Why would it need to open on 3 sides?

We would like to have access to the lift from our house as well, so two sides would work. Maybe front and back.

"We would like to have access to the lift from our house as well, so two sides would work. Maybe front and back."

Prepare to hemorrhage money.

Front and back access is not difficult but it does require another rated door, interior hardware and a lifting rail and motor on the long side of the cab.

To find the shaft size you must determine the lifting mechanism which will depend on acceptable noise, available overhead (at top floor), smoothness of operation, and tolerance for maintenance. The platform sizes are standard because that is how they are rated for loading classifications.

A reasonable model is a ThyssenKrupp LEV II or (LEV II Builder) model. It isn't very quiet and requires a 9 ft headroom at the top level but it is not too expensive. I'm not sure if it needs a pit but it would be a shallow one if so.

For doors at each end the smallest cab platform would be 36" X 48" and the overall size to the inside face of the enclosure walls would be 55 1/2" x 52 3/4". The side lifting mechanism puts the doors about 6" off center on the enclosure.

As the cab platforms get larger the enclosure increases the same amount. Larger cabs are 36x60 and 40x54. Residential elevators are not required to meet ADA (Federal handicapped) standards so it is assumed someone in a wheelchair would go in and out without turning around. Therefore, it would be good if the doors most likely to be used by someone in a wheelchair are on opposite ends of the cab (in one and out the other without backing up).

Are you thinking of installing a "home elevator" or a "wheelchair lift" (aka "platform lift")? It's hard to draw a distinct line between the two but, at least in my mind, platform lifts are designed to be functional at the lowest possible cost while home elevators are designed to blend into the residence more and are therefore quite a bit more costly.

Platform lifts are often used where the total rise is less then 5 ft but I think there are some that can go as high as 12 feet. Sometimes they are enclosed and sometimes - especially with shorter lifts that are located indoors - the lift is left open. Some platform lifts will allow for two "stops" in addition to the lowest level but most only have a single stop. And generally, one enters the lift from one side and exits from the far side, although there are a few that are made for exiting to the side of the entry.

Home elevators can have a vertical rise of up to 50 feet and can usually handle multiple stops. The LEV can have up to five stops. i.e. ground level plus 4 additional stops. And, most home elevators allow you to have cabs with either a single door, two doors (either located across the cab from each other or at 90 to each other) or even door on three sides of the cab.

I have the Thyssen Krupp LEV that Renovator8 mentioned and have no complaints at all about it being "noisy." Mine has the 40x54 cab and we originally considered getting a cab with two doors but then, after a minor revision of our plans, were able to make the single door model work. A family member who uses a mobility scooter has no difficulty driving the scooter into the LEV and them backing it back out when she reached the second floor. I'm not sure if she would have been able to turn the mobility scooter if we had wound up with a two-door model with the doors at 90 degrees to each other.

In trying to give you guidance, it would be helpful to know how your home, your garage, and the MIL addition are laid out with respect to one another. I.e., is the MIL addition going to be above the garage or to one side of it? Even a rough sketch would be helpful.

"Front and back access is not difficult but it does require another rated door, interior hardware and a lifting rail and motor on the long side of the cab. "

You are heading up into light commercial, much more expensive than typical home units.

ThyssenKrupp Access is ceasing operations.

You might try Savaria Eclipse. They've got front/rear and front/side door options. Front/rear/side isn't allowed by code (max 2 doors on a car), and quite frankly it would be an engineering nightmare.

The difference between an elevator and a platform lift is that an elevator has a fully enclosed cab and a vertical platform lift has an open top (though it can ride inside a shaft). There are different drive mechanisms as well, but that's how you recognize which one you're riding in.

Can you post a floor plan? Is it just going from garage to 1st floor or also up to a 2nd floor?

Here is a link that might be useful: Savaria Eclipse

The OP said the lift would travel up one level. Normally a wheelchair lift would not pass through a floor but there are some that can do that, mostly of British design and a bit scary looking.

The private location, short rise and small cab size of this elevator would prevent it from being a commercial design even with 2 doors.

"The private location, short rise and small cab size of this elevator would prevent it from being a commercial design even with 2 doors."

The unit design to have two operable doors starts requiring a cab that has a much more substantial design than typical residential grade equipment.

It is still not fully commercial, but well past a simple residential lift.

Adding a second door to a home elevator doesn't change the cab construction, load rating or hoist equipment. These cabs are just 3/4" veneer plywood on a light steel frame with up to 2 doors opposed or adjacent to each other.

Here is a link that might be useful: elevator cab configurations

Do you need an elevator? Or will one of the stair chair lifts meet your requirements? They are much less expensive. In fact I was just at an estate sale and saw one that was for sale for $400 asking price....

We put space in our house for a residential lift, but did not put it in yet to save the $$.