This week readers “ask the Guru” about purlins needed to rebuild a salvaged steel building in Iowa, some guidance on insulation due to potential moisture issues, if doors and windows are include in a Hansen Building Kit.
DEAR POLE BARN GURU: I am putting up a building using salvaged steel pillers and trusts. It originally had 2x6x14 purlins. The pillers are spaced every 14 feet. An engineer said I would need 2×12 to handle the load. That seems like overkill as the original building stood for 40 + years without issue. Roof is 4/12 pitch. I am in NW Iowa and I am building on the same area as the original. What is your opinion for trust size. Thank you. DENNIS in FOND
DEAR DENNIS: Your engineer is privy to far more information than I am as to your salvaged building and climactic loads. He or she also is a highly trained professional with at least four years of education and another three years working under direct supervision of a registered engineer. I am going to defer to your engineer (and I am not a registered design professional). If you truly feel something less should be adequate, discuss further with your engineer. It could be higher graded material would allow for a lesser dimension (but may not be less expensive).
DEAR POLE BARN GURU: I just had a new pole barn built and need further guidance on insulation, thermal barriers, etc. It is a 40x50x14 with 4/12 pitch scissor trusses. It is wrapped with the ThermaGuard radiant side facing out directly under the metal roof and walls. No ceiling planned as the bottom chords of the trusses are only 2/12 pitch. I live in the lower edge of the 4A climate zone (middle Tennessee) and live down in a hollow beside a creek where humidity stays pretty high. I’m concerned about moisture being trapped when I add more insulation and finish the inside since it already has a radiant moisture barrier facing out under the metal. What would be the best way to proceed? Polyiso board, XPS, or Rockwool under the inside, or something else and should I leave an air space in between or radiant barrier on the inside as well? Plan to cover the inside with part metal and the rest OSB or shiplap and will probably leave the roof as is with only more insulation added. Planning a loft across the back wall as well, but no heat or A/C planned as of now. Thank you for any advice on how to proceed. DAVID in BETHPAGE

DEAR DAVID: Welcome to a world where there is no joy, as insulation discussions are best had before construction begins.
Making some assumptions:
You do not want to tear out any of the reflective radiant barrier, you have vented eave overhangs, vented ridge and scissor trusses are designed to support a ceiling.
Install some sort of ceiling and either blow in fiberglass above it, or install Rockwool batts at ceiling level.
Walls add 2×4 bookshelf girts flush to inside of columns and install 7-1/4″ Rockwool batts. Do not leave an air space between batts and barrier.
Your walls will now dry to inside, so you may need to mechanically dehumidify, especially is you do not have an under slab vapor barrier.
DEAR POLE BARN GURU: Are doors and windows included in the kits? KEVIN in BANDON
DEAR KEVIN: We typically provide all doors and windows to best meet your wants and needs. This assures you of a proper match between both building code and product fit requirements.


This leaves “in hangers” between trusses as your only viable (and practical) design solution.

DEAR POLE BARN GURU: I have one more question for you I have a cabin that has 2×6 stud walls 12′ high that I put 2″ foam under slab and 2″ on the side walls so from under slab to top of walls on the exterior is completely covered in foam with 2″s of closed cell spray foam sprayed to the interior of the 2″ pink. Then 5″s of closed cell sprayed on the roof for a hot roof. My problem is I’m heating this building with electric boiler and my bills have been quite high. In the house side I have vaulted ceilings so not much I can do there but my garage ceiling is 12′ with no insulation at that level because of the hot roof in your opinion if I blew in insulation at the 12′ ceiling height what would you do between the blown in and hot roof I’m worried about creating a moisture problem and mold and thinking I should vent that area above the garage too the outside what’s your thoughts thanks. CHRIS in HIXTON
DEAR ERIC: 4 foot on center makes for an awful lot of holes to dig and posts to set, not to mention becoming very limiting on width of openings like windows. We would recommend (of course with engineer’s approval) glulaminated columns every 12′ or even 16′). Outside of this, it is an acceptable approach, provided you can attach your splash plank to adequately transfer shear loads. We always recommend insetting roof purlins between trusses using engineered hangers.
Mike the Pole Barn Guru responds:
DEAR POLE BARN GURU: I have an existing 40 x 60 pole building, built in the late 80’s. It has double trusses spaced 12 ft apart. I would like to extend it from 60 to 72 ft. We originally were thinking we would extend using stick frame construction but now I am wondering if this will affect the integrity of the existing building. I would like to leave the end of the pole building in place and add a door into the new space at each end. Your advice on the best way to go about this? The extension is planned for a bathroom and laundry space and would have a concrete floor. Thanks for your help. WENDY in VANCOUVER
Purlins are then in perfectly straight lines, allowing for pre-drilling of roof panels (this eliminates misses). Others may try to align purlins over top of trusses using butt end splices. This makes for a very poor connection attempting to get adequate fasteners into 3/4″ (1/2 width) of truss top chords. When purlin joints are lapped, it causes a stagger of the purlins, resulting in inability to pre-drill and a significant chances of screw misses.
Reader BRAYTON in NORTHEAST WASHINGTON writes: “I’ve been previewing your website and am glad I found it!
DEAR POLE BARN GURU: My barn project has been a long drawn out process. The project stalled for 6 months but has picked back up again. I’m using rough cut lumber. Unfortunately, the wood has a grey color to it (probably from dirt, mold or algae on the surface).
DEAR SCOTT: It was bad enough when your tin guys put bubble wrap over your housewrap. Compounding your having spent your hard earned money on both, is closed cell spray foam should have been applied directly to inside of steel siding. Water under a bridge at this point. You should fill balance of wall cavity with unfaced rock wool and no interior vapor barrier. Wall will now dry to inside (meaning you may have to mechanically dehumidify). You did not say if your added lean to has an attic space or not. If your intent is to insulate with plane of roof (purlins) here is some guidance: 
Mike the Pole Barn Guru writes:

