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Insulation, Truss Spans, and Pit Material

Today’s Ask the Pole Barn Guru discusses reader questions about an option to layer insulation between purlins, the actual building width for 36′ trusses, and the recommendation against the use pit material when performing site prep.

DEAR POLE BARN GURU: Hi, I have the traditional roll type insulation with the white backing. My question is if I’m able to add more insulation between the purlins on top of the existing insulation for added r value and what type would you recommend if so? Thanks OWEN in VIVIAN

DEAR OWEN: Metal Building Insulation (MBI) is not my favorite design solution for post frame insulation (read more here: https://www.hansenpolebuildings.com/2011/11/metal-building-insulation/).

You can add more insulation to interior of what you have, without having to perforate white vinyl of you MBI. I would recommend adding unfaced Rockwool, as it is not affected by moisture and has a relatively high R value per inch of thickness compared to fiberglass or cellulose. Do not add another interior vapor barrier, as this would allow for moisture to become trapped between two vapor barriers.

DEAR POLE BARN GURU: You really are a wealth of knowledge. I’ve been watching your Youtube videos as well, very helpful.

I’m intrigued by your pole barn kits, and I had just one more question about raised heel trusses:

It’s my understanding that post spans are actually building widths minus 3 inches. So for a 36 foot building, the span between posts is 35’ 9”, correct? If that’s the case, are raised heel truss lengths in this example also 35’ 9 to the edge of the post? Or the full 36’, with the eave skirt board resting under the additional 1.5 inches of the bottom chord length?

Thanks again for your time!!! MATT in CHENEY

DEAR MATT: Our buildings (as are most Pacific Northwest Buildings) measure 36 feet from outside of column to outside of column. This allows for 12 sheets of steel plus the lap on the 12th piece (covering 36′ 1-1/2″ roughly) to be installed without having to rip the last steel panel lengthwise. Pressure preservative treated splash planks, headers, etc. will be applied to exterior faces of columns, giving a framed finished width of 36’3″.

DEAR POLE BARN GURU: Hi. In your building manual it notes not to use pit material on the building pad. If the site is leveled, I’m not sure what the function of any modified is or why no pit material in specific. We’ll be doing a slab at some point and common practice would be to put down some clean 3/4″ so if it’s beneficial to have stone on the building pad would it be more cost efficient to just put the clean stone down to start with? Thanks. KEVIN in WEST CALN

DEAR KEVIN: #1 reason to not use pit run is it is difficult to auger holes through.

#2 because it is round, it does not compact well

#3 It creates voids allowing for free flow of liquid water beneath slab

You do want to allow for two to six inches of clean sand or sandy gravel compacted immediately below your under slab vapor barrier.

This entry was posted in Constructing a Pole Building, Pole Building How To Guides, Trusses, Concrete, Columns, Insulation, Pole Barn Questions, Pole Barn Design and tagged pit material, insulation, site prep, building width, truss span, rock wool insulation on March 15, 2023 by admin.

Purlin Spacing, Wall Insulation, and Roof Sheathing

This week the Pole Barn Guru answers reader questions about purlin spacing for 2×8 that span 17 feet, wall insulation recommendations, and if roof sheathing is needed for a new shop.

DEAR POLE BARN GURU: I need to span 17 feet with 2×8 purlins. Do I need to go 12 inch on center, or can I double 2x8s 24″ on center? Will deck with 7/16 OSB and install standing seam metal roof. BRAD in SPARTA

DEAR BRAD: IRC Rafter span tables are available online here: https://codes.iccsafe.org/content/IRC2021P2/chapter-8-roof-ceiling-construction

Scroll down to Table 802.4.1(1) (this would be for a minimal snow load).

Assuming 2×8 #2 Southern Pine 24″ on center will span only 13’1″ (even 2×10 #2 will only span 16’6″).

Going to a spacing of 16″ on center 2×8 #2 Southern Pine will span 17’1″.

DEAR POLE BARN GURU: Hello, I am looking to insulate the walls of my pole barn and plan on putting up vapor barrier. I insulated the ceiling last year and used Tyvek® basically to hold up the insulation as I can’t afford the steel yet. My question is should I also put up a vapor barrier on the ceiling? Thanks in advance, I appreciate the guidance as this is not my expertise. CHAD in GENESEO

DEAR CHAD: Henry County is Climate Zone 5A.

