Orientation to optimize for light is not as critical for a high tunnel as it is for a greenhouse structure that will be used for winter production and has a more substantial frame

•Above 40°N latitude, orient the length of a single high tunnel east to west

This orientation allows low angle light from the winter sun to enter from the side where it will not be blocked by ribs of the frame

This orientation is acceptable because the angle of the winter sun is much higher at these latitudes

This orientation avoids the shadow that would occur from the greenhouse just to the south of it in an east-west layout

Single bay high tunnels can be oriented perpendicular to prevailing winds to accommodate maximum air flow if structure has roll-up sides

Multi-bay high tunnels should be oriented parallel to prevailing winds

Commercial greenhouses are required to meet structural standards to withstand various loads

In contrast, high tunnels are generally not required to meet structural standards, which is one reason why they are inexpensive

Specifications are in place for high tunnels in some countries such as Holland

However, high tunnel structures should be built strong enough to withstand severe weather

•Dead loads are gravity loads that are constant throughout the structure's life

These include fixed equipment such as fans, suspended heaters, and water pipes, however, these are typically not found in high tunnels

Long term crops that are suspended from the frame, such as trellised tomatoes, are often considered dead loads

•Live loads are temporary or short term

These include wind loads, snow loads or any other environmental stress

Short term crops such as hanging baskets (though not usually produced in high tunnels) are considered live loads

Basic wind speeds for greenhouse structural designs are 90 mph for most of the US; high tunnel structures are generally not framed to withstand gusts of this magnitude

44 mph wind creates a live load of 5 psf (pounds per square foot)where as 62 mph wind creates a 10 psf live load

Strong seasonal winds are a concern

High tunnels placed perpendicular to prevailing winds typically receive the most damage

The lightweight hoop structure acts like an airplane wing that creates uplift when air passes over it

Values for wind uplift should ideally not exceed the structure's dead load

The best protection against uplift is to ensure that posts are driven at least 24 inches into the ground

Many high tunnel structures are not under production during winter

Snow loads vary considerably by geographic location

Snow with a one inch rain equivalent will load a structure with 5.2 psf (pounds per square foot)

One inch rain may equal 12 inches of light, fluffy snow or 2 to 4 inches of heavy, wet snow

A high tunnel built from ribs of 20 foot pipe bent to create a 14 foot wide X 6 foot high structure will withstand only about 10 psf

Other factors influencing snow accumulation include building exposure, roof slope, and heat loss (from the heating system) through the roof

If snow loads are heavy, various strategies can be used to minimize damage

Orient the structure so prevailing winds blow the snow off the high tunnel

Remove the plastic in the winter if not under production

Utilize portable heaters to melt the snow load

Manually remove snow, for example, brush from the inside using a long-handled broom

For example, high winds may be associated with a snowstorm