Tag Archives: frost walls

Rebuilding, Post Spacing, as well as a Frost Wall

I this weeks blog, the Pole Barn Guru talks about, rebuilding a pole barn, ideal post spacing and a frost wall.

DEAR POLE BARN GURU: Hello, I recently disassembled a 36 x 100 pole barn and am rebuilding it at my house. It was covered with 2″ reinforced paper faced roll pole barn insulation with a 1″ foam board between the insulation and the metal. While removing the roll insulation it received many tears in the paper face. I would like to install a 6mil vapor barrier over my lumber then reinstall the roll insulation followed by the foam then the metal. Is this a good idea? The building will be heated and air conditioned but will not receive any kind of wall covering inside of the vapor barrier. Thanks DEAN in CORYDON

wind damageDEAR DEAN: I can’t say I am a huge fan of rebuilds for several reasons – damaged materials end up being used and it is pretty well impossible to keep from having holes in the roof steel which are going to cause leaks.

You should seriously consider the involvement of a RDP (Registered Design Professional – architect or engineer) to insure what you are rebuilding will meet Code requirements.

One problem right away – the foam board between the framing and the steel. Throw it away or resell it on Craigslist. The foam board pretty much negates the strength of the steel cladding due to the lack of rigidity of the insulation. It will also contribute to the possibility of slots forming around the screw shanks, due to movement of the building framework.

You should use a well sealed building wrap between the wall framing and the steel siding, then the insulation. If you are unable to repair the tears in the paper facing, you can use visqueen on the inside for a vapor barrier, however it (or paper facing) should be covered with an inflammable material to prevent possible fire issues.

DEAR POLE BARN GURU: Hello, I’m in Oklahoma which has high winds and severe weather. I am leaning towards having a garage built that is 20x24x10. How far apart should the columns be spaced? We have no HOA in our neighborhood and I haven’t reviewed the neighborhood covenants.  I’m really wanting to be smart on this because it’s a lot of money that I want to be solid investment. My goal is to save money, but be so cheap that building falls apart.  Thank you for your time. SHANE in OKLAHOMA

DEAR SHANE: The real answer does not come from column spacing, it comes from investing in a fully engineered post frame building which is specific to your building upon your site. Given your concern is for wind design, unless you have a site which is well protected from the wind in all four directions (buildings, hills or evergreen trees 30 feet or greater in height) you need an Exposure C for wind. You can get pricing on a variety of Vult wind speeds and determine what wind design you are willing to invest in.


DEAR POLE BARN GURU: I purchased a pole barn kit a couple years ago and I am just now getting around to building it. My county approved everything but they added an exception. They say that I need to add some frost protection. Either a frost wall or some sort of shallow frost protection. There are no plans for such in the blueprints and it is required by code here. So my question is what do I need to Do? Doing a concrete frost wall almost makes buying the pole barn kit unnecessary. I should of just did a stick built if I’m basically building a foundation.  I live in Bonneville county Idaho. Just wondering if you have come across this situation here and what the buyer needed to do? CAMERON in IDAHO FALLS

slab edge insulationDEAR CAMERON: You can do a Shallow Frost-Protected Foundation without having to thicken the slab edge – you can backfill on the inside of the vertical insulation board with sand. In the event your Building Official requires this to be added to your plans and sealed by the engineer, there would be an added investment for redrafting and sealing two new sets. For more reading: https://www.hansenpolebuildings.com/2016/11/frost-protected-shallow-foundations/.





Alaska Concrete Slab

Ever feel like things tend to happen in threes? This past week, my three times event has been Hansen Pole Buildings Designers and their clients asking about “Alaska Slabs”.

Concrete foundations, for buildings other than pole buildings, traditionally consist of three parts.  Footings are wide areas of concrete at the base of foundation walls. Usually footings will be twice as wide as the foundation walls they support. The footing thickness will be dictated by the number of stories being carried, with a minimum of six inches. Footings spread the weight of the building evenly into the soil to prevent cracks and sways in the structure above. Foundation walls are six inches or thicker and extend from the top of the footings to the base of the building.  A concrete slab, poured inside the foundation walls forms the floor or subfloor of the building and can support non-structural interior partitions.

