There are seven key construction features that need to be addressed when building or remodeling a double-curtain-sided finishing building, reports consulting agricultural engineer Larry Christenson of Kalona, IA.
Two such types of finishers are used primarily in the Midwest. The first features a flat, insulated ceiling with some type of mechanical ventilation for cool weather operation. The second unit is naturally ventilated all seasons.
The second type of structure features either insulation on the roof line or a raised, insulated ceiling with some type of continuous ridge opening or box chimneys to provide exhaust of warm air.
Following are seven features Christenson says hog producers can use to add longevity to those structures:
1. Overhang enclosure: Many of both types of finishers utilize an overhang on both sidewalls formed by the extension of a truss chord. Most agricultural builders in the Midwest enclose this overhang with metal trim to protect it from the elements and to restrict bird entry.
Christenson recommends covering the bottom of the overhang with a solid material or solid soffit.
"This will eliminate the entry of dust and moisture-laden air into the attic area," he says. Warm air migrates from the animal room as the curtains begin to open from the top down. Warm air and dust rises and travels up along the sidewall toward the bottom side of the overhang. The closed soffit will keep the dust from collecting on the bottom side of the roof metal and settling on the insulation, reducing its effectiveness.
Also, warm, moist air is restricted from the attic area. During cool weather this moist air would condense on and deteriorate the underside of the roof metal and fall into ceiling insulation, causing serious damage, explains Christenson.
The air from the animal room should also be restricted from the attic to prevent recycling of contaminated air back into the animal room in those buildings with ceiling inlets for cool season mechanical ventilation.
Wind-driven snow is also restricted from entering the attic area with the use of solid-soffit covering, says Christenson.
2. Attic air openings: These inlets are needed to allow fresh air to enter and moisture and warm air to exit the attic area. A second function for these openings on double-curtain-sided finishers with flat ceilings is to provide air entrance for cool season room ventilation when exhaust fans are used, he points out.
Make sure there are adequate openings into the attic area for ventilation air before it enters the animal space.
"When you close the sidewall overhangs (soffits), the only place we can bring the air in is through the ridge vents and gable extensions," explains Christenson. His recommendation is to add a gable extension to both ends of the building by extending the roof and gable end out at the top of the wall and forming a horizontal opening to allow air passage into the attic area. This extension can provide a 12 in. or greater opening across the endwall. It should be built with a door to close the majority of the opening during extremely cold weather operation.
Christenson says producers should install roof ridge vents so they provide about half of the needed opening area into the attic for those facilities using cool season mechanical ventilation. His choice is the high profile, 10-ft.-long units with a wide throat opening. Low-profile vents may plug when there is significant roof snow load, he points out.
3. Vapor barrier and proper sealing: Install an adequate vapor barrier and seal all openings between the animal room and the structural interior. This is vital to keeping animal moisture, gases and dust from making contact and causing deterioration to the framing lumber, insulation or steel sheathing, says the Iowa agricultural engineer.
The sidewall vapor barrier should be installed on the inside of the wall and all seams and joints properly caulked.
For buildings with ceilings, apply the vapor barrier to the bottom side of the insulation before the covering is attached. Insure that all joints and seams between the ceiling covering, sidewalls and endwalls are sealed to eliminate air leaks.
For roof insulation, one method of construction is to place 4x8-ft. sheets of rigid board insulation between the roof purlins and the roof steel. Joints must be sealed on the bottom side to prevent moisture from traveling into the joints and condensing when it strikes the roof metal, causing deterioration.
The best method is to add a full-coverage vapor barrier on the underside of the insulation and/or framing.
The same naturally ventilated building as previously described can be constructed using a scissors truss to support a raised, insulated ceiling. An effective vapor barrier and caulking can easily be installed to add longer service life to the building.
4. Sidewall curtain openings: Finishing building curtains should seal tightly against the sidewalls when closed during winter, Christenson emphasizes. Use a large staple at the top of the curtain opening to hold the stay rope flush to the sidewall. The standoff bracket at the bottom of the curtain should be rigid to firmly hold the lower end of the stay rope.
"Without adequate tension in the stay ropes, winter winds will pull the top of the curtain away from the sidewall and allow heat to escape the animal room," he says. Properly installed hardware, which firmly seals the closed curtain against the building, will reduce air loss and thus the heating expense.
5. Durable ceiling material : Use a durable ceiling material to extend the service life of your building. Remember the covering on a flat or raised ceiling adds significantly to the structural integrity of the building.
Christenson recommends using ribbed steel, aluminum, fiberglass or plywood with some type of protective covering for the ceiling material.
Polyethylene sheeting is a less durable product. This cross-laminated sheeting, when used on the ceiling, provides no structural integrity and no fire resistance, he says.
6. Siting: A large number of hog buildings have collapsed the past several winters in the Midwest due to drifting snow at farm and building sites. Producers should evaluate the building site with regard to snow drift and roof snow load potentials, Christenson says.
Buildings should be sited at least 100 ft. (140 ft. recommended) south of a farmstead shelterbelt.
"This will keep the buildings out of the snow drop or catch zone created by the windbreak," he explains. This distance will still provide northern direction wind protection for the buildings.
A set of buildings placed at an open site should also be protected from snow drifting and the potential for large snow accumulations on sheltered building sections. At an open site, the northern-most building provides a windbreak for the other buildings and may result in large drifts across the sheltered areas of buildings to the south. Christenson suggests producers consider installing a snow fence or use large bales at a 50-to-70-ft, distance to the north and west to form a temporary snow fence.
7. Roof snow load: Evaluate potential snow load accumulation at your building site. Christenson advises producers to think about increasing the potential snow-carrying ability of buildings by adding 10 lb. of roof-bearing capacity at about 1% of the total building cost. "That is very economical insurance," says Christenson.