Shop Under Garage?

[Kevin Post]

My wife and I are building a new home this summer. One of the requirements is a dedicated shop rather than having in in the garage or basement of our house.

I've been talking to the general contractor who has suggested using prestressed concrete planks for the garage floor. This would create a basement under the garage that could be used for my shop. He said he's done it for other people.

Pro:

• He says it costs less and requires less maintenance than an accessory building. (no roof, siding, etc.)
• The county where I live restricts accessory buildings to 750 sq. ft. I will have a 3-car attached garage that is nearly 800 sq. ft. The SWMBO is unlikely to allow me to build a 750 Sq. Ft. shop. My shop is already bigger than the max I could have as a separate structure.
• I can have heat, electricity and water more easily than I could in a separate structure.
• I can heat the space with hydronic heat in the concrete floor as I plan to do with the basement in the house simply by adding another zone.
• Because the shop will be below-grade, it will stay cooler in the summer.

Concerns:

• Lighting: There will be few if any windows so natural light will be poor.
• Ventilation: I don't want the shop connected to the air-handling system from the house to avoid dust, fumes and noise making their way into our home. How do I bring fresh air into the space without freezing in the winter?
• Noise: The walls, floor and ceiling will be concrete. I'm told that unless the walls are covered with some sort of noise-dampening material, the space is very noisy. (Imagine running a tablesaw in a cave.)
• Moisture: I'm concerned that moisture will damage my tools. Will I need to purchase and run a dehumidifier?
• Getting items in and out of this space will not be as convenient as would a traditional garage-type structure. I am not planning to put a garage door on the space. I was thinking about a 6 foot wide opening with double doors.
• I was concerned about having a low ceiling that would make handling sheet goods a pain. He said they'll just dig the basement deeper.

Here are some pictures of a house under contruction: (not mine)




I'd be interested in your thoughts and ideas on this. Do any of you have a shop like this or know of someone who has done this?

-Kevin

[Jeff Sudmeier]

Kevin,

I would not even consider doing this unless the contractor was able to build it with 10 foot walls. About a foot of the walls is used up for the concrete planks and the supporting beams. You are going to want a lot of lights in order to light this space. Also, I would want a door into the rest of the house, if at all possible. Keep this area clear as a second way to escape your shop in case of fire. It would worry me being trapped under my garage with only one way out.

It is going to be a little echo prone down there, but you can resolve that by putting up stud walls and insulating them around the outsides. With the stud walls in place, I don't think the ceiling would cause as much echo.

As far as heating the space, I would look into a separate source of heat, whether that be electric, a hot dawg heater, etc. Like you said, you may not need cooling in the summer.

All in all, I think that it would be a wonderful solution, if you can figure out good access to it. It is something that I will be keeping in mind when I build my house.

[Dave Richards]

I think if you can do as Jeff suggests and go deep enough, you should have no problems. Keeping the space warm will prevent problems with moisture. The only downside I see to this sort of thing is access and lack of natural light.

My bride and I had a house designed a few years ago and plan on using the space below the garage for the shop. The lot the house was designed for had problems that made it unsuitable for us so we're looking for another lot.

We will use insulated concrete forms for the basement and garage and either prestressed concrete beams for the garage floor or maybe some product such as Lite Deck which an aquaintance suggested.

The ICFs will help with noise and temperature. You might consider them. We did discover one builder who said they aren't good but they'd never used them. We found many other builders who like them and several who have built their own houses with them. One guy even went to the roof on a two story house with ICFs. He said heating costs were incredibly low and you don't hear any road noise. This guy is up by Welch, MN.

Just for fun, here's a sketch I've been working on from the plans. It isn't complete but would give you an idea. Yes, the garage is bigger than the house. That's the way it should be, right. Garage is 32x50.

[Kurt Strandberg]

Yes, the garage is bigger than the house. That's the way it should be, right. Garage is 32x50.

Excellent thinking,

I've always told people I want to build a garage/shop with an attached house on the side.

Kurt

[Ray Bersch]

Kevin, I have used pre-cast concrete foundations in homes that I have built, they are manufacutered using an insulating board material as a form and then shipped to the site - these basements have proven to be warm and I have noticed that they muffle the sound quite a bit - so, that would lead me to believe you would get the same or better results with IFC's -

Moisture problems are caused by two factors; high humidity (in the summer) and ground seepage. You can't change the outside humidity, just condition it on the inside, but you can sure as heck solve the seepage problem during construction. Be sure your builder uses plenty of clean stone around the foundation with footing drains to daylight, also put plenty of stone under the slab ( 4" inches is code around here - I suggest six to eight inches) also with drains to daylight - that takes water away and prevents hydrolic pressue from building up under and outside the foundation, then add some extra waterproofing to the exterior wall before backfill - there are several water-proofing products that do a great job. If your lot has a high water table, then take additional precautions - your builder should help. This is very cheap insurance and will pay down the line because seldom is water seepage evident within the first few years after construction unless something is done wrong. These improvements should not be too costly.

