I am planning on building a garage apartment with living space above the garage.  The walls and roof would be SIPS.  Does anyone have any sugestions or experience on how best to insulate/isolate the living space from the garage below?  I would like to insulate below my floor trusses to maintain the area between and through the trusses for plumbing and HVAC (within building envelope).  Since the insulation does not need to provide structural support I was thinking about a vapor barrier on the bottom side of the trusses, covered by one or two layers of XPS foam sheets.  Does anyone have any suggestions?

Thanks,

Torben

I should probably clarify the other option I was thinking about was affixing a SIP panel to the bottom side of the floor joists.  My concern was if this would be as easy to seal as the XPS foam and of course the relative cost.  I was hoping someone would have some experience or thoughts about this.  I think this would be an issue anytime you have living space above a garage in a SIP home.

Torben-

Im having a similar issue that I am running into building my own house; a 1800sqft cape with a 2 car garage underneath. For the walls I will be going with 8-1/4" eps sips w/ 1/2" eps sheeting to prevent thermal bridging. For the roof I am going with a hybrid of closed cell/ open cell foam or a hybrid of closed cell foam/ celulose. My goal is to economically achieve close to a r40 in the walls and an r60 in the roof.
Since its just about impossible to find a garage door with a super tight seal (if anyone knows of one please let me know!) I think my biggest weak point will be my insulating barrier between the first floor and garage. My plan was to just use plain old fiberglass between the floor joists and 2" eps sheeting on the garage ceiling. From what I understand the biggest weak point with Fiberglass is the fact that air easily flows through it which is why you get convective loops in wall and roof applications, which in turn greatly reduces its effective r value. With the first floor you have a cold surface on the bottom and a warm surface on top, so you shouldnt get the same convective loops that you get with fiberglass in the wall and roof. To me this seems like a fairly cost effective way to do this, but will it be enough....? I dont know.... Id really like to get some feedback as well.

Nick

On the garage door:

How about building your own using 4" sip with a carriage door type veneer on the exterior.

I have a dual bulb seal on my garage door which has eliminated almost all of the sealing issues. One bulb is installed conventionally on the exterior jamb. The other bulb is mounted to the sides of the door sections. Since there is only seal to seal contact, no wood or metal to seal contact, there is no wear. The seals remain pliable and seal well for going on 4 years now.

You could utilize a SIP floor panel (depending on spans) to create an insulated floor for your apartment. Some beams may be needed if the spans are longer than 16-18', but this would easily solve your insulation problem. Mechanical systems may need to be boxed out on the edges of the garage though.


Joe Quinn
Regional Sales Manager
Enercept Building Systems
(800) 658-3303
[email protected]

How about installing an insulated garage door and insulating and conditioning the garage instead. You do live in Florida, so wouldn't a nice cool garage to tinker around in be the thing to have.

If you did the above, then all you would need to install is drywall for your thermal barrier for fire code.

This morning my unconditioned garage was a comfortable 64 degress while 33 deg. outside, just off the engine heat 14 hours ealier

Sip walls for the garage?

B_Edwards;

yes 4"walls / 6" roof,  insulated overhead door

I don't think code will permit a conditioned garage unless it has it's own dedicated HVAC system. The air form the garage must remain isolated from the living area because of hazardous fumes. Also, if there is living space above the garage, the sheet rock on the garage ceiling is required as a thermal barrier, no matter what design you end up with. The thermal barrier could be an alternative (code approved) material in lieu of sheet rock however...

Has the house already been designed? If not, consider using SIP's for the floor system like Joe Quinn suggested. Have the SIP manufacturer recess the beams into wall pockets so the floor panel sits directly on top the wall panel. This makes an excellent (and strong!) insulating joint. Frame in-between the beams to create an area for mechanical systems. The roof panels would rest on top the floor panels with beveled lumber. In my mind this is a cost efficient way to achieve your design/use goals.

I'm interested in learning your final design!

John

Guy - I have a stand-alone SIP's garage and was struggling to figure out how to insulate the doors. If I understand correctly, your solution is a very good one. Can you take a pic and post it?

Thanks
John

My final design is steel floor joist above the garage. Fiberglass bats in the space between joists (for sound attenuation as well as insulation). The bottom of the joist will consist of a vapor barrier covered with 3/4-inch Rmax insulation board and then 5/8-inch gypsum board (approx R35). I finished permitting last month and have substantial sitework before I'm pad ready. I'll install insulated garage doors so I can later add a separate mini-split AC for the garage. I'll try to post pictures once I get to the interesting parts. This site has been a great help in learning more about what appears to be a very promising building system. The permitting was a challenge and I'm sure building will be another set of challenges. As part of the required energy calcs for permitting detailed energy simulations indicate this will easily achieve a HERS 5 plus star rating. I plan to post what kind of construction cost and energy efficiency I end up achieving. I think those kind of results are the proof of how good a system really is. By the way I also would like to see the double seal done on a garage door. I know that is also the weak link in what I am doing.

I have been told that fiberglass doesnt make a very good sound barrier, some modular builders make buyers sign-off that the fiberglass will not do a sound proofing. I am asking more than making a statement.














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There are very few things that are light or inexpensive that would make a sound barrier. The fiberglass is documented to noticibly reduce sound transmission through an assembly (versus leaving it hollow). See this website regarding STC numbers for wall assemblies: http://www.stcratings.com/assemblies.html I think a builder would be foolish to knowingly let a buyer keep the impression that fiberglass batts will soundproof a floor or wall. That would open them up to all kinds of unhappiness down the road.