As General Contractors, we understand the need to be able to effectively communicate between the architect and the Owner. We also understand that plans are never perfect and far from perfect in some cases. You don’t have time to deal with the unpleasantries associated with having to explain the plans and details to the shell contractor because he is not taking the time to read them thoroughly. Or even worse, having to find a creative way to provide a change order to the Owner during construction phase, because the shell contractor did not provide a timely RFI, ask the proper questions, or plainly, just not being a team player and bid the plans as is with the intention of issuing change orders in the future. All of these things as you know bring a certain level of added stress to the Owner, Architect, and you, the General Contractor, adding to an already stressful project. Some of these things could have been avoided with just communication, attention to detail, and professionalism.
We want to offer you a better, stress free option.
From the bidding stage, our proposals are very detailed thus saving you on time from having to do take offs for the shell. Our take off process analyzes the plans thoroughly and identifies inconsistencies. Inconsistencies, errors, and omissions are identified and submitted with formal RFI’s along with the initial proposals. We believe in transparency. This attribute many times wins us the project even thou we are not the least expensive.
We are fully licensed and insured. We carry a 2,000,000.00 liability and 1,000,000.00 workman’s comp. (not exemption as many shell contractors do). Our objective is to earn your long-lasting business by being a sub-contractor that you can trust and know that the shell will be built according to plans, specifications, and on time. You will see that working with us will be a breath of fresh air with our professional approach. Dealing with architects or engineers in regards to the shell will be 1 last task for you. And you can expect the level of professionalism required.
Residential Shell Construction in South Florida Explained
Residential Shell construction in South Florida is the stage that focuses on the primary structure of the building. The structural engineer will design the shell to withstand high wind velocity, in accordance with the Florida Building Code for uplift (negative pressures), wind pressures, and shear strength from the foundation to the roof structure.
Many industry professionals consider this to be 50% of the project as it relates to the work. As there are many forms of shell construction for different purposes and different techniques used, I will focus on the more commonly used techniques using reinforced masonry construction for South Florida and its coastal areas.
The shell is divided into 6 major components: Site Work, Footer/Foundation, Reinforced Masonry, Tie Beam, Slab, and Roof Structure and Sheathing. You can write a book on each of these components, but for the sake of this explanation of shell construction, I will summarize each component.
Site work: In the design phase, the engineer will require a soil test, where a separate testing company will perform the test and provide results of the sub-soil conditions with Code acceptable recommendations for the test results. Once received, the engineer will base his foundation design around the soil test. In South Florida, there are 4 common sub-soil conditions that you will find, and they are muck, Lime rock/coral, sand, and a mixture of sand and rock. The mixture of sand and rock is usually what will meet the minimum sub-soil standard of compactable material that will reach 2,000 psi after compaction as per the Florida Building Code requirement. Lime Rock and coral in some parts of South Florida are almost as hard as concrete. So hard, that this condition can be expensive when it comes to excavating as manual excavating is not desirable nor cost-effective under these conditions. Other materials such as sand and muck will either have to be removed and backfilled with compactable material or Piles would have to be used.
If the soil test results show an inadequate sub-soil condition for a typical spread footing, then the engineer may elect to go with one of the pile options. The soil test results will show the expected depth of coral rock which is usually between 10’ to 40’ below grade. As there are other pile options, the most commonly used piles for residential construction are pin piles, helical piles, and auger piles. Pin piles work like a nail and when used, it is hammered into the ground until refusal. In other words, until the hammer used can not push down anymore because it has reached the bedrock. The equipment used to nail in the pine piles are usually a small mini-excavator that is about 5’ wide, and if space for this is an issue, they also have a manual hammer that can be used. Pin piles don’t have much capacity and are better suited for additions and hard to reach places. Helical piles have a stronger capacity and work like a screw. If too much weight is placed on a pin pile, settling can occur. Whereas the helical and auger piles work like screws into wood, they grip the soil and rock alike to prevent settling. Unlike the pin pile, the helical and auger piles go down to a specific depth as recommended in the soil test. Helical piles are good for additions, existing buildings where settling has occurred, and new construction. Auger piles are usually the preferred method for new construction. They have the strongest capacity, but the process is very messy therefore, the use of auger piles in existing construction is not desired.
Once the Shell Contractor knows the type of foundation that will be used, he/she will have to determine if there is any site work to be performed by comparing the existing site elevation vs. the proposed finished floor elevations (FFE). To determine this, he will need an existing survey with elevation points if the construction drawing site plans do not provide this information. At this point, he/she can decide if de-mucking is necessary, how much backfilling will be required, etc to prepare for excavation or preparation for the foundation.
