ARe you putting a new roof on your finisher this summer?

With profits returning to the hog industry, producers with older facilities are making plans for repairs this coming summer season. I’ve talked with a number of producers this past week who have older curtain sided finishing barns who are planning on replacing the roof steel on the south side due to corrosion issues, especially on the SW quadrant of the facility.

If you are one of these producers, now is the time to re-evaluate your ventilation system needs. The reason the SW corner of the barn has rusted roof steel is that most likely your ventilation system only has 20-25 cfm/pig total fan capacity. This generally means the curtain must open with big pigs in the barn when it is relatively cold outside for heat relief in the barn. This results in steam condensing on the roof steel and soffits. Not only does moisture condense on the steel, but also all of the gases and dust that are in the exhaust air.

Most newer curtain sided barns now have 35-38 cfm/pig total fan capacity. This means the barn stays in mechanical ventilation longer and it is much warmer outside when the curtains need to open for heat relief. As a result, there is less condensation and depositing of corrosive materials on the roof steel and soffits.

Many producers have been asking about the possible addition of fans to their facilities as part of re-roofing project. A good idea in my opinion, but there are several cautions that go along with this recommendation.

If you add fans (generally 2-24” or 1-36” fan to an end wall) you will need to add ceiling inlets. It does no good to add fans if you can’t get air into the room.

In addition to ceiling inlets, review your total attic inlet openings (generally south soffits). When the old roof steel is removed most of you will examine the condition of the ceiling insulation, especially along the outer wall. If you don’t have knee-braces in the facility, you will be limited on how much air you can bring in along the soffit since you will need to install insulation stops higher up on the truss-chord to maintain a minimum insulation depth at the outer edge of the ceiling. If you have knee-braces you can be more aggressive in lowering the insulation stop and allowing air to enter the attic via this opening.

In the 4-state ventilation workshops we recommend 1 square foot of attic inlet for every 400 cfm of fan capacity that will be pulling air from the attic. If you provide 1 square foot per 800 cfm, you will add 0.05” of static pressure to your ventilation system and any dirt on soffit screens, improper installation of insulation stops or chutes, etc will have a bigger negative impact on the overall performance of your ventilation system.

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