Track 2: The small home

15 diagrams.

CondensationInWall

Air leaking through a gap carries far more moisture into a wall than vapor seeping through solid materials. On a cold surface, it turns to water.

Text description

A cutaway of an insulated wall in winter, outside on the left and inside on the right. From outside in, the layers are siding, a drainage gap and weather barrier, sheathing, insulation and drywall. It is cold outside and warm and moist inside. Warm, moist indoor air leaks through a gap in the drywall, such as around an outlet box, and moves up through the insulation to the cold back of the sheathing. There the vapor turns to liquid water. Wet insulation loses insulating value, and mold and rot can follow. Short arrows show that a little vapor also seeps slowly through the solid drywall, carrying much less water than the leak.

ControlLayers

Each control layer should wrap the whole house without a break. Trace each one around a drawing and ask about every gap.

Text description

A simplified cross-section of a small house showing the control layers as continuous loops, listed in order of importance. 1, water: the outer skin of roofing, siding and the weather barrier behind it sheds rain. 2, air: an air barrier inside, sealed at every seam and gap. 3, vapor: whether you need a vapor retarder, and where it goes, depends on climate zone, so it is not drawn. 4, heat: a band of insulation unbroken around the whole house, roof, walls and floor. Near the left eave, the air barrier has a gap, labeled: a break in the air layer, ask how it is handled.

FootprintShapes

Same floor area, different outlines. The square has the least wall, the rectangle the longest south side, and the L-shape the most wall and corners.

Text description

Three floor outlines seen from above, each with 576 sq ft (about 54 m²) of floor, with south at the bottom. A 24 by 24 ft square has 96 ft (29 m) of outside wall, a 24 ft (7 m) south wall and 4 corners. A 16 by 36 ft rectangle with its long side south has 104 ft (32 m) of outside wall, a 36 ft (11 m) south wall and 4 corners. An L-shape has 112 ft (34 m) of outside wall, 24 ft of south-facing wall in two parts, and 6 corners. South walls are drawn with a heavy line.

FootprintsToScale

Six small-home types drawn from above at the same scale. The trailer and container types are far narrower than the rest.

Text description

Six floor footprints seen from above, all at the same scale, with a 20 ft (6 m) scale bar. The sizes are examples, except the widths the lesson gives. From left: a tiny house on wheels, 8.5 ft (2.6 m) wide, the legal width on major highways, with a trailer hitch at one end; a cabin on a fixed foundation; a small conventional home built on site, the largest outline in the group except the modular; a modular home made of two factory sections joined down the middle; a shipping container home, about 8 ft (2.4 m) wide and long and narrow; and an earth-sheltered home with soil banked against three sides. A dashed square on the small conventional home shows 400 sq ft (37 m²), the size limit in the IRC tiny house appendix, not counting lofts.

FoundationTypes

Four common foundation types. In cold places each one reaches below the local frost depth or uses a frost-protected design.

Text description

Four simplified sections side by side, not to scale and with no dimensions. Slab: a concrete pad poured on the ground, with insulation laid out flat around its edge, one kind of frost-protected design. Crawlspace: short foundation walls that reach below the frost depth, with a floor above and a crawl space under it. Basement: deep foundation walls with a full room below ground and a concrete floor. Piers: posts or columns that go down below the frost depth to firm soil, holding the house up above the ground. A dashed line across all four marks the local frost depth, which your building department sets.

GlazingByOrientation

Window area by side for a cold or mixed US climate: most glass on the south, some on the east, little on the west and north.

Text description

A plan view of a rectangular house, north at the top, with its long side facing south. Windows are drawn on each wall. South: most of the glass, because the low winter sun shines in and the high summer sun is easy to shade. East: some glass, for morning light, though low summer morning sun is hard to shade. West: limited glass, because hot summer afternoon sun is hard to shade. North: small windows, which give soft light but get little direct sun and mostly lose heat. A shaded wedge below the house shows that passive solar glass should face within about 30 degrees of true south.

HrvExchange

An HRV swaps stale air for fresh air and passes heat from the outgoing stream to the incoming one. The two streams never mix.

Text description

A schematic of a heat-recovery ventilator, outside on the left and inside on the right. Stale, warm air from the kitchen and bathroom enters the unit from the inside and crosses a core. Fresh, cold outdoor air enters from the outside and crosses the same core in a separate path. In the core, heat passes through thin walls from the warm stale air to the cold fresh air, but the two airstreams do not mix. The fresh air goes on to the rooms, warmed. The stale air goes outside as exhaust, cooled. An ERV works the same way and also passes some moisture. The unit has fans and filters, so it uses some electricity and the filters need cleaning.

HumidityRange

Keep indoor humidity below 60 percent, and ideally between about 30 and 50 percent.

