Air Sealing Detail: floor sheathing to crawlspace?

[graham]

I'm looking for an air-sealing detail and realize I've never dealt with this situation as new construction, only retrofits:

Vented crawlspace with wood-framed crippled wall atop foundation. Airtight layer is floor sheathing, wall and roof sheathing. What suggestions do you have to connect the floor sheathing to the wall sheathing, when the wall sheathing needs to run continuously (earthquake country) from mud sill to top plate? In other words, how to connect the perimeter of floor sheathing to the wall sheathing when the wall sheathing runs an additional 24" below the top of floor joists?

Thanks in advance!

[Cindi Anderson]

I would never do a vented crawlspace so the rest is moot.  Build it right so your clients don't get sick from mold, with a conditioned crawl.

[em...@haydenrobinson.com]

Hello Graham, 

I’ve held for writing since I haven’t air tested these details. But nobody seems to be responding.

I haven’t faced your exact pony wall/vented crawl space issue, but analogous conditions. If memory serves, what I have drawn is what Lstiburek diagrams in his Builders Guides: a non-adhesive seal between the inside of the sheathing and the sill plate and gasket between the sill plate and the floor air barrier. I’m guessing this has already occurred to you… 
Hayden

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[Albert Rooks]

We were all waiting for you Hayden. :)

I recall that Tessa and Randy during Randy’s Artisan Group leadership period as well as Dan Whitmore worked this out and handily met the test in a couple of different ways. One might have been a house in Ballard with acoustic sealant at sheathing top of rim joist- but it wasn’t inspectable and was backed up with tape at the bottom to sill.

The other might have been the old “floppy bits” method of membrane taped to floor air barrier before wall framing and then dropped down and around to the front bottom of heating and taped there.

Neither are very elegant but it’s a demanding detail as evidence that it challenges Graham.

It would be nice if we could thicken the wall and just put the air barrier on the inside by membrane or sheer wall and then just connect to the top of floor. But I guess we don’t do things like that in this region. Those darn frames with sheer layer outside.

Hope you’re all doing well. Nice to see this platform being used:)

Best,

Albert Rooks.

Sent from my iPhone

On Jul 9, 2024, at 04:05, em...@haydenrobinson.com wrote:



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[Thomas Corwin]

It's quite possible to have a healthy house w/no mold issues and a vented crawlspace.   They are everywhere in the pnw.

Thomas Corwin
epochbuilders.com
360-790-5132

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[Thomas Corwin]

Couple of options:

>>pouring a ratt slab under the house and making it a conditioned crawlspace can be a great option. I personally prefer this option if it's possible.

>>one of the simplest and easiest is a flash and batt (2 part poly spray foam w/batts) in the floor joists.  Insulation contractors do this all the time.  Then use SIGA fentrim tape from exterior wall sheathing to concrete. 

 

>>Alternatively from the spray foam, in the floor joists you could use solid batt insulation with SIGA Majpel taped at the bottom of the floor joists.

>>You could seal the interior, facing up, side of the floor sheathing, similar to a zip wall or using a roll on product (like prosoco).  NOTE: ive never done this but i would consider it. 

 

>>for a house where theres no budget for floor air sealing, ive had good results with all tile flooring and marmoleum flooring.

Thomas Corwin
epochbuilders.com
360-790-5132

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[Floris Keverling Buisman]

Graham,

Attached detail is 50% of the solution as it is for a new build (and if you are reframing the wall in a retrofit).

If the wall remains in place - The issue is that you need airseal "through" the bottom plate. 

you can tape to the bottom plate on the inside - to the floor sheathing

and 

On the exterior - you tape the top plate/floor sheathing and bottom plate together with TESCON VANA and then use the 

two beads of CONTEGA HF as the connection to the continuous wall sheathing- 

See here, were we used CONTEGA MULTIBOND instead of HF, but that is less cost effective.

