Say you were doing a new build. How would you insure the attached garage didn't transfer fumes into the house. Estimate they share a wall 15 feet long.
Say you were doing a new build. How would you insure the attached garage didn't transfer fumes into the house. Estimate they share a wall 15 feet long.
So, this is mostly relevant!
My shop is in the basement. My wife has the nose of a bloodhound. I have to be very careful about what i do.
Doors open, minimize chemicals inside. If thats not feasible (which in the summer its really not) i use a box fan blowing out of the shop sealed to the door.
I also did my best to make the ceiling/floor as airtight as possible. Thats didn't seem to do jack E36 M3, so....
Its about airflow and ventilation. Drawing fresh air in and exhaust the funes.
Exhaust fan in the garage to keep it at a slight negative pressure relative to the house. Or pressurize the house! 
In reply to Stampie :
I mean, if the fumes are trapped in the garage that isn't exactly good either...
And when you're exhausting the fumes, you've got to do it in some way that they don't just get sucked back in elsewhere! That's what happens at my parents' place, but it's an older house that was built before fiberglass was invented....
I cut a 16" square hole in the side of my garage and put a shuttered exhaust fan in there. Granted, it's detached, but even this relatively tiny fan will create a bunch of negative pressure. That should be all you need to isolate garage air from the house.
Before cutting the hole I tried a few different box/window fans, and just couldn't get a good enough seal to create a reasonable cross-breeze with them. The fan-in-the-wall will make a 10mph breeze come through the window 30' away on the opposite side of the shop.
Yup. Negative pressure is the answer.
Typically, you put the garage floor 8" below the ground floor. It also helps to slope the garage floor at 1/4" per foot towards the overhead doors. Gasoline fumes, among others, are heavier than air.
Weatherstrip the door to the house, and seal any penetrations in the common wall.
I sprayed a bugeye in primer in the attached garage.
Next wee, Mrs NOHOME said to call a contractor and build a detached garage.
You guys are missing the difference between a problem and an opportunity.
Pete
Duke said:Typically, you put the garage floor 8" below the ground floor. It also helps to slope the garage floor at 1/4" per foot towards the overhead doors. Gasoline fumes, among others, are heavier than air.
Weatherstrip the door to the house, and seal any penetrations in the common wall.
This is the kind of thing I'm looking for. The garage will be conditioned space so wasn't wanting to do huge air exchange stuff. While sharing a wall I don't have to have a door between the two. Would closed cell foam between the two help?
General garage smells have never been a problem but anytime I had to paint a car in an attached garage it was a nightmare. To the point where I bought a HF pop up garage for painting because no amount of pressure, positive or negative, sealing etc keeps that smell out of the house.
Duke said:Typically, you put the garage floor 8" below the ground floor. It also helps to slope the garage floor at 1/4" per foot towards the overhead doors. Gasoline fumes, among others, are heavier than air.
Weatherstrip the door to the house, and seal any penetrations in the common wall.
Couple of minor notes...
-Pretty sure code requires a 4" variation in height, not 8". 8" would be a different problem, because maximum allowable stair rise is 7 3/4"
- Though the code requires a slope on garage floors, the vast majority of garage floors in the South seem to be poured level.
- The floor level difference would only help with fumes that are heavier than air. For shop odors, that may not always be the case.
If you have no door, it helps a lot. The attached garage will require a 5/8" fire code drywall separation, so a great deal of air gaps will already be handled. Seal the penetrations, including the joint between the bottom plate of the wall and the floor. Foam won't add much.
You STILL want negative pressure.
If the garage is conditioned, consider a separate system. If they are the same system, your return air ducts will be a big problem.
I think I need to amend my comment above...
I don't think the building code permits ducting to go from a garage to a residence at all.
In new construction, the garage would have to have an independent HVAC system.
If you notice the shop is under the house. And not finished yet so any fumes created will drift upstairs The lakeside boat house doors can be opened as well as the garage doors opened and the service entrance door shut.
