Tend & Keep Natural Building · Lesson 1 of 7 · Choosing a method Course home
Natural Building · Lesson 1 of 7

Choosing a method

Cob, straw bale, timber and stone
About 30 min to read5 partsWall calculatorHands-on practice

For most of history, people built homes from what was underfoot and close at hand: earth, straw, timber and stone. Those homes were warm in winter, cool in summer and beautiful in a way that's hard to describe and easy to feel. Natural building brings those materials back, now with modern knowledge and, increasingly, a clear path through the building code.

This course is honest about both sides. Natural walls are healthy, quiet, low in embodied energy and deeply satisfying to build as a family. They're also more labor, need careful protection from water, and take some patience at the building department. The first decision is which method fits your land, your climate and your hands.

By the end of this lesson you will be able to
  1. 1Explain the difference between thermal mass and insulation.
  2. 2Compare straw bale, light straw-clay, cob, timber and stone.
  3. 3Match a method to your climate, budget and skills.
  4. 4Estimate the materials for a small building's walls.
  5. 5Know which methods have a written path in the building code.
Part 1

Two jobs a wall can do

Every wall controls heat in one of two ways. Understanding the difference is the key to choosing well.

A wall can store heat, or stop it. The best homes do both. THERMAL MASS · cob, adobe, stone INSULATION · straw bale, straw-clay day night Soaks up the day's heat, gives it back hours later. Best where days are warm and nights are cool. warm insidecold outside Slows heat from passing through at all. Best where winters are cold or summers hot.
Many natural homes combine them: insulating straw walls outside, with earthen floors, plasters or an inside cob wall for mass.
High desert, Mediterranean

Mass shines

Warm days and cool nights: thick earth walls even out the swing.

Cold winters

Insulation first

Long, cold stretches need walls that hold heat in. Straw leads; add mass inside.

Mild and damp

Breathable and dry

Moisture is the bigger enemy than cold. Big roofs and breathable plasters matter most.

Part 2

The methods, side by side

Insulation

Straw bale

Bales of straw (the stems left after grain harvest) stacked like big bricks and plastered inside and out. Fast walls, excellent insulation, a written path in the building code.

Insulation + some mass

Light straw-clay

Loose straw coated in clay slip and packed into forms around a wood frame. Thinner than bales, easy to fit around windows, also in the code.

Mass

Cob

A stiff mix of clay soil, sand and straw built up by hand in layers, with no forms. Sculptural and strong; best in mild climates or paired with insulation.

Structure

Timber frame

Heavy posts and beams joined with pegs, often filled in with straw. Carries the roof so the walls don't have to.

Mass + durability

Stone

Beautiful, nearly permanent, and slow. Most often used for foundations, garden walls and fireplaces rather than whole houses.

Natural walls are thick. That's part of their beauty.Typical stud wall2×6 framing with insulation6.5 inLight straw-clayabout 12 in, plus plaster14 inStraw baleabout 18 in, plus plaster each side20 inCoboften 18–24 in, thicker at the base22 inStoneoften 18 in or more18 in024 in
Thick walls make deep window seats and sills, and a quiet, solid feel. Plan for them early: a 20×20 ft footprint with bale walls has noticeably less floor space inside than one framed with studs.
MethodInsulationMassLaborCode path
Straw baleExcellentLow (plaster adds some)Fast walls, slow plasterBuilding code appendix
Light straw-clayGoodModerateModerate; needs drying timeBuilding code appendix
CobPoorExcellentHigh; hand-built in layersCode appendix since 2021; local adoption varies
Timber frameDepends on the infillLowSkilled joineryStandard wood codes, often with engineering
StonePoorExcellentVery highMasonry codes; engineering in earthquake country
Part 3

Estimate your walls

Try the 20 × 20 ft footprint from Off-Grid Systems Lesson 1, or the small studio you'll plan in Lesson 7 of this course.

Try it · your own building

What would the walls take?

You'll need
—
The wall
—

Assumes common two-string bales about 14 × 18 × 36 in. Straw bale R-values come from the building code's straw bale appendix: about R-1.3 per inch of thickness laid flat and R-2 per inch on edge. Includes 10% extra for waste. Planning numbers only.

Bale sizes vary. Measure the bales you can actually buy before you finalize a design, and buy dry, tight bales from a grower who stores them under cover. Wet bales can't be dried out once they're in a wall.
Part 4

Mixing methods is normal

The most successful natural homes rarely use one material alone. Each does what it's best at.