DEAR POLE BARN GURU: My girlfriend and I are looking to start an aquaponic greenhouse system/farm. We are building a polycarbonate gable style greenhouse 30’x96′-120′ and we are needing to attach a post frame building to the greenhouse in an “l” shape off the shop end. We are/were originally looking to keep the house (4bed/3bath) one level roughly 50×100 splitting the post frame building 50/50 shop and house. But after looking at some of your projects we aren’t opposed to building a taller but shorter home with attached shop still 50×50. My question is in attaching the green house have you ever designed or worked with projects like this? CHRIS in FORT MADISON
DEAR POLE BARN GURU: If I am building a 30×40 with 10 foot side walls, and I can only have a maximum peak of 17 feet, so roughly a 6/12 pitch, if I had attic trusses, how tall would the open space be in the attic room? If I can go taller and have a 8/12, or 9/12 pitch how tall could the open space be in attic? Thanks. KRISTI in SAGINAW












DEAR MARK: Your roof purlins appear to be adequate to support this type of a snow load. As to trusses, I would reach out to Morton Buildings with your site address and they should be able to pull up truss drawings for your building. If not, you would need to retain services of a Registered Professional Engineer who could do an actual inspection of your trusses and run calculations to determine exactly their capacity.
DEAR ANDREW: Can and should are not often same.
DEAR DAVE: Unless your window’s vinyl frame was actually damaged, in most instances a glass company can do a repair of just broken glazed portions. I would suggest a call to Capital Glass in Reno (775)324-6688 as this appears to be in their wheelhouse and they service Fernley.




We typically would use 2×6 #2 on edge for these recessed (between truss pairs) roof purlins. Here are the calculations:
Reader GUY in SHELTON is probably wishing he would have ordered a new Hansen Pole Building right now. He writes:
Kudos to you for doing a D-I-Y. Sadly you were lead to a product (Prodex) claiming to be insulation, however in reality it is a condensation control, and only if totally sealed.
As time allows, remove roof Prodex, have two inches of closed cell spray foam applied to roof steel underside, and increase thickness of blown in attic insulation to R-60.
They did not refill the tank until 7-20 21. They filled it from 62% to 80%! It only took from 92% down to 62% to heat the building ALL winter!
Mike the Pole Barn Guru writes:

Provided you have adequate available space, you may want to tweak your footprint dimensions in order to optimize your return for your investment. As steel comes in three foot widths and lumber in two foot lengths, your most cost effective dimensions of length and width will be multiples of six feet. In your instance, I would recommend 36 feet wide and 84 feet long.


Well John, you have left out a crucial part. One no proper pole barn should be without. Plans designed and sealed by a Registered Professional Engineer specific to your building at your site. To build without them is, in my humble opinion, fool hardy and I cannot endorse your plan of attack or methods of construction without them. Outside of this – attempting to field construct your own roof trusses is not a good choice. Prefabricated trusses are truly a bargain, especially when considering risks involved should your home made trusses collapse injuring or worse killing you or a loved one.
He was furious because he did not want heavy equipment, like a crane, run across his yard to lift his roof up. Luckily we were able to talk him down and assured him when he came home from work his roof would be up in place and there would be no tire tracks.

This very same adage holds true with those punting at their own building design….engage a trained professional. Or even better, a complete post frame building package structurally designed by a trained professional. And when I talk about “trained professional” in this context, I mean plans sealed by a Registered Design Professional (RDP – architect or engineer) specifically for your building on your property.
In areas where there has been a history of ice forming along the eaves causing a backup of water, an ice barrier that consists of at least two layers of underlayment cemented together or of a self-adhering polymer modified bitumen sheet shall be used in lieu of normal underlayment and extend from the lowest edges of all roof surfaces to a point at least 24 inches inside the 
Do you think that mix of 1.5” and 3” nails for the connectors would be sufficient or should I really consider just temporarily attach the hangers and replace the temporary attachment with the 3” nails? If that is the case, is there an issue driving 3” nails basically tip to tip through the hangers?


A quick solve for anywhere in the country and any method of construction – to the eave outside of all corner and sidewall columns, attach a pressure preservative treated 2×6 from grade, up to the level of the trusses. In most cases two 10d galvanized common nails spaced every nine inches will be an adequate connection. As these 2×6 will be in contact with the ground, they should probably be treated to at least a UC-4B standard. Your building’s skirt board and any other exterior mounted framing can now be attached to the face of these 2×6. Using this method allows for siding to be installed normally, without any undue compensations to get it to lay out properly.




“We would happy to provide some advice for this situation. Let me first say this is why we stress so much to inspect and inventory wood as they arrive up front. You are probably correct in your conclusion they came with the mites in the bundle. If the bundle would have been opened then we could have probably avoided your current situation.
This is actually fairly important, not just to determine how many boards can be toted around a jobsite by one person, but also in calculating the dead loads which must be carried by structural members such as roof trusses and rafters.
The beauty of pre-drilling pilot holes for roof and wall screws is perfectly straight lines. Straight screw lines are truly a thing of beauty – there are few things in life as pleasing as looking across a wall or roof and seeing the screws lined up like soldiers.