However as others have mentioned my wife has the nose of a bloodhound ( and the mouth of one too come to think of it.). So anything remotely smelly is announced like a bloodhound baying. Fans and if there is a nice breeze or wind off the lake the baying is noticeably reduced. Her particular objection is the smell of cutting disks.
In the winter I have ear muffs to deal with the baying objection. That evening I get sour faced looks until my eyes close in bed. With luck I'm forgiven in a month or two. ( unless I reoffend) !
My goal in the next 7-10 years is to seal up the shop with sheetrock but before that happens I'll need to completely empty it.
Hmmm,- I guess I'm condemned to the remaining years of my life to smells hurting my ears.
In reply to frenchyd :
If that shop is a garage for an automobile, it doesn't meet the building code. Living space over a garage should have a fire separation (5/8" drywall) to the garage.
My thoughts, which have probably already been said here:
No door between garage and living quarters.
Completely separate HVAC.
Sprayfoam the hell out of any wall or ceiling, whether it touches living quarters or not.
Depending on climate, heat exchanger or make-up air unit to exchange air with outside.
Change/ shower room to leave your stinky clothes and boots in the garage.
New build, most of this is easy. Old build will require some disassembly here and there.
The bathroom might be a dream...
In reply to SV reX :
Actually, I don't believe there is a level change requirement at all any longer. But 8" is good practice. It just requires 2 steps. Frequently there is a 4" landing slab outside the garage/house door.
As others have said the keys are, separate HVAC systems, lower pressure in the garage and a lower floor. Not having a door will help a lot but if I were doing a new build I'd separate the garage and the house with a short breezeway and put doors in. I'd design it so that the breezeway could be enclosed and turned into a mud room if someone wanted to in the future. That gives you all the isolation for your car stuff with an arrangement that won't seem weird when you go to sell it.
Why would code require a step up from the garage to the home level floors? IOW, why can't they be the same level?
I also do not see the need for sloping garage floors, even tho I live where it rains and snows. The small amount of water that comes off the car after I drive it into the garage evaporates.
I do see the need to have separate HVAC from the house. I tried painting a very small part in the basement of my house and upstairs smelled of paint for a couple of days - never again!
I also can't paint in the garage, I paint outside then bring the parts in the garage to cure - if I can leave them outside for a while all the better but if it's cold or raining they have to come in.
I can see why the bride would complain about grinding smells coming thru upstairs......my best advice is to build a shop separate from the house. Other than that, LOTS of ventillation.
I tell all my customers that it is false economy to not finish the interior of a garage when building a new home. If left unfinished it almost never gets done.
In Frenchy's case I have done retrofits in "full" garages. It requires 3 to 4 days of no rain and subs lined up to bust it. Sometimes emptying into a few enclosed trailers in drive (hardest part). Insulate and hang rock in one day. Finish rock next day. Reload.
Always interesting how much "stuff" doesn't get put back in. 
In reply to MiniDave :
Both are to keep volatile liquids and fumes -in particular, gasoline - heading away from living areas rather than towards them.
MiniDave said:Why would code require a step up from the garage to the home level floors? IOW, why can't they be the same level?
Combustible vapors (like from gasoline) tend to accumulate at floor level, so the step up helps prevent those vapors from seeping into the house. The same reason that gas fired appliances installed in the garage, like water heaters or furnaces, are required to be installed a minimum height above the floor - I believe that number is 18".
SV reX said:In reply to frenchyd :
If that shop is a garage for an automobile, it doesn't meet the building code. Living space over a garage should have a fire separation (5/8" drywall) to the garage.
Shhhh! Don't tell please. Cars parked in there now are "projects". And have no fuel. Any vehicle parked inside during the winter is a mistake ;-) I do have one piece of sheet rock screwed up. ( more to keep it out of the way than anything else).
Actually, I need access to the bottom of the floor since I have a burl oak flooring of 22" wide planks going in. Then a brass edging strip followed by Bloodwood and another brass edging strip before I use the wide planks of white hard maple.
3&1/4 inch screws will go in from the bottom. ( yes, the sub floor is that thick.)
Once that flooring is finished in the great room I'll stuff insulation in to reduce noise and put the Firerock up in place
Neat way to install that flooring.
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