching stuff like this.

[@CogitoBcn]

Excellent video, the best one I've found. After 2 years researching about how to insulate my unvented vaulted ceiling, watching a hundred videos with contradicting information I got some conclussions that have been confirmed in this video: - the 2" gap between insulation and roof only applies to vented ceiling - you can fully fill insulation between rafters (with no gap) if: a) is a warm roof (exterior rigid insulation) or b) is a cold roof (no exterior insulation) but you add a smart vapour barrier and you are *extremely* cautious with avoiding vapour barrier perforations. Thanks very much!

[@ASIRIDesigns]

@@CogitoBcn So glad it was helpful! One caveat if you use the airtight smart membrane in a conditioned/unvented assembly - you need to use a vapor diffusion port at the ridge as a means of moisture removal if it happens to accumulate in the cavity. Check out this article from Building Science Corporation for more detailed information: buildingscience.com/documents/building-science-insights-newsletters/bsi-119-conditioned-unconditioned

[@CogitoBcn]

Thanks very much for providing this information and the link, I totally forgot about vapour difussion ports. Can I assume that they work and are relevant also in single-pitched roofs?

[@DitDitDitDahDahDahDitDitDit]

Love your videos. I’m glad you’re talking about emissions from spray foam, which could be manageable if we only knew what they were and for how long they might persist. Further, please, let me say that, while I feel very positively towards mineral wool, I apply the same standards to it and all other materials used in construction. Many products are fabricated using chemicals like formaldehyde, so we need to concern ourselves with the possibility of the off-gassing of those chemicals as well. If mineral wool is going to be placed not only in the exterior walls, but also in the interior walls for sound proofing, then covered over quickly with drywall, its release during construction could be slowed. We have to measure home interior air for pollutants to know these things. Covering the drywall could slow off-gassing, and lead to exposure of the building occupants. There have been instances of off-gassing from drywall too. We need to start measuring for the presence of pollutants in all of the materials that could harbor and release them, then we’d be equipped to take the necessary actions to keep people safe. There simply is no conscionable excuse for not conducting safety studies of this kind. The companies involved would be well advised to do it themselves, get out in front of this issue, and take whatever actions may be needed. Relevant scientific and professional societies should concern themselves with this subject as part of their ethical practice responsibility.

[@DrEsDub]

Great video, but I have a question about the assembly you propose at 2:45. I'm about to build an unvented assembly that looks almost exactly like this, but my research has pointed me to using closed cell foam as the only safe vapor barrier option (3"), with insulation batts for the remaining depth in 2x8 rafters. I worry that with the assembly you propose, condensation will eventually rot the underside of the roof sheathing. Given a 4a climate zone, are you stating that I can do this with just a smart membrane as you picture? Any additional risk with double 5/8 drywall preventing inward drying?

[@_r_ma_]

In the example with an unvented roof with hybrid (C.I. and batt) insulation, how would you detail the attachment of solar panels over say 6" of EPS foam?

[@Rondeaunotrondo]

My understanding is that there are still Condensation risks with any type of dense pack or batt against the underside of the sheathing without venting even with a variable smart membrane. I understand your concerns with spray foam. But I don’t see a way around using it for retrofit situation’s with a Unvented assembly that will not get a new roof. Any mention of exterior insulation on the roof equals a new roof which is incredibly expensive especially with exterior insulation ( I agree this is the best.)

[@ASIRIDesigns]

@@Rondeaunotrondo Your understanding is absolutely correct, the smart vapor membrane is only as effective as preventing condensation if it's properly air sealed. Something I recommend if people end up using this technique is to provide either a vapor diffusion port at the ridge to help dry out any moisture that could accumulate, or use a vapor permeable adhered underlayment in combination with a vented roof covering to help dry out the sheathing. The second strategy is preferred.

[@Rondeaunotrondo]

Thank you. What if there is no venting, and exterior is not being touched?

[@ASIRIDesigns]

@@Rondeaunotrondo I would honestly recommend not insulating at all at that point if you're unable to vent it or touch the exterior. We've actually got a video on our channel about weighing those types of decisions, I believe it's called "Sometimes it's better NOT to insulate".

[@Rondeaunotrondo]

I hear ya. Roof won’t be replaced for another 10 years. Putting ducted mini split in there after realizing ductless head was not great and want to make sure it’s in the envelope. Hoping a flash and batt (correct ratio) approach with intello airbarrier on the interior will work. Will have spray foam 3rd party commissioned. Damned if you do. Damned if you don’t. The world of retrofits and building science. Appreciate your insights.

[@catherinehebson4447]

I am wondering the pros and cons of unvented vs. vented? Would one be more forgiving to a house that tends towards a high relative humidity? It seems an unvented assembly could be fewer materials?

[@Rainbirdddd]

Intello plus rockwool is my personal strategy for my upcoming home build 👌 - not a fan of spray foam and poly isonis expensive - I'm in Zone 3 coastal SC

[@traviswubker2674]

Great video!

[@catherinehebson4447]

I have another question-- but first, I want to thank you for this video- It is incredible!! In the case of a vented deck for a vaulted ceiling, could I fill between the rafters, below the air channels, with batting and then fasten rigid insulation boards beneath the rafters to get to the desired R value? I know furring the rafters is an option, but there are some specifics that make it tricky in my case. Thank you, again!

[@markmartin7384]

It should work In my opinion

[@justinlynch6691]

Joe Lstiburek would say you need a vented roof over your conditioned roof to prevent ice damming.

[@justinlynch6691]

Also it's not just expensive it's more square feet than a vented attic so it is less efficient

[@2point..0]

As always Liked#19 N Subscribed!!! I am going to be designing and building in the state of Maine, a Passive Solar Double (Skillion or Clerestory) Shed Roof house low sloped (Contemporary Modern) with Exposed Wood Ceilings beams and trying to learn Chief Architect!!!

[@abacab87]

Our code no longer allows a vapor barrier of any type. I would assume that is because no assembly is perfect and moisture will get in one way or another. That has been my experience when ripping houses apart. Houses need to breath.