Cup of Joe - Flow-Through Assemblies

Cup of Joe
Flow-Through Assemblies
Once we understood the need for air control and vapor control layers and started putting them in to our buildings to develop an enclosure, we saw that, once they became wet, they could only dry in one direction.
The climate zone the building is in makes a difference in the failure that occurs. Example: Buildings in a cold climate with vapor BARRIERS on the inside, could only dry out. In buildings in a hot-humid climate, vapor BARRIERS could only dry in. This seems obvious now, but it didn't become obvious until we did it.
We then saw the need to slow down the vapor transmission rather than attempt to stop it altogether. This vapor throttle helped to control condensation in these enclosures. We still needed to control air flow to keep moisture-laden air out, and found it easiest place to design and install an air control layer was on the outside of the wall. We found these airtight but more vapor-open assemblies to be more forgiving in that they helped increase durability of the wall.
Then we found that installing rigid insulation outside of the air control layer helped keep the interior wall cavity from condensing on the back of the sheathing as vapor could now flow through the assembly.
This wall works even better if between the cladding and the rigid insulation, a small amount of airflow can occur and if the rain that gets behind the cladding can dry out. So we needed a gap.
Oh, and don't try to undo all the progressive steps we have made by now installing a vapor BARRIER on the inside finish of the wall. Vinyl wallcoverings are just such a BARRIER. Don't use them. No matter who tries to convince you that you could use perforated vinyl without trapping the vapor. You can't. Not oil-based or epoxy paints, either.
The same technology works for a roof but not for a slab. Slabs are always touching the wet ground and you absolutely need a vapor BARRIER under your slab. But 2 out of 3 ain't bad.
If you want to see more like this, consider coming to one of our seminars!
www.buildingscience.com/upcom...

[@Mrcool12684]

Hey Joe! been learning and studying BS and you are popping up everywhere and it is absolutely bad ass to learn from ya. I am just a normal carpenter and planning on starting a passive / high performance residential renovation or building company in the next few years and just wanted to say thanks for all you've done and like your ability to teach and not take SH&# from people that think they know how to build!

[@inkhole]

Hi Joe. Are you intending to continue this series? I for one very much hope so.

[@kenmarcou]

Loving these. Thank you so much!

[@markodeen4105]

Who knew that Meatloaf was a Building Scientist !

[@MrBiron1]

So if I do have a vapor open assembly can I put a rain screen then put vinyl panels on the interior. Diffusion into an air gap..... The manufacturer recommends that is to prevent holes... I want to pressure washed the bottom of my garage....

[@trans4md74]

Joe, while watching this video, I couldn’t help but wonder if, by your description, a well air-sealed ICF wall would serve as such an assembly. I’m not sure if the WVT of the EPS and concrete would meet your definition of, “flow through”. I appreciate all of your content!

[@l0I0I0I0]

Watched most of your vids, TY!!! Vapor permeable insulation BOTH on the outside AND inside of the vapor throttle. WHAT 2 product would you recommend for the vapor throttle if price is a concern and if not?

[@MrBiron1]

Delta Fox or 475 membranes

[@l0I0I0I0]

Nice thank you!

[@nikojansen9648]

Would a (vapor) flow through assembly also be beneficial in hot humid climate like Florida?

[@CC-qr1cs]

Very interesting idea. However when you talked about interior finishes I’d be worried about an occupant not being aware of how the wall works and putting up a retrofitting a finish that may be detrimental to the wall assembly as designed. Building occupants can always mess up a beautifully designed building. But you know that!

[@davidbruce5377]

Joe is 5 to 10 perm vapour throttle good? I have 7 perm in my dry both sides assembly

[@paulbooij7594]

It does not appear that you read comments, but I will ask anyway. Air molecules are smaller then water molecules. How does water vapor move through a vapor retarder, but stop the smaller air molecule?

[@buildingsciencecorporation8434]

Air is a mechanical mixture of nitrogen (N2) molecular weight 28 and oxygen (O2) 32. Water (H2O) has a molecular weight of 18. Mass is only one of the factors. Size also matters, but not as much as you would think. Water molecules are about 2.75 angstroms (0.275 nanometers). Nitrogen molecules and oxygen are both about 3.0 angstroms. Water molecules are smaller. Having said that... the vapor flow by diffusion through a material is complicated by the polar nature of the water molecule, adsorbed water mono layers, capillary condensation and surface diffusion. Look up Lord Kelvin and the BET theory…then have a stiff drink.

[@MrTooTechnical]

Fuk ya. Go Canada

[@carrabellicusp]

Joe you’re a three out of three