Helpful? 0

Are sealed electrical boxes needed for the airtight drywall approach when using drywall gaskets?

I'm planning to use the airtight drywall approach to air-sealing in a single room renovation.

As I understand it with internal walls the concern is penetration into the attic. So I'm using drywall gaskets from Conservation Technology to seal the drywall at the top (and bottom plates). If the top-plates are well sealed do I need to worry about air-sealing the electrical boxes? Warm air could penetrate but not rise into the attic (or more likely in Zone 2) warm air won't ever get from the attic behind the drywall to enter the room.

The external walls are block and won't have dry-wall on them; they will have American Clay. So the drywall gaskets here will just be for the ceiling/wall join. I know that sealing electrical boxes in external walls is recommended, but I assume that's for air penetration from the outside (not top) which isn't a concern for us.

On a related question: in cooling season is air-sealing the ceiling so crucial? Why doesn't the AC cooled air stay low in the house while the super-heated attic air stays high? Is it primarily a question of pressure or wind wash rather than temperature? Or is this an example of something that's crucial in warming season (cold outside/warm inside) but not as crucial in cooling season (where low to the ground sealing is more important, e.g., under doors).

Thanks,
James

Asked by James Howison
Posted Fri, 07/20/2012 - 18:09
Edited Fri, 10/12/2012 - 15:57

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5 Answers

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1.
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James,
If you are following the Airtight Drywall Approach, you only need airtight electrical boxes on exterior walls. Ordinary electrical boxes are fine for partition walls, as long as you have installed gaskets are caulk along the top plate of the partition walls.

Q. "In the cooling season, is air-sealing the ceiling so crucial?"

A. Yes. You don't want cool conditioned air to leave your house; nor do you want hot, humid exterior air to enter your house.

Q. "Why doesn't the AC cooled air stay low in the house while the super-heated attic air stays high?"

A. To some extent, the stack effect has the effect you describe. However, since the delta-T in summer is much less than the delta-T in winter (in most climates), summertime stack effect is not as strong as wintertime stack effect. During the summer, air can leak out of your house in many ways -- through cracks in your walls, rim joists, or mudsills, for example, or due to wind effects which pressurize one side of your house while depressurizing the other side of your house. Another leakage mechanism is an unbalanced HVAC system with duct leakage on one side (either the supply side or the return side of your duct system). To replace the escaping air, outdoor air enters your home through other cracks -- for example, cracks in your ceiling that allow hot attic air to enter.

Answered by Martin Holladay, GBA Advisor
Posted Sat, 07/21/2012 - 06:31

2.
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Thanks Martin, appreciate the reply. So, in short, yes to stack effect but not that strong and probably outweighed by pressure related factors. And when the air has to come from somewhere the last place you want it to come from is the super-hot attic.

Since we're about to put some new bathroom fans in we'll definitely be depressing the house when they are on, so really good sealing of the ceiling would help ensure that the outside air comes from the coolest possible source (or at least not the hottest possible source).

Answered by James Howison
Posted Mon, 07/23/2012 - 17:07

3.
Helpful? 0

James, an option so as to not sadden your home, is to install Panasonic bath fans that are mini HRVs. Then you may have a happier house. I just feel bad to see anyone depressing their home as I build homes and hand them over hopeful that they will have a long joyfilled life.

Answered by aj builder, Upstate NY Zone 6a
Posted Tue, 07/24/2012 - 09:38

4.
Helpful? 0

:) Nicely done, AJ, nicely done. Actually I hadn't considered that option. It's pretty expensive upfront ($350 vs $110 for 80cfm exhaust only model) but I like that it is balanced (no ugly door undercut). Max cfm is 40, though, which falls below the requirements for bathroom fans. More importantly I doubt it would evacuate the (depressing!) smells fast enough (a crucial requirement :)

But definitely something to thing about in the future, if we actually get the house tight enough to make additional ventilation cost effective.

Answered by James Howison
Posted Tue, 07/24/2012 - 09:56

5.
Helpful? 0

James, 25 years ago, I updated my bathroom to be a zero VOC room. Absolutely zero VOC from start to finish, from entry, to task, to departure and reoccupation.

Hint. I properly located my vent intake. CFM required? way less than 40cfm. Neat trick, still figuring on becoming a zillionare from my invention.

Answered by aj builder, Upstate NY Zone 6a
Posted Sun, 10/14/2012 - 14:48

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