  1. A stone or concrete foundation lifts the walls high above splashing rain and damp ground.
  2. A timber or post frame carries the roof, especially where earthquakes or heavy snow make engineering important.
  3. Straw bale or straw-clay walls wrap the house in insulation.
  4. Earthen plasters and floors add mass, breathe moisture in and out, and give the rooms their glow.
  5. A cob bench or interior wall beside the woodstove soaks up heat and holds it all evening.
  6. A wide roof overhang keeps rain off the walls. Builders say natural walls need "good boots and a good hat," which is Lesson 3.
The design opportunity

Natural materials invite curves, niches and hand-shaped details that would cost a fortune in conventional building: a rounded window seat in an 18-inch wall, a sculpted cob bench, a lime-washed wall that glows at sunset. It's where the "wow" lives, made by your own family's hands.

Part 5

A path through the code

Natural building isn't a loophole. Several methods now have their own appendices in the International Residential Code (IRC), the model code most states build on.

MethodCode appendixSince
Straw baleStrawbale Construction (Appendix S, later AS; Appendix BJ in the 2024 IRC)2015 IRC
Light straw-clayLight Straw-Clay Construction (Appendix R, later AR)2015 IRC
CobCob Construction (Monolithic Adobe) (Appendix U, later AU)2021 IRC

Appendices are optional: each state or local building department decides whether to adopt them. The California Residential Code includes the straw bale and cob appendices, but they apply only where adopted, so ask your local building department which ones they accept. Where an appendix isn't adopted, codes still allow "alternative materials and methods" with supporting evidence. Lesson 6 walks through both paths.

The straw bale appendix includes tested fire ratings: plastered bale walls can earn a one-hour rating with clay plaster or a two-hour rating with cement plaster, under specific conditions. Straw packed tight and plastered doesn't have enough air inside to burn easily.
Hands-on practice · one muddy afternoon, plus a week of drying

Make and test sample blocks

Every natural builder starts by testing the local soil. Your family will mix several small test blocks from your own dirt, let them dry, and then test them like engineers.

You'll need

  • Soil from your land (dig below the dark topsoil, where it's more clay)
  • Coarse sand and a handful of chopped straw
  • A bucket, a tarp and old clothes
  • Small molds: milk cartons cut down, or a simple wooden box about 4 × 4 × 8 in
  • A ruler, a spray bottle and markers
  • Your soil jar test results, if you did it in Off-Grid Lesson 3

Do it together

  1. Make three mixes. By volume: 1 part soil to 1 part sand, 1 to 2, and 1 to 3. Add a little straw to each and just enough water to make it stiff, like cookie dough.
  2. Do the ribbon test. Squeeze a mix between thumb and finger into a ribbon. Longer ribbons mean more clay.
  3. Fill and label the molds, pack them firmly, and pop them out after a day.
  4. Let them dry in the shade for about a week. Measure their length before and after to see how much each one shrank.
  5. Test them. Look for cracks, scratch them with a coin, drop them from knee height onto grass, and mist one side with water.
  6. Choose a winner: the mix with few cracks, little shrinking and the hardest surface.
AGES 5–8

Little builders

  • Mix the mud with their feet on the tarp, the way cob is really made
  • Pack the molds and decorate the labels
  • Do the drop test and say which held together
AGES 9–14

Older builders

  • Measure and calculate the shrinkage as a percent
  • Record the results in a table and graph them
  • Run the wall calculator for a building they'd like to make

Keep the best block and your results. You'll use your winning mix in Lesson 5 for plasters.

Closing

Built from the place itself

There's something right about a home built from the land it stands on: walls from the soil under your feet and the straw from a nearby field, shaped by the hands of the family who'll live there. It's slower than a kit and more forgiving than you'd think. And it's beautiful in a way that only comes from care.

Next, before any wall goes up, we design the home itself: small, well-proportioned and full of light.

Worksheet

Your Lesson 1 worksheet

Work through these together. Your answers save on this device as you type, and print cleanly for your records.

For your homeschool records

Progress record

What this lesson practices:

  • ScienceTesting and classifying materials by their properties; designing to reduce heat transfer (NGSS 2-PS1-1, 2-PS1-2, MS-PS3-3).
  • EngineeringPlanning and carrying out fair tests of design options (NGSS 3-5-ETS1-3).
  • MathArea, volume and percent change (Common Core 5.MD.C.5, 6.G.A.2, 7.RP.A.3).
  • HistoryHow people have built with local materials across cultures and centuries.

Standards mapping is a draft. If you use charter or ESA funds, confirm it with your education specialist.

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