Tag Archives: IECC

Engineer Andy Ponders Insulation and Condensation

Engineer Andy Ponders Insulation and Condensation

Loyal (and prolific) blog reader ANDY in OXFORD writes:

“First, THANK YOU for providing so much valuable information in your blog, free of charge. I’m an engineer, quite handy, with construction experience. But everything I know about post frame construction, I learned from you. I’ve been planning for over a year, and I’ve read your first 1700 or so blogs. I’m about to place an order with Catherine Suarez, (she’s been very patient, by the way) for a 30x36x11. 6/12 roof with vented soffits and ridge, gable overhangs, and dripstop on roof steel. Location is north Mississippi, 30’s in winter, 90’s in summer with 60% to 80% humidity any time of year. It will be used as a dedicated woodworking shop, heated just above ambient in winter (except when I’m working there) and cooled only when I’m out there (rarely) in summer. I know you must get tired of insulation/condensation questions because you get so many of them. But it’s not something that’s intuitive to most of us. It’s the thing I’m least confident about. And I HATE rusty cast iron. I plan to install plywood or OSB ceiling with blown insulation above. House wrap between wall steel and girts (I would have never thought of house wrap), and craft-backed insulation between the commercial girts. Oh yes, and a good vapor barrier under the slab. So my question is . . . is this sufficient? What would Mike do??Thanks again for what you do.” 

Mike the Pole Barn Guru writes:
Thank you very much for your kind words, they are greatly appreciated. If I ever have to give a technical presentation on post-frame buildings, can I recruit you for my front row?

Post frame construction appears so simple at first glance, yet is highly technical and (like most things) it is in the details where they either work as expected or fall flat (literally). A set of calculations for even a simple rectangle can easily run over a hundred pages in verifying every member and connection!

Catherine is a dream. I love her clients as they know exactly what they are investing in and it makes for an extremely smooth process for all involved.

For some reason insulation and humidity are crucial areas seemingly left as an afterthought in far too many builds, often when it is too late to make economically sound corrections.

Lafayette County, Mississippi is in Climate Zone 3A (for reference). If you were building for a residence, 2021’s IECC (International Energy Conservation Code) would have R-49 ceilings, R-20 walls and R-10 slab perimeter insulation down two feet.

What would I do?

Even though you are probably not doing radiant in-floor heat, I would lay R-10 EPS insulation sheets on top of a well sealed under slab vapor barrier. If not, when it is 90 degrees F. and 80% humidity, the dew point is 83 degrees F. Your soil temperature could well be less than 70 degrees F., meaning you will have a damp floor from condensation.

For walls, a Weather Resistant Barrier and bookshelf girts are both winners in my book! I have become a proponent of rock/stone/mineral wool unfaced batts as they remain unaffected by moisture (and humidity) with a well-sealed 6mil clear poly vapor barrier inside. You have probably read this article: https://www.hansenpolebuildings.com/2013/03/roxul-insulation/

Ceiling – I do still like blown in fiberglass for value vs. return. I would specify 18 inch energy heel trusses to allow for full thickness of R-49 insulation from wall-to-wall, in conjunction with vented eaves and ridge.

You will want to make certain you order a well insulated and wind-rated overhead door for your woodworking shop. Keep in mind, door manufacturers do tend to stretch reality with their insulation claims https://www.hansenpolebuildings.com/2017/02/high-r-value-overhead-doors/.

Concrete Slabs on Grade for Cold Climates

Concrete Slabs on Grade for Cold Climates

My lovely bride and I have a shouse (shop/house) in Northeast South Dakota, where it can tend to get chilly in Winter. Reader TERRI in DULUTH is in a similar situation and writes:

“What type of slab for cold climates do you recommend?”

Well Terri, thank you for your patience in awaiting a response, your email address was not included with your question, so I was unable to message you back as quickly as I would have liked.

PLEASE – If writing an “Ask the Pole Barn Guru” question include your email address.

Injecting some humor (sadly, I have to point it out as not everyone gets it) – I would recommend a concrete slab.

Before diving into this subject – accept one fact, concrete slabs will crack. If you are expecting otherwise, you are setting yourself up for disappointment.

First key to a successful slab is excellent site preparation: https://www.hansenpolebuildings.com/2017/02/building-site-preparation/

Second – insulate your slab’s perimeter. 2021’s International Energy Conservation Code (IECC) provides guidance to meet energy code requirements for every county within our country. Begin by looking up your Climate Zone: https://codes.iccsafe.org/content/IECC2021P1/chapter-3-re-general-requirements

I will cheat and tell you Duluth (St. Louis County) is climate Zone 7.

Scroll down to Table R402.1.3 to find Insulation Minimum R-Values.

In Climate Zone 7 your slab perimeter must be insulated to R-10 and be four feet in depth. 

Weirdly enough, Minnesota’s Building Code only requires footings to be at 60 inches of depth in your area (https://www.revisor.mn.gov/rules/pdf/1303.1600/2015-01-23%2012:37:31+00:00). 

Although actual frost depth in your area is more like 80” in depth:

I would probably look at augering holes no less than 72 inches in depth, using a bottom collar of 18 to 24 inches (per your engineered building plans). This would allow you to trench between building columns and install R-10 rigid insulation along your building’s perimeter to a depth of four feet.

If you are going to do radiant in-floor heating you should be placing R-10 beneath your slab and on top of a vapor barrier of no less than 6 mil visqueen (I prefer 15 mil thickness to reduce chances of perforations during pouring).