Floris

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[Markus Barrera-Kolb]

Hello Graham,

There shouldn't be any reason why your engineer can't make the shear connection through the 1st floor wall bottom plates into the floor diaphragm without the sheathing being continuous across that joint. That way you can make the air barrier transition with a  membrane of your choice. Hold-downs and/or seismic straps will likely be part of the lateral system as well, but these shouldn't interfere with that connection.

Cheers,

Markus 

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[Thomas Corwin]

Good morning Graham.  Thanks for posting, I love geeking out on details like these and hearing everyone's great ideas!

I was thinking about your assembly details this am and it occurred to me that typically with continuous exterior wall sheathing you are allowed to split the sheathing at a horizontal line of blocking, (depending on if it's shearwall A, B, C, etc, there are different requirements for blocking thickness and o.c nailing pattern).  One idea is you could split your wall sheathing at the bottom plate of the wall.  You could wrap the floor air tight layer down to the exterior face of the rim joist & this would allow access to your floor sheathing air tight layer to connect with your wall sheathing air tight layer, after the walls were stood up.  Then add the lower wall sheathing.   Carpenters wouldn't be sad by this assembly either.

Thanks again for posting!

Thomas Corwin
epochbuilders.com
360-790-5132

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[Dylan Lamar]

Hi Graham,

I’d do the “floppy bits” method Al describes (I’m going to use that name from now on! Ha!)

Alternatively get the engineer to spec an alternate method of transferring shear down to the floor rim. Could be done with simpson plates/straps on the exterior for example. Allowing the wall sheathing to break at the floor sheathing plane so the gap can be taped in a way that can be inspected.

I have tried to have framers caulk the floor sheathing edge before applying the wall sheathing (cont from floor to wall) and I have not once been successful. I even forgot to do it when I was doing the framing myself on a tiny house, Ha! 

dylan

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[graham]

Thank you Hayden & Albert! Tricky, convoluted, air barrier! FYI, Dan Whitmore suggested air sealing the floor decking to the rim joist (which is ideally engineered material without joints) then running the wall sheathing part way onto the rim, sufficiently for structural nailing, and sealing the wall sheathing to the rim as well, before filling in sheathing below. Not my typical choice for foundation detail, but it is what it is, and sometimes it's necessary (flood zones, etc.). I'm inclined to side with Dr. Joe when he says "At the end of the day, recall that the best crawlspace of all is filled with concrete and called a slab—or dug out and called a basement." (https://buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces) ;-)

[Albert Rooks]

Nice to see this continuing. “Floopy Bits” is a Canadian term and it’s surprisingly useful. It also describes membrane connection from an exterior air barrier at sheathing to the under side of trusses at roof. Another tricky location due to stacked members.

And nice to read a post from PHNW founder Hayden Robinson who graciously hosted the startup PHNW org in his Ballard office. 

In this string I also learned the Dylan Lamar has made a mistake. It’s surprising, but it makes me feel much more human since I mostly live having to correct my frequent errors.

Thanks all for your contributions. It’s great to read your posts rather than world news.

Best,

Albert Rooks.

Sent from my iPhone

On Jul 13, 2024, at 22:18, Thomas Corwin <t...@epochbuilders.com> wrote:



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[graham]

I knew I was posting in the right place, thank you all!

Regards,

Graham

[Scott Mizée]

I've been learning more about conditioned crawls lately, Cindi.  Can you suggest any good resources where I might learn more?

Thanks!

Scott

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Scott Mizée

c 971.235.0249      e miz...@gmail.com

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[Thomas Corwin]

Hi Scott,

Check this link out,

https://hammerandhand.com/best-practices/manual/8-crawlspaces/8-1-general-guidelines/

It has some great assembly details.

Thomas Corwin
epochbuilders.com
360-790-5132

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["S. Mizée"]

Thank you! I will!

—sent via iPhone 

Scott Mizée

mizees@gmail.com

On Aug 2, 2024, at 5:27 PM, Thomas Corwin <t...@epochbuilders.com> wrote:



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