As you can guess, the past month has been about erecting exterior walls for our home - I call this wizardry!
Much has been made of wizardry since Harry Potter wielded his first wand, but "The Wizardry of Walls" is an entirely different kind of casting. In this case, we are casting spells in concrete using ICF (Insulated Concrete Form) construction.
ICF construction has been in existence for decades, but it's not yet typical in this area for residential construction. Typically, walls are framed in wood, sheathed in wood and insulated. ICF walls cost an additional 20% or more than wood-framed walls. However, to achieve the same level of integrity and energy efficiency in a wood-framed wall you would spend at least 20% more. We opted for ICF, for various reasons, but mainly because ICF walls are more fire-resistant (we live an unsafe distance from the closest fire station, and even further from a water supply that might deter a fire, as we learned from the Amity Fire Chief in the last chapter of this blog).
There are many manufacturers and types of ICF blocks, but, universally, interlocking blocks with a cavity for rebar and poured concrete are stacked to form the walls. Commonly, there are internal furring strips sandwiched between two 2.5" layers of polystyrene insulating foam (hence the name, Insulated Concrete Form). The furring strips hold the two sides of the block together and allow exterior siding and interior wall board to be attached to the walls - different block manufacturers use different types of material for this furring, typically plastic or steel.
A Team of Wizards
There are four wizards involved in giving our house a proper foundation and exterior walls: the structural engineer, the excavation contractor, the foundation contractor and the ICF contractor. We might not see a magic wand in their tool boxes, but each one employs a certain art, if not magic, to their trade. Each one studies the building plans, internalizes the numbers, maps the result in his mind, measures and measures again, and then finally builds their portion of the exterior wall, each one counting on the other. We are fortunate to not only have the best wizards on the job, but also ones who are willing to collaborate with each other for the best possible result.
In the planning stage, a structural engineer is involved in the design of the walls, taking into account materials and other factors that affect the integrity of the structure. The engineer drafts instructions and graphics, determining how each element of a wall will be constructed. Although some structural details are typical, often in custom buildings the engineering is enormously complicated. Our design includes 3 gables ("A" shaped rooflines) that require special consideration because, in these particular walls, there is more window than wall.
The excavation contractor, while not actively involved in building walls, meticulously carves out the ground to the exact footprint of the house, plus working room, and sets the stage for the foundation. Using a machine called an excavator (a 30,000 lb. monster with a big scoop on an arm) and a laser level, the excavation of the site is done to reach the correct soil and exact depth prescribed by the plans for the concrete footings. A difficult dig or sloppy excavation means that corrections will have to be made to build the footings. Our excavation seemed to be perfect, with no surprises (like giant boulders or unexpected soil types)- it looks like a big chocolate layer cake.
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| Excavation, Forms and Footings |
Next, the foundation contractor builds wooden forms around the footprint of the building and in other locations under the structure as prescribed by the plans, and he fills the cavity inside the wooden forms with a network of rebar (steel rods) to strengthen the concrete. The lower part of the wooden form shapes the footing and the upper part shapes the wall and determines the height of the wall. For example, basement walls are typically poured as part of the foundation of a home. Since we will have ICF walls, we will only need footings without a poured concrete upper wall.
After the construction of wooden forms, and an inspection by a county building inspector, forms are filled with concrete. When the concrete it set, the wooden forms are stripped away. The footings are stage two of walls. The placement of every foundation is obviously critical to both the site of the building as well as a final result of a building constructed according to its plans. The placement of our foundation is meant to maximize the site lines of our beautiful view, and the excavation and foundation contractors studied and measured and truly labored with us to be sure we had it right.
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| ICF blocks, from footings to first floor |
For the past two weeks, the ICF wizard has been meticulously stacking blocks, measuring and cutting each block to construct walls and building a wooden frame ("window buck") to hold the poured concrete out of the opening for each window. Tomorrow (7-23-12), there will be another parade of concrete trucks up, up, up our driveway to fill the first level of foam blocks with concrete. Once the concrete is poured, the walls, location of windows and other openings, are literally, written in stone. The second level of the home will follow after the rough plumbing, radiant heat tubing system and main floor framing.
The next blog in this series, "Monkey Do [It Yourself]" will bring you news of our first D.I.Y. projects in the construction of our home.
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