Garage Sim Build Insulation Question

[BushwoodBlaster]

I'm in the middle of building out my spot. I'm in Los Angeles County within 3 miles from the beach so nothing crazy weather-wise most the time. I want to reduce noise coming out of my garage and into the garage so I have decided to insulate all the walls with Rockwool Safe n Sound, add a new garage door that is steel backed and has poly foam of 10,94 r value and will do something similar to the side entry door for the garage as well. The one thing I'm looking for feedback on that some on this forum may have some expertise or ideas for is what do with my ceiling/roof rafters. The garage is an old build and was not built with any venting. I want to avoid cutting any holes in the side of the garage and roof where the vents would normally be. My original idea was to use the same safe n sound product (yes it doesn't have a listed r-value but I think it's sufficient at 11+ for my area) in the 2x6's in the ceiling right above my lighting which will be IC rated but wouldn't actually have the batts around them anyway since I have 2x6 joists and they can actually sit at the top of the joists above the lights. If I do this my only concern is that I will have an attic with absolutely no venting (maybe in this climate it doesn't matter that much?), I could also later when I redo my garage roof shingles add a solar powered attic vent on the roof. The other idea I came across was using open cell foam in the roof rafters which would close the attic space off which it seems would make venting unnecessary. I am going to be treating the garage as an office space/garage golf sim and parking spot for an EV. Want it to me somewhat energy efficient with my HVAC system in there and to have decent sound deadening to not disturb neighbors if I'm playing late at night. Any feedback would be appreciated. The space with the ceiling you see in the pictures will be drywalled once I get my new garage door and side door in. Any feedback or options would be appreciated.

[Capz65]

I'll be following this closely. I'm doing the same in my detached garage. Rockwool safe and sound, drywall, mini split heat and A/C. The garage door was junk so I replaced it with a gate kit and wood slats for now. Question. I replaced the horizontal ceiling joists with rafter ties just like you have above. But I did not add the cross member T's to the front and back walls like you have. Are these structurally necessary? A framer approved what I did but after seeing your pics I'm second guessing.

[Capz65]

And how thick? And where did you source the safe n sound? I'm having a hard time finding 24" wide.

[BushwoodBlaster]

I'll be following this closely. I'm doing the same in my detached garage. Rockwool safe and sound, drywall, mini split heat and A/C. The garage door was junk so I replaced it with a gate kit and wood slats for now. Question. I replaced the horizontal ceiling joists with rafter ties just like you have above. But I did not add the cross member T's to the front and back walls like you have. Are these structurally necessary? A framer approved what I did but after seeing your pics I'm second guessing.

They may or may not be structurally necessary depending on your specs, I am not an engineer however this is what my framer thought would be the best. My framer did not use the A35s for the cross member T's but we added them and a ton of blocking because I was able to do it cost effectively with workers I have used for projects in the past and why not just over engineer it the first time so I don't have to sweat if it was done perfect or not. I can climb across it like a monkey now with the blocking and additional joist hangers we added. Here are two pics of how it is looking now. The original framer did come back and add the shear walls to reinforce the walls as well.

[BushwoodBlaster]

And how thick? And where did you source the safe n sound? I'm having a hard time finding 24" wide.

The 16" I just got through home depot. The 24" stuff is way harder to find and I currently don't have any. Stuff is harder to get now with supply chains having been backed up for so long. For thickness are you asking about the safe n sound? It only comes in one thickness which is 3" so that it provides a gap between the wall and the batt which helps with sound reduction. Safe n sound isn't meant for exterior walls or attics per se but it's basically the exact same material just 1/2" less than their normal 16" r-15 batts which are 3.5". Since it's a garage that's detached it would never need to pass any kind of r-value requirement unless being used as a living space and even then if you installed safe n sound inspector wouldn't generally know the difference between that and the regular r-15 batt tbh, the stuff is so much better quality than the crappy pink fiberglass stuff that I find it hard to believe many people would even think twice about looking more into just thinking you upgraded to a rockwool batt. Safe n sound from reports are at minimum r11 although some people I saw claiming they had a higher r value.

