Site Preparation

Part of Permanent Shelter

The best-built shelter on a badly chosen site will fail. Water will pool against your walls, frost will heave your foundation, and erosion will undermine everything you built. Site preparation is the work you do before you build — and it determines whether your structure lasts 5 years or 50.

Selecting a Building Site

Not all flat ground is good ground. Walk the area after a heavy rain and observe where water flows, pools, and drains. The ideal building site has these qualities:

Quality	Why It Matters
Slightly elevated	Water flows away naturally, reducing flood risk
Gentle slope (2-5%)	Allows drainage without requiring major leveling
South-facing (Northern Hemisphere)	Maximizes winter sun for warmth and light
Protected from prevailing wind	Reduces heat loss and structural stress
Well-drained soil	Prevents foundation settling and moisture problems
Away from large trees	Roots damage foundations; falling limbs damage roofs
Access to water source	Close enough for daily use, far enough to avoid flooding

Sites to Avoid

• Valley bottoms and hollows — Cold air sinks and pools here. These are frost pockets and flood zones.
• Hilltops — Maximum wind exposure. You will burn more fuel heating and spend more effort on repairs.
• Directly beside rivers or streams — Flood plains can extend much farther than you expect. Look for high-water marks on trees and banks.
• Under cliff faces or steep slopes — Rockfall and landslide risk.

Reading the Terrain

Before clearing anything, spend time observing:

Water signs: Lush green vegetation in a dry period marks underground water or poor drainage. Moss on the ground means persistent dampness. Erosion channels show where water flows during storms.

Wind signs: Trees leaning one direction reveal prevailing wind. Build your long axis perpendