i read about it here. it involves an initial layer of pine shavings, which you add to monthly or so (without removing the old stuff). They recommend scratching or mixing the old litter occasionally
(or put feed on the floor and have the hens do it for you). The idea is with monthly additions of litter and frequent stirring, you can let the shavings accumulate, helps with insulation in colder winter months. Then once or twice a year you shovel it all out and begin again. I hope that someone who has done this will write because it's been a while since I read about it and am anxious to hear from people who use the method so I can try it myself (now that my chicks are out in the coop)