Foundation: The footer/foundation is designed based on the weight of the building and sub-soil conditions. If inadequate sub-soil conditions exist as previously mentioned piles may be used. In this case, the piles work as legs and the sub-soil is less of a factor. A grade beam will be used instead of a typical spread footer. The grade beam will be installed above the piles and the steel welded together to form a continuous steel connection from the grade beam to the piles. The grade beam consists of reinforced concrete, as does the footer, but works more like a tie beam that is in the ground. A typical grade beam will be 16” x 16” and will have 3 number 7 rebars on top and bottom and 2 mid-span with #3 stirrups @ 12” on center (OC) (as an example). A typical spread footer will be 16” x 12” and will have 2 #5 rebars continuous. In both instances, tie-downs will be installed within the grade beams or footers for the reinforced masonry that will happen after the foundation concrete pour.
In the planning stage of the foundation, larger projects require shop drawings of the steel. Before commencing, you will want to submit the drawings to a steelyard where they will order all the steel and provide a takeoff of all the quantities and sizes for your review and provide drawings of the project that include the steel layout for the structural engineer’s approval.
Before working on the foundation, a proper layout is important. Any errors at the foundation level will follow you all the way up. At this point is when you lay out your windows, doors, columns, and any other critical points on the wall where steel reinforcing is required.
Before the concrete pour, the electrical sub-contractor will connect the grounding wire to the foundation steel. There is an inspection for this called grounding steel inspection. This grounding wire will later be connected to the grounding points in the electrical meter. This method is being used in conjunction with grounding rods and copper pipping of the water supply lines.
The concrete used, depends on the structural design. Typical concrete used is 3,000 PSI. Costal construction usually requires 5,000 psi because the properties in the concrete are optimal for the salt air environment. It is important to manage the delivery properly. If the truck takes too long to arrive, the driver adds water so that the concrete doesn’t dry up. It is important to note that too much water weakens the concrete. Also, the placement of concrete is an important decision. If you can deliver the concrete straight from the truck, you are guaranteed a stronger concrete because you will have to mix in less water. If delivery straight from the truck is not possible, then the use of a hydraulic pump will be necessary. However, water will have to be used in order to properly pump through the hoses. This does not mean that the concrete will be weaker, just proper care of management of the travel delivery time and observing how much water is used in the pump mix. Pump sub-sub-contractors like to use a lot of water to prevent clogging in the hoses. Be sure to indicate the rate of slump to both the truck driver and the pumping company personnel. Usually between 6” – 8” slump is optimal. Larger construction projects usually have an engineer testing and observing each truck delivery. This may not be economically viable in smaller construction projects.
The foundation design may be of stem wall construction or monolithic slab construction. If it is a monolithic slab, then the slab is part of the foundation. Otherwise, the slab is what is called a “floating slab” and is poured after or during the tie beam pour. In either case, it is important to remove any organic material beneath the slab to avoid any air pockets that may contribute to cracks on the slab in the future. In a monolithic slab with inadequate sub-soil conditions, it is somewhat designed to hold up its own weight so the soil beneath is not a major concern as a floating slab. However, it is still necessary to compact the soil beneath the monolithic slab properly for optimal curing during the curing process or cracks may still occur. Even though some cracking may happen, and a crack-free warranty is not possible, following these steps will increase your chances of a successful pour.
The Florida Building Code requires for the treatment of subterranean termites in foundations, slabs, and the perimeter of the building upon final inspection. Subterranean termites are different than dry wood termites. They have been known to eat through the drywall. Some believe they cause damage to your home quicker than the dry wood termites.
Reinforced Masonry: As in every stage, a proper layout is important. The block layout is where masonry openings are identified such as window openings, doors, columns, etc.
In residential CBS block construction, the shell structure is made from CBS block and reinforced concrete that is reinforced with rebar. The type of concrete used varies from 1,500 PSI concrete to 5,000 PSI. 5,000 PSI concrete is typically used for coastal areas where salt in the air can corrode the reinforced concrete. The steel reinforcing increases the PSI strength of the concrete. For example, regular 3,000 PSI concrete reinforced with steel can become 7,000 PSI or greater depending on the steel design. The reinforced concrete improves the sheer strength of the concrete. The tie-downs that were previously mentioned in the foundation, travel up through the CBS blocks into the tie beam tying the foundation, blocks, and the tie beam together. The blocks also have horizontal bracing every 2 courses of block. They are called truss ladders and are installed inside of the mortar that mends the blocks together.
