Tag Archives: roof condensation

Cupola Sizes, Insulation for a Ceiling, and Structural Pieces

This week the Pole Barn Guru tackles reader questions about cupola sizes, the proper way to insulate a shed ceiling, and a structural materials question.

CupolaDEAR POLE BARN GURU: What base size and height is correct for a cupolas for a 32’ wide by 36’ long by 35-40’ high with a 10 over 12 pitch roof? Thank you for your answer. NANCY in SPENCER

DEAR NANCY: This may answer some of your questions: https://www.hansenpolebuildings.com/2015/09/cupola/. As to actual height of your cupola(s) – this is totally subjective based upon what you feel looks best.

 

DEAR POLE BARN GURU: I’m desperately trying to figure out the proper way to insulate my pole shed ceiling. The Purlins run parallel rather than peak to eves. And there are no soffits or vents to be had. I have metal roofing with fiberglass roll insulation between roofing and purlins that has the vapor barrier backing. I’m afraid to slice holes in this vapor barrier as it may cause the metal roofing to condensate. My purlins are conducting cold temps in winter and when the heat hits them, they grow mold in some places as they’re very cold – or hot in the summer. Can I install the paper back fiberglass between purlins and be okay? I’m hoping would slow moisture down. but allow it to dry as well. IDK I’m in the NW mountains of Oregon, we do get low temps and snow and the shop is mildly heated in winter. I can’t afford to redo the roof or go with blown in foam. Is there another way? Can I use fiberglass batting safely? My end goal is to have tin roofing on the ceiling, is that okay? Sorry to bother you with such a common question but I haven’t found anyone with my exact issue. Thanks so much for your time and I sincerely hope to hear from you, big fan, DAVE in GALES CREEK

DEAR DAVE: Appreciate your being a big fan – thank you!

No, you cannot/should not install paper (kraft faced) backed fiberglass insulation between your building’s roof purlins. This would create a system with two vapor barriers, trapping moisture between them. Start by looking to what is probably your source of moisture – your concrete floor. If you do not have a well-sealed vapor barrier underneath it, use a sealant on top of your concrete to reduce moisture coming up through your slab. After you have your steel ceiling in place, blow in fiberglass insulation above it, and install vents in each gable end and under your ridge cap.

 

DEAR POLE BARN GURU: What is the type of steel (cold roll, stainless, etc.) used and the thickness of the trusses and main poles holding the structure up. ERIC in PAHRUMP

DEAR ERIC: 40 years ago I provided a post frame building kit package for a tire dealer in Pahrump!

Most steel roofing and siding is cold roll formed. These panels most typically have SMP paint (https://www.hansenpolebuildings.com/2014/05/smp/) over a galvanized or galvalume substrate. There are Building Code minimum requirements for residential steel roofing substrates (https://www.hansenpolebuildings.com/2020/11/minimum-steel-substrate-coating/). Hansen Pole Buildings use two-ply (for interior spans) 1-1/2″ width (2x lumber) chords and webs for prefabricated roof trusses, assembled with 16, 18 or 20 gauge galvanized steel pressed in connector plates. Plate thickness is determined by truss engineers to meet tension requirements. Main roof supporting members may be either glulaminated or solid sawn timbers, depending upon eave heights, roof slope, applied wind and/or snow loads, dead weight of roof assembly and availability of materials in a given market. Actual sizing will be determined by our third-party engineers.

 

Condensation Control, Mother/Daughter Addition, and Vapor Barrier for Roof

Today the Pole Barn Guru answers readers questions about condensation control in a small garage with a gravel floor, the possibility of adding a “mother-daughter” unit to her house, and “ribbed vapor barrier” for a shed roof.

DEAR POLE BARN GURU: Recently purchased a metal garage kit, 24X26. No insulation. Two garaged doors. Gravel floor with plastic under grave. I am getting condensation on some days, that makes my cars, etc have like a dew on them.

My rib looks to be 1” and 7” between ribs. How do you install a wall vent with the ribs? JODY in ALTON

Machine ShopDEAR JODY: First step is to take care of your source. Pour a concrete slab on grade with a well sealed 10-15mil vapor barrier underneath. As you have no thermal break between your warm moist air inside building and roof steel, have two inches of closed cell spray foam insulation applied to underside of roofing. You would be better served to vent eaves and ridge, than just gable vents. If gable vents are your choice, look for vinyl vents with a snap ring as they can be installed on ribbed steel siding.

Using inward vent base edges as a guide, mark area to be cut on endwall steel INSIDE, make hole cut square with steel sheet (vertical cut lines parallel to steel ribs). Cut hole with appropriate tools.
Push vent base through hole in steel from inside.
Note word “TOP” on base when positioning. Vents installed with top side in any direction other than up will allow water to leak into building.
While holding vent base in place, snap face into base from steel exterior by pressing firmly (this takes two people).

 

DEAR POLE BARN GURU: I’m interested in building an attached mother/daughter addition to my home. Do you have plans for that? Approximately 600-700sq ft. NANCY in MONROE TOWNSHIP

Floor PlanDEAR NANCY: Thank you for your interest in a new Hansen Pole Building. Every building we provide is custom designed to best meet the wants, needs and budget of our clients. We offer a floor plan design service for folks just like you: http://www.hansenpolebuildings.com/post-frame-floor-plans/?fbclid=IwAR2ta5IFSxrltv5eAyBVmg-JUsoPfy9hbWtP86svOTPfG1q5pGmfhA7yd5Q 

 

DEAR POLE BARN GURU: We are having a 50×30 all metal building. We were advised to get ribbed vapor barrier for roof. We have searched everywhere. Is it called something else? SHANNON in OLEAN

DEAR SHANNON: We are also not familiar with any product known as a “ribbed vapor barrier”. We would normally recommend use of roof steel with an ICC factory attached (https://www.hansenpolebuildings.com/2020/09/integral-condensation-control-2/). If this is not an option (or if you are using closed cell spray foam directly to underside of roof steel), next choice would be a radiant reflective barrier – look for six foot wide rolls with an adhesive pull strip attached for ease of installation.

 

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.

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