Stable Floors without the Hassle Published in the Colorado Real Estate Journal
Multifamily developments can range from simple single-story duplex buildings to several stories of numerous units. They may be constructed of wood, steel or concrete. The ownership may be retained by the original developer or the units sold to individual buyers. Some projects may have common areas for the use by the tenant/owners or consist of simple living units with minimal common amenities.
One thing all these buildings have in common is a main level floor!! OK, that may not be worthy of the drum roll you were hearing as I was leading up to this subject. Floors are certainly not that exciting. Well, they shouldn’t be anyway. How can someone get excited about their main level floor? It is something you walk on. You expect it to be level and it should remain dry. You don’t want it to squeak. The clinking of the glass in the dining room cabinet when you walk on a bouncy floor can be annoying. A floor should be out of sight and out of mind.
So, how do designers make sure floors are seen and not heard? As most developers and managers of multifamily projects along the Front Range know, our soil here is not too friendly. Mainly, it consists of clay that tends to expand when it gets wet and shrink when it dries. These conditions can play havoc on main level floor systems placed directly on the soil, such as slabs-on-grade. As the soil moves, so does the slab, and everything on it. This is not good when you have just installed an expensive tile surface to make the units more attractive to potential buyers. Cracks are not attractive! These types of floors may be acceptable in a basement, but most multi-family structures do not include basement levels. What is a designer to do?
One approach is to remove these unstable soils to a particular depth. The area is then replaced with a more stable soil and compacted back into place. The slab is then poured directly on this new material. Although the condition is improved, this approach still does stop movement of the floor.
There are ways to strengthen these slabs-on-grade to resist the dreaded cracking and offset the uplift pressures of the soil. The most cost-effective method of strengthening the slab is to use post-tensioned cables, which pre-compress the concrete to control cracking. The slab becomes stiff enough for when the soil wants to lift the slab (it has to lift most of the building, which usually is enough weight to offset the lifting pressures). But, these systems are only good for certain expansive soils and are less effective for smaller building footprints.
Another commonly used system is a structural floor set off the ground. This system eliminates the interaction of the unstable soil from the floor. Often these floors consist of wood framing. But, wood must be kept a minimum distance away from the soil to avoid deterioration. The resulting crawlspace must then be ventilated to control the growth of mold in these enclosed areas. Not a pretty sight! Steel floor framing is an option, but the floor sheathing still is typically wood. What is needed is a stable floor material that will not rot.
This brings us back to concrete. (Remember, it is not “cement”! That’s the powdered stuff in the concrete). But, the issue with these floors is they require expensive forming systems to support the wet concrete until it cures. This brings us to a new floor system that does deserve a drum roll!
Tella Firma™ is a patented system that provides a stable floor for multifamily structures. This system eliminates floor movement due to direct interaction with Colorado’s unstable soils. Your floor will be seen, but not heard from again!
What is Tella Firma™? First, a grid of piers is installed across the footprint. Then, Tella Firma™ lifting mechanisms are placed at each support. A slab with tensioning cables is poured directly on the ground, and the cables are pulled like any other post-tensioned slab system. Then the magic begins! The threaded rods of the lifting mechanisms are turned from above, lifting the slab off the soil to create a void space of typically 4” to 8”. This void separates your floor from the harmful effects of the unstable soil. The slab is supported by the grid of piers. The structure is then built directly on top of this structurally suspended slab.
This system has been used in Texas, where they have similar expansive-type soil, in more than 800 structures. Four such systems have been built in Colorado in the last year, with more being planned. With the concerns over annoying lawsuits in the multifamily industry, a stable floor system helps eliminate one possible area of contention. These systems are cost-competitive compared to other systems that attempt to provide similar stable floors. Plus, the lifting mechanisms, which remain embedded in the slab floors, allows for future adjustability of the foundation if ever needed!
Discover the peace of mind of knowing your floor system will not bother you again!