Tag Archives: Frost Protected Shallow Foundation

Minimizing Excavation in Post Frame Buildings Part II

Minimizing Excavation In Combination With Post-Frame Frost Protected Shallow Foundations Part II

In our last thrilling episode Snidely Whiplash had tied our fair damsel in distress, Nell Fenwick, to railroad tracks.

Oops – railroad engineers are not what most of you were expecting!

Continuing with a simplified solution response to reader DAVID’s ideas regarding site preparation and Shallow Frost Protected Foundations (SFPF) for post frame buildings.

Dear David ~

Thank you for your patience. As you may know from reading this column, I tend to research everything to best of my abilities prior to writing an article or responding to questions. Areas of site preparation and concrete flatwork are ones where I have a more limited amount of personal experience, so I have been doing a plethora of reading and contacting (and discussing) with concrete experts. I also am not married to a position, as better information becomes available, I take advantage of it.

Article you reference in (1) has been updated since you last perused it. Even though many RDP (Registered Design Professionals – architects and engineers) specify sand over under slab vapor barriers, I have now become a “no sand above vapor barrier” school convert.

To follow, a summation of my thoughts in regards to this subject, with top of slab being fixed 3-1/2” above grade.

(a) Excavate entire site to remove organic materials. Area to be excavated should be a minimum of three feet outside of actual building foot print. Depth of excavation below zero point (grade) should allow for any concrete thickness greater than a nominal four inches (3-1/2″ actual), two inches of insulation board (if desired), two to six inches of sand or sandy gravel and six to 12 inches of sub base. Assuming a nominal four inch slab, total depth of excavation should be 16 inches if doing a FPSF.

(b) Auger holes for columns, stand columns in augered holes and backfill with concrete per engineered plans.

(c) Install splash plank/skirt board, with board bottom even with grade (zero). There would be no reason to increase dimension to greater than 2×8, as vertical insulation boards prevent any concrete in a slab thickness greater than a nominal four inches to “leak” to outside world.

Side bar – 2×10 or 2×12 pressure preservative treated material will be available, however many times only via special order. If any portion were to be entirely embedded below grade, then appropriate treatment level would more probably be UC-4B – as UC-4A treatment levels are strictly for ground contact.

(d) Place vertical and horizontal insulation boards for FPSF – backfilling with sand or sandy gravel sufficiently to hold vertical insulation boards in place.

(e) Place sub-base, then base material, compacting in lifts.

(f) Place 15mil vapor barrier (make sure to run it up insides of splash planks); Under slab insulation (as desired); pex (https://www.hansenpolebuildings.com/2016/08/pex-tubing/), rebar and/or mesh, and then pour the slab.

This minimizes excavation by eliminating need for a trench.

 

Brick Ledge on a Pole Building

Brick Ledge on a Post Frame (Pole) Building

Whilst it would not be my personal preference for finish on a post frame building, there are instances when either aesthetics (trying to match other existing structures), local Planning Departments or HOAs (Home Owner Associations) mandate use of brick or stone exteriors. Whether for a wainscot or covering an entire wall (or walls) if full thickness stone or brick becomes a solution, it must be adequately structurally supported by a footing.

I truly had not given this subject much thought, until reader JASON in COLLEGE STATION wrote:

“Hello, thanks in advance for sharing some of your knowledge and experience with pole barns.

I have been looking at the construction details on your website and have a question about the bottom “skirt board”. Could this detail be designed so that the board does not show below the metal but the metal terminates on a concrete slab that extends a little? I am guessing this is how someone would do it if they needed a brick ledge. If so what is the best way to achieve this?

Thanks again for your advice.”

Jason’s question actually read like a multiple dilemma.

First, a question is hiding a building exterior pressure preservative treated skirt board (aka splash plank). Simple answer is yes, building is already designed so this can be done. Skirt board should be placed per engineer sealed building plans, showing drip edged base trim bottom four inches above grade. This allows for a nominal four inch thick (finished thickness 3-1/2”) sidewalk, driveway, landing or other concreted areas to be poured against exterior of splash plank, coming in ½ inch below bottom of drip edge. Any such pours should be along a grade sloping sufficiently away from building a minimum slope of 2%, to keep water from pooling against building.