Text description

A horizontal scale of indoor relative humidity from 0 to 100 percent. Below 30 percent is marked drier than ideal. From about 30 to 50 percent is marked ideal. From 50 to 60 percent is still acceptable. A heavy line at 60 percent marks the EPA advice to keep humidity below 60 percent. Above 60 percent, condensation and mold are more likely. A marker at 70 percent shows a winter-morning reading that is too damp.

LoadPath

The load path: weight travels from the roof, through the framing and walls, into the foundation and out into the soil, with no breaks.

Text description

A simplified cross-section of a small house, not to scale. Snow load presses down on the roof. Arrows trace the load down the roof slopes to the walls, down the walls to the foundation, and out into the soil, where it spreads. The parts are numbered in order: 1 roof covering, 2 roof framing, 3 walls or posts, 4 floor framing, 5 foundation, 6 soil. Inside, live load from people, furniture and stored food presses on the floor. On the left, wind pushes sideways on the wall and can lift the roof, so a dashed line shows that the parts must be tied together from roof to foundation. A note says this is a concept only, and that sizes, spans and connections come from the code, an engineer or a licensed builder.

PermitPath

The usual path from permit to move-in. Work must stay open until it is inspected, and plan review can send you back for changes.

Text description

A step-by-step flow from top to bottom. 1, zoning check: confirm the use and placement are allowed. 2, permit application: submit plans, a site plan and fees. 3, plan review: the department checks the plans and may ask for changes, which loops back to the application. 4, inspections during building: often at the foundation, at framing, at rough-in, when wiring, plumbing and ducts are in but walls are still open, at insulation, and others as required. Keep work open until it is inspected. 5, final inspection: the inspector checks the finished work. 6, certificate of occupancy: the document that says the home can be lived in. A note says the details vary by place.

RValueHeatFlow

Doubling the R-value roughly halves the heat that flows through. Each extra step costs more insulation for a smaller saving.

Text description

Three blocks of insulation side by side, with the warm inside on the left of each and the cold outside on the right. The first is R-15 and lets a set amount of heat through, shown as four arrows. The second is R-30, twice as much, and lets about half as much heat through, shown as two arrows. The third is R-60, four times as much, and lets about a quarter through, shown as one arrow. A note says the wall area and temperature difference are the same in all three.

SampleFloorPlan

A sample small plan: long side to the south, living space and most glass on the south, bedroom and bath on the north, kitchen and bath sharing a wet wall.

Text description

An example floor plan seen from above, north at the top, 32 by 18 ft (about 9.8 by 5.5 m), with a scale bar. It is a planning sketch, not for construction. Along the north side, from west to east: a bedroom with a window for light and escape, a bathroom, a storage closet, and an entry with two doors, an outer door and an inner door, to keep cold air out. Along the south side is one open room: a living area to the west and a kitchen to the east. Part of the kitchen sits right below the bathroom, so they share one wet wall and the water and drain lines stay short. Most of the windows are on the south wall, where low winter sun comes in. The east wall has one window for morning light, the west wall one small window, and the north wall two small windows.

ThermalMassDay

Sun through south glass arrives in a few midday hours. Thermal mass soaks it up and gives it back slowly through the evening and night.

Text description

A chart of one sunny winter day from midnight to midnight, shape only, not to scale. A tall, narrow hump shows heat from the sun coming through south glass, from about 8 am to 4 pm, peaking at noon. A lower, wider hump shows heat given back by thermal mass, such as a concrete or tile floor in the sun. It starts in the late morning, peaks in the evening and tapers off through the night toward dawn. Night hours are shaded at both ends of the chart.

ThreeRuleSets

Three sets of rules, often from three offices: zoning says what goes where, building codes say how, and health rules cover septic and wells.

Text description

A diagram with your project at the top and arrows to three boxes. Zoning: what can go where, such as allowed uses, minimum home size, setbacks from property lines, and RVs as full-time homes; handled by the zoning or planning office. Building codes: how it is built, covering structure, fire safety, electrical, plumbing, heating and energy, through model codes such as the IRC, IECC, NEC and the UPC or IPC; checked by the building department. Health rules: septic systems and private wells, such as whether a septic system can work and where a well can go; often handled by a county or state health office. A dashed box at the bottom says to also check private rules, such as deed restrictions and homeowner association rules. Offices and names vary by place.

VentilationTypes

Exhaust and supply systems use one fan and rely on leaks for the other half of the swap. A balanced system controls both paths.

Text description

Three small house sections side by side. Exhaust ventilation: a fan in the wall pulls stale air out, and fresh outdoor air leaks in through gaps wherever it can. Supply ventilation: a fan pushes fresh air in, and stale air leaks out through gaps. Balanced ventilation: one fan brings fresh air in and another sends the same amount of stale air out. An HRV or ERV, shown separately, is a balanced system that also passes heat between the two airstreams.