For your walls, I would recommend unfaced Rockwool either R-30 with a well-sealed interior vapor barrier or R-20 with R-5 well sealed continuous insulation boards on the interior (Comfortboard® 80 or EPS).

As you have under 8000 heating degree days, a ceiling vapor barrier would not be required. Hopefully your attic insulation is Rockwool as fiberglass is affected by moisture and loses R value when exterior temperatures drop. Make sure your attic space is properly ventilated (https://www.hansenpolebuildings.com/2018/03/adequate-eave-ridge-ventilation/).

DEAR POLE BARN GURU: Hello, I am building a 36x50x12 shop with 5:12 roof pitch, that will be conditioned space. The plan is to build out the interior with 2 small bedrooms and a bath then the rest open floor. I am putting in a ceiling at 12′ and will insulate the walls and ceiling leaving the roof uninsulated. Building is located in South Central Texas near La Grange. Does the roof need sheathing and felt or can I just lay the metal roof directly on the purlins? What about adding house wrap to entire building, walls and roof? Being in Texas, heat is biggest factor and with the a/c pumping inside I want to keep attic space vented correctly to keep moisture from building up. I plan to have large soffits to allow for soffit venting then ridge vent on roof. One of my biggest concerns is keeping out all the elements, including creep crawly bugs and concerned the garage doors will be source intrusions. It is my understanding that a sectional garage door is best for keeping out the elements vs roll up type. Can a garage door be truly sealed from all elements including bugs from crawling in? STEVEN in SUGAR LAND

DEAR STEVEN: Roof probably does not need to be sheathed unless your design wind speed is 140 mph or greater (Code requirement) or your engineer specified it. Do NOT housewrap roof, order roof steel with an Integral Condensation Control factory applied. Order raised heel trusses so you can have full attic insulation depth from wall-to-wall. While a sectional garage door is best, there is never a 100% guarantee of keeping crawling critters out – because you are going to open door at some point.

This entry was posted in Insulation, Pole Barn Questions, Pole Barn Heating, Pole Barn Design, Roofing Materials, Constructing a Pole Building, Pole Barn Planning, Ventilation, Professional Engineer and tagged roof sheathing, steel sheathing, rock wool insulation, purling spacing, roof load, purlin span, vapor barrier, roof sheathing OSB, wall insulation on January 18, 2023 by admin.

Help! My Barndominium Vaulted Ceiling Drips

Help – My Barndominium Vaulted Ceiling Drips

Reader HOMER in PIEDMONT writes:

“I called in today and was referenced to send an email –

I have come across your website and have gained a vast amount of knowledge – I was hoping to get some more information on my situation – I also understand that you actual don’t sell insulation and that any advice you give me might not benefit your business – I am willing pay a consulting fee if you like or if i can purchase any products through your company that will help me get out of this pickle i will be more than happy to –

So my situation (the pickle)

I built a 30×60 barndominium with vaulted ceiling (the purlins on top are 8″) i used about 1/2″ to 1″ of closed cell spray foam all over it then laid the typical pink batting insulation in it – the issue I am having is I am in Oklahoma – on a morning of a cold night – when the sun comes out it heats the metal roof up and creates condensation – hence a ceiling that rains throughout the day – it seems to happen closer to the peek more than the bottom portion of the ceiling

I have tried pulling some of the batting insulation out of the middle section to help create more air space – it did seem to help a bit but still saw condensation on the spray foam insulation – when i removed my test panel (also i used 3/8 bead board for my interior sheeting)

On the peak of the roof I didn’t use the foam vent ridge cap but filled it in with spray foam (I was going for air tight) which might be more of the issue

I truly am sorry to bother you with this issue and any help or direction would be greatly appreciated – please reach out via email or phone and I am sorry if I didn’t give enough detail to paint the picture that I am facing.”

Mike the Pole Barn Guru says;

Thank you for reaching out to us. Our goal is to assist our clients from making crucial (and often costly) errors they will regret forever. While your circumstance is crucial, it can be rectified.