Try adding natural light, use your imagination, - in the photo there is plenty of space on the side of the foundation to add at least one window, but if a retaining wall were built so that more foundation is exposed, another window or two could be added and the retaining wall does not need to be high, just a couple of feet - consider double hung or casement windows rather than typical basement windows. Also, consider using wood framing for parts of the foundation that are above ground, cheaper and less mass to heat and cool (and also shown in the photo.) My current house has almost 1,000 sqft of living space in the basement - but the whole back of the house is above ground and wood framed with plenty of windows. It is all done properly and no one would think it is a "finished baement."

If noise is a concern, consider a block or concrete wall between the shop and the rest of the basement, then frame it out, insulate and sheetrock it.

I think you may end up spending more than what a 750 sqft shop would cost, but you will get much more and much better space with a lot less maintenance over the long haul.

Ray

[Jim Andrew]

Can't say I'm crazy about the styrofoam wall systems. You can not pour
fast like with metal forms, have to wait for the concrete to set up before
you can pour up higher on the forms, and you can not vibrate the concrete.
This would allow for pour seams and even small pockets of air. If you have
ever seen a basement poured, they stack the concrete up 2 or 3" on top
of the forms, and sometimes have to add concrete after vibrating. The
termite guys tell me that termites can live in the foam and they can't get
the chemical to them. So it is hard to kill termites when you have that
type system. The other thing is the cost. The last basement I considered
using that system, even if I had done the work myself, the basement would
have cost more than hiring a basement contractor with aluminum forms. Jim

[Ray Bersch]

Jim, I think you have some wrong info on pouring this type of foundation. A different mix is used than with a metal or wood formed pour and it is accomplished in one pour. The pours I have witnessed have actually been pumped not poured. Set up time is longer and the cost is likely to be higher.

Termites do not live in the foam forms. In fact, they would not even penetrate the foam. Extermination of termites is best accomplised by treating the ground around the foundation and the nests. Interior treatment is not appropriate unless there is infestation and with a poured foundation, that infestation will be in the wood above ground - with a block foundation, termites can penetrate cracks in the block and move up toward the wood frame - not the case with poured foundations.

I often have problems with subs who have learned to do things one way and will find fault with anything they are not familiar with - so ask around.

[David LaRue]

I have assisted in the construction of a several precast concrete homes in the Detroit area. The whole house was concrete block, with precast floors & wood truss ceilings. We used corefil in the block walls for insulation, and we drywalled the walls, and skimcoated plaster on the ceilings. You could not tell the building was concrete when it was done. The houses hold their heat, and stay cool because once you heat or cool that mass it stays very consistant. I woul not hestitate to make a house this way, and having a shop below the gargare mkes sense to me especially if it is a walkout.

[Rob Russell]

The idea of a basement shop with ~ 10' ceilings would be a dream to me. Radiant heat in the floor is definitely the way to go. You will likely need a dehumidifier for the summer - consider a drain for it. Window wells for natural light also provide a source of fresh air if you're spraying finishes. Just make sure the window wells are properly sealed and I'd suggest running drain pipes from the wells down to your curtain drains. Even if you can't do the windows, with lots of light it'd still be a nice shop. If you can, fit a sleeve for an A/C unit in the end wall. That would help keep the shop dry in the summer, too.

If I had the opportunity to build a shop like that, I wouldn't hesitate for a minute. I would also consider enlarging the garage a tad - the extra depth width is handy in the garage for snowblowers, lawn mowers, et al. That fact that the basement under the shop gets bigger is just pure coincidence .

Rob

[Rick Christopherson]

New Edit: That's what I get for not reading the entire thread. I had no Idea this thread was a year and a half old when I wrote this.

There are a lot of postings here and I stopped reading about halfway through them all.

Part of my 1800 sqft workshop is under the garage using pre-stressed flooring. The area under the garage is my primary machining area.

Because most of my basement is below ground with poured concrete walls such as yours, the temperature remains fairly constant at 60 degrees year round, although it does warm up if I leave the back doors open in the summer.

