Ground sheet with a bivy?

Having a bivy makes a groundsheet redundant. WP bottoms mean you can save the weight.

Awesome, Im glad you posted this, I was just about to ask this question myself.

I always use a tyvek groundsheet with my bivy to increase the life of my bivy. It adds only 4oz.

Hi Chris,

“The top of the Raven Omni is made from Black Intrepid, a 20 denier DWR treated fabric that performs as well or better than anything in its weight class. The bottom is Black Sil-nylon”.

Silnylon is great at repelling water when used overhead as a shelter. The tautness and angles involved when silnylon is used as an overhead shelter assist the material in its ability to repel water.

When used as a bottom in a bivy configuration the material is neither taut or at any angle.

“Even the 1sts sil is only waterproof to around 2 psi which is commonly overcome in some applications”.

Elbows, hands and knees will easily overcome this 2 psi limit when pressure is applied in a very localized area of your silnylon bivy bottom.

Simply said, if the ground is or gets wet and you press down in any small area of the bivy floor with any of the aforementioned body parts you run the very real risk of getting wet!

Now here is the caveat. I use my silnylon bivy without a groundsheet all the time.:O

If your ultimate desire is to stay dry, carry the groundsheet.

Here are a few more basics for picking a campsite.

Look for a flat, level and semi elevated area to set up your tarp and bivy.
If at all possible set up camp on the leeward side of a mountain or hill.
Use forest duff such as leaves and sticks to make a berm that will divert running water away from your bivy in case of rain.
Even a bathtub style floor will not make up for choosing a poor campsite.

Take a look at some of these shelter tips from Ron Moak’s Six Moon Designs website.

Party On,

Newton

Thanks all – this is great information!

I use one with my bivy just mainly for a little more protection and waterproofing from the ground.

My groundsheet of choice is the polycyro groundsheets. You can buy them from some of the cottage guys (GG, MLD, etc) or go to your local hardware store and pick up the window heat shrink kits. The ones sized for a sliding glass door can be cut in half to make two giant solo groundsheets and weigh about an ounce each. Super cheap to purchase and plenty durable and waterproof so far.

I like a small footprint of Tyvek to protect the floor of any shelter I am using. I know that may throw some into SUL terrors, but it extends the life of my gear. I cut it smaller than the perimeter of the shelter so any water running off the sides isn't captured by the footprint. I just want to protect the center area from punctures and mud. With SUL, I assume some gear life is sacrificed. YMMV :)

You absolutely do not need a ground sheet with a bivy. For mine, I treated the bottom with a coating of seam sealer (see http://jwbasecamp.com/Articles/Silnylon1/index.html), which dramatically improves the waterproofness (is that a word?) of the floor and makes a groundsheet unnecessary.

Treating the floor takes about 10 minutes and $10 in equipment, and your bivy will be a lot tougher as a result.

-"Simply said, if the ground is or gets wet and you press down in any small area of the bivy floor with any of the aforementioned body parts you run the very real risk of getting wet!"

You make a good point, but my real world experience doesn't line up with that. Maybe I'm lucky, but last summer in the Grayson Highlands I experienced some of the heaviest rains I've ever seen and our entire campsite was flooded with running water for a good 15-20 minutes and my sil floor kept me dry as a bone. I'm talking a good 1/4 – 1/2 inch of water. Deep enough to where even if I had a ground sheet the bivy would've been wet.

And before anyone calls me out it was a great sheltered and well drained spot, but it was an INTENSE rain.

Adding a ground sheet to a bivy is somewhat redundant. But, do you plan on inserting the pad inside the bivy or outside? Outside, then you may want to protect the pad from pucntures with a ground sheet. I think the Raven is large enough to put the pad inside. The other consideration with an inflatible is punctures. If camping in the desert, the a more substantial ground sheet like Tyvek may be in order to hel protect the pad from punctures.

I use a custom made silnylon 133g ground sheet with my Trailstar and bivy. It protects my bivy from puncturing and gives my a half the floor area sized dry zone to spread kit around and keep it dry. Groundsheet is a must for me with the bivy.

I, too, use a groundsheet. While I have mostly used a polycro (Ace Hardware window film actually) sheet, last weekend I tried something new since it was just an overnighter – a drycleaning bag.

It worked flawlessly and surprisingly was very puncture resistant. It weighed very little, although (gasp) I didn't weigh it. It was almost 6' long after I "opened" it up by cutting it along each long edge. Didn't worry about the hole in the middle for the hanger to come out since I didn't expect rain. A short length of packing tape will fix that.