According to Johns Manville, a minimum of 1-1/2″ of closed cell spray foam is required in order to provide an adequate air and vapor barrier (we have always recommended two inches, as we feel it is better to be safe than sorry). Right now, the underside of your closed cell spray foam is cool enough on those cold mornings so warm moist air rising inside meets it and condenses. This is more pronounced as you approach interior peak due to warm air rising.

If it was my own roof – I would remove all fiberglass roof plane insulation, increase thickness of closed cell spray foam to at least two inches, then fill balance of 2×8 cavity with either open cell spray foam or rock wool batts (rock wool is not affected by moisture and does not lose R value during cold temperatures).

Only other possible solution (have not tried, so is only hypothetical) would be to mechanically dehumidify the interior of your barndominium to a degree low enough to eliminate your challenge. This would probably need to be under 20% relative humidity – so low as to become uncomfortable to live in (Dry, itchy skin & eyes) and causing shrinkage of wood in floors, cabinets, doors and furniture.

This entry was posted in Pole Barn Design, Pole Building How To Guides, Building Contractor, Ventilation, Building Interior, Insulation, Pole Barn Questions and tagged condenses, condensation, barndominium, closed cell spray foam, rock wool insulation, pink batting insulation on January 10, 2023 by admin.

Does My Pole Barn Need a Vapor Barrier?

Does My Pole Barn Need a Vapor Barrier Above the Metal Ceiling?

Reader DAVID in BALDWINSVILLE writes:

“I have a new pole barn with bubble vapor barrier under roof metal. I am installing a metal ceiling with R-38 cellulose in the attic. Do I need a vapor barrier above the metal ceiling? The barn will be heated somewhat in winter.”

From Mike the Pole Barn Guru:

Kudos to you for recognizing bubble wrap products advertised as ‘insulation’ are, at best, a good vapor barrier if properly sealed!

My son Brent is working on his doctorate at UMass Amherst, so I utilized Building and Construction Technology information from their Department of Environmental Conservation in penning this response.

My concern is with blowing in cellulose above a steel ceiling. From UMass:

“Wet insulation of any stripe is bad. But cellulose is hygroscopic. It’s able to soak and hold liquid water. Undetected leaks can wet cellulose causing it to sag within framing cavities. Water leaks can compress the blanket of fiber and in extreme cases, can create a void space, degrading its thermal value. Another concern is that chemicals used to protect cellulose from fire make it potentially corrosive in wet environments. Tests conducted by the Oak Ridge National Laboratory show chemical treatments used to treat cellulose can cause metal fasteners, plumbing pipes and electrical wires to corrode if left in contact with wet, treated cellulose insulation for extended periods of time. “

I’d much prefer to see you blowing in rockwool as it remains unaffected by moisture. Last thing you want is to have damp cellulose insulation chemicals eating holes in your ceiling.

According to building scientist and founding principal of Building Science Corporation Joe Lstiburek, “Plastic vapor barriers should only be installed in vented attics in climates with more than 8,000 heating degree days.”

As your site has under 8000 heating degree days a year, you should not have a ceiling vapor barrier. You do need to ensure your newly created non-conditioned dead attic space is adequately ventilated at eave and ridge (https://www.hansenpolebuildings.com/2018/03/adequate-eave-ridge-ventilation/).

For extended reading on heating degree days, please see: https://www.hansenpolebuildings.com/2022/11/what-is-degree-day/

This entry was posted in Ventilation, Building Interior, Insulation, Pole Barn Questions, Pole Barn Planning, Pole Barn Structure and tagged cellulose insulation, rock wool, ceiling vapor barrier, rock wool insulation, heating degree days, metal ceiling, vented ceiling on January 3, 2023 by admin.

Insulation Options for an Idaho Barndominium

Insulation Options for an Idaho Mountain Post Frame Barndominium

Loyal reader LORISTON in NAMPA writes:

