This Wednesday the Pole Barn Guru answers reader questions about adding wool bat insulation between purlins against an R-7 vapor barrier, and the Guru’s thoughts on Knee Braces in post frame construction.
DEAR POLE BARN GURU: Hello We have an existing pole barn that has an R-7 vapor barrier. The vapor barrier is between the metal and the 2×6 purlins. We would like to insulate the ceiling and maintain the vaulted ceiling look. We are using a 5.5″ wool bat insulation. Can we put the bats in between the purlins in direct contact with the vapor barrier or do we need an air gap between the vapor barrier and the new insulation? If an air gap is needed, how much space is required? Will it need to be vented? SARA in ANACORTES
DEAR SARA: Building Codes require a continuous one inch air space from eave to ridge above batts, as you propose. This would require adequate ventilation at eave and ridge as well. Your best option is to remove your current condensation control blanket, have two or more inches of closed cell spray foam applied directly to roof steel, then fill balance of cavity with Rockwool, without a vapor barrier below.
DEAR POLE BARN GURU: What type of bracket is used at the bottom of a double sliding pole barn door where the closed doors meet. CHUCK in GORDAN
DEAR CHUCK: CENTER GUIDE & STOP
One required for each bi-parting door pair.
Center guide may be mounted to a pressure treated column cutoff piece or embedded in concrete.
Locate guide at door opening center point. Sliding door bottom laterals will hook into center guide.
For proper closure, each bottom horizontal is to be cut or notched 1/16” short for center verticals to compensate for center stop thickness.
DEAR POLE BARN GURU: Hello, I’ve read through your website and it seems that I don’t need these knee braces but I figured I’d write and ask about what you think. Total size of the building is 80×40 14ft height and approximately 7 feet to the pitch of the roof. The building had these knee braces and also metal cross bracing between each post. I want to remove the knee bracing to be able to build offices inside this thing. Thank you. MIKHAIL in EVANSVILLE
DEAR MIKHAIL: While knee bracing is generally ineffective, they should never be removed without approval from your building’s original engineer, or after a thorough analysis has been done by a competent engineer. It appears your building has (or is in process of) been recently added onto. Engineer for your addition should be able to advise on your knee brace concerns. Hopefully, he or she has accounted for increased shear loads to endwalls (by adding to length of building). As length-to-width ratios increase, shear loads can become greater than what simple through screwing can provide. Under severe (but not extreme or approaching building code minimums), this could result in catastrophic failure.
