New Construction 101: FOUNDATIONS
New homes in Chicago offer their lucky owners lots of advantages over rehabbed homes. One advantage is the quality of the space below grade level: the basement.
The primary function of a foundation is to provide solid support for the structure above grade. In Chicago, basements have been viewed as an opportunity to add much needed living space in a densely populated environment where land is costly and constrained.
Up until the 1910 or so, limestone, brick, or terra cotta block were the most typical materials used. These materials certainly did a great job of supporting the structure above ground as demonstrated by how many of the buildings of this age are still standing today. Unfortunately, they are very difficult to waterproof and the basements don’t typically offer the type of headroom that today’s new homes allow. The typical Chicago basement was 6’6”-7’6” in height with a thin concrete floor. During heavy rains, the basements would seep and floors would often buckle as the unreinforced, thin concrete would crack against the pressure from water below. Occasionally, they would also experience sewer back up as the floor drains were directly connected to the sewer system. In addition to seepage and sewer back up, existing homes are susceptible to a third source of moisture, condensation. Basements of existing homes, once heated to room temperature, can experience condensation against the cold, ground temperature foundation walls. This can result in mold growth and musty odors.
Finished basement of a typical new construction home in Chicago. Tall 9+ foot ceilings, and finishes that match the main levels of the home integrate these spaces in look and feel with the floors above. Waterproof and light filled, these spaces are far superior to below grade finished basements in older homes.
New homes are built with reinforced concrete foundations which are much stronger and deeper than the foundations historically used in Chicago. They are required to have drain-tile, which is a perforated pipe that runs under the floor, next to the footings, the lowest point in a basement. Drain-tile collects moisture under the slab and directs it to a pit, which has a pump that pumps water away for the foundation, helping to keeping it dry.To prevent sewer back ups, new homes are required to have an overhead sewer system. The system is 100% effective at preventing sewer back up. Existing homes that have finished basements often have bathrooms and plumbing without an overhead sewer. A large rain could cause water to backflow into the basement through these drains. This has become especially important in recent years with massive spring storms straining the city’s 100+ year old sewers. New homes, though, are unaffected by these events.
Modern foundations are made with reinforced concrete. The Steps in the build process are:
1. Excavation of the site.
2. Deep/wide footings are poured over reinforced steel bars.
3. Forms are placed to build the walls of the foundation, also made of reinforced steel and poured concrete, attached with steel reinforcement to the footings.
4. Drain-tile, basement plumbing, and gas, water, and sewer utilities are brought into the basement.
5. A level gravel floor is installed, then a vapor barrier, then steel reinforced concrete is poured 4+ inches thick to make the floor.
Once the foundations walls are poured, the construction of the frame shell can begin.
The photos below illustrate the process and provide captions with detailed explanations. I hope you find this segment useful, please like this page and we’ll be discussing framing and structure soon!
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Workers preparing freshly cured footings for foundation wall forms at the site of two adjacent foundation walls. The steel dowels protruding up will pin the foundation wall to the footings when poured. — at Chicago, IL.
Same footing from a different view. Note the Steel Re-inforcing Dowels inserted in the footings to anchor the foundation wall to the footings and prevent shifting.
The picture is with foundation walls poured and forms removed. The exterior has been backfilled and crushed stone has ben spread on the floor, awaiting rebar and concrete. The steel dowels set into the footings are now integrated into the poured concrete foundation walls.
A poured foundation, freshly cured with a black waterproofing coat applied to the exterior. Once backfilled, this coating will help keep the foundation walls dry.
A similar, freshly cured foundation, with a 4 inches of foam applied to the outside of the foundation walls, commonly referred to as an insulated foundation. This foam reduces thermal loss to the earth, keeping the basement more comfortable and improving efficiency. It also reduces the likelihood of condensation inside the basement as the walls are kept closer to interior wall temperature. This improves air quality by eliminating the third possible source of water, condensation, and eliminates the possibility mold and a “musty” basement.
A finished foundation wall, with underground plumbing and draintile in place. Next steps are vapor barrier and.or insulation, and the reinforced concrete slab. — at Chicago, IL.
A nearly complete finished basement of a new construction home. Note the finished concrete floor, and the green wallboard on the below grade portion of the foundation wall. The concrete floor can be covered in carpet, tile or other desired finish. This floor will be polished, stained and left exposed for a very modern, low maintenance finish. The green wallboard is moisture resistant. Although this home builder provides insulated foundations, which eliminate condensation, the moisture resistant green-board is a “belt and suspenders” approach to home building. Eliminating problems related to moisture and water vapor is a hallmark of a quality homebuilder.