Tag Archives: roof condensation

Dear Pole Barn Guru: Do I Need Vapor Barrier?

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 or Saturday 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: Builder just built a pole barn, 36x53x11.  Great looking.  I was planning on finishing the ceiling and insulating it.  Because of this he left out the vapor barrier, said you don’t need that If you are insulating the ceiling?

True? PERPLEXED IN PENNSYLVANIA

 DEAR PERPLEXED: I will assume you have a steel roof. If so, your builder has done you a huge disservice by not using a vapor barrier. Why builders so often do this is beyond my comprehension.

In all probability you are going to experience condensation problems. Before you get the ceiling in, you are going to have dripping from the underside of the roof steel onto the floor, usually at every purlin.  Once the ceiling is installed, prepare for damp insulation (reducing its efficiency), as well as mold forming within the attic space. Not a pretty sight and eventually the decay could cause failures in the roof members.

From where you are at now your best, albeit not inexpensive, solution is going to be to spray foam the underside of the roof steel. You also need to provide adequate ventilation to the attic space you will be creating. If you have enclosed vented soffits on each sidewall and a vented ridge it should prove adequate. If neither of these are present, you can add gable vents. Each end would need a minimum of 3.18 square feet on net free area, with the vent placed in the upper one-half of the attic.
DEAR POLE BARN GURU:Will roof trussing work on 6 foot center for a 30 by 60 hay barn with 2 by 4 purlins? VASCILLATING IN VIRGINIA                 

DEAR VASCILLATING: Trusses – certainly they will work spaced one every six feet, however unless you are willing to place sidewall columns every six feet, it will necessitate having headers (truss carriers) between the columns. On the purlins, depending upon your snow load and grade of available lumber, you might need to place the purlins on edge. It is very probably your idea is not the most cost effective design solution. I would encourage you to investigate sidewall columns placed every 12 feet, with double trusses at each interior column and 2×6 purlins or larger joist hung on edge between the trusses. This is going to be the best design solution structurally and is almost always the most cost effective.

Dear Pole Barn Guru: Vapor Barrier & Compaction Questions

Welcome to our newest feature: 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. 

Email all questions to: PoleBarnGuru@HansenPoleBuildings.com

 

DEAR POLE BARN GURU:  Will 5/16″ foil/bubble/foil work as a vapor barrier/insulation against the condensation problem you address? SWEATING IN POLAND, IN

DEAR SWEATY: The product you are referencing is a “double bubble” product, which has two layers of air cells trapped between aluminum foil facings. As long as the seams are securely taped tight, the product you have referenced should perform adequately as a vapor barrier.

Personally, I wouldn’t spend the extra money for the “double bubble” as it adds no appreciable R-value, and could potentially cause issues with the steel being able to function properly as a diaphragm.

For less cost and easier installation, I would recommend “single bubble” vapor barrier with aluminum facing up, white vinyl facing down. This product is available with a tab on one side, with an adhesive pull strip attached. This allows for positive sealing between rolls, without the need to try to tape.

DEAR POLE BARN GURU:  I’m having a pole barn constructed do I need to level the site first and put the stone down before they start? The contractor says he doesnt want me to do that until they put the barn up. AWW SCHUCK, INDIANA

DEAR SCHUCKS:

From a builder’s standpoint, I would agree totally with your contractor, unless your site was leveled AND properly compacted, prior to construction starting.

 Whether making the site level or not, prior to building remove topsoil and stockpile for later use in finish grading. In frost prone areas, remove any clays or silty soil from within the future building “footprint”.

 Now why would I prefer to build on a site which is out of level? The holes for the building columns need to extend the distance specified on the plans into native soil (or the compacted equivalent). If fill is brought onto the site, and has not been compacted, then it increases the depth of the holes your builder must dig.

 When you do level your site, replace subsoil removed from around building with granulated fill to help drain subsurface water from building. Distribute all fill, large debris free (no pit run), uniformly around site in layers no deeper than six inches. Compact each layer to a minimum 90% of a Modified Proctor Density before next layer is added. Usually, adequate compaction takes more than driving over fill with a dump truck, or earth moving equipment.

 Also refer to my blog on adequate compaction – enter “compaction” into the search box in the upper right – scroll down a bit to find more information on how to do this.  Good Luck!

 

 

 

Ask the Guru: Is Vapor Barrier Required?

For those of you just joining Mike the Pole Barn Guru’s Blog – Mondays are now “Ask the Guru” where you can submit construction and building product questions for Mike to answer in upcoming Monday segments of this blog.  If it is a topic Mike is not well versed in, or a new product he has not yet been exposed to –  he will do “due diligence” in his research and give you his best advice.

Submit questions to: PoleBarnGuru@HansenPoleBuildings.com

DEAR POLE BARN GURU:  Finishing & insulating inside pole barn that was here when purchased last year. What are your thoughts on vapor barriers for ceiling between the metal and insulation?

Also in quandary over no over hangs for soffit vents it’s a Mo**on with the gable ends venting where trim meets the ribbed siding, snow blows inside currently and not sure if after I have it closed in it will still do so and get insulation wet (fiberglass). Thanks BLOWING IN, IN OHIO

 

DEAR BLOWING: It is essential to have a vapor barrier between the roof steel and any conditioned area below. In the event there is not a vapor barrier between the roof purlins and the roof steel, there are some options. The best choice, is also the most work.  Remove the roof steel, install a reflective insulation on top of the purlins and reinstall the roof steel, using larger diameter, longer screws than what originally held it in place. Spray foam insulation could be placed on the underside of the roof steel (may be cost prohibitive), or reflective insulation could be installed under the roof purlins, as long as all of the seams are tightly sealed.

Assuming you are placing the fiberglass insulation at ceiling level, there should not be a vapor barrier below it. You want any warm moist air from inside the building to be able to rise into the dead attic space, which must be adequately vented. Venting can be accomplished by a combination of sidewall eave vents and a vented ridge, or by gable endwall vents.

 If snow is coming in under the gable end/rake trim, the screws can be removed from the gable face of the trim, expanding closures can be placed along the edge of where the trim lies, and then reinstall the trim using metal-to-metal stitch screws. The expanding closures should be placed so the lower edge of the closure is just covered by the trim.

 In any case, you want to be certain any fiberglass insulation will not get damp, as it will lose its effectiveness, as well as possibly contributing to decay of any wood members it is in contact with.