This section requires input from a structural engineer, but in the mean while we found some useful information about the difference between Slab on grade vs. Pier and beam foundations which allows a crawl space.

In general it seems that slab on grade is very common and much more cost efficient if well built. New piping materials allow very low damage risks which makes accessibility issues less of a problem. Moreover, a concrete slab gives thermal mass to the house which can help in radiating heat from the sun or from heating and stays cool longer on hot days. Pier and beam foundations are more suitable for cold weather with freezing temperatures and allow access through the crawlspace. Both foundations will require insulation to avoid loosing heat through the floor. 

Slab on grade allows better thermal mass which means it can stay cooler during hot days; it does require insulation to avoid heat from the home "escaping into the ground" on cold days when heating is on. If radiant heating is installed in a slab on grade it can absorb the heat and radiate it slowly into the room.

Slab on grade requires compacting the earth before laying the foundation to avoid, they work well on clay soil and in general they are more cost effective.

More about slab on grade on this website

Here is an example of combining radiant flour in slab on grade taken from this website

Pier and beam foundations support the building above the ground and allow a crawlspace which may make maintenance of installation easier. This crawlspace, though, gives access also to rodents and will also require good insulation to protect from the weather. The pier can be made of wood or blocks or casted concrete and can go to different depths depending on the earth type, weather conditions etc.

For more information about pier and beam foundations check these website.

Here is an example of radiante heating combined into a wooden flooring taken from this website