Even though it has not yet been completed, your spancrete will have a topcoat of concrete applied over the planks. I had the foresight to install a floor drain in my garage before the topping was poured. Even if your contractor tells you that you can’t do this, do your homework, because you may find that with the proper conditions you can, and spancrete is one of the first necessary conditions. I would also recommend getting some type of strap or threaded stud between the planks before the topcoat is poured. This will give you mounting points for firring out the ceiling with wood strips. This is something I hadn’t planned ahead for, but wish that I had.

Also, a couple of years after the house was finished I began to notice that road salt was dripping off my truck and penetrating the 2” topcoat, even though there were no cracks in the garage floor. (I think current code might call for a thicker topcoat today for this very reason.) It was flowing between the spancrete planks in a single area, but this was right over my tablesaw. I corrected this a couple of years ago by epoxying the garage floor, which is great. My recommendation is that you epoxy the floor within the first year for a better finish. If you do it soon enough after the pour, you don’t even need to prep the floor.

[Ed Weiser]

If I had a choice, I would place as many windows into the space as possible. Even if this means window wells, I believe it would be worth it. My shop is in my basement now and even though square footage is not a problem, the absence of natural light is unpleasant. Do everthing you can to secure natural light. On the subject of air conditioning, assess your needs carefully. Cooling will not likely be a problem--dehumidification will. Don't oversize your unit. In floor heating would be great and could easily work off your home system as a separate zone without transfer of any dirt or dust into the house. Lastly, DO NOT bury your DC ducting in the concrete slab. The reasons are many including potential for water infiltration, encouraging excess cracking of the slab, potential interference with your heating system and, most of all, the total absence of flexibility if you decide in the future to change your shop layout! Hope this helps. I've learned from the mistakes I've made (many.) Good luck. Building a house can be very exciting (and stressful without proper planning.)

[Karl Laustrup]

I agree with what's been said before, make the ceiling 10'.

My other suggestion would be to make the garage 30-32'W x 28-30' D. Extra shop space and added bonus of extra room in the garage for storage.

Your concerns are valid, but none are beyond a solution.

[Kevin Post]

Jeff Sudmeier wrote: As far as heating the space, I would look into a separate source of heat, whether that be electric, a hot dawg heater, etc.

I'm curious... Why would you choose this method of heating the space rather than heating it the same way the basement of the house is heated? Since I'll already have everything necessary for the basement floor, it seems to me that putting PEX tubing in the shop floor would work best. The shop would just be a separate zone on the existing system.

-Kevin

[Bill Lewis]

This sounds like the perfect solution. Given you guys probably have a frost depth requirment for footings of about 10' deep up there in WI its nothing to make a useable space below the garage. Just like it is more cost effective to build "up" rather than "out", it seems follow that it will be significantly cheaper to build "down" vs. build "stand-alone".

Just some thoughts:
High ceiling yes, minimum of 9' obviously more is better.

Moisture shouldn't really be a problem if the drain tile and foundation moisture-proofing are done correctly.

A level walk-out is pretty much a must, like the one in the picture.
A 5' to 6' doorway is also really a must if you intend to get any equipment and projects in and out. One suggestion I have is to install a functioning French Door, the active door works as your day to day entrance, and the passive door can be opened when needed (jam bolts). Use at least a half glass door to let in some natural light. Oops, I re-read your post, and you mention that. You can however get taller than 6'8" doors which might also be useful. 6'11" is the next size up.

Stud out and insulate walls and ceiling. Hydronic heat is perfect for the space. How much do you guys use air conditioning in WI? Being so much below ground, you may not need it.

How waterproof is the garage floor/ceiling? that'd be my main concern. It would certainly have to be sloped adequately for ice/snow melt to drain to garage door.

Have you had a chance to look at any other similar construction that has been completed, and lived in?

[Michael Cody]

I think this has a lot of merit ... making it deeper to get more ceiling space is a sound suggestion, depending on your lot grade and drainage, even making a bigger garage sounds better. The cost to heat/cool will be significantly less in a basement shop. That is one of it's biggest advantages in a cold climate w/humid summers -- WI or MI same kind of thing. There isn't any better insulation than a few feet of dirt. Lighting is needed in any shop, sure it's a bit more here, but the comfort of the steady temp would make it worth it to me. Now if you can do a walkout that's even better. If not I would put in some kind of 4x4 or 6x6 hatch with a lift to bring stuff up & down with ..

Another nice thing is not having to go outside to go to the shop ... no carrying things in/out through the weather, etc... a lot of advantages IMNSHO. Of course I always wanted to build an underground house too .. but that is just me.

One question though -- how do you keep water from leaking down twixt the concrete planks?? Melting snow, etc... has gotta seep down. Even with a poured floor after time this can be a problem. I suspect it's coated some how or maybe some kind of drain system. But I've never seen this type of construction.