Today’s Ask the Guru answers reader questions about insulating a shed used for vehicle storage and a “workshop to piddle in,” the addition of eave light panels to a structure, and if it is possible to build a small building to house a well.
DEAR POLE BARN GURU: Thank you in advance for your time to answer my question! I have a 30×40 x12 pole building that I want to insulate. This will be used to store my vehicles in and to have a workshop to piddle in. Want to have a mini split system to heat or cool only when I’m out in the shop. I have Tyvek between the metal siding and purlins on the walls. I have a ridge vent the entire length of the building with the condensation barrier under the metal roof panels. I just started to frame my walls 16″ OC for batt insulation and was going to put up metal panels on the ceiling and lay batt insulation on that. Is this ok and/or should I add vapor barriers anywhere. What are your thoughts on this? Thanks again MARSHALL in SALISBURY
DEAR MARSHALL: You will need to have an appropriately sized air intake (either eave or gable vents) in order to prevent possible mold and/or mildew in your attic. Use unfaced batts (Rockwool would be my preference, with fiberglass second). Your walls will need a vapor barrier, ceiling will not.
DEAR POLE BARN GURU: I would like to put in polycarbonate “windows for my eve light on a 36×56 pole barn. The light vents will be on the east side of the pole barn. I would like to do this myself. Do you have a simple how to or a video? These are NOT on the roof. HOLLY in MILACA
HOLLY: We can provide 19 pieces of 3′ net width coverage by 3 feet tall polycarbonate panels, as well as steel “z” flashing needed for your transition from polycarbonate to steel siding and appropriate screws to attach. Along with this, you will get a Chapter from our Construction Manual to detail installation. To save on delivery costs, we can have these all available for you at our Browns Valley, MN facility. Please reach out to Materials@HansenPoleBuildings.com for pricing.
DEAR POLE BARN GURU: Have residential well, need a small building has this been done? CHRIS in ELMGROVE
DEAR CHRIS: Yes, it has been. Post frame (pole) buildings start to lose economy of scale as footprint dimensions decrease. Below roughly 24 feet square, other forms of construction may prove to be more cost effective. A factor playing into this is most jurisdictions exempt from building permits structures below a minimal square footage.
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) 
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 POLE BARN GURU: What screw is best for installing metal panels on the ceiling to wood trusses. MICHAEL in WENTZVILLE 
“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?
