How Houses are Built – the Components and Materials

Houses are the most common structures that we build. There are many components and materials that can be used to construct a house. The basic components of a house include the:

• Foundation
• Support Structure
• Roof
• Floors
• Interior Walls
• Exterior Insulation
• Exterior Wall Finishes
• Roof Finishes

Together these components create an overall integrated system that create a structurally sound house, encloses the house to protect it from the weather, and creates your rooms and spaces. Let’s take a look at each.

Foundation

The foundation is the system your house sits on, transferring all the weight of the house to the ground. Foundation systems can vary depending on the type of soils and local building traditions, but basically boils down to the following components:

Footings

Footings are the “feet” upon which the house ultimately sits, transferring all loads to the ground. Footings are typically made of concrete and must have a width and a thickness that can support whatever loads are required.

Concrete is a material that works great for vertical (gravity) loads counteracting these compression forces. However, it does not work well for point loads, which cause it to bend if not counteracted with some other material. Concrete footings will have reinforcing steel bars (rebar) in them to assist with this.

Footings must sit upon compacted soil that is below what is called the frost line. The frost line is the depth at which moisture in the soil freezes in winter. Soil that freezes expands and can cause damage to foundations. This depth can vary depending on the severity of the cold, but standard frost line depths are established by local building codes.

In the U.S. frost depth can range from a few inches in the warmest sections of the country to many feet deep in the coldest.

Foundation Wall

The foundation wall is the vertical component of the perimeter foundation. It is the element that the perimeter structural walls sit on and is the element that holds back the soil for basements.

Foundation walls are typically built of either concrete or concrete block, though some historic houses were built with brick or stone foundation walls.

Foundation walls must handle vertical loads as well as any horizontal loads from soil pressure, which increases with soil depth. Additionally they must handle any horizontal loads carried by the house structure. Concrete and block foundation walls have rebar added to them to counteract these horizontal loads.

Concrete slab

Concrete poured on the ground between foundation walls or perimeter walls is called a slab. Slabs are used as the base floor surface in basements as well as for houses without basements.

Pier-and-Beam

Some houses without basements are constructed with raised first floors. Some of this has to do with regional climate, typically in warmer regions, some has to do with intermittent seasonal flooding, and some has to do with traditions or preferences.

A raised first floor typically uses what is called a pier-and-beam foundation. In addition to the perimeter foundation wall, intermittent concrete piers are placed beneath the house to support beams for the first floor framing.

The area between the soil and the flooring above is called a crawl space. Such spaces must be ventilated and have access to them. Any plumbing lines that run in the crawl space should be insulated to protect against freezing.

Other components

Gravel Base: Before a concrete slab is poured the soil must be compacted to alleviate future vertical movement. Crushed gravel is then used as the actual base material on which the concrete is poured. This gravel allows contractors to create a level surface, allows for proper drainage of moisture in the soil away from the concrete, and provides a buffer that reduces the impact of soil movement which can cause cracking of the concrete.

Perimeter Drainage: An additional means of controlling moisture in the soil is the perimeter drainage system. This system is composed of round clay drain tiles that have gaps or holes that allow for moisture to seep into the them. These tiles, placed within a continuous gravel bed adjacent to the foundation footing, create a pipe in which moisture travels by gravity to either a sump pump which forces the moisture into the local storm drain system or to an exterior fallout point.

Moisture barriers: Moisture in the soil can often have enough pressure that can allow it to penetrate through concrete. To counteract this a plastic sheet is placed below the slab and on the outer face of the foundation wall, especially at a basement. An alternative to the plastic sheet on the foundation wall is a spray-on waterproofing membrane that creates a more contiguous and uniform protection layer.

Insulation: In cooler and colder climates rigid insulation is often placed on the outer face of basement and foundation walls and sometimes beneath portions of the slabs in order to provide a barrier to cold soil, to provide protection for the water proof membranes, and to provide protection from soil pressures.

Radon system: A large portion of soils have small amounts of radioactive minerals. This radioactivity, though very minimal, can seep through concrete as radon gas and concentrate into basements causing health problems. To counteract this a series of vertical pipes are placed through the slab which then rise vertically through the house to the roof to ventilate this gas. A vapor retarder, often as the water membrane, must be placed under the slab to assist with limiting the radon gas.