The three concrete components: footing, foundation wall and slab, are usually done in three distinct steps. Each part of a traditional concrete foundation needs to be formed, poured and finished, and then needs to dry and set for about a week before the next part can be started. The process adds greatly to the expense of a building project and is a big part of the time involved.

Any water which freezes under a traditional concrete foundation can and will cause damage.  As water freezes, it expands with enough force to lift the entire building.  As the ice melts, it leaves an open pocket of space below the foundation. With each successive freeze/thaw cycle, the pocket expands. The result is a jacking action which lifts the building, eventually cracking walls, causing doors and windows to not open and close properly and opening seams for even more water damage.

Besides the simple solution of using isolated footings – such as in pole building construction, where pressure preservative treated wood columns are embedded into the ground below the frost line, there may be another solution.

The typical solution is to make sure the bottom of the footings extend deep enough into the ground so as they are beyond the reach of frost. This is why concrete foundations are often called “frost walls.” The “frost line,” or the depth of maximum penetration of frost is, of course, different for each region. In the far southern portion of the United States, no freezing is expected, so the frost line is considered to be at grade. Get into the upper Midwest or northern New England and the line of maximum frost depth can be more than eight feet into the ground. In areas such as this, a lot of digging, a lot of concrete for foundation walls, and a very expensive building project can be expected.

Where the Hansen Buildings offices are, along the Minnesota-South Dakota border, I’ve seen the frost reach seven feet deep!

In Alaska, and other locations where traditional frost wall foundations are prohibitively deep and prohibitively costly, different solutions have been experimented with, affording mixed results.  To help builders in these areas, the U.S. Department of Housing and Urban Development sponsored studies on foundations which are called Frost-Protected Shallow Foundations or FPSFs. FPSF designs use insulation on the outside of shallow foundations to protect them from frost heaves. The theory is a heated building will transfer enough of its heat through a shallow foundation to keep water below it from freezing.

One of the simplest and most effective designs is a fairly conventional concrete slab thickened to 18” or 20” at the outside edges and insulated on the outside face.  Although based on designs used in Scandinavia for decades, this came to be known as the “Alaska Slab” foundation.

The Alaska slab foundation and other FPSF designs have proven to be effective for heated buildings, but what about unheated storage buildings like garages, shops and barns?  Well, the Alaska slab foundation was the inspiration for a good solution for small storage buildings too. Using a similar thickened slab, either floating on the ground, or at a slightly higher elevation than the ground around it, works well at keeping water away and preventing frost heaves.

Besides reducing the depth of trenches and the amount of concrete required, a floating concrete slab foundation can be poured monolithically (all at once).  This means just one concrete delivery and one drying period, for savings in both time and cost.

Properly designed monolithic floating concrete slab foundations are approved for use on garages and accessory buildings by many municipalities, across the U.S.  They need to be heavily reinforced with steel rebar to prevent them from cracking under building loads and to help spread those loads over a wide swatch of ground.

Like conventional floor slabs, monolithic floating slabs should be detailed with properly located control joints. Interior columns and interior load bearing walls should not be supported on these slabs.  Instead, they should be mounted on 8” deep concrete pads which are completely isolated from the slab with properly designed expansion joints.

Although some code jurisdictions allow the use of monolithic floating concrete slab foundations on detached garages and accessory buildings of up to 2,000 square feet in area, most restrict them to just 24’x24’ (576 square feet) or less. Before considering a floating monolithic slab foundation the Building Department should be consulted to confirm they allow the use for buildings of the size being considered.

Pole buildings can be mounted to FPSF designs by use of properly designed and sized wet set brackets. These brackets are going to add to the overall cost of the building project, in some cases significantly.

Monolithic floating slabs are not recommended for use on sloping sites and on sites with mucky or soft clay soil. Top soil and all organic material like sod and roots must be removed from the area of any new concrete slab.

For post frame (pole) building construction, the quickest and least costly solution still remains the traditional embedded column foundation.