Gap between ceiling insulation and drywall

[clonedad]

Hey all!
See attached image. Planning to hang some ceiling drywall. Won’t have attic access, so insulation needs to be done before drywall. Will having an air space between the drywall and the insulation like this cause any issues? If so, should I instead staple the insulation to the inside of the studs, or to the face of the studs? Just curious if there are any downsides to having a pocket of airspace between the insulation and drywall, whether it be insulation, moisture, or sound related.

 

[Firebrick43]

Nice warm and open spot for rodents to nest

 

[jack stand]

I'd be inclined to move the insulation up into the rafters and make that your insulation "envelope". But to answer your question, no that air space is fine but the insulation needs to continue to the adjoining walls.

 

[billconner]

The rating of fiberglass batts is based on a tight fit, preventing "convective looping". I think this gap will lessen the R value. I would want the insulation in contact with the ceiling.

BTW not sure what codes you are subject to if any, but most codes in US require attic access.

IRC:

R807.1 Attic access.

Buildings with combustible ceiling or roof construction shall have an attic access opening to attic areas that have a vertical height of 30 inches (762 mm) or greater over an area of not less than 30 square feet (2.8 m2). The vertical height shall be measured from the top of the ceiling framing members to the underside of the roof framing members.
The rough-framed opening shall be not less than 22 inches by 30 inches (559 mm by 762 mm) and shall be located in a hallway or other location with ready access. Where located in a wall, the opening shall be not less than 22 inches wide by 30 inches high (559 mm wide by 762 mm high). Where the access is located in a ceiling, minimum unobstructed headroom in the attic space shall be 30 inches (762 mm) at some point above the access measured vertically from the bottom of ceiling framing members. See Section M1305.1.3 for access requirements where mechanical equipment is located in attics.

 

[Bucko]

Personally I would pull it down so you can bring it to the edge and not have it compressed. When insulation gets compressed it diminishes its "R" value. Also put baffle channels in so you don't block the soffit vents.

As a side note its also good to stay away from drywall joints over door and window openings as it has a higher chance of cracking. Its one of the reasons sheets are installed horizontal and not vertical so you don't have one continuous seam up the wall. Also you typically start with the ceiling so your first wall sheet can be butted up to the ceiling and support the ceiling drywall. You already have most of your wall sheets up but you can put that filler piece tight to the ceiling and leave any gap between two wall sheets.

 

[NUTTSGT]

Pardon me, but I'm looking at this on my phone so it's hard to tell. Are those batts just sitting atop the bottom cord of the trusses or are they attached to something ?

 

[MerlinsBeard]

Based on your picture, my initial thought would be baffles against the ceiling for shingle ventilation (from soffit to ridge vent) with fiberglass batts in the rafters, followed by ceiling drywall with an access door where you can blow insulation (taking care to avoid blowing insulation into the soffits).

I don't think fiberglass batts laying on the trusses by itself will do very well if you plan to condition the space.

 

[K'ledgeBldr]

It should look something like this-


The insulation batt should be in contact with the drywall. An air gap as you photo’ed creates a path for cold air from the exterior wall.

 

[billconner]

Unless you can get the Kraft pape facing to create an air tight membrane, I'd be concerned for cold air in that cavity and condensation on the bottom of drywall.

 

[racecougar]

Not the best photo, but it's what I have on this computer. Bring the batts down into the cavities and staple the kraft facings to the framing.

 

[John 37]

I Would put your drywall (or sheet wood) on top of your ceiling beams. That way they're available for mounting lights and other items. They're also useful to hang things from when your walls are full. Storage is always a problem in workshops. To quote a wise man, "Space, the final frontier"
BTW, don't run wiring in the insulation. It can overheat on high load.

 

[K'ledgeBldr]

BTW, don't run wiring in the insulation. It can overheat on high load.

What!???
“Wiring” runs through insulation all the time.

Wire “overheating on high load” is because of “load” not insulation. And breakers are the safeguard.
BTW- insulation doesn’t burn.

 

[Firebrick43]

What!???
“Wiring” runs through insulation all the time.

Wire “overheating on high load” is because of “load” not insulation. And breakers are the safeguard.
BTW- insulation doesn’t burn.

Agree with you on the wiring.

Fiberglass itself doesn't combust, but allows fire to go right through it as if it wasn't there.

Rock wool and cellulose will actually retard a fire. Of course they well still smolder but they give time for people to get out.

 

[billconner]

BTW, don't run wiring in the insulation. It can overheat on high load.

That generally applies only to knob and tube wiring, and probably not much of that bring done new.