“We are in the initial phase of preparing for our residential post frame home and are excited to partner with Hansen Buildings when ready. Thank you for all the amazing information and supporting your clients. Question: I am targeting a highly efficient design, with >r-40 walls and >r-60 roof. There is a lot that I do not know and humble to learn from others. My mechanical engineering background helps. I would like your advice on a wall and roof design that meets my targeted R-values incorporating (from outside to inside) metal siding, >3/4″ rain screen, rock wool >2″ external insulation, Zip insulated r sheathing for WRB and thermal break/R-value increase, laminated Timber Tech glulam columns with bookshelf / commercial girts, closed cell spray foam internal insulation around 3″ thickness, fill remaining thickness from spray foam to inside edge column with insulation (recommendation would be helpful on type of insulation), internal insulation on inside of wall for thermal break if needed or helps, with final residential area having 5/8″ sheetrock and shop area having metal inside finish. We have not solved how to create a space for utilities on the outside wall as we would prefer to run them on inside of columns or thermal break insulation. We are contemplating internal framed 2×4 walls spaced away from post frame wall to create a space for utilities. No water will be run on external walls, only power, low voltage, gas, telephone as reference. Suggestion on how to run utilities with this highly efficient wall design would be appreciated. Roof is similar to wall, just horizontal with >r-60 performance, as we are targeting a conditioned attic space. Roof exception may be a second zip sheathing layer over the insulation (under rain screen/standing seam metal) but to be determined. Climate Zone 6 region in the Idaho mountains for reference. Post frame columns and wall will be on a full foundation wall with thickness based on wall design. Performance is priority over cost, targeting an air tight and efficient living space. Your experience and practical approach are greatly appreciated. Best regards and thank you.”

Mike the Pole Barn Guru writes:

Thank you for your very kind words, they are greatly appreciated.

Rather than add an expensive and structurally unnecessary concrete foundation wall, I would recommend embedded properly pressure preservative treated wall columns (as my first choice), columns above grade set into wet set brackets on concrete piers as my second. Either of these can be insulated using R-10 EPS (Extruded Polystyrene) insulation boards. I would run them on the inside of the splash plank, with the top even with the top of the slab, extending down two feet, then outward horizontally two feet.

In Climate Zone 6, I normally would not look towards spray foam as my go to choice, however conditioning your attic and your desire for air tightness come into play, so here goes:

Walls (out-to-in): Steel siding over 2×8 bookshelf girts; 4″ of closed cell spray foam applied directly to inside of wall steel and balance of cavity with either open cell spray foam or rock wool (rock wool being my preference). No internal vapor barrier or continuous interior insulation boards as we want walls to dry to interior, without trapping moisture in the wall cavity.

Roof (out-to-in): Standing seam steel over 30# felt or synthetic ice & water shield (second preferred) over 5/8″ CDX plywood. Zip sheeting is OSB and screws just do not hold well into OSB. We can specify 2×12 roof purlins in order to get a deep cavity for insulation. Closed cell spray foam 5-3/4″ (R-40) plus R23 rock wool (5-1/2″).

This combination will require mechanical removal of humidity.

My normal recommendations would be:

Walls (out-to-in): Steel siding over a Weather Resistant Barrier, over 2×8 bookshelf girts. Fill the cavity with two layers of R15 rock wool. Add R-10 EPS well-sealed on interior. This wall will now dry to the outside.

Roof (out-to-in): Through screwed steel with an Integral Condensation Control factory applied, or standing seam steel over 30# felt or synthetic ice & water shield (second preferred) over 5/8″ CDX plywood. Roof trusses with 22″ raised heels, vent eave and ridge. Blow in R-60 on top of ceiling. This eliminates the expense of heating/cooling a dead attic space.

In either instance, I would have no fears or concerns about running non-plumbing utilities within your wall insulation cavity.

This entry was posted in Roofing Materials, Barndominium, Pole Building How To Guides, Pole Barn Planning, Shouse, Steel Roofing & Siding, Ventilation, Footings, Insulation, Pole Barn Questions and tagged closed cell spray foam insulation, concrete piers, rock wool insulation, wet set brackets, extruded polystyrene, spray foam, R-10 EPS, bookshelf girts, pressure preservative treated columns on September 22, 2022 by admin.

How to Insulate a Post Frame Shop

How to Insulate a Post Frame Shop When No Advance Considerations Were Made

I encourage clients to give some serious advance consideration when erecting new post frame (pole) buildings to any eventuality of future climate control and a need for insulation.

Reader MAC in MILLVILLE writes:

“40 x 30 want to insulate. It will be used as a storage/workshop. I included pictures so you can see what I have. What’s the best way to insulate? I plan on doing metal ceiling liner and most likely plywood on the walls. There is no vapor barrier under the concrete either. I do have a vented ridge and soffit. I hope I provided enough information to be able to answer my question.”

