Now that you have your tinder materials gathered and drying, you have chosen your optimal fire site, and you have ensured that it is protected from threatening elements both horizontally and from above (to the best of your ability), there’s one more threat to your fire: the cold, damp ground.
Conduction (again, one of the three forms of thermal transfer) is the most effective (and potentially most detrimental in this application) form of thermal transfer. This means that it is also a significant threat to our fire because the cold, damp ground can “suck the life” right out of your fire-making endeavors. In simple terms, protecting your fire from the elements from above and on all sides is often not enough. If the ground is damp and cold (or worse, covered with snow), then you are going to need to protect your fire from that as well. We will achieve this with elevation.
Elevating your fire gives you two major advantages: A) distance from the cold/wet ground and B) more oxygen.
You can elevate your fire in several ways. Depending on your circumstances, a simple wood platform from several two to three inch diameter logs split in half can do the job in most cases.
WARNING: DON’T JUST SET YOUR DRY PROCESSED TINDER ON A FIRE PLATFORM OF WET ROUND LOGS!
You just worked really hard to procure and process the driest tinder possible. Why would you then turn around and ruin that dry tinder by putting it on wet logs? For the love of all that is holy… take an extra moment to split these logs in half with an axe, hatchet or knife exposing the dry insides of them and then lay them on the ground (flat, dry side up, of course) parallel to each other on the cold, damp ground (or even directly in the snow) to improvise your fire platform. NOW you can lay your precious dry tinder on your platform. Don’t be lazy and take shortcuts like that. “The Devil is in the details”, as they say… or in this case, neglecting the details could result in death by hypothermia. So just don’t.
You could even lift your platform with a few pine boughs or a couple of perpendicular logs under your platform for additional protection… or even fashion makeshift “legs” for your platform in extremely wet or snowy conditions. These “upgrades” in elevation may or may not be absolutely necessary depending on your circumstances, but all options should be on the table and at the ready in case you need them.
An “upside down fire” is another clever way to use your fire build as an elevation mechanism as well. Or even build a suspended fire almost like torch that you stick in the snow that supports your fire until it is more established. Your circumstances will obviously dictate which solution will best meet your needs.