Tag Archives: termiticide

How to Pour a Slab on Grade

How to Pour a Slab on Grade in an Existing Barndominium

Reader PAUL writes:

“I have an opportunity to purchase a barndominium that has the posts set in 20” wide 40” deep peers. Unfortunately the county where this is located does not require a footing. All city codes in this area require an 8”X 36” footing. What solutions do you recommend for pouring the slab now that the shell has been erected?”

Most post frame buildings have shells erected then slab poured, so this should not be an issue. A pressure preservative treated splash plank should be in place around this building’s perimeter. It will become forms for your slab. Snap a chalk line on the inside of splash planks up 3-1/2″ from bottom, this will be top of your slab.

In Climate Zones other than 1 through 3, you will need to frost protect the building perimeter. This can be done by trenching around the edge of the building to required depth – 24″ in zones 4 and 5, 48″ in 6 and greater. It is usually easiest to install R-10 rigid insulation on the inside of the splash plank, with top of insulation even with top of slab to be poured. This also precludes any need to UV protect vertical insulation.

Depending upon how the site was prepared, you may need to excavate inside of this building. 

If in “frost country” a sub-base 6” or thicker should be first placed across the site. To maintain frost-free soils sub-base should be such as no more than 5% (by weight) will pass through a No. 200 sieve, and it is further desired no more than 2% be finer than .02 mm.

Prior to pouring, 2” to 6” of clean and drained sand or sandy gravel is spread below where concrete is to be poured. Mechanically compact fill to at least 90% of a Modified Proctor Density, otherwise slab could sink.

In areas prone to subterranean termites treat prepared soil with a termiticide barrier at a rate of one gallon of chemical solution per every 10 square feet.

Install a good, well-sealed 15mil vapor barrier below any interior pour, to stop moisture from traveling up into the slab through capillary action. Overlap all vapor barrier seams by a minimum of six inches, then tape. Vapor barrier should extend up column sides and to splash plank top. 

Minimum R-5 (R-10 being preferred) insulation shall be provided under full slab area of a heated slab in addition to required slab edge insulation R-value for slabs as indicated in International Energy Conservation Code (IECC) Table R402.1.2 Footnote (d).

In most instances, over properly compacted fill, 15 psi (pounds per square inch)  EPS (expanded polystyrene) or XPS (extruded polystyrene) insulation has adequate compressive strength to support a five yard dump truck on a nominal four inch slab on grade.

Consider this: 15 psi equals 2160 psf (pounds per square foot), making this greater than assumed compressive strength of most soil types.

If not using fiber-mesh or similar reinforcement additives to concrete mixture, place rebar (reinforcing steel rods) in slab center to add rigidity to concrete to aid in minimizing cracking.

Pre-construction Termite Treatment

Why would anyone building a pole barn, barndominium, shouse or post frame home need to be concerned about treating for termites? Isn’t pressure preservative treated wood going to solve any potential long range problems from pesky termites?

Regardless of whether you build a post frame (pole) building, stick frame, steel frame or even concrete building – if there is any cellulose (wood) based product in your building – you are vulnerable to termites. I have even heard a story about a man who had bags of Sakcrete™ (https://www.hansenpolebuildings.com/2012/11/concrete/) stored in his garage and termites ate away the paper bags!

Properly pressure treated wood will be termite resistant until it is cut or bored and those areas are not protected afterwards.

There is an old adage of “an ounce of prevention is worth more than a pound of cure” is absolutely true, especially when it comes to building and preventing termites. While it is nearly impossible to prevent anything from happening one hundred percent, pre-treating area where your building is to be constructed, can drastically increase your chances of remaining free of termites.

Goal of pre-construction termite treatments is to form an in ground chemical barrier keeping subterranean termites from coming up from the soil to feed on wood structures or wood/cellulose inside them. Because the area to be treated is free of obstructions (such as a building), this type of treatment is less labor intensive, and requires less termiticide to be used, making treatment less expensive than treating an existing structure. Another benefit of pre-treating is your exterminator can cover every square inch of ground, creating a more secure barrier.

In order to properly treat for termites during pre-construction, area will need to have termiticides applied several times at different stages. Your exterminator will need to be in close contact with you or your builder in order to accurately arrange treatments. Your building design and type of soil it is being built upon may cause some variation in barrier application.

While methods can vary a bit depending on building codes for your specific area, first step for pre-construction termite treatment is usually to treat before a concrete slab is poured. Once land has been graded area should be treated. This is usually done by treating with a termiticide barrier at a rate of one gallon of chemical solution per every ten square feet.

While termites cannot bore into or eat concrete, slabs can crack with time creating perfect entry points for them. If surrounding soil has not been treated, termites can make their way to slabs, through cracks, and into the main structure.

Final pre-construction treatment comes with last grading, but prior to landscaping. It is recommended that a trench be dug approximately four to six inches deep and at least twelve inches from building out into the yard. Four gallons of termiticide is applied for every ten feet surrounding the building in a continuous spray.

After building is complete, it is still a good idea to keep protective barrier intact. This can be done by taking care not to disturb the soil surrounding the foundation in the twelve inch radius. If you plan to add a deck, porch, or other addition to your building, protective barrier should be extended an additional twelve inches into yard from new structure.

A more extensive pre-construction treatment can also be done in place of or in addition to the above mentioned spray method. This type of treatment is known as “rodding” and is carried out by injecting a permethrin based termiticide gel deep into the ground.

Traditional spray methods only allow termiticide to penetrate about one inch into the ground. Rodding uses a metal pole four to six feet in length, and is filled with termiticide. Pole top has a knob keeping pole pressurized. This pole is repeatedly pushed into and pulled out of ground to remove soil, leaving behind deep holes. This is done until a grid pattern of holes, approximately eighteen inches apart is formed. These holes are then injected with termiticide gel in order to keep termites away from the area.

A proper pre-construction termite treatment can last anywhere from two to five years. Even though these treatments are quite effective, it is still recommended to inspect your building periodically for any damage or signs of termites. Also, try to keep the area surrounding  the building free of residual wood or other cellulose based material, as these attract termites. This will ensure your structure is continually protected and will head off any potential infestations before they begin.