This is the lesson most families look forward to: raising the walls. With the foundation set and the roof plan in hand, a crew of friends and family can stack the bales of a small home in a weekend. It's one of the last great community building traditions, like the barn raisings of old.
We'll cover the two straw methods with clear paths in the building code: straw bale, which stacks whole bales like giant bricks, and light straw-clay, which packs clay-coated straw into forms. Both make warm, quiet, thick walls.
- 1Choose between load-bearing and infill straw walls.
- 2Buy, store and stack bales the right way.
- 3Plan courses, offsets and wall heights within the code's limits.
- 4Mix clay slip and build a light straw-clay wall.
- 5Run a safe, happy work party.
Load-bearing or infill
The bales hold up the roof on a wooden box beam. It uses less lumber and is beautifully simple. The code allows it for one-story buildings, sets limits on how much weight each foot of wall can carry, and requires the walls to be compressed (squeezed down) before plastering so they don't settle later.
A timber or post-and-beam frame carries the roof, and the bales are stacked around or between the posts. The roof can go on first, so the bales stay dry while you work. Engineers and inspectors know how to check a wood frame, which makes approvals easier, especially where earthquakes are a concern.
Straw bale, step by step
- Buy good bales. Tight, dry bales of wheat, rice, barley or oat straw, not hay (hay has seed heads and leaves that rot and attract pests). The code requires at least 6.5 lb per cubic foot and no more than 20% moisture.
- Keep them dry. Store bales off the ground on pallets, under a roof or tarps, and have them delivered close to when you'll use them.
- Start on the toe-up. Lay the first course on the raised sill from Lesson 3, pinned or tied down.
- Stack in running bond. Offset each joint at least a quarter of a bale from the one below, like brickwork.
- Make custom bales. Use a bale needle to retie a bale into shorter pieces for corners and openings.
- Stuff every gap. Fill gaps up to 4 inches wide with flakes of straw or straw-clay, packed tight.
- Frame the openings. Set wooden window and door boxes (bucks) as you go and fasten the bales to them.
- Cap and tighten. Finish with a top plate or box beam, and compress load-bearing walls before plaster.
- Trim and check. Shave the wall faces flat with a string trimmer, then check moisture before the first coat of plaster.
How high, and how many rows?
From the straw bale appendix: unrestrained wall height is limited to a multiple of the bale thickness, from 5 times (plain plaster) to 8 or 9 times (pins or reinforced plaster), with absolute limits of 8 to 12 ft depending on wind and finish. Joints must be offset at least a quarter bale. Check the code table for your exact case.
Light straw-clay
Light straw-clay (sometimes called slip-straw) is loose straw tossed in a runny clay mix, then packed lightly into forms around a wood frame. When it dries, it's a light, insulating, fire-resistant wall that's easy to shape around windows and odd corners.
R-1.6 per inch
The code's value. A 12 inch wall is about R-19, close to a standard 2×6 wall.
12 inches or less
The code limits it to 12 inches so the wall can dry all the way through.
Infill only
It doesn't carry the roof. A wood frame does, usually one story unless a professional designs it.
How it's made
- Make the slip. Soak clay soil or bagged clay in water and stir it into a smooth slip about as thick as heavy cream.
- Toss the straw. Spread straw on a tarp, pour slip over it, and toss it like a salad until every stem is coated but not dripping.
- Fill the forms. Clamp boards or plywood to the frame, drop in the straw-clay, and tamp it lightly, especially at the edges and corners.
- Slide up. Move the forms up and keep going. The mix holds its shape right away.
- Let it dry. Build in warm, dry weather. The code requires 20% moisture or less at 4 inches deep before plastering, which can take weeks.
A safe and happy work party
Wall raisings are joyful, crowded, busy days. A little planning keeps everyone safe and makes sure the work is good.
- Loose straw burns fast before it's plastered: no smoking, sparks, grinding or welding near it
- Fire extinguishers and a charged hose on site
- Sweep up loose straw at the end of every day
- Dust masks for shaking out straw, and gloves for bale twine
- Bale needles and string trimmers handled only by adults
- Lift with legs, and carry heavy bales in pairs
- Little ones: carry flakes for stuffing and stomp slip on the tarp
- Older kids: stuff gaps, measure and mark offsets, tie custom bales with help
- Adults: stack, pin, set bucks and run the tools
- One crew leader who checks every course for level and offset
- A cook and a water station. Feeding the crew is half the tradition
A wall raising is a gift your family gives and receives. Neighbors who helped stack your walls will always feel part of your home, and you'll owe them a day on theirs. That's how communities used to be built, and it still works.
Build a straw-clay or bale test wall
Build a small test panel your family can learn on, then track how fast it dries by weighing a sample, just like a building scientist.
You'll need
- A small frame: four 2×4s screwed into a 3 × 3 ft square, set on bricks or a pallet
- Two boards or plywood strips for slip forms, and clamps
- Clay soil or bagged clay, water, a bucket and a tarp
- A bale of straw (not hay)
- A kitchen or postal scale
- Or for bales: three bales, a pallet, and wooden stakes for pins
Do it together
- Mix the slip and check it coats your hand like heavy cream.
- Toss the straw on the tarp until it's evenly coated.
- Fill the frame with forms clamped on both sides, tamping lightly, then slide the forms up and finish.
- Make a sample brick from the same mix in a small box, weigh it, and write down the weight.
- Weigh it daily for two weeks and graph the weight. When it stops dropping, it's dry.
- For bales: stack three bales on a pallet in running bond, pin them with stakes, and stuff the gaps.
Little builders
- Stomp the slip on the tarp
- Toss the straw and carry it to the forms
- Read the scale each day with help
Older builders
- Run the course calculator for your Lesson 2 plan
- Graph the drying curve and calculate the percent of weight lost
- Measure and mark joint offsets on the bale test
Keep the test panel. In Lesson 5 you'll plaster it.
Thick walls, warm hearts
There's a moment, when the last bale goes in, when everyone steps back and sees the shape of a home standing where there was only a foundation that morning. It's thick, golden and quiet inside, and it was raised by your family and friends together.
Next, we cover those walls with earthen and lime plasters, and lay a floor of earth you can live on.
Your Lesson 4 worksheet
Work through these together. Your answers save on this device as you type, and print cleanly for your records.
Progress record
What this lesson practices:
- EngineeringDesigning within constraints and testing a prototype (NGSS 3-5-ETS1-1, MS-ETS1-3).
- ScienceProperties of materials and evaporation (NGSS 2-PS1-1, 5-PS1-1).
- MathMeasurement, division with remainders and graphing data over time (Common Core 4.MD.A.1, 4.NBT.B.6, 6.SP.B.4).
- Life skillsSafety, teamwork and organizing a group project.
Standards mapping is a draft. If you use charter or ESA funds, confirm it with your education specialist.
Sources for this lesson
- 2015 IRC Appendix S — Strawbale Construction (bales, stacking, height limits)
- ICC — 2024 IRC Appendix BJ, Strawbale Construction
- ICC — 2015 IRC Appendix R, Light Straw-Clay Construction
- Straw Bale Studio — light straw-clay code summary
- California Straw Building Association — Appendix AS and AR with commentary