For a nominal fee a RDP (Registered Design Professional – engineer or architect) can design an appropriate and structurally adequate support, varying in design due to individual building sites’ frost depths. Using a frost-protected shallow foundation in frost prone regions (read more here: https://www.hansenpolebuildings.com/2017/09/post-frame-frost-walls/), could possibly be part of a design solution, with some sort grade beam, whether it be poured reinforced concrete or properly pressure treated wood. Either will need to be engineered appropriately based upon material weight and strength of  soil to give continuous support.

I’d personally consider either thin brick, or a cultured stone veneer. Ultimately it will probably be least expensive design solution providing and meeting needed objectives. Framing, including columns and their embedment, will need to be engineered to support added dead loads from thin brick (depending upon pattern and thickness thin brick can weigh nearly seven pounds per square foot). Structural members need to be engineered to have limited deflection. Bookshelf girts might well be part of an engineered design solution: https://www.hansenpolebuildings.com/2011/09/commercial-girts-what-are-they/.

 

Frost Foundations, Painting Metal Buildings, and Hawaii

Today the Pole Barn Guru answers questions about frost protected shallow foundations, repainting metal buildings and a kit in Hawaii.

DEAR POLE BARN GURU: What type of frost foundation would you use if planning on doing a finished space in part of the building? ERIC in WINTERSET

DEAR ERIC: I’d do a Frost Protected Shallow Foundation using embedded columns with a concrete footing below and a bottom collar which would be 24 inches or more below grade. I’d backfill the inside of the vertical insulation with sand and pour a slab on grade. Read more here: https://www.hansenpolebuildings.com/2016/11/frost-protected-shallow-foundations/

 

DEAR POLE BARN GURU: Hi I’m located in Ramsey Mn do you guys paint pole building or just sell the paint? I think my building is 30×60 I’m looking to have it repainted let me know thanks, Zach or if you know someone that does good work to call to have it done. ZACH in RAMSEY

DEAR ZACH: We do not paint pole buildings or sell the paint. You will want to read this article: https://www.hansenpolebuildings.com/2013/01/repainting-steel/.

 

DEAR POLE BARN GURU: Hi, I came across some of your buildings at Home Depot website. It might be possible to get one of your buildings thru them here to Hawaii. Can you provide treated lumber in your kits? Terrible termite problems here, untreated lumber eaten in several years. Thanks, MARC in KONA

Post Frame HomeDEAR MARC: We’ve provided many post frame building kits to the Hawaiian Islands and our system is set up so all pressure preservative treated lumber is automatically selected for buildings going to Hawaii. Generally buildings for Hawaii are shipped in containers from the Port of Seattle, as shipping costs are lower than obtaining the components on the islands.

 

 

 

Post Frame Frost Walls

From reader Paul in Bismarck: “How do you deal with the requirement for a 4 foot frost wall on buildings that will have plumbing installed in them. Typically, the concrete footing on a stick built structures qualifies as the frost wall. How is this accomplished with a pole building that will be used as a residence?”

 Mike the Pole Barn Guru writes:

I would look towards a variant of the Frost Protected Shallow Foundation (FPSF) system as a solution.

Set the columns in the ground so the base of the column is at or below frost depth. Backfill the bottom portion of the hole with premix concrete, making sure to not have the concrete more than 24 inches above grade. You will have to dig a trench along the outside of the columns all the way around the building. The trench will need to be approximately 24 inches deep and the width will vary depending upon the location along the building perimeter (it will have to be wider at the corners). After the skirt boards/splash planks are installed, place a 24 inch tall minimum R-12 expanded or extruded polystyrene insulation board on the outside of the skirt board, with the top edge four inches up from the bottom of the skirt board.

Extruded polystyrene insulation will be placed horizontally outward (in the trench) from the vertical insulation. In your climate, probably a minimum of R-12 along the walls and R-15 at the corners. The corner area will extend at least 80 inches along the walls from each corner and out 48 inches. The balance of the walls will be out 36 inches.

slab edge insulationNow the difference between “typical” FPSF and the post frame version – instead of pouring a thickened slab, backfill on the heated side of the vertical insulation with clean sand, then just pour a slab on grade inside the building. There is no “magic” to the insulating value of concrete, so I see no reason to throw concrete into making the edge of the slab thicker when it is merely being used as backfill and supports no downward weight.

Areas without the extreme cold winters Bismarck has could get by with lesser amounts of insulation.

Download a free copy of The Revised Builders Guide to Frost Protected Shallow Foundations here: https://www.scribd.com/document/341135783/Revised-Builder-s-Guide-pdf