Tarp as an open roof (flat fly / group fly)

A tensioned sheet only stays smooth when there is even pull on all sides. Rain falling on a horizontal surface finds no way down. It collects at the lowest point, pushes it further down, and that makes even more water run there. These water pockets can become surprisingly heavy and overload the sheet, the grommets or the supports.

A slope breaks this cycle. If one side is lower, the water runs straight off to the edge. With large sheets, a raised point in the middle also helps – a pole underneath or a line pulling up to a branch. The sheet then takes the shape of a shallow tent roof from which water runs off in all directions.

The open sides have an advantage: air can flow through and you can see all around you. That makes the flat fly an ideal living area in sun and light rain. But it also has a drawback: wind can get under the sheet from every side.

For a flat fly you need four or more anchor points: trees at a suitable distance or poles, for example trekking poles. Each pole is guyed with two lines running outwards at an angle so it does not topple. Tensioning hitches that can be tightened again make fine adjustment much easier.

Plan the slope deliberately. The run-off should not flow onto the path, into the seating area or onto the cooking spot, but to a place where it bothers no one. At the first drops, check whether water is collecting anywhere and re-tension.

One variant is the sloping wing: two opposite corners are guyed high and two low. The sheet twists, sheds rain well and gives some wind protection on the low side.

Fires and stoves must only be run at a good distance from the tarp. Hot air and sparks rise, and many sheet fabrics melt or burn from heat alone, long before a flame touches them. Always check the local rules too: fires are forbidden in many places or allowed only at fixed spots, and fire bans often apply in dry weather.

A high flat roof acts like a sail in wind. Gusts can knock over poles, tear out grommets or rip the whole sheet loose. Lower the roof or take it down in good time before anything breaks – not only once something is already flapping.

Look up before setting up: dead branches above the spot can fall in wind. In snowfall a flat roof is unsuitable, because snow does not slide off and its weight can tear the sheet.

The open roof is ideal for group camps, as a cooking area at a distance from the flame, for breaks in the rain and as sun shade. A single large sheet creates a shared space where everyone can sit, eat and talk in the dry.

As a sleeping area it is only suitable in calm weather. In driving rain, which the wind blows in at an angle, you will get wet under an open roof. For the night the flat fly is therefore often combined with closed forms such as an A-frame or a lean-to, which sit lower and have a weather side.

Practise the setup first in good weather in the garden or on a meadow. Try out how high you can raise the corners, where best to build in the slope and how to raise the centre. A garden hose or watering can shows you whether the water runs off where you want it.

Also practise lowering it: how quickly can you get the roof down low if the wind suddenly picks up? Anyone who has tried this once without pressure acts more calmly and quickly when it matters.