Insulating stick-built ceiling - need some guidance

[jblmoon]

I have a 20x17 detached garage with an old stick built ceiling that I'm trying to finish up as a recording studio here in Southern California. I'd like to install a mini-split AC but first I'll need to insulate. My plan is to insulate the walls and ceiling with rockwool and cover with fire-retardant acoustic fabric, as is often done in professional studios, in order to deaden the space acoustically. The walls are easy - 16 on center.

The ceiling is what I'm struggling with. At the top of the walls I've got rafter ties running every 32” on center (they look like joists but I'm fairly certain they are just ties). Here are my questions:

1. How do I install rockwool in the ceilings with the ties spaced so far apart? Make a grid out of strapping? Ferring strips? I don't want the rockwool to hang or sag since it will only be covered by fabric. They make rockwool in 24" and 16" widths.
2. Is it safe to assume the ties can handle the weight of insulation? I know they aren't intended to support much weight since they are just holding the roof and walls from flattening out. But insulation isn't super heavy. Will this be okay?
3. Will I have any issues with abandoning drywall altogether, as I plan to do? (FYI, I will end up using a small area of drywall for the mini-split location)
4. Do I definitely need insulation in the ceilings with this minisplit AC and southern california summers? Or will the mini-split be able to handle the space with just a bit of an extra ding on my electric bill? I have two different friends with similar studio spaces here in town with uninsulated ceilings and they both told me "not to worry about insulating it".

 

[PoorUB]

If it were me I would install the more of collar ties at every 24 inched and hang the centers of the ties to the peak if the roof. The 1x1 strapping every 6-8 inches run perpendicular to the collar ties to hold the insulation. Then you also have something to hang the fabric to.

 

[jblmoon]

If it were me I would install the more of collar ties at every 24 inched and hang the centers of the ties to the peak if the roof. The 1x1 strapping every 6-8 inches run perpendicular to the collar ties to hold the insulation. Then you also have something to hang the fabric to.

Could I just skip the extra ties and do the strapping every 8 inches and call it a day? Guess it might sag a bit.

 

[rayra]

reinforce the center of the collar ties like a K or W truss to the roof rafters. Then skin the bottom side of the collar ties with drywall and stuff with insulation as you work across the ceiling.

 

[jblmoon]

reinforce the center of the collar ties like a K or W truss to the roof rafters. Then skin the bottom side of the collar ties with drywall and stuff with insulation as you work across the ceiling.

Not planning on using drywall for a number of reasons which is why I'm trying to figure out how to keep the insulation held up.

 

[nadogail]

i have seen recording studio wall as and ceiling covered with the fiber inserts from Egg Crates. The object was to avoid a hard flat surface to minimize the transmission and reflection of acoustics. They were glued up with mastic.

 

[K'ledgeBldr]

Staple chicken wire to the ties, lay the rock wool inplace, then cover w/acoustical cloth.

 

[jblmoon]

Staple chicken wire to the ties, lay the rock wool inplace, then cover w/acoustical cloth.

This is an excellent idea actually

 

[ambenz]

I used ultralight Johns Manville rigid foil faced sheathing (R value of 6) hung with carwashers and drywall screws.
Filled in the cutouts with expanded foam, since the pic was taken I trimmed the foam.
Just another option.

 

[Stuart in MN]

The ceiling is the most important place to insulate for climate control so you don't want to go without it (plus for a recording studio you need all the sound deadening you can get). I'd probably use 2x2 strapping perpendicular to the rafter ties. They do make fiberglass insulation in 48" widths, but if it's an old garage those ties may or may not be exactly 48" apart. I *think* you can get rock wool 48" wide but you'd have to check on that. I've seen people use 4x8 sheets of rigid foam but I don't know about the fire retardancy...you don't want melted foam dripping down in the event of a fire.

 

[PoorUB]

This is an excellent idea actually

It will sage something terrible with a four foot span. Same reason I said to add more collar ties then use strapping. Keep the sag under control.

 

[firebirdparts]

The normal way in that size building is 2 x 6 on 24" centers.

 

[billconner]

Are you unconcerned about outside noise? Rockwool or fibreglass will do nothing to prevent transmission of exterior noise through walls and roof/ceiling.

Did you consider placing rockwool between rafters instead of ties? No framing needed.

 

[NUTTSGT]

Is this the same structure you started the other thread on ? A 15x18 that is already insulated with a single 15A circuit that you were turning into an office ?

 

[jblmoon]

Are you unconcerned about outside noise? Rockwool or fibreglass will do nothing to prevent transmission of exterior noise through walls and roof/ceiling.

Did you consider placing rockwool between rafters instead of ties? No framing needed.

The rafters are also 4 ft on center and I’m not concerned about sound transmission really.

 

[jblmoon]

Is this the same structure you started the other thread on ? A 15x18 that is already insulated with a single 15A circuit that you were turning into an office ?

Yes! Not already insulated though... And by office I meant studio - I just didn’t clarify there.

 

[billconner]

The rafters are also 4 ft on center and I’m not concerned about sound transmission really.

The roof rafters are 4' on center? What is the roofing deck that's spans 4'?

 

[jblmoon]

The roof rafters are 4' on center? What is the roofing deck that's spans 4'?

Ahh I’m sorry - I just went out and measured and the rafters and ties are both 32” on center. I don’t know why I had 4’ in my head…

 

[billconner]

Still a wide rafter spacing. Ties are often every other rafter.

I think you add a tie between each one and use 16" batts. I think you are only cooling so maybe put paper faced batts with paper up. Should work fine. Might batten fabric to ties.

The acoustic panels I've used (designer of performing arts facilities) I've used 2" rigid fibreglass panels with fabric wrapped. I don't know if that rigid fibreglass will span 32" or not, but cost might be offset by new ties. Just a thought.

 

[jblmoon]

Still a wide rafter spacing. Ties are often every other rafter.

I think you add a tie between each one and use 16" batts. I think you are only cooling so maybe put paper faced batts with paper up. Should work fine. Might batten fabric to ties.

The acoustic panels I've used (designer of performing arts facilities) I've used 2" rigid fibreglass panels with fabric wrapped. I don't know if that rigid fibreglass will span 32" or not, but cost might be offset by new ties. Just a thought.

This sounds like a reasonable solution. What's the best way to add a "tie" when there are no rafters in between the existing ties? They would be sort of fake ties but I'm not sure what to screw them to.

 

[PoorUB]

Pictures would help.

 

[billconner]

toe into top plate or a structural screw from under top plate would be where I started.