Added note I just got off the phone with someone who specializes in foam insulation about the attic and not even mentioning my application they said they generally use rockwool for soundproofing which makes me think the foam is kind of garbage for sound reduction. Leaning more and more towards putting in safe n sound at the top 1/2 of the ceiling joists and putting in a solar attic fan coming out of the roof at some point. was thinking about something like this https://www.amazon.com/Solar-Attic-F...ustomerReviews

This could just be overkill and completely unnecessary and is why I am posting here in the 1st place

[Capz65]

I think I will add the cross members at the hip ends to be safe. If we get two feet of snow here in MA I'll be sweating thinking about it. And I'm sure the 24" safe and sound is drifting somewhere on a cargo ship with no one willing to work at the docks to unload it. Crazy what's going on. Unprecedented. Is there much difference between the comfortbatt and safe and sound as far as sound dampening? Also I have read that foam is useless for soundproofing.

[Capz65]

What are your garage dimensions? After seeing what your framers did I'm now thinking of beefing up the roof supports.

[Capz65]

In your original pics, with just the rafter ties, is the roof structurally sound at that point? The joists from hip to hip are additional correct? Not structurally necessary, just as you said, overengineering? I ask because I stopped at the rafter ties, reasoning that if the rafters can't spread the walls can't fall outwards. Now I'm unsure.

[BushwoodBlaster]

We removed all the cross beams and added in these ceiling joists. The framers believe the roof was structurally sound in the original picture I uploaded without the blocking or hardware. The cross members were always part of the framing that was done so i'd imagine you don't want to bypass that. The only thing they came back to do was add shear walls in a section for additional support. For peace of mind another guy added tons of blocking, A35s, and joist hangers which is probably way overengineering in my climate. With snow load on your roof I personally wouldn't take any chances and I would beef it up way beyond what you think is needed and probably would consider talking to an engineer given that climate. I don't get more than mild to slightly heavy rains occasionally hitting the roof here.

I have a 17wide x 19 deep garage. I know silly size. The comfortbatt for sound deadening theoretically would not be as good in a 2x4 stud because it doesn't leave any gap between the wall and the batt. Having that dead space is part of what helps reduce the sound and why that product is specifically 1/2" less than the comfortbatt.

[Capz65]

I'll add the vertical joists at the hips. I'm not too worried this has stood for decades with just 3 ceiling joists. What are your plans for drywall? I read two layers of 5/8" is best for sound dampening. But whoa the added cost!

[Capz65]

Oh just saw the plywood installed on the studs. Drywall over that? Foam panels?

[Brettster]

Wow - that looks over-engineered for sure and likely to last a lifetime! I'm starting with a 12'x16' shed which has an advantage of a gambrel roof. With everyone I've talked to and the numerous times I've researched it all I can come up with is to cut out the 3 ceiling joists that are in the unit now, leaving me with the 6 or so collar ties down the length of the structure and then maybe put some scissor boards in both gables for additional support and be done.

I understand that the whole point of gambrel roofs though are to allow for removal of ceiling joists, or for additional 'second story' space above. I live in Northern Indiana, we can get up to 90" of snow annually, and big storms of 1'-2'... but from what I've seen the last few winters being here is that snow slides right off the steep gambrel roof and never piles up. Part of the reason we moved and bought this house 2 years ago - I thought it would finally be my golf simulator space, and it's turning out that way.

[Capz65]

Brettster, it's hard to tell but it looks like those collar ties could be placed too high to act as a replacement for the ceiling joists. With a steeper pitch like you have, the forces pushing the walls outward are less than a shallower, hip style like I have. But regardless of pitch, the rafter ties (collar ties) should be in the lower 1/3 of the full length of the rafters.

[BushwoodBlaster]

Oh just saw the plywood installed on the studs. Drywall over that? Foam panels?

The plywood you see is just additional shear wall bracing in that spot only. I'll most likely rip strips of plywood to make everything flush unless the drywallers have another method they prefer.

I'm going with the safe n sound in the entire garage. I'll just do one sheet of 5/8" all around and call it a day. I think it's going to be extremely quiet with that application. If I was a recording technician or something like that then I would take additional measures but I think this application is going to be more than adequate for the neighbors to not be bothered late at night and for us to not have much outside noise if we want to watch a movie on the big screen. I live near an airport and used a similar application for my entire house which is very quiet. The biggest noise leakage is the windows which even meet a standard above what is needed for the area. My biggest source of leakage is going to be the garage door and the side door which I am doing without any lites/windows and both of those are going to be foam insulated as well.

[BushwoodBlaster]

On the sloped part I'm using a durovent rafter vent to ensure there is airflow in that part of the rafters. On the over engineered part with my abundance of blocking does anyone have any thoughts on just laying the batts across the top of the joists and blocking in comparison to packing it in each square?