 

[John 37]

Thast may be the case in the US but is agianst our wiring code in UK.
Current in a wire causes heat. The higher the current, the more heat. All cables exibit a voltage drop when passing current. Watts = volt drop x current. If this heat cannot escape, the temperature continues to rise, eventually to the point of isulation failure. Here cables are rated to carry different max current depending on their instalation. The protection system should be chosen to take this into account.
We allow insulation to pass through insulation to a max od 4" without de-rating.

 

[beemerphile]

Rock wool and cellulose will actually retard a fire. Of course they well still smolder but they give time for people to get out.

I've never seen Rockwool smolder, even when attacked with a torch.

 

[John 37]

Agreed but pvc wiring insulation burns really well.
Better than giving people time to get out is not to start the fire in the first place.

 

[billconner]

Thast may be the case in the US but is agianst our wiring code in UK.
Current in a wire causes heat. The higher the current, the more heat. All cables exibit a voltage drop when passing current. Watts = volt drop x current. If this heat cannot escape, the temperature continues to rise, eventually to the point of isulation failure. Here cables are rated to carry different max current depending on their instalation. The protection system should be chosen to take this into account.
We allow insulation to pass through insulation to a max od 4" without de-rating.

Doesn't your ring system result in typically much higher current in a single conductor?

 

[CombatNinja]

The little air gap from the bottom chord to the kraft facing is the least of your problems. What about the 3 foot gap above it? Not being a smartass here, trying to make a point. Ideally, of course, fiberglass batts fit snugly in their cavity without being compressed and are encased on all six sides. That is how you get the rated r-value. Unless you are going to put some sheathing or even cardboard or rigid foam or something on top, you'd be wasting your time worrying about an inch gap at the bottom. You really need something on top up there to prevent air washing over that fiberglass.

 

[Firebrick43]

I've never seen Rockwool smolder, even when attacked with a torch.

Like the fiberglass, I wasn't talking about the insulation itself. More the structure that its installed in. Never seen anyone say that rockwool makes a wood walled structure its installed in fireproof? Have you?

 

[beemerphile]

Like the fiberglass, I wasn't talking about the insulation itself. More the structure that its installed in. Never seen anyone say that rockwool makes a wood walled structure its installed in fireproof? Have you?

No, I misinterpreted your statement to be that the insulation smoldered, which I haven't seen. Rockwool is all I use these days as nothing else has its collection of properties (sound deadening; fire, bug, and water resistance; low/no VOC emission; and so on.)

 

[CombatNinja]

Rockwool is pretty amazing stuff when compared to the old standard fiberglass. Other than being a bit more expensive, zero drawbacks.

 

[Firebrick43]

Rockwool is pretty amazing stuff when compared to the old standard fiberglass. Other than being a bit more expensive, zero drawbacks

I have experienced even more itchiness compared to fiberglass. But yea, its what I use in wood wall with 16" bays. I still use cellulose in ceilings.

Even fiberglass has its place in pole buildings as it can bought in 8' wide bats.

 

[beemerphile]

I have experienced even more itchiness compared to fiberglass.

Quite the opposite of my experience with it.

 

[Firebrick43]

Quite the opposite of my experience with it.

maybe its a difference in brands? I was using owens corning. Also I was cutting it to shape with a japanse hand saw. Never been so itchy before with insulation.

 

[beemerphile]

maybe its a difference in brands? I was using owens corning. Also I was cutting it to shape with a japanse hand saw. Never been so itchy before with insulation.

I use what used to be called Roxul. I cut to shape with a Grip-Rite Stone Wool Insulation Knife

 

[John 37]

Doesn't your ring system result in typically much higher current in a single conductor?

It shouldn't do. Our typical power ring uses a 32A breaker. A 26A cable comes out of that, goes right round the socket outlets covered and back into the breaker. The current can travel both ways round the ring. All the sockets have both cables going into them as does the circuit breaker.

 

[billconner]

32 amps at 220 volts around 7000 watts. Compare to 15 amps at 120 or 1800 watts. Also seems we have many more circuits - 36 or so in our house - so total load in house is spread across even more conductors.

 

[John 37]

32 amps at 220 volts around 7000 watts. Compare to 15 amps at 120 or 1800 watts. Also seems we have many more circuits - 36 or so in our house - so total load in house is spread across even more conductors.

Sounds like you do. We have typically about 10 circuits.

 

[billconner]

Not unusual to have 10 or more in kitchen alone. I really don't think you'd find much heat generated by (code compliant) wiring in US houses. Only knob & tube is not suppose to have contact with (thermal house) insulation.

 

[jetnow1]

kraft paper is supposed to be in contact with drywall to reduce fire spread. Fiberglass will not burn but kraft paper sure will.

 

[rayra]

racecougar is correct and the OP's picture shows the batts installed totally improperly.