Rafter Tie Ceiling + Insulation Questions

[bluejk09]

I just bought a house with a 23’ x 23’ detached garage built in the 90s. Pretty simple build with vinyl siding and foam board insulation (no Tyvek as far as I can see) on the sides and then 2x6 rafter ties 48” on center up top. I’m hoping to finish the garage as much as possible with drywall + insulation for the walls and then some type of ceiling with insulation.

My big question is how to handle the ceiling with those 2x6 rafter ties 48” on center. I figure if insulation and a ceiling are even possible at all, I have to go as light as possible which would rule out drywall. I was thinking the lightest would be blown cellulose and steel roof panel ceiling. I estimate weight would be somewhere around 2.5 pounds per square ft (0.6 lb/sq ft for roof and 1.9 lb/sq ft for insulation).

Two Questions.

1. Do you think the 48” on center 2x6 rafter ties are enough to support the steel roof and blown cellulose (roughly 2.5 lb/sq ft)? I can get a structural expert to advise, but right now, I’m just looking for a gut check from you all from your experience. If a beam is necessary, the project probably won’t happen.

2. Weight aside, is steel roof and blown cellulose a reasonable roof plan for rafter ties where there’s no attic access? Basically, I’m wondering how this install goes. Install one steel panel, blow in cellulose above it, install 2nd panel, blow in cellulose above that panel, and so on. How do you insulate the last panel with insulation when there’s no attic access? Maybe glue some batt or foam board on the top face of the panel instead of blown cellulose and then install?

Any insight is greatly appreciated!

 

[billconner]

With the hangers - 1x6? - you're probably OK. I'd double check the nailing oh those hangers.

Probably vent baffles at edges with eave and either ridge or gable vents. 60/40.

 

[tarmy]

I just did mine last winter. For drywall you are gonna need 24oc for 5/8” fire rated ceiling boards. Add some 2x6 or 2x8 in there and go at it, use screws not nails.

 

[billconner]

Yes - for drywall 48" won't work. Will for metal - just check the metal specs.

 

[bluejk09]

With the hangers - 1x6? - you're probably OK. I'd double check the nailing oh those hangers.

Probably vent baffles at edges with eave and either ridge or gable vents. 60/40.

Assume we're talking about the blue for hangers. Center is 1x4 and rest are 1x6. Would it help to add more hangers? That'd be easy.



Check the nailing just to make sure they're still solid?

Soffit vents and (2) of these vents. There are no vent baffles so I assume that's something I should add if I do a ceiling?

 

[bluejk09]

I just did mine last winter. For drywall you are gonna need 24oc for 5/8” fire rated ceiling boards. Add some 2x6 or 2x8 in there and go at it, use screws not nails.

"Add some 2x6 or 2x8" as in add more rafter ties to get 24oc? Or just add them like you would furring strips? Your ties look newer and more robust and inspire more confidence for me than mine haha Nice looking space!

 

[billconner]

I'd probably be OK with one hanger per rafter tie, so a few is better. I've never have seen this practice written about or any reference to it in codes, but observation tells me it's been used a lot and works.

I think the metal liner panels and cellulose is a great choice. I'd add the vent baffles and blow the cellulose right up to them. Like this kind of.



I think you'd want 16-18" of cellulose.

 

[tarmy]

"Add some 2x6 or 2x8" as in add more rafter ties to get 24oc? Or just add them like you would furring strips? Your ties look newer and more robust and inspire more confidence for me than mine haha Nice looking space!

My comment was intended to say that get some appropriate sized rafter boards(Length x depth) and space them in between the existing rafters. You could ad one or two in each bay. 16’oc would be what I would do as I am an overkill kinda guy. The cost/effort is minimal.
My garage was built about 25 years ago by the PO and was never finished inside. Those prefab trusses were built with a snow load calc. in mind. They are beefy enough at 2’OC for what I was doing. From what I can see in your pics I would likely insert 2 rafters in each bay for a 16”oc.

 

[Firebrick43]

My comment was intended to say that get some appropriate sized rafter boards(Length x depth) and space them in between the existing rafters. You could ad one or two in each bay. 16’oc would be what I would do as I am an overkill kinda guy. The cost/effort is minimal.
My garage was built about 25 years ago by the PO and was never finished inside. Those prefab trusses were built with a snow load calc. in mind. They are beefy enough at 2’OC for what I was doing. From what I can see in your pics I would likely insert 2 rafters in each bay for a 16”oc.

I assume you mean ceiling joist?

 

[tarmy]

I assume you mean ceiling joist?

Yes, my bad. For some reason I locked into rafters after looking at one of his pics.

 

[SBAG]

I would put up 1x4 internal girts/strapping and you should be able to hang whatever you want off of them.

 

[bluejk09]

I'd probably be OK with one hanger per rafter tie, so a few is better. I've never have seen this practice written about or any reference to it in codes, but observation tells me it's been used a lot and works.

I think the metal liner panels and cellulose is a great choice. I'd add the vent baffles and blow the cellulose right up to them. Like this kind of.



I think you'd want 16-18" of cellulose.

Cool, thank you. I'm in MI so I figured I'd need a minimum of 13-14" for R-49 with the goal being more

 

[bluejk09]

I would put up 1x4 internal girts/strapping and you should be able to hang whatever you want off of them.

No concerns about putting a bunch of load on rafter ties?

 

[billconner]

I converted garage to living space and put 20" in, even in eaves by sloping ceiling at edges. Now snow stays on that roof longer than house or any roof around.