Start by sealing your concrete floor – as this is going to be a moisture source you do not want inside of your new building.

Roof/ceiling – no provision has been made to prevent condensation from happening beneath your roof steel. Sadly I see this occur far too often, as builders, kit providers and local lumberyards just lack knowledge needed to be able to educate and make best recommendations to their clients. You could either (a) remove roof steel, add a method of condensation control (such as a Reflective Radiant Barrier or sheathing such as OSB or plywood with either 30# felt or a synthetic ice and water shield) and reinstall steel using new, large diameter screws. This is highly labor intensive and your roof may not have been designed to support the weight of adding sheathing.

Best solution will be to have two inches of closed cell spray foam applied to the underside of roof steel at roughly two dollars a square foot. Not an inexpensive solution when its need could have been prevented with better advice up front.

Cumberland County is in Climate Zone 4A, as such you should have a minimum of R-49 ceilings and R-20 walls. Perimeter of your slab should be insulated two feet deep with R-10.

I would dig a trench two feet deep around your building, up tight to its pressure preservative treated splash plank and install R-10 rigid board XPS insulation from the height of the top of the slab down two feet. Install a metal, cement board, or cellular PVC panel to conceal any insulation portion left exposed above grade. If cement board is used, it should be a type not reinforced with wood fibers. Install a metal cap as an insect guard to conceal the top horizontal edge of both insulation board and closure panel. Seal cap to splash plank with mastic.

Once you have a ceiling liner in place, blow in R-49 or greater thickness of fiberglass insulation.

For walls, I normally like to see a Weather Resistant Barrier (like Tyvek) between framing and siding. As you do not have this, I would use R-21 unfaced Rockwool stone wool insulation, as it is not affected by moisture. Place a well-sealed 6mil clear plastic vapor barrier over the inside of insulation prior to placing plywood on walls.

This entry was posted in Concrete, Workshop Buildings, Insulation, Pole Barn Questions, Roofing Materials, Pole Building How To Guides, Pole Barn Planning and tagged closed cell spray foam insulation, rock wool insulation, concrete floor seal, metal ceiling liner, rigid board XPS insulation, cement board, insulation, cellular PVC panel, condensation, sealing concrete floor on September 15, 2021 by admin.

Insulated Bookshelf Wall Girts

While we United States residents like to think of ourselves as perhaps the center of our universe, post frame construction appears world wide.

Reader JONATHAN in HALIFAX picked Alabama as his state when he filled out his online request for information when he wrote:

“What insulation do you suggest between bookshelves of wall?”

With so many post frame buildings being used for residences, commercial buildings, shop/houses and barndominiums, properly addressing how to insulate has become of utmost importance.

I am going to take a stab and guess your Halifax is in Nova Scotia, rather than Alabama. My lovely bride and I made a stop there on a cruise from New York City a few years ago – beautiful area (and I got a Harley-Davidson T shirt).

If so, you are in what would be an equivalent to our IECC (International Energy Conservation Code) Climate Zone 7. For wood frame walls, this would require an R-20+5 or R-15+10, where your plus value is for continuous insulation.While continuous insulation is most often usually on exterior of framing, Martin Holladay – editor of Green Building Advisor feels confident in it working as well on inside of framing. Given this, I would put a Weather Resistant Barrier (https://www.hansenpolebuildings.com/2016/01/determining-the-most-effective-building-weather-resistant-barrier-part-1/) between wall framing (bookshelf wall girts) and siding, then fill your cavity with rock wool (as it is not negatively affected by moisture), then use rigid foam insulation inside of your framing. You can glue these sheets to your framing (bookshelf girts) to eliminate any thermal bridging from fasteners and then glue your interior finish to it. Make sure to tightly seal your rigid foam boards and to caulk along the bottom of exterior walls to get a good seal. Built in this fashion, your walls will ‘dry’ to the outside, reducing the need for dehumidifying inside.

Of course you will want to get approval from your local permit issuing jurisdiction before moving forward.

For extended reading on rock wool insulation please see https://www.hansenpolebuildings.com/2013/03/roxul-insulation/