Tie Beam: After the block is installed, its time to form up the tie beams and columns. The blocks have already been laid out to give enough spacing for columns, door openings, window openings, etc. You want to be sure to properly secure form boards to avoid any blowouts. A blow out can occur when the form board is not properly secured to account for the weight and pressures that occur during a concrete pour. Most blowouts happen at the bottom of columns where most of the weight and pressure is accumulated. At the beginning of the pour, the concrete is wet and running and needs at least an hour to cure enough to where it can hold its own weight. There are different methods of securing form boards such as 2×4’s, cross bracing, drill ties, etc. There are different methods and a good amount of thought should be placed on bracing to prevent loss and injury. Remember, Safety First!
If the structure is 2 stories or greater, then an aerial slab may be required. Additional forming and post shores will be required at this stage. The aerial slab and tie-beam should be poured continuously. In some cases, an engineering design will be required to make sure proper bracing is used to prevent injury or loss. During the pouring process, special care must be taken to make sure that no one walks beneath the form boards. Aerial slabs and beams should continue to be formed during the curing process for at least 7 days until it reaches the minimum desired compressive strength to prevent cracking or compromising its structural integrity.
If floor trusses or floor joists are used instead of the aerial slab, then the same process that is used in roof framing and sheathing will be used at this time.
Slab: As mentioned earlier in the foundation, if a monolithic slab is the design preference, then the slab would be poured together with the foundation. If it is to be a floating slab, and the site conditions allow for a simultaneous pour with the tie beam, then the slab did at that time. If not, then the slab will be poured after the tie beam. Usually, if the tie beam has columns, then the slab can’t be poured together with the tie beam because the form boards will be in the way. There are other ways around this, but each site condition is unique. Whether it has to be poured separately or together, it is critical that it is done when there is no rain in the forecast. In South Florida, a downpour can happen within an hour of having a sunny day and will just mess up your pour. The key to a successful pour is to have a good concrete pumping company and concrete finishers on hand. Always make sure that the finishers use a laser to monitor the elevations and if using wire mesh, make sure that you use proper mesh chairs to hold them in place. Wire mesh is a steel mesh that is used inside of concrete slabs for reinforcement. If the finishers step on them, which they always do, the steel mesh chairs hold them up so that the steel remains in the middle of the concrete as it is intended. Otherwise, they fall to the bottom and will lose its purpose.
I have seen some contractors pour after the roof is up, and in my opinion, it is not a good idea. It creates problems with ladders, and this poses safety issues for the roofing framers. It is better to pour the slab and have a solid surface for the roofing framers to work on.
Roof Framing and Sheathing: The final and last stage of the shell construction. In the planning stage of the shell construction, it is important to order the trusses first. This includes floor trusses if required. The process of the trusses is lengthy and should be done at the beginning. The process is as follows: Plans are provided to the truss manufacturer. They provide a preliminary drawing for the Engineer of records (EOR) approval. The EOR gives initial approval or comments. The truss manufacturer provides drawings and engineering of the trusses/floor trusses. The EOR signs. Now the truss shop drawings are submitted to the municipality for approval. Once approved, then it is safe to put the trusses into production. Depending on the size of the project and the workload of the truss manufacturer, there is usually a 4 to 6-week lead time. Once trusses are delivered, the shell contractor will decide if the trusses are small enough to erect by hand or order a crane to help erect the trusses. Usually, a crane is the best way to go. At this point, you want to make sure that all your materials are on site the day before. Materials such as plywood, fascia boards, and engineering wood. While you have the crane there, you should have the crane lift the sheathing up onto the roof. The truss installer will usually have a truss stand that will hold the plywood in place for storage. Depending on the size of the building, it is usually a good idea to have the crane company’s rep do a site visit to make sure that the proper crane is provided to do the work. The ability of the crane operator to have good visibility is critical, otherwise, the shell contractor will have to account for walkie talkies for communication.
Now that the project for the shell construction has reached its final stage, clean up and storage of excess materials is critical for the upcoming subs. A clean workplace is a productive and efficient workplace. As a leader, if you educate your employees and subs to work safe, clean, and organized, you will always have a successful construction project. This habit also helps with inspections. As long as an inspector sees a clean worksite, he/she is more likely to be more lenient on his/her inspections.