Support Structure

The support structure sits on the foundation system and holds the house up. This typically consists of a wall framing system made of small-sized wood or steel components that create panels that are placed around the perimeter of the house. Other materials such as masonry, structural steel, concrete, or structural panels can also be used.

The support structure carries loads from the roof and any upper floors down to the foundation and is designed to also counteract horizontal forces from wind.

The structure integrates other materials to create an enclosure for the house that acts as a barrier from water and wind. These materials can include:

• Sheathing: Framing systems use large panels placed across the exterior faces of a house to create the base of the enclosure. Houses using structural steel have framing panels between the steel columns which are then covered with sheathing.
• Moisture barrier: This barrier can consists of tar paper, plastic sheets, or sprayed-on systems, and is installed over the sheathing or onto the masonry, concrete, or structural panels to prevent water from getting into the wall system.

Roof

The roof covers the house and provides a barrier to water and snow. Roofs are typically constructed of wood or steel framing members, often as pre-fabricated trusses, and then covered with sheathing and a moisture barrier. The roof can also be built of structural steel with metal panels spanning between the members. Houses built with a concrete structure will typically have a flat roof built of a structural slab.

Roofs are typically pitched upward significantly in one or more directions to allow for effective drainage of water and snow. “Flat” roofs are gently sloped to allow for drainage of water to either roof drains or to the roof edge using scuppers through a low wall at the perimeter of the roof, called a parapet.

Pitched roofs can come in a variety of forms, including:

• Gable, which slopes in two opposite directions with vertical end walls

• Hip, which slopes in each direction

• Gambrel, which has two differently-sloped segments on each side of the roof.

• Shed, a roof that slopes in one direction.

• Barrel vault, which is a curved roof.

Sloped roofs typically overhang the exterior wall beneath it creating what is called an eave. The eave allows for water to fall away from the face of the wall. The bottom of the eave usually has a horizontal member, called a soffit, that runs from the outer edge of the eave back to the wall.

Roof drainage on sloped roofs is directed by metal valleys where two slopes intersect and by gutters at the bottom edge of the roof. The gutters are then tied to downspouts which take the water down to grade level where it is discharged away from the house.

Flooring Systems

Flooring systems on soil are typically poured concrete slabs. Floors above slabs are typically built of framing in the form wood joists or trusses made of wood or small steel components. These are then covered in sheathing as the base floor.

Structural steel framing uses beams and joists with concrete-filled metal panels spanning across them for the floor.

Concrete framing uses structural concrete floor slabs that are tied in to the beams and columns of the structural system.

Interior Walls

Interior walls are typically non-structural, meaning they only act as dividers between rooms without carrying any structural loads. These are most often made from framing components that are then covered with gypsum board panels. Interior walls can also be built from masonry, either as exposed brick or as brick or concrete blocks covered with plaster.

Exterior Insulation

In addition to the moisture barriers mentioned above, the perimeter and the roof of the house need to have continuous insulation to provide protection from hot and cold weather, thereby allowing for consistent and comfortable temperatures inside the house and minimizing the amount of energy needed to heat or cool the house.

Framing systems typically use batt insulation, which comes in narrow rolls of fiberglass mats of different thicknesses relating to various levels of insulating performance. This matting is often covered on one side with kraft paper to act a a vapor barrier. These batts are stuffed between and attached to the framing members.

Masonry and concrete wall systems often use rigid insulation boards applied to the exterior face of the walls on top of sheathing and applied to the top of the roof framing. These can sometimes act as the wall sheathing as well. The moisture barrier is typically applied over the rigid insulation.

Rigid insulation boards on the exterior surfaces have an advantage in performance over batt insulation as it places the thermal barrier outside of the wall systems rather than in the wall system. This provides an uninterrupted layer of insulation that is not broken by the framing system.

Rigid insulation boards can also be used in lieu of batt insulation over the framing system to get the same continuous barrier.

Alternative insulation systems include insulated concrete masonry blocks which come with insulation integrated into the blocks, and structural insulated panels with have rigid insulation sandwiched between structural panels. These can be placed as vertical structural walls.

Exterior Wall Finishes

Exterior wall finishes are installed over the wall systems. There are numerous options of material, including the following:

• Brick: Non-structural brick, also called face brick, is made from fire-baked clay and stacked on an extension of the foundation wall. Face brick is placed about 1″ from the framing wall creating a cavity that allows any moisture that gets through the brick to make its way back through the wall via wicks, thereby protecting the wall system from moisture. Brick comes in a wide variety of sizes, styles, and colors, and can be laid in a wide variety of patterns.

