Insulating Florida Detached Garage.

[timdoesthings]

So a year or more ago (probably more) I asked a question on here under a different account that I have since lost access. The question was in regards to cooling and an electrical upgrade to a cmu built 25x25 detached garage, this is for a woodshop. I have since added a 18K mini-split this week after having upgrading the garages branch circuit to a full on subpanel. I have added vented soffit and am ready to insulate. My question is what do you all recommend in terms of insulation. I am not worried about the walls but rather to attic space. The space is currently open and I want to install insulation, drywall and seal it in well to help the AC. The AC is not mainly meant to keep it cool and heated when needed but mostly to dehumidify to protect tools and to make it somewhat comfortable for working in. My idea was to install batt insulation and then drywall that. My questions are as follows:
1. What R value? I read different opinions, some say high and some say low because attic will not be used. The entire attic area is 2x4 construction, 24" OC.
2. Do I need to install a vapor barrier? I think the answer to this is no.
3. Should I install a radiant barrier on the roof underside to help reduce heat levels? Garage door is facing north, garage is shaded partly by live oaks.
4. Should I insulate with foam board my 8 x 16 garage door?

Here is some info that may help with these answers:
1. CMU block, 10 feet high walls 25 x 25 foot with hip roof.
2. North facing garage door and decent shade by live oaks on garage itself
3. Fully vented soffit, with ridge vent.
4. CMU block is fully sealed and does not breath as the previous owner painted it with sealer paint outside and inside (plastic test showed no moisture transfer).
5. Going to install mold and fire resistant drywall for insurance purposes.
6. Garage floor is sealed.
7. Have large ceiling fan installed running 24/7 and also willing with install a dehumidifier if AC struggles to dehumidify.
8. Garage is a shop, no cars. Shop is used for my wood working hobby and my wife does her taxidermy work in it so humidity control is important.
9. Due to the rafter arraignment the attic is not a useable space to store items except for a small sliver down the middle. So nothing will be stored up there.
10. I live in Northwest Florida, close to Alabama.

I figured batt insulation with facing facing down into garage, then drywall installed and taped with edges and any other areas sealed with foam to make it airtight. I will only have three conduits going up and over so pretty much near zero penetration. I also plan on installing a direct drive garage door opener so there will be little to no penetration into the attic.

I hope that helps. This project has been on going. I moved in 3 years ago and have just finally upgraded my electrical to run my table saw (240 volts). I've been accelerating this project as I miss messing about in the garage and also these past few years I have had to clean tools over and over again (aircraft mechanic, machinist tools and woodworking tools have all been subject to corrosion issues due to the humidity.

Any help would be appreciated.

 

[Airboater]

I would hang drywall then just get blown in insulation. Thats going to be the easiest and most cost-effective solution. I'm down in Miami and just had insulation blown in my attic over whatever was left on the old fiberglass insulation. It made a HUGE difference.

 

[acer66]

Besides to make sure the building envelope is airtight before doing anything and the more R value the better but besides that got not much.
My garage door faces south west and in the summer even up here was getting too hot to touch in the summer.
Putting foam boards in there made a huge difference.

Just a question about #5
Your insurance requires mold resistant drywall in the garage?

 

[Steve68!]

I'd do icynene spray foam in the rafters, R22 attic batting in the ceiling, and then insulation in the walls and add foam board to the garage door,

In the land of humidity everything helps! I have a metal building and everything rusts,

my neighbors have the foam in there attic in the heat of the summer there attic is, 85*

I did R22 attic batting in my last house, mainly in the flat ceiling part of the house, my kids always told me there rooms were cold in the winter and I agreed, after that the rooms were completely different, no cool in the winter,

My personal experience blown in insulation *****, buddy had it redone in his house, removed and then reblown, no difference, new insulation, new windows, what changed was the replacement A/C unit, just my experiences in the land of heat and humidity,

 

[timdoesthings]

Besides to make sure the building envelope is airtight before doing anything and the more R value the better but besides that got not much.
My garage door faces south west and in the summer even up here was getting too hot to touch in the summer.
Putting foam boards in there made a huge difference.

Just a question about #5
Your insurance requires mold resistant drywall in the garage?

Technically they require fire resistant board. OSB which is what I wanted to throw up in the first place is frowned upon so drywall with a fire resistant rating if I want the insurance to cover it for the amount I need. I have a full shop for almost every trade in it. I am a aircraft mechanic by trade, woodworker by side hustle and off-road rig builder by hobby but I do it all when it comes to roll cages, to engines, etc.. Honestly my garage has more money in it than my actual house.

 

[timdoesthings]

I'd do icynene spray foam in the rafters, R22 attic batting in the ceiling, and then insulation in the walls and add foam board to the garage door,

In the land of humidity everything helps! I have a metal building and everything rusts,

my neighbors have the foam in there attic in the heat of the summer there attic is, 85*

I did R22 attic batting in my last house, mainly in the flat ceiling part of the house, my kids always told me there rooms were cold in the winter and I agreed, after that the rooms were completely different, no cool in the winter,

My personal experience blown in insulation *****, buddy had it redone in his house, removed and then reblown, no difference, new insulation, new windows, what changed was the replacement A/C unit, just my experiences in the land of heat and humidity,

My issues with foam on the rafters in the ridge vent. Does is negate the vet altogether? And if that is the primary means of cooling the attic what is the approach post spray to prevent air and moisture from entering the attic space and sitting idle.

 

[driver50x]

I am building a very similar shop, except wood construction . Also in Florida. I am thinking of going with R-38, 12” thick batts in the ceiling. I plane to use metal ceiling panels. I’m also wondering if the insulation backing should go up or down.

To me, the cost of spraying on insulation does not make sense if you don’t plan to use the attic.