This Wednesday the Pole Barn Guru answers reader questions about a home owner asking builder to install housewrap on the roof, the best solution to insulate underside of roof, and what the best fastener for screwing steel to ceiling or roof trusses would be.
DEAR POLE BARN GURU: Pole Barn Guru, thank you for your knowledge. I have a customer wanting house wrap around the exterior of a 30×40 pole barn. Is house wrap to be installed in between purlins and roof steel or will I need a radiant barrier to prevent condensation? Home owner says house wrap on the roof as well but I’m not sure if that’s the route he really wants to go. House wrap on side walls in between girts and side steel is also the best route correct?
Thank you for your kind words, they are much appreciated. Provided your client will not be doing closed cell spray foam on walls, use house wrap between girts and wall steel. For his roof, housewrap is totally incorrect, as it allows moisture to pass through and become trapped between wrap and roof steel – potentially causing premature degradation. If your client is not closed cell spray foaming directly to roof steel, then order your roof metal with an Integral Condensation Control factory applied (Dripstop, Condenstop or similar) https://www.hansenpolebuildings.com/2020/09/integral-condensation-control-2/. If roof steel has already been ordered (again assuming no closed cell spray foam being applied), then you do need some sort of a thermal break – such as a well-sealed radiant barrier.
DEAR POLE BARN GURU: Hi Mike, I built a 32’X40’X12′ pole building, (Shop) I used 1 1/2″ foam board on the inside walls, (on the inside of the girts) I can’t decide how I should insulate the underside of the roof. I have had a couple Spray Foam guy’s quote it , that’s pricy. Of course, the best R Value etc. at the most reasonable price is what I am looking for. In some of your post you have mentioned Rockwool that has gotten my attention. I see they make it up to R30. One thing that sticks in my mind is, my builder suggested not to use an insulation that will give insects a place to live. What would be your suggestion for underside of Roof insulation. Thank you. JIM in SPRING HILL
DEAR JIM: If your building has no current provision for controlling condensation on underside of roof steel, then two inches of closed cell spray foam applied directly to steel is your best insulation option. If you desire a greater R value, you can go thicker, or add open cell.
DEAR POLE BARN GURU: What screw is best for installing metal panels on the ceiling to wood trusses. MICHAEL in WENTZVILLE
DEAR MICHAEL: Most people are using #9 or #10 diameter 1″ screws. If you have ceiling framing 24 inches on center and want to utilize strength of ceiling liner panels to help transfer wind shear loads, then 1-1/2″ long diaphragm screws would be a better design solution.
“Wet insulation of any stripe is bad. But cellulose is hygroscopic. It’s able to soak and hold liquid water. Undetected leaks can wet cellulose causing it to sag within framing cavities. Water leaks can compress the blanket of fiber and in extreme cases, can create a void space, degrading its thermal value. Another concern is that chemicals used to protect cellulose from fire make it potentially corrosive in wet environments. Tests conducted by the Oak Ridge National Laboratory show chemical treatments used to treat cellulose can cause metal fasteners, plumbing pipes and electrical wires to corrode if left in contact with wet, treated cellulose insulation for extended periods of time. “
Now – on to your question at hand. For your walls, it appears most folks do exactly as you propose and build a 2×4 wood stud wall inside of their PEMB’s (pre-engineered metal building) steel wall girts. You will want to completely fill your wall cavity with insulation – I would recommend rock wool, as it is not affected by moisture (here is information on one particular product 
“We are planning to build in southern Missouri a 30′ x 36′ x10′ post frame home on a rocky slope terrain. We want it on stilts. It would be 3′ on one end and 7′ on the other end approximately. We are planning to put reflective bubble wrap on the floor joists with the subfloor on top then place down rock wool and another subfloor on top. We have 99% humidity most of the year (10 months for sure), lots of rain. We do not want a crawl space; we know the horrors of the crawl space. We may enclose the high end using a simple temporary enclosure to dry it out as needed. We are going to use a mini split heating system and composting toilets. No worries about placement of the utilities and pests. Would this be a sound construction system?
