# Does Spraying Foam on Edges of Studs Actually Effective at Air Sealing?



## cloves (Aug 2, 2009)

Hi everyone, 

So I have seen online that people use the spray foam in a can and run a line of foam around the perimeter of there stud walls (Part that has the outside plywood) and then put in there fiberglass batts.

Is this actually a smart and effective way of air sealing?


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## Windows on Wash (Aug 30, 2011)

Can be but caulk is probably easier here.


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## chemman (Apr 2, 2012)

Yes, use caulk. Save the foam for big gaps.


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## cloves (Aug 2, 2009)

the arrow I drew actually just points to the corner but I meant to mark the whole strip. the problem with using caulk in this situation to go up and down the stud Bay is that caulk does not expand that much.


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## Bud Cline (Mar 12, 2006)

cloves said:


> the arrow I drew actually just points to the corner but I meant to mark the whole strip. the problem with using caulk in this situation to go up and down the stud Bay is that caulk does not expand that much.


Why would it need to expand? Caulk would be a lot more cost-effective and achieve the same end results.


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## joecaption (Nov 30, 2011)

There should be no gaps there to fill.
Looks like a waste of time and materials to me.
Not going to do a thing to stop thermal bridging, or stopping the chimney effect inside the wall cavity.


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## ront02769 (Nov 28, 2008)

Waste of time and $$ IMHO. Just finishing up on an energy star certified new home in MA, inspected periodically from the git go by the energy star guy, no caulking, foam, whatever around the studs in the location you show. Yes to California corners. Yes to r-21 walls. Yes to r-38 ceiling, yes to NON-EXPANDING foam around windows and doors. But caulking there, not so much. Ron


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## SeniorSitizen (Sep 10, 2012)

Use your time to put the insulation in right with the flanges stapled to the 2x4 edges and seal the drywall at the top plate to prevent cold air from filtering down from the attic, interior walls included.


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## chemman (Apr 2, 2012)

I did what the OP is describing. The exterior of my walls are 2' by 8' TG XPS board. The boards were mostly put together in a hurry leaving all kinds of gaps and tons of air intrusion. I caulked all the joints and around the perimeter of the stud bays with Alex Plus and installed rock wool. NO air movement now. Now if the OP's walls are assembled tightly then its probably overkill. Wait for a windy day and feel around with your hand for drafts.


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## Gary in WA (Mar 11, 2009)

Yes, it is a smart way to air seal against infiltration/exfiltration which severely degrades your FG R-value; https://docs.google.com/viewer?a=v&q=cache:23GL573L8rsJ:www.insulex.net/Links_files/Understanding%2520R-Value%2520-%2520Fine%2520Homebuilding.pdf+density+of+fiberglass+insulation+to+stop+convective+loops&hl=en&gl=us&pid=bl&srcid=ADGEESjB5jT6D-pmr_diIjOC-wZLxLcL4M5mbUnQEx_wbazuubbVf8rsdQ_J7E_qb_p6rK4lzPkaHsJJw_pncDyBqyCJUCz2zaxO3wozHJ5XSnommOF0XWF7o9tMOge2FIXRCxwhJgNT&sig=AHIEtbT0wgPl1yn5T5V8M8l_EeA2F-qvvA

It also stops any air movement to the attic (heating climate= warm air rises, no cold air coming down), contributing to the "stack effect"(also seal the wiring holes and ADA the drywall; http://www.wag-aic.org/1999/WAG_99_baker.pdf

http://www.buildingscience.com/documents/information-sheets/air-barriers-airtight-drywall-approach/

Furnace filters are made of fiberglass- do a great job of air filtering, not blocking air.http://www.buildingscience.com/documents/information-sheets/installation-of-cavity-insulation/

Yes, follow your good plan- page 21, 22; http://www.engr.psu.edu/phrc/training/understandingbarriers.pdf

Air leaks (through plywood sheathing-stud joint/wire holes/under bottom plate/ around top plates can also be dangerous to your health; http://www.buildingscience.com/docu...ir-leaks-how-they-waste-energy-and-rot-houses

The batt facing does not require stapling (IF proper framing on-center spacing was used- it will support from studs---- to be an effective vapor retarder- if using as an air barrier instead of drywall, then yes- tape all perimeter); https://docs.google.com/viewer?a=v&...0pf2_7&sig=AHIEtbQylPzdnxaB0Oqk9yRrrdP1VBztDg

Gary
PS. older houses had solid board sheathing on walls, many gaps. Newer ply/OSB have many gaps/cracks from framing lumber differences (studs are mostly 3-1/2"; plate is big/little from that, leaving a gap as the sheathing moves with seasonal RH changes (hence required gaping of sheets)- it's not a boat....


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