Example - for a 3-bedroom, 2,000-sq.ft. home, with an exhaust-only ventilation strategy, and a target ventilation rate of 50 CFM you would need to install a 50 CFM fan with an adjustable-speed DC motor for continuous operation.
Quick Answer. Trenches were built during World War I to protect stalemated troops on both sides from artillery and rifle fire. Although the war began with rapid movement of the German army, when the Allied forces stopped the Germans, both sides dug trenches to help avoid losing territory they had gained.
1 Trenching is done using a Ditch Witch trencher, which makes a 12â deep and up to 150 foot of trench. 2  Every additional foot costs 50 cents per foot at 12â deep. 3  Deeper trenches require additional charges. Trenching is done using a Ditch Witch trencher, which makes a 12â deep and up to 150 foot of trench. 2  Every additional foot costs 50 cents per foot at 12â deep. 3  Deeper trenches require additional charges.