it definitely is possible. My parents (empty nesters) built their home a few years ago and did exactly that. They do have a 1st floor master, and large entertaining areas but only 2 br and one bath upstairs. The bedrooms upstairs are on the opposite side of the garage so the main space has the same roof height as the garage, with 10 or 11' ceilings and the other side is 2 story. The only thing it will affect is your front elevation. A good architect will be able to make it work.

What's a "modified 2 story"?

What is it about a 1 1/2 story that you don't like? Because having only part of the main floor with a second floor above it is what I would consider to be the definition of a 1 1/2 story.

I thought a 1 1/2 story meant that the height of the wall, not the amount of space. I could be wrong but if part of your second story is in the roof and not under it (ie...you use some type of dormer) then you have a 1 1/2 story.

Now to be fair I thought a modified two story was any time you had a full ceiling height and full stairs but over only a portion of the home. Which would really mean your only two choices for having a second floor with less space than your first floor would be modified two story or 1 1/2 story.

1 1/2 stories are very popular for a reason. They are an incredibly cost effective way to get more above grade square footage. I can't visualize what the OP is asking about the garage so I can't comment on that.

A modified two story is a very common style of home where we're moving. Typically the 2nd floor bedrooms are over the garage and a small part of the main floor. The kitchen/living/dining/entry area is under a vaulted ceiling. The stairs usually lead up from the vaulted area - hence any sound from the main floor bounces right upstairs. Here's a link to a photo - looking down from the stairs of a modified two story. http://activerain.trulia.com/image_store/uploads/agents/chrisfritchteam/files/DSC_0763.JPG

We're building in Minnesota and I wouldn't want the extra cost of heating such a large vaulted area.

In theory, maybe that could work without vaulted ceilings and a staircase that leads up from a quieter area of the house.

"We were thinking we could put some of the main floor under the garage roof"

I think I should clarify that statement. Here's part of the plans we've created so far. So you can see part of the kitchen and dining area which would have the second floor bedrooms above it. We were thinking that the half bath and mudroom (in the green area) could go under the roof of the garage. The garage would have a lower roof height than the rest of the house.

Hire an architect. You really need the help of someone who has training both in historical styles and modern building methods. The integration of external and internal design happens during the entire design phase, not after a floor plan is developed.

Here's a crude drawing to show how a 1 1/2 story house doesn't have to have low ceilings or dormers. You can either have a stepped roof line, or a higher slope would get you a straight line. You can also reduce the size of the 2nd floor to get a lower sloped roof. Dormers are often used in a 1 1/2 story in order to get windows in on the sides, and to increase useable floor area. But they aren't strictly necessary.

One concern I would have in trying to put part of your main floor under the garage roof is that you'll end up looking like you've got a bigger garage than you really do. Big, obtrusive garages are widely derided here, so I wouldn't imagine this would be a look you'd want.

Dormers are essentially required for attic (in the roof) square footage. I am not a building code expert but I am pretty sure that bedrooms require windows, assuming you want bedrooms on more than either end of the house they require dormers. As to your first drawing, houses similar to that (I forget the style) can be very striking and are very nice. I am not sure that they are cheaper to build than just going straight up, especially in Minnesota wher the snow load on the second roof is going to have to get transfered down to the foundation. If your plan has walls that will carry that load then it might be great, but that would essentially eliminate an open floorplan. I would think that the additional bracing required to have an open floorplan, modifications to the roof (essentially turning one roof into three), and the additional complexity of the plan would significantly eat into the cost savings that were the whole reason for the lesser square footage.

Looking at the floorplan, I am assuming Lauren doesn't mean adding square footage over the garage roof, rather, building a second floor on most of the first floor (all that is not covered by the garage roof) and putting some additional one floor only square footage under the roof that also covers the garage. I think that would be fine, especially, if you can get the garage entrance turned sideways.

I have more livable square footage in the "attic" of my 1 1/2 story design than on the first floor, and this is after accounting for the attic space behind kneewalls.. Putting living space over a covered patio and over a garage uses the attic volume that would otherwise be empty and is how you can invert the ratio of 1st versus 2nd floor living space.

I missed the part that it's about saving money. In that case, I think a standard 2 story is the best bang for your buck. You only have 1 roof, and 4 walls. Having a part stick out the side means you have to roof that part, and support the exterior wall on the second floor that didn't have an exterior wall beneath it.

People get hung up on cost/sq' without realizing that not all sq feet are equal. Cutting out a bedroom that's already got a foundation beneath it and a roof above it may not save you anything, whereas making your kitchen smaller or eliminating a bathroom would save thousands.

If cost is the number one reason you want a smaller second floor, I would probably frame up some extra space upstairs so it's the same size ad the main floor, and then wall it off so you don't have to finish it.

Even if you have your garage doors on the side, you've still got this giant thing sticking out the side of the house.

Lauren-we have a 1 1/2 but it sounds very similar to what you are describing. I'm not exactly sure what you are meaning. We have main floor master - no rooms above it for noise control. 2 bedrooms and a bath are upstairs and they are above the living room/dining room/kitchen. The roof above master is tall as if something could be under it but nothing is so the roof line is fairly consistent. From the front you can't really tell there is a 2nd floor. There is a front facing smaller dormer that is part of the stairwell and it lets in a lot of light but from the outside I dare say you can't tell if it's an active dormer or not. From the rear is where you can see the second story and they are full height (8 ft) ceilings and nice sized windows.

This thread is a month or so old, but I wanted to bump it up in case the original poster is still around and thinking through building options. We live in MN and our two-story is exactly what she describes-- we have an upstairs with fewer square feet than the main floor, and part of our house is under the same roof as the garage. We have about 1300 main floor square feet and 900 up. Our house is the typical two-story box with attached 3 car garage on the side, but behind the garage, under the same hipped roof, is our family room, which measures about 26x15. The ceiling in there is somewhat vaulted since there is no living space above it. It lives well for us having more main floor square feet, though we only have 3 bedrooms upstairs. Our basement is finished with additional 1250 sf which includes another bedroom and an office, so we do have that flexibility if needed. Hope this helps.

That's really helpful info! Thanks!