• Concrete masonry: A variant of brick, concrete can be molded into individual units and installed as a finish material. These concrete units come in a variety of colors and finishes.

• Siding: Siding consists of narrow but long strips of material placed horizontally or vertically directly onto a wall, and can also consist of larger panels. Materials can include wood, vinyl, fiber cement, and metal as aluminum or steel. Wood must be primed and painted unless a weather resistant wood such as cedar is used. Fiber cement can be painted or come with integrated colors. Vinyl and metal come pre-finished and don’t require painting.

• Shingles: Overlapping wood shingles can be used as siding. They have the ability to create interesting patterns through the use of special shapes. Shingles are often made from long-lasting wood such as cedar that doesn’t have to be painted, but can be primed and painted if desired.

• Stone: Stone is a natural material. It is cut in quarries as large blocks then cut further into refined sizes and finishes. Stone can also be found as loose material called “rubble”. Stone comes in an amazing variety of materials and colors, can be cut and installed in an array of patterns, and can have numerous textures from smooth to rough.

• Metal panels: Large panels used as a variation on siding is another exterior finish option. Panels can be flat or can be profiled such as with corrugated metal. Flat panels should have an integrated backing material to keep the face flat, otherwise the material will start to “wave” creating what is called “oil canning”.

Roof Finishes

Shingles: The most common residential roofing material, shingles are small-scaled thin pieces of wood, asphalt-impregnated sheet material, fiber cement, plastic, stone, or metal that are overlapped to provide for effective water drainage. These materials provide a wide array of styles, colors, and patterns.

• Wood: Wood shingles are typically made of weather-resistant material such as cedar and are combustible. These shingles are typically narrow tapered pieces of wood that are nailed to the roof sheathing and overlapped to provide for effective drainage.
• Asphalt: Asphalt shingles consist of a thin base material, organic or fiberglass, which is impregnated with asphalt and then covered in granular material of a variety of colors and types. Asphalt shingles tend to be rectangular with tabs that interlock the shingles. Architectural asphalt shingles are thicker and come in a variety of shape options.
• Fiber cement: These are similar to fiber cement siding, with integral color.
• Plastic: These are lightweight but combustible shingles.
• Terra Cotta: The most common form of terra cotta roofs are Spanish tile. These are typically formed into rounded shapes that overlap as rows that run from top to bottom of the roof and used in moderate to warm climates.
• Stone: Stone shingles are traditionally made from slate or flagstone, which is cut to thin pieces that can then be nailed to the roof substrate. Stone is durable but heavy, and can sometimes crack causing water to infiltrate beneath them causing roof damage.
• Metal: Metal shingles are long-lasting and tend to be decorative in their effect, typically made of copper. They were more common historically.

Metal panels: Metal panels consist of narrow but long formed sheets that interlock with adjacent sheets or joined via the board and batten process. Metal panels are either natural material such as copper, terne – a steel sheet coated with an alloy of lead or zinc with tin, or coated aluminum.

Penetrations

Various types of elements penetrate through the exterior surfaces of a house. The most obvious openings in walls are for doors and windows.

Additionally, ventilation grilles are used for attic and crawl space venting, and ventilation strips occur at roof eave soffits and at roof ridges. Laundry rooms must have dryer vents to the exterior. Roof penetrations can include plumbing vents, toilet exhausts, mechanical attic vents, skylights,and chimneys.

Utility services also create penetrations. Overhead power lines must get into the house through an outside wall. Gas lines must rise from underground outside the house before penetrating the exterior wall going in. Water lines have spigots for outside watering.

Each penetration must be made watertight. Wall penetrations typically have sealants applied at their perimeter joints with the walls. Roof penetrations typically have special flashing to direct water away from the penetration.

End Result

Our houses can be built of a variety of components mixed and matched as needed for the region, climate, and our own preferences. Building a home that successfully integrates these components will provide a comfortable house that we can enjoy for a lifetime.

All photos and graphic images are by Cayl Hollis unless noted otherwise.

Top image: Partial Photo by Jaksmata
Wikimedia Commons: www.creativecommons.org/licenses/by-sa/3.0/deed.en