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What is a ground sheet
A ground sheet is an impermeable barrier designed to prevent moisture from the ground from pressing through the bottom of a tent. Ground sheets also reduce the wear and tear on the tent bottom fabric by protecting the tent fabric from rough material and surfaces on which tents may be set up.
Why they are frequently necessary
Traditionally, backpacking tents use various forms of nylon. Often this nylon may be waterproof when not under stress, but when used on the bottom of a tent, where body weight presses down on the material, water may press through the material either through small or large breaks in the waterproof barrier, whether the breaks are from wear or the breaks are integral to the weave or factory treatment of the fabric.
Ground sheets are also nice to have in cases where pitching a tent is not necessary. In the southwest, when Iíve been backpacking with no chance of rain and no bugs to speak of, Iíve enjoyed many nights sleeping out under the stars using
Where to pitch to minimize the need for a ground sheet
The environment can make a difference in how much the groundsheet helps.
In the northeast, where soft forest duff predominates and pine needles are short and flexible, I find I rarely need a ground sheet. If I take the time to find a spot without many rocks or sticks, I can take a few minutes to clear anything left that is sharp before setting up my tent.
In other parts of the country where I may have to pitch my tent on rocky ground, desert ground with sharp cacti barbs and coarse sand, or amongst the long, sharp, and stiff needles of western pines that easily poke through tent fabric, I find I almost always prefer to use a ground sheet. I still try to minimize the potential for sharp materials to poke through my tent bottom, but end up relying upon the ground sheet to fully protect the tent.
Choosing tent sites carefully can also reduce or eliminate the need to use a ground sheet as a moisture barrier. Like when tarping, pitching your tent on a slight rise can serve to prevent water from rushing under your tent when it rains. Avoid pitching your tent in a depression if there is any chance of rain.
Ground sheet materials
Iíve used everything from really cheap shower curtain liners (remove the heavy magnets and trim as necessary), to thin plastic sheeting, to Tyvec house wrap as ground sheets. Some tent manufacturers also make tent specific ground sheets. While liners and sheeting are effective, I find them to be too fragile for long-term use. The manufacturerís offerings tend to be too heavy and expensive for my taste. For me, Tyvec is both a durable and inexpensive option (look for scraps at nearby housing construction projects).
Groundsheets should be shaped about the same as your tent floor though they should be a few inches smaller. If thereís any chance of rain, the groundsheet must not stick out from the sides of the tent. Should it do so, it would only serve to collect and channel water on top of the ground sheet, under the tent, and potentially through the tent floor, exactly what the ground sheet should be preventing.
How to use a ground sheet
For the most part, ground sheets are most effective when used under the tent. The one time when this may not be the case is for those hikers with dogs that share the tent. These hikers may choose to use a ground sheet inside their tents. They do this for primarily two reasons: One, to prevent the dogsí claws from scratching or putting holes in their tent floors and/or two, to prevent the muddy paws from dirtying the tent floor.
On the Appalachian Trail and subsequent hikes, I used a silnylon (silicon impregnated nylon) tent. While silnylon is, in theory, not impregnable, it does take considerable pressure to push water through the nylon. As such, Iíve never seen water in my tent associated with anything other than either condensation or holes worn into the floor (in the corners where my ground sheet couldnít protect the tent floor).
Knowing the properties of silnylon, I decided to forgo the use of a ground sheet along the A.T. and never regretted that decision. When using my tent, I was usually on either soft duff or on tent platforms. Neither surface posed significant danger to the waterproofness of my tent floor.
On the Pacific Crest Trail, the Continental Divide Trail, and other desert hikes, I used a Tyvec ground sheet and it was absolutely necessary. Desert hiking through cactus spines and barbs as well as stiff pine needles posed significant poke hazards to the tent floor fabric. In the desert, Iíve also used the ground sheet to protect my sleep system when sleeping out under the stars.
While I've never to my knowledge had water come through my silnylon due to pressure I usually make a point of almost sitting or lying on my sleeping pad while in my tent. I do this for two reasons: it's easier on my body to sit on the forgiving pad; and it may spread my weight and therefore reduce the pressure at any one point that may otherwise become a point where the water presses through. I assume the thickness or density of the pad may make a difference but Iím not sure how to quantify it. I use a 2.5Ē think Big Agnes Air Core pad.
I also try not to twist around on my full weight when maneuvering inside my tent. Rather, I lift myself up a little to turn and then allow my weight to settle down on my pad again. I imagine this can also help minimize wear and tear on my tent.
Last updated, August 15, 2006.
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