How to pitch a tarp for wind: ridge height, orientation and tension

Wind affects a tarp in three ways. It pushes on the fabric, it gets under the edges, and it loads the guylines and stakes. Pitch choices reduce some of that. A lower ridge presents less fabric, turning an open end away from the wind limits how much air moves through the shelter, and tight guylines stop the sheet flapping. None of these settles how a shelter will behave in strong wind. The Shelter studio has no wind load model, so the trade-offs are set out below rather than a rating for any pitch.

Lower the ridge to present less fabric

A lower ridge puts less fabric above the stakes, so there is less area for the wind to push on. It also narrows the gap under the edges. The cost is headroom. For a 3 m wide tarp, the cross-section (the triangle seen from an open end) is floor width × ridge height ÷ 2. The working for two ridge heights is:

cross-section at 1.0 m = 2.24 × 1.0 ÷ 2 = 1.12 m²
cross-section at 0.8 m = 2.54 × 0.8 ÷ 2 = 1.02 m²
ratio                  = 1.02 ÷ 1.12 = 0.91, about 91%

Dropping the ridge by 0.2 m keeps about 91% of the cross-section. The fabric above the stakes is 20 cm lower at the ridge, and the floor widens by 0.30 m (2.54 − 2.24 = 0.30 m). The wall angle falls from 41.8° to 32.2°. Whether that trade suits a night depends on how much headroom the sleeper needs and how much wind is forecast. The figures do not say how much wind a shelter can take.

The ridge is one lever. The ridge height sets the wall angle, and the full set of sizes and heights is in the A-frame geometry guide. The guy geometry in the guyline length guide decides where the edges sit once the ridge height is set.

Turn an open end away from the wind

An A-frame has two open ends, one at each end of the ridge. An open end that faces straight into the wind lets air blow through the shelter. Common practice is to turn a closed side toward the wind, or to drop the windward end lower than the other. These are approaches people use, not tested solutions, and the right choice depends on the ground and the forecast.

The plan view in the Shelter studio shows the geometry. It takes the ridge bearing and the wind direction, both in degrees true, and the wind is the direction it blows from. A ridge bearing of 0° runs the ridge north to south, so the open ends face north and south. A wind from 0° meets an open end straight on. A wind from 270° (west) meets a closed long side. The 3 × 3 m plan at a 0.8 m ridge, ridge at 0° and wind from 270° shows this. Change the wind direction to see which open end it reaches.

The plan view shows direction only. It does not show the force of the wind, how the fabric moves or how the air behind the shelter is disturbed.

Pitch order for a windy site

A windy pitch goes in a fixed order, because each step changes the one after it.

1. Check the forecast for the wind direction and speed, and for any change during the night.
2. Choose the ground, then look up for branches and leaning trees before you mark the stakes.
3. Set the ridge height. Lower it if the forecast is strong and the headroom can be spared.
4. Set the ridge bearing so that the open end you least want in the wind faces away from it.
5. Stake the edges, tension the guylines and check the ridge height again once the fabric has settled.

Keep the guylines tight as the fabric sags

Fabric sags after it is pitched, and wind pulling on it makes the sag change. Sag lowers the ridge and lets the walls move, which changes the geometry the figures describe. Check the tension at the start of the night and again after a change in the wind, and re-tension any line that has gone slack. A line cut to the planning length has no spare to take up sag, so keep a little length in reserve when you cut. The guyline length guide shows how the end guy length follows from the ridge height and stake distance.

Tighter is not always better. Tension on a line pulls the stake or the anchor as well as the fabric, so a line pulled hard against a weak anchor can be the first thing to fail. The model does not test anchors, and the figures here give geometry only.

Plan for a shift in the wind

Wind direction can change during a night, and a pitch that suits the main forecast direction may not suit a shift. Check the forecast before you pitch, and plan the open end for the direction that matters most. Decide now what you will do if the wind turns: re-tension a line, move an edge, or take the shelter down. Do not assume the wind will stay where it was at dusk.

Look up for branches before the wind starts

Dead branches can fall, and a gust makes that more likely. Check the trees around the pitch before you choose the spot, not after the wind starts. A dead limb directly above the sleeping area is a reason to move the tarp. The campsite guide covers overhead hazards and ground in more detail.

Wind chill when the air is cold

Wind lowers the feel of cold air on bare skin and on damp clothing. The Feels-like tool uses the wind chill index used by the US National Weather Service and Environment and Climate Change Canada. Wind chill is applied when the air is 10 °C or colder and the wind is faster than 4.8 km/h. Outside the conditions for both indexes, the tool says neither applies and uses the air temperature as the reference. For background on the index, see the wind chill explained guide.

The link above sets air at 2 °C with a 30 km/h wind. That is inside the wind chill range, so the tool shows the wind chill result, its risk band and a frostbite time. The wind chill formula does not use humidity; humidity matters for the heat index instead.

Keep stoves and flames outside the shelter

A tarp is fabric held up by cord, and a stove or open flame inside it puts that fabric at risk. Keep the stove and any flame outside the shelter, placed so that smoke and sparks do not drift into the fabric. Fire rules for the area apply as well, and they can be stricter than the wind allows.