Re-roofing a 1960’s Pole Barn
Reader JEFF in GRESHAM writes:
“I have an older (built in the 60’s?) pole building that needs a new roof. It is a typical metal over 2×6 purlins (Purlins 2′ on center, trusses 12′ apart). Current roof is corrugated metal attached with ring shank nails with rubber washers and it leaks (unsurprisingly). The roof had a spray on coating 15 years ago which helps, but again, it leaks and it needs a new roof. I would like to do standing seam roof but since the roof needs to act as a shear diaphragm If I tear off the old metal, I need to sheet the whole thing so those are two substantial projects in their own right (#1 tearing off and then #2 re-sheeting…) . I tried taking a pry bar to find out the difficulty of removing the old nails and it was stuck so securely I ripped the head off the nail rather than nail of the roofing and I estimate there are about 6000 of them! Thinking about it and doing some research, I think it’s possible to go over the existing corrugated roofing with standing seam using wood strips over the corrugated. I’m still concerned about things like condensation occurring if I do that and not sure if it would be unlikely, infrequent, or maybe much worse than what I see now. Obviously frequent and substantial condensation is just going to lead to rot and problems. I’ve looked at the added weight and its about 1.4 lbs per square foot using 24Ga standing seam = pretty trivial compared to snow loads so I think it’s unlikely to be an issue. I’m interested in knowing what advice, experience, and tips the Pole Barn Guru can offer for this situation. Please see attached .pdf for a visual of the scenario at hand. Thanks!?”
Yes, those old nails are tough to remove. Most standing seam steel is not stiff enough to span between purlins, so it is nearly always recommended to install over solid sheathing. Even if it will carry this span, it is likely to droop between purlins and if stepped upon, by accident, between purlins expect it to buckle.
Next challenge – those roof trusses are probably not designed to carry more than bare minimum loads. You want to add as little weight as possible. It might behoove you to have them inspected by a Registered Professional Engineer to insure they will be structurally adequate to handle any added weight.
Assuming trusses are structurally adequate, I would pull out every nail I could and, for ones where heads break off, once old roofing is removed, pound them in. Sheet roof with 19/32″ CDX plywood, install 26 gauge standing seam over a synthetic underlayment. There is no real reason to go to 24 gauge, other than a salesperson’s commission. Make sure to vent ridge and have adequate air intakes and condensation should then be a non-issue.
DEAR CHAD: Unlike all Hansen Pole Buildings with spans of 40 foot or less (where we have our interior double trusses always designed to be able to support at least a minimal ceiling load of five pounds per square foot), most pole barn trusses are not ordered or designed to support any sort of a ceiling. Many times trusses will have a stamp on them stating truss spacing and loads, if so, you want a Bottom Chord Dead Load of 5 psf or greater. If nothing else, truss manufacturer’s stamp will tell you who fabricated those trusses and you can reach out to them to verify adequacy. If they do not have records available, or are no longer in business, you should engage a Registered Professional Engineer to perform a field inspection to verify adequacy, or to provide an engineered repair.
DEAR DAN: Every Hansen Pole Building is fully engineered to meet or exceed your jurisdiction’s minimum design wind speed requirements (in Ventura county Vult = 100 mph). When wind is a client concern, we always recommend designing to higher than minimum design wind speeds. In many instances, added investments are minimal. Most important is designing to correct wind exposure for your particular site. Most other providers sell Exposure B rated buildings, when many sites are actually Exposure C. For extended reading on wind exposure, please read: 
DEAR POLE BARN GURU: Would it be possible to install a 1/8- 1/4 ‘’ steel plate C-shaped with a “tail” extending from back side to tie a bottom chord and king post together and then cut out a 6’’ section to allow for a garage door opener install. GABE in SIMCOE 
DEAR POLE BARN GURU: How do I get drawings quickly for a large pole barn, post frame? JAMES in LITTLE SILVER
