Yes, steel beams and very good waterproofing.

I briefly looked into it. It can be quite cost effective. It's more per sf than regular basement space, but cheaper than above ground space.

We decided against it. However, we are getting a mini version in the form of a tornado shelter underneath the front porch. It will be accessible from the basement.

A friend of mine has a barn constructed with steel beams and concrete panels (brought in by truck, lifted into place by a crane) for the floor. I believe that barn cost more than my house. It is amazing, though.

I received a verbal quote of about $20k to build out under an approximately 400-440 sq ft garage.

I believe there was a topic created on this earlier. Some people said they would like to do it if it were not for cost. Others in colder climates were concerned about the room temperature since the space above would not be a heated area.

I plan on doing this myself and using it as an excercise room.

That's exactly what I saw it used as, a home gymnasium. There's a Visbeen plan I like, called Parkgate. It has a 3-car garage with a basketball court underneath. I'd love to send my kids down there to tire themselves out, especially in the winter when they're snow-bound and stir-crazy. A space like that would be perfect for dance/gymnastics, karate, rock climbing, etc. And being under the garage, they could make all the noise they want.

I plan on insulating the foundation anyways, so insulating that space too would have to get included.

Here is the past thread.

Here is a link to the product we used:

Here is a blurb about the product:

Spancrete® hollowcore plank is a precast, prestressed concrete slab used primarily for structural roof and floor applications. The concrete is cast over a bed of prestressed wire strands, producing an incredibly strong product that tolerates high load capacities and can be used to cover long spans. The Hollowcore panels have continuous voids in them that reduce weight and cost, and also may be used for electrical or mechanical runs. Hollowcore also has excellent fire resistance.

I only have one estimate so far, and it was very reasonable at 5,000. We lost our home to fire, and some people mentioned this would be fire safe, but the main reason, was because of Tornados. The basement we are going to have will be a full walkout, so more exposure.

We have just spent all evening this evening in the basement of our rental, because of funnel clouds and tornado warnings..... so I think this is a must have in our mind.

I have always referred to our "lower garage" as the "the bunker"! The main level garage is just the garage where we park our cars but we have ridden a few storms out (including last years where we had to replace windows and the roof) in our "bunker".

Here is a link that might be useful: the bunker

My parents built a home 21 years ago. It is a concrete and steel structure covered in stone. They have a 2 car garage over a deep 1 car garage. Lots overhead steel beams.

We have a "bunker" too. Our front veranda is poured concrete, then flagstone and a huge room underneath - 14 foot ceiling. 38 ft x 10 ft. It wasn't on our drawings, but GC brought it up when the guys were putting up the wall forms. Like "free" space. Great for tools, etc.