Tag Archives: re-roofing

Creating a Thermal Break

Welcome to Ask the Pole Barn Guru – where you can ask questions about building topics, with answers posted on Mondays.  With many questions to answer, please be patient to watch for yours to come up on a future Monday segment.  If you want a quick answer, please be sure to answer with a “reply-able” email address.

Email all questions to: PoleBarnGuru@HansenPoleBuildings.com

DEAR POLE BARN GURU: Have recently purchased a home with an existing pole building on it. The pole building is in nice shape but we will be replacing the roof panels. My question is about moisture control. The existing roof framing is like a typical house frame roof, with trusses on 24″ centers and a roof deck of 5/8 osb. Would a synthetic roof felt be the proper choice before installing the new roof panels or would you recommend something different? I see a lot of references to AV1 as a thermal break but I believe the roof deck would accomplish this. Any help would be appreciated.

Thanks again. CORN FARMER in Burr Oak, MI

DEAR CORN FARMER: Thank you very much for being a loyal reader. Synthetic roofing felt should work just fine for your application, as the roof sheathing will provide the thermal break necessary to prevent condensation issues. One concern – if the current OSB is installed directly to the top chord of the roof trusses, 2×4 purlins will need to be placed on top of the sheathing in order to give the roofing screws something to “bite” into (OSB will not adequately hold screws). The 2x4s can be placed flat wise and should be nailed through the sheathing into the top chord of each truss with two 16d galvanized common nails (even better if the nails are ring shank to aid in preventing withdrawal). We had a similar circumstance when re-roofing my wife’s home a few years ago, and we opted to use A1V reflective radiant barrier draped loosely over the purlins, in order to more effectively utilize the reflective coating on the outer face of the insulation to assist against heat gain in the summer.

Mike the Pole Barn Guru

DEAR POLE BARN GURU: Is it possible to build a pole structure into a moderate hillside? By way of either setting extra poles and laying 4×4 or 6×6 timbers horizontally to retain the soil against the structure and waterproofing the timbers and incorporating adequate drainage. I really don’t want to invest in building a separate retaining wall as this would create a “gap” between the wall and pole structure to collect debris and snow in the winter. I’ve received poured wall estimates in the range of $30,000-$44,000 just for a foundation making that route unfeasible. My plans are for a 40×60-64×14 structure with attic trusses. Any input you may have is greatly appreciated.

Brett in Dewitt, MI

DEAR BRETT: Yes, it is possible to building a pole structure into a moderate hillside. The easy way – build a concrete or ICF (Insulating Concrete Forms) foundation wall to support areas which require a “cut” into the hillside and mount the building to the top of the wall by means of brackets. (Read about bracket mounting here: https://www.hansenpolebuildings.com/blog/2012/09/concrete-brackets-2/)

I am not expert on concrete foundation work, but the estimates you are seeing appear to be more than sufficient to excavate, form and pour an entire full basement along with a concrete slab in the bottom and have money left over.

(To get an idea of foundation costs read: https://www.hansenpolebuildings.com/blog/2011/10/buildings-why-not-stick-frame-construction/)

I actually have personal experience with a situation probably far more dramatic than yours, which you can read about at: https://www.hansenpolebuildings.com/blog/2012/02/grade-change/

Mike the Pole Barn Guru

Re-roofing with Shingles

One of our clients, who invested in their new Hansen Pole Building in 2008, contacted us today to inquire as to if the building they ordered would support composition shingle roofing.  My darling wife (and editor) said to me as she read this, “Haven’t they constructed their building yet, or why do they need to replace the roof already?”  My answers: “Yes and poor installation”.  They built their pole building in 2008, but did not pre-drill their roof steel.  They had screws all over the place, many of them not hitting purlins.  You guessed it – they basically created a colander.  So now they figured it was easier to replace the steel with shingles.  Not so.

The building was originally designed to support 29 gauge steel roofing, the post frame industry’s standard. 29 gauge steel roofing only weighs about 63 pounds per 100 square feet of coverage. Roof purlins at 24 inches on center add about 75 pounds per 100 square feet and the roof trusses 62 pounds. All told, the dead weight of the steel roofing/roof purlin/roof truss assembly is about two pounds per square foot (psf).

Although any structural assembly involving lumber has a fairly significant built in safety factor, Hansen Buildings uses a roof truss top chord dead load of 3.3 psf. This gives a safety cushion of 65% above actual dead loads.

Standard asphalt shingles weigh 235 pounds per 100 square feet and require asphalt impregnated (felt) paper underneath, which weighs another 15 pounds per 100 square feet. These must be installed over (at a minimum) 7/16” oriented strand board (osb). The osb adds 47 pounds per 4’ x 8’ panel or 1.47 psf. Code requires a shingled roof to be designed to support the weight of a re-roof, so the minimum design dead load for a shingled roof would be 6.69 psf. The roof truss industry typically uses a minimum top chord dead load of seven psf for roofs with shingles.

Even ignoring the weight of a reroof, the shingled roof assembly would weigh 4.34 psf, which would be more than 30% greater than the dead load the roof system was designed to support.

The answer to the question asked was – no.  There is more to the story which compounds the “fix” to their problem, but let’s just say “it would have been better to do it right the first time.”

While the probability is unlikely, due to the longevity of steel roofing, if you feel you ever might consider reroofing your pole building with composition shingles, it would be best to order your building with the roof having a dead load carrying capacity of no less than seven pounds per square foot.