The new footprint will roughly be 24x40' and 1.5 story.

Nice size! I would wall off part of it for a clean room like for your spray booth.

1) ceiling height of main shop space

Do you want a vehicle lift? Lower is better for heating and cooling, but more air space is nice too. Tall ceilings are also better for flipping long things about. 8ft is too low in reality.

2) hydronic radiant floor heating of main shop space

Your feet will love you Do you need to cool the space too? Hydronic can cool also.

3) gambrel vs Gable roof. Will be installing solar so a 12 in 12 Gable seems like a better option but limits room functionality up stairs. A gambrel offers two different roof angles allowing some panels to maximize light in winter and some in summer.

Solar good, can't help on design as that is a personal decision.

4)cmu vs poured concrete vs stick framing off a traditional stem wall foundation. Plan was to utilize an exterior insulation system with roxul comfort board. We are in a subterranean termite area.

ICF would be the best for insulation, noise abatement, and zero termite issues. With wood costs up, it may well be very comparable.

The upstairs will be utilized as a home office and workout space and will be conditioned separately via a ductless system with the stairs/upstairs isolated from the shop space below.

Radiant continued upstairs too. Why use two heating systems? Just dual zone it. Also for radiant I would be looking at geothermal, especially if you have a pond onsite.

I keep dreaming about a vehicle lift and for a small garage/shop an in floor unit would work great and could also be utilized as an adjustable height assembly table.

@Sayn3ver

At least 10 foot ceiling more if you want a vehicle lift.

Add enough space for a real spray booth.

I’d also suggest you head over to the garage journal forums. There are a lot a well documented shop builds. Go ahead and join and ask your questions there as well.

https://www.garagejournal.com/forum/

At first glance it may seem too vehicle centered but there are several fab shops and wood shops as well. After all a building is a building. 

Ron

Best advise I can give is build it twice as big as you think you need  .  Im also huge fan of ICF. Not sure what kind of ants you have that like EPS thats a new one for me.  I never had any ant issues with ICF but NJ is a strange place so who knows.  I would also lean towards gambrel roof for the extra space.  As I said no matter how big you make it 4-5 years you will be wishing it was bigger.  Some ICFS do offer thicker foam on one side or extra foam that will slip into the block to maximize the thermal mass effect.  For a home the air tightness is huge factor but a shop with bay doors its going to be leaky no matter what. 

Perhaps think of:
-  pre-wire for solar+battery backup+automotive charging.  In our area we have time of day hydroelectric billing so battery could offset those costs.  If you're also thinking of any other electrical expansion in the future, say landscape or additional buildings, now's the time to run those conduits through to outside from your new panel.  Especially if you're pouring walkways outside.
- security, ensure your entryways are structurally reinforced for heavy duty locks and such. pre-wire for alarms
- run some ethernet cables for computers or routers, but also for PoE security cameras for the future.
- intercom to the house
- design for diving rain, I wish I had more front overhang so I could leave my doors open in the rain
- and a bugbear for me, my shop/garage opens to the prevailing wind, so every darn leaf, blade of grass, or driveway dust blows into it when I have the doors open. I'm constantly sweeping It out.

just some thoughts.  I'm prepping my build for next year, so thanks for starting this topic.

It's not necessarily the extra floor that raises the cost when you put an apartment above a garage, it's all of the ancillary work with utilities and such that goes into making it a livable space.  Plumbing especially, if you have to tie back to a sewer line instead of running to a septic field.

I went with 10 feet high for my shop which allowed large ceiling fans, with ducted dust extraction, and overhead air cleaner, and can still stand 8 foot boards up below both.


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@Sayn3ver
I just went through the process of a new build shop covered it from womb to tomb, lots of info you may find helpful it’s a very long thread but I think worth your time to peek at start from the very beginning getting a Archetect and ends with me setting the shop up

https://www.festoolownersgroup.com/workshops-and-mobile-vehicle-based-shops/whats-a-good-shop-size/

My town will never approve a full second floor nor do I like the aesthetics, as most of the neighborhood are small post wwII ranchers and 1.5story cape cods and bungalows.

They do not want illegal apartments in people's garages.

Best I can do is a 1.5 story for an office/home gym above.

I am still debating between gable and gambrel attic trusses. I am trying to get rough quotes from local suppliers. I need rough costs before I waste my architect's time and my money drawing up multiple versions of the project.

I'm not even sure if I can get an attic truss made locally that's rated for garage floor load and deflection criteria (L/480 50 psf, 3000lb load in 4.5"x4.5" per IBC). I want to place a saltwater aquarium (~2200lbs) up in the office in addition to workout equipment for the workout space in the other half of the upstairs area)

I may have to use deep open web floor trusses and parallel chord scissor roof trusses unless I have them design a structural ridge for the roof and use conventional 2x12's for rafters landed atop the floor trusses. I'd like to avoid the structural ridge to avoid having the gable ends be load bearing to give me more flexibility for a large door or garage door on the street facing gable end. Plus I'm unsure of the size beam needed to span 40ft.

The desire to clear span both length and width interior spaces drives up costs and limits options.

As much as I like the durability and fire resistance of solid beams and dimensional lumber, the speed, spans and flattness of floor and roof trusses is hard to argue with.

I appreciate the feedback so far and after doing a ton of online reading I think a 10ft ceiling height is a good compromise on workability (during construction and shop use), price, conditioning costs and lighting equipment costs.

I've recently built a new shop and house and have a number of the features you discussed and two years of experience living and working in the space. My workshop (and attached house and garage) are on one level, slab on grade with a hydronic heating system. There's a simple shed roof with ceiling heights of 10 feet on the low side and 16 feet at the peak (building is 24 feet wide). By building a box with a shed roof construction costs were kept down, for example the roof is framed with 2x14 LVL's at 24 inches on center, spaning the entire 24 foot width. By using a 2 foot module material waste was kept to a minimum. Wall framing are 2x6's on the low wall and 4x6 on the high wall for structural reasons.

In the workshop lighting is from high bay LED pendant lights (bottom of lights are 10 feet above the floor) which give more than enough light, and is supplemented where needed with task lighting. One feature I really appreciate is the hydronic system, it's silent and the space has a nice, even heat. There is a small wood burning stove to supplement the heat, and dispose of scrap wood and sawdust, plus a ceiling fan to circulate the warm air. South facing windows are designed to let sun in during the winter months and shades the sun during summer months. On the north side there are floor to ceiling windows that let in even north light, and the view of Mt. St. Helens (I'm in SW Washington). Garage doors are 9 feet tall, aluminum with frosted glass that lets in light, but conceals what's inside the garage. There are seals all around the garage doors that keeps cold, wind, rain, and snow out. In addition the garage door tracks are parallel to the sloping ceiling, thus increasing headroom. Instead of a traditional chain driven garage door opener there is a direct drive wall mounted motor, much quieter, takes up less space, and has a battery backup in case the power goes out.

One feature I strongly suggest are having floor outlets with cover plates. They supply power to most of my tools that are located in the center of the shop. My advice is to take the time to think about what you want to achieve with the space and design the space to realize those goals. Plus consider longer term uses and how the space may accommodate those uses. In my case I'm retired and aging, so there are no floor level changes, adding to my long term safety and comfort.