Post Frame Building Insulation

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Pole Barn Guru’s Ultimate Guide to Post Frame Building Insulation

When it comes to insulating any building (not just post frame ones – like barndominiums) there is a certain point of diminishing returns – one can spend so much they will never, in their lifetimes, recoup their investment.

Here my ultimate guide to post frame building insulation is based upon practicality and obtaining the best possible value for investment.

There are some basics applicable to any steel covered building:

Under any concrete slab on grade inside a building, place a well-sealed vapor barrier. Read about under slab vapor barriers here: https://www.hansenpolebuildings.com/2017/11/vapor-barriers-slabs-grades/.

Between roof framing and steel roofing – please do not assume condensation is not going to be a problem. At some point in time it will become one and if precautions are not taken regrets will happen. Condensation under roof steel is maybe number one of the issues I am asked to assist with.

Least expensive financially, but does take some extra labor hours, especially if it is windy – a single air cell layer reflective radiant barrier. Six foot widths will install much quicker than four foot. Make sure to order with a six foot width NET COVERAGE and an adhesive tab along one edge with a pull strip. Without an adhesive tab all butt edges will require seam tape, not expensive, but adds lots of time. Do not waste your money on adding an extra approximate R 0.5 for double bubble (two layers of air cells).

For a slightly great investment in materials, hours of labor can be saved by the use of an Integral Condensation Control bonded to roof steel. This would be my product choice. https://www.hansenpolebuildings.com/2017/03/integral-condensation-control/.

Next higher cost would be sheathing the roof with either OSB (Oriented Strand Board) or plywood on top of roof purlins. Roof purlins will need to be spaced appropriately so sheathing seams fall on purlins (16, 19-3/8 or 24 inches on center). Roof truss top chord live load must be increased to allow for greater dead loads. Either 30# felt (asphalt impregnated paper) or an Ice and Water Shield must be placed between sheathing and roof steel. Roof screws must still be placed to go into purlins, as thin sheathing is inadequate to adequately hold screws.

Bigger financial investment, but no extra labor involved is to have two inches of closed cell foam sprayed on the underside of roof steel. This will prevent condensation and is noise deadening. As a rough budgetary figure, plan upon spending roughly two dollars per square foot of roof surface.

Storage/Utility Buildings

If you ever believe anyone might ever have a future desire to climate control your building then provisions should be made for making it easiest to make future upgrades.

For now we will assume this building is totally cold storage. If it might ever (even in your wildest dreams) be heated and/or cooled include in your initial design, walls with a Weather Resistant Barrier (https://www.hansenpolebuildings.com/2016/01/determining-the-most-effective-building-weather-resistant-barrier-part-1/) between framing and siding. 

Taking walls one step further would be ‘commercial’ bookshelf wall girts (https://www.hansenpolebuildings.com/2011/09/commercial-girts-what-are-they/).

In roof – have trusses designed to support a ceiling load, ideally of 10 pounds per square foot (read about ceiling loaded trusses here: https://www.hansenpolebuildings.com/2016/03/ceiling-loaded-trusses/). 

Trusses should also be designed with raised heels to provide full depth of future attic insulation above walls (https://www.hansenpolebuildings.com/2012/07/raised-heel-trusses/).

Make provision for attic ventilation, by having an air intake along sidewalls using enclosed ventilated soffits and exhaust with a vented ridge.

Any overhead doors should be ordered insulated – just a good choice in general as, besides offering a minimal thermal resistance, they are stiffer against the wind.

Equine Only Use

Same as storage/utility however ventilation is essential (and often overlooked). (Read more on stall barns here: https://www.hansenpolebuildings.com/2012/08/stall-barn/)

Garage/Workshop/Man Cave/She Shed/House/Shouse/Barndominium

Many previous recommendations are going to be repeated here. Ultimately it is going to depend upon willingness to include higher R values in initial budget, rather than having increased utility bills forever.

Start with a Frost-Protected Shallow Foundation – post frame version (https://www.hansenpolebuildings.com/2016/11/frost-protected-shallow-foundations/) with sand on the inside rather than a thickened slab. This makes for an excellent and affordable design solution.

For walls, we will again work from generally ascending price and R values.

On low end would be having installed a weather resistant barrier beneath wall steel, in conjunction with commercial bookshelf wall girts. Fill insulation cavity with unfaced batt insulation and cover inside face of wall with a well-sealed six ml clear visqueen vapor barrier. As an alternative to fiberglass would be mineral wool insulation as it is not affected by moisture (https://www.hansenpolebuildings.com/2013/03/roxul-insulation/). This method can be entirely done D-I-Y.

I have personally used BIBs (https://www.hansenpolebuildings.com/2011/11/bibs/) in several buildings, including my current barndominium home. It does require a certified installer.

A Weather Resistant Barrier can be eliminated by the use of a ‘flash coat’ of two inches of closed cell spray foam against the inside of wall steel. Balance of wall cavity can be filled with batt insulation. (https://www.hansenpolebuildings.com/2016/07/advantages-spray-foam-over-batt-insulation/).

For added R value and a complete thermal break, add two inch rigid closed cell foam boards to inside of framing. To maintain thermal break integrity, glue foam boards to inside of framing and properly seal all seams. Gypsum wallboard can be glued to the face of foam boards.

After ceiling has been installed, have insulation blown into dead attic space, following Energy Star™ guidelines (usually R-45 to R-60).

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