Site Selection

Avoid sites with inconvenient access, excessive water, poor quality soil, high winds, or low light levels. Ideally tunnels have year-round access, even when crops are not being grown, to allow for snow removal and other maintenance. Existing or potential access to irrigation water is essential, and access to electricity is desirable for inflation fans and mechanical air movement. Some growers have made use of micro-solar power systems to support these loads. It’s desirable to have good access roads and be close to wash/pack facilities. When siting your first tunnel(s) keep in mind future tunnel locations, so that your “build out” over the years allows for efficient access, materials handling and potential for multi-tunnel heating systems, etc.

The site’s topography should allow for drainage of “worst case” storm water and snow melt away from tunnels. A relatively level site is important to minimize structural stress on the tunnel due to uneven snow load. Moderately breezy sites can be helpful for passive ventilation, but high-wind sites create risk of damage to structure and/or plastic covering. TTrees can provide a windbreak but consider their future height when locating tunnels to avoid shading. Also note that dense hedge rows or locations too close to wooded areas can reduce passive ventilation.   

Tunnels should be slightly elevated compared to the surrounding soil in order to allow water running off the cover and drain away from the interior, and to allow snow melt to move away from the tunnel when the ground is frozen. On some sites it is advisable to create a raised pad for tunnels. Some growers install tile drainage, French drains, or curtain drains along the inside or outside of tunnels to carry excess water away from growing areas. Water running through/under a tunnel takes away soil heat, prevents good root growth, and can create muddy working conditions. Orienting tunnels along east-west axis provides optimal light for winter production, and a north-south axis is best to avoid shading inside the tunnel in other seasons, though most crops will have more light than they can use in the summer.  If using primarily passive ventilation in a low wind site, it may also be worth considering the direction of the prevailing wind when orienting the tunnel.

Construction. Do not skimp on the structural integrity of tunnels, as this can lead to collapse in bad weather. Plan for extreme snow and wind. Gothic style tunnels will shed snow better than Quonset hut style structures. Well-set ground posts, cross-ties, and other features that anchor the tunnel and keep it rigid are essential. Doors and vents should close securely to prevent winds from opening them in storms and seal well to help retain heat. It is advisable to have a plan to lower and secure roll up sides for the winter or during high winds. When building a tunnel, avoid driving equipment over future growing areas, as this can create compaction. Installing large doors in end walls or having removable / roll-up end covers to allow for tractor access can make tillage and addition of bulk soil amendments easier than with small equipment. Head houses or other structures make sense for storing tools and equipment, seed, and potting soil, rather than taking up valuable growing space in the tunnel.

Zoning and codes. Before you build, contact your state and local agencies to find out about regulations and tax policies for high tunnels. Some states and towns may require building permits; setback requirements and building codes vary among municipalities. Some consider tunnels to be real property (subject to tax) and others do not. It may be helpful to be very clear with local officials that the structure is not permanent and is used for producing agricultural crops.