If the vertical sheeting, or wall panels, of your steel building, are not securely connected to the foundation or improperly weather-proofed, your building is vulnerable to the elements. When moisture or pests enter a structure, they can create severe damage to the metal, insulation, and other steel components.
The base condition for your steel building is of utmost importance in creating a secure and weather-proofed foundation connection.
What is the base condition?
The base condition surrounds the perimeter of the building and consists of a lateral structural support member. Additional base trim is an option.
- Base conditions form a direct connection from the wall panels to the foundation, providing anchored support for the walls of your building.
- Typically, when pouring the foundation, a notch or ledge is created in the concrete to allow the bottom of the panels to extend below the floor.
- The notch, which is about 1-1/2 inches X 1-1/2 inches and adds protection against air and water infiltration.
Adding a notch or ledge to the foundation is highly recommended to prolong the life of your building.
Base conditions come in different types, depending on the intended use of the building atop it. The metal building manufacturer or a general contractor experienced in assembling pre-fabricated metal buildings can tell you which base conditions best suit your project.
Option: base angle
The base angle is a standard or default base condition used for steel buildings. It is generally included in the building estimate unless you specify a different base condition or an estimate without the base condition.
- The base angle is an L-shaped single member attached to the wall panel and foundation.
- The fasteners are exposed for easy attachment.
- The base angle can come primed or galvanized to protect it from the elements.
- The base angle is usually connected to the foundation with concrete anchors.
However, to extend the panels below the top of the slab with this option, the foundation must have a minimum one-inch sheet notch. A chemical reaction may occur between the concrete and the wall panel that causes local discoloration if the panel comes into direct contact with the foundation.
Adding one inch to the perimeter of the foundation in which to place the notch increases the cost of the slab above the cost of other base condition options. Also, if the base angle is too small, the fasteners are closer to the edge of the foundation slab. Then the concrete is more vulnerable to chipping or breaking.
Option: base girt or base channel
A base girt is an option designed for buildings resting on piers instead of a solid slab foundation. The base girt is a Z-shaped member that matches the rest of the wall girts.
One end of the Z attaches to clips on the steel columns about six to eight inches above the column base, the other end attached to the panel. Unlike the other base condition options, the base girt does not attach directly to the pier foundation.
A base girt can also be used for buildings without a foundation.
- The girt is fastened about three inches above the finished floor.
- This method of using a base girt is typically found in agricultural buildings with dirt or gravel floors.
- If used with a concrete foundation or footer, it requires a one and a half inch by one and a half inch notch at the frame lines.
A base channel can be used in a steel building resting on a concrete slab foundation. A base channel is also appropriate with stem walls. The base channel is a C-shaped member resting on the slab and is commonly used in metal buildings that require a liner panel or interior wall installation.
- The C-member is placed with the length of its back flush against the foundation.
- One vertical side is ready for attachment to a liner or interior wall panel; the other vertical side fastens to the outer wall panels.
- A base channel typically requires a notch in the slab foundation to allow the exterior wall panels to extend below the level of the foundation top.
Both the base girt and the base channel are liner ready.
Option: Base trim and deluxe base trim
The base condition includes a trim piece added to the standard base angle, and it is meant to keep out air, moisture, and pests. Base trim also prevents the wall panel from directly contacting the foundation where discoloration could occur. It provides a connection point to the slab and a ledge upon which the bottom edge of the wall panel rests.
- The base trim is recommended for metal buildings in regions of extreme weather.
- A foundation notch is not required but is often used to add an extra level of protection.
- Base trim also makes it easier to install wall panels when there is no foundation notch.
- It also seals the building base better than a closure strip.
Deluxe base trim provides maximum protection (and cost-effectiveness) by combining base trim with a base angle. Deluxe base trim can conceal wall fasteners while protecting from the elements and does not require a notch in the foundation.
Option: base trim + base channel
Combining the base trim and base channel solves two problems with a single option.
- The base channel provides a connection point with liner panels.
- The need for a notch in the foundation is eliminated with the base trim.
- No need to add an inch to the foundation perimeter.
A combination of the base trim and base channel can improve the building’s look, although the building materials add to the cost.
The bottom edge of the wall panels on steel buildings can provide an avenue for moisture and varmints to come inside when the structure simply rests on a concrete foundation, piers, or the ground. The proper base condition can eliminate the problem as well as add an easy way to install liner panels and prevent the steel panels from touching the concrete and creating a discolored spot or allowing rust to develop.
Most base conditions require a notch in the foundation to allow the bottom of the wall panels to extend below floor level, which adds to the cost of the foundation. However, that cost may be negligible in comparison to the damage water and pests can create if they get into the interior of the building.
The base angle is standard with most steel buildings but opting for a more sophisticated option can prolong the life of your structure.