[jbrah]

Getting ready to put up drywall in this room (pics below). I've got 1/2" rigid foam board on the framing (and 1/2" rigid foam in the stud bays sealed in place with spray foam; so cavities are 3-1/2" deep for the R15 batts). I'd like the drywall install to be airtight so that interior air doesn't flow into the stud bays. Reading some articles on the "airtight drywall approach" and most mention drywall gaskets, but don't show pics of what this is. And searching HD and Amazon don't show any product that looks suitable for covering the framing perimeter.

So what is this stuff?

I could use polyurethane adhesive, but thinking something more flexible would be better, which I assume gaskets are.

 

[Chris616]

Possibly as shown in the photos below. Where I live we use the type of electrical box on the left for uninsulated interior walls and the type on the right for insulated exterior walls. We call the sealing surface a gasket. There is also foam material covering the wire inlet holes to reduce air movement through the box. In our scenario we would be putting up a polyethylene vapour barrier before the drywall.

Chris

 

[Windows on Wash]

Nothing needed. Did you seal behind the outlet boxes? We normally just caulk and seal around the boxes after the drywall is up.

Just seal the bottom of the drywall where it meets the subfloor. Tape and mud take care of the rest.

Did you air seal the outer wall prior to insulating?

 

[jbrah]

Nothing needed.

Just screwing the drywall to the framing (+ mudding) is sufficient for air sealing drywall so that air doesn't migrate into the wall cavities? Seems like all the sites talking about airtight drywall are using either gaskets or caulk/adhesive.

Did you seal behind the outlet boxes? We normally just caulk and seal around the boxes after the drywall is up.

Yes, I used canned spray foam behind all the boxes, so the wire penetrations are all sealed.

Did you air seal the outer wall prior to insulating?

Yes, all the stud bays were lined with rigid foam, which was sealed in place with canned spray foam.

Just seal the bottom of the drywall where it meets the subfloor. Tape and mud take care of the rest.

On that point, after drywall and paint, I'm going to remove the tiles you can see in the pic. Then put in new flooring (vapor barrier and probably some synthetic wood-look boards) on the concrete. So I need to have a small gap between the drywall and the concrete so I can run the new flooring to underneath the drywall, right?

 

[Windows on Wash]

You don't want the drywall touching the concrete. With regards to the flooring, the base molding normally covers the intersection between the drywall and the flooring.



You can seal that bottom edge to the drywall and concrete with a sealant or backer rod for proper air seal.

 

[lenaitch]

While not directly related to 'drywall sealing' the attached are common here when using poly vapour barrier.

 

[Nealtw]

If nothing else I would block the air coming beside the box and add tape around the box

 

[Windows on Wash]

If the back of the box is sealed with foam, you just need to seal between the drywall and the box edge.

 

[jbrah]

Nothing needed. Did you seal behind the outlet boxes? We normally just caulk and seal around the boxes after the drywall is up.

Just seal the bottom of the drywall where it meets the subfloor. Tape and mud take care of the rest.

Good point re: mud. I wonder why so many sites talking about air sealing use a caulk between drywall and framing. I guess its another layer of air sealing in case the first one fails. Practical difficulty with caulk is you have to apply it, but before screwing drywall all the way in, you have to cut out for all the openings (elec boxes, switches, windows), so caulk is close to cured by the time you run the screws all the way in.

Thanks for the explanation; I'll skip the caulk on the framing.

You don't want the drywall touching the concrete. With regards to the flooring, the base molding normally covers the intersection between the drywall and the flooring.



You can seal that bottom edge to the drywall and concrete with a sealant or backer rod for proper air seal.

I was thinking I'd use canned spray foam, but I like the backer rod idea - less work than trying to cut off excess foam right up against a concrete floor. I take it backer rod is an air barrier?

If the back of the box is sealed with foam, you just need to seal between the drywall and the box edge.

Yep, I'll use spray foam gun to seal the junction of drywall and box edges. Wire penetrations at the back of box are already sealed with foam.

 

[Windows on Wash]

Backer rod is an air barrier. Called foam is probably cheaper, but make sure it is window and door foam (i.e. closed cell).

 

[ron45]

Just a reminder unless you don't believe, then forget this reminder.

https://www.energyvanguard.com/blog/23818/Myth-A-House-Needs-to-Breathe

"" Have you heard that one before, that you shouldn't seal up your house too tightly because a house needs to breathe? It's a common myth, but that's all it is - a myth. Houses do NOT need to breathe. People do.

I think the origin of this one may lie in the supertight, superinsulated houses of the 1970s, when they hadn't yet figured out how to look at the house as a system. They sealed up the houses to eliminate all the energy wasted on infiltration, but they forgot one key detail. Tight houses need mechanical ventilation.

A house cannot be too tight in my opinion. Yes, a tight house can have problems, but it's generally not because of the air sealing. The problem is the lack of systems thinking. Here are the three main problems that sometimes occur with tight houses:

Poor indoor air quality (IAQ)
Backdrafting of combustion appliances
High humidity, mold growth
The solution to the first of these problems is mechanical ventilation. We understand this now. Random leaks don't bring in fresh air, so we seal up the house as tight as possible and then intentionally bring in air from a location where we know it will be as fresh as possible (i.e., not off the roof or over the garage).

Backdrafting combustion appliances can be dangerous. When air is coming down the flue pipe and into the house, the exhaust gases aren't going up the flue pipe. That changes the combustion process, making it more likely to generate carbon monoxide and dump it into the house. Not good.

Atmospheric combustion appliances, like the gas water shown here, use air from the space around them for combustion. The solution here is to isolate them from the living space and give them their own air supply for combustion air. Building codes now require "high-low" vents for combustion air. This isn't for ventilation; it's air for the water heater or furnace to use in combustion, so the room where these combustion appliances are should be air sealed and insulated to isolate it from the living space.

The third problem, humidity, is often solved by proper sizing of the cooling system, a good ventilation system, and materials that don't trap moisture. An oversized air conditioner doesn't have long enough run times to dehumidify very well. A ventilation system will remove internally generated moisture before it becomes a problem.

The need for materials that don't trap moisture is true for many houses. Unless you're in a one-way climate, like Minneapolis or Miami, putting plastic in your walls will trap moisture and grow things. Houses don't need to breathe, but they do need to be able to dry out when they get wet.

Here, then, are three rules that we could substitute for this myth about houses needing to breathe:

People need to breathe.
Don't mix combustion air and people air.
Houses need to be able to dry out. ""