Question about Roxul (Rockwool) with 32" OC rafter ties

[earthwyrmjim]

I set up a home gym in my garage for barbell training, and it gets overwhelmingly hot/cold in NE Ohio for ~2-4 months out of the year, so naturally I want to insulate so I can heat/cool for those months and train without dying of heat stroke or hypothermia. The problem is that my garage only has a rafter tie for every other rafter, so I end up with 32" OC 2" x 6" x 24' ties that I need to insulate between. I really don't want to install more 24' rafter ties just to cram insulation between them (assuming I can, haven't done the trig to figure that one out), and I'd like to avoid cheaping out by hanging fiberglass if I can.

So my question is:

For 32" OC rafter ties, can I install rockwool "sideways" (i.e. cut ~32" lengths and rotate 90 degrees)? Are there any major problems that may arise from doing this? Only thing I can think of is possible sagging from each segment being double the weight for the same bearing surface area, and excessive amounts of waste since batts are 47" long.

 

[Bert_]

What are you doing for a ceiling. That may dictate the need for additional joists more than the type of insulation.

 

[Kaizen]

I’ve tried this method before and it *****. More joints to leak air and cutting it all leads to issues. Roxul does hold nice with a friction fit but you will have to put up strapping. Put up strapping 24 on center and run it the right way with one batt cut to fit so like 10”. Still waste though.
Calc putting up drywall and blown in. I know ruxul is about double what fiberglass is.


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[The Cobbler]

I would get quotes on blown fiberglass. you will be amazed at how inexpensive it is, in comparison to buying the batts, and you don't have to fight with it since it's done for you

 

[earthwyrmjim]

What are you doing for a ceiling. That may dictate the need for additional joists more than the type of insulation.

I don't plan to hang anything on the ceiling joists, just want to insulate and call it a day. I'd only be adding additional ceiling joists for the sake of fitting rockwool properly, or if I absolutely had to hang drywall for some reason.

I’ve tried this method before and it *****... Calc putting up drywall and blown in. I know ruxul is about double what fiberglass is.

I was afraid of that. I really don't want to put up any drywall if I can avoid it since these 2x6s are spanning 24 feet and the drywall would add a lot of weight. Despite that, I'd like to avoid the cost and labor of drywall since I really don't want or need it in my garage. Though, if I did hang drywall, I could add a hell of a lot more insulation up top with blown-in fiberglass than if I used rockwool...

 

[earthwyrmjim]

I would get quotes on blown fiberglass. you will be amazed at how inexpensive it is, in comparison to buying the batts, and you don't have to fight with it since it's done for you

Hm. Is there a way to get blown-in without hanging drywall? I'm not super concerned about the appearance.

 

[The Cobbler]

you would need some sort of covering for the insulation to lay on

 

[Kaizen]

Hm. Is there a way to get blown-in without hanging drywall? I'm not super concerned about the appearance.

6 mil plastic. Use little pieces of cardboard at staple locations to keep them from pulling through. Might even work to hold roxul in place. If it sags you can add some strapping.
Second thought why not just get gym membership? Probably a lot cheaper


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[earthwyrmjim]

6 mil plastic. Use little pieces of cardboard at staple locations to keep them from pulling through. Might even work to hold roxul in place. If it sags you can add some strapping.

Hm. I might go this route. It's very nearly half the cost to do loose fill instead of rockwool batts. Only objection I have to loose fill is that rockwool would be easier to work with if I ever need to access wiring.

Second thought why not just get gym membership? Probably a lot cheaper

Couple reasons:

1. Will be using the garage for more than just training. I will eventually have a shop in my garage for woodworking, but that's still a ways away.

2. I don't live near any gyms with barbells (looking at you, Planet Fitness), and even if I did I think I'd still have a home gym. It's way too convenient, and I can't justify not training since it's 20 steps away. Benefits beat the steep upfront cost IMO, especially if I keep training for years.

 

[Steve in UT]

Back in the 70s, my parents had that new fangled cellulose blown in, and they used plastic and stapled it with a string under the staple to keep it from pulling thru. They blew the insulation in pretty dang tight before they smashed it down and put up the sheetrock. So plastic with the right item under the staple could be a good option.

 

[Bert_]

If you do plastic at least get the reinforced stuff. Pull it tight and nail a one by two underneath each joist. It might not sag too bad.

You should probably also consider how much weight your rafters can handle. A metal ceiling might be an option. Would look a lot nicer than plastic.

 

[Kaizen]

Hm. I might go this route. It's very nearly half the cost to do loose fill instead of rockwool batts. Only objection I have to loose fill is that rockwool would be easier to work with if I ever need to access wiring.







Couple reasons:



1. Will be using the garage for more than just training. I will eventually have a shop in my garage for woodworking, but that's still a ways away.



2. I don't live near any gyms with barbells (looking at you, Planet Fitness), and even if I did I think I'd still have a home gym. It's way too convenient, and I can't justify not training since it's 20 steps away. Benefits beat the steep upfront cost IMO, especially if I keep training for years.

Yea don’t think I’d blow a foot up there unless everything is done. No fun trying to wade through it and not fall through


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[LXAwolf]

The blown in stuff super easy. Filled an attic in a home built in 1951. Just adding the attic reduced my power bill $50/$60 a month. Plus if you get 10 bags they let you use the machine to blow it in for free. Just get a good dust mask.

 

[Notgrownup]

I did thin 1/4 osb with blown cellulose insulation in my shop. It was the cheapest way to get decent r value and looks ok.

 

[nadogail]

I would, if I had the right to vote in this election, go for panels (maybe drywall) and blown in.

I remember threUniversity of Alaska suggesting using sawdust or ground up newspaper for insulation; about 65 years ago. Those materials would probably not be acceptable today.

 

[earthwyrmjim]

Update: https://i.imgur.com/IVixLje.png

I became increasingly more vain in my quest to insulate my garage and decided to fully finish the walls and ceiling. Based on everyone's input in this thread, I settled on using cellulose loose-fill insulation in the ceiling with 1x2 strapping on an air barrier to hold it in place and minimize sagging. For the walls I ended up putting 5/8 drywall over rockwool batts (which were hella easy to install and I would definitely use them again).

Based on Bert_'s suggestion and Ohio building code, 2x6s are woefully inadequate for 24' spans so I'm probably going to install corrugated steel roof panels over the strapping to finish the ceiling. They won't add much weight, and would definitely look better. As it stands, I've added well over 1 lbs/sqft of dead weight with the insulation on already under-rated lumber dimensions, so I'd like to minimize more dead weight going forward.

Even with the strapping, I do still have some pretty bad sagging in some spots where the strapping is farther apart than it should be. I may add some more strapping in those spots to reconcile that, but overall I'm happy with the turnout. Also I'm pretty sure I've used more staples in one day than I have in my entire life. Some of the staples seem like they're ready to pull through, so I may add some additional strapping parallel with the joists just for the guarantee.

I appreciate the input from everyone. Am a noob at most DIY things and you've sent me down many rabbit holes with the ideas you offered. Learned quite a lot in a short amount of time.

 

[Kaizen]

Good job. Cut little pieces of cardboard and staple through those into the plastic. Keeps it from pulling through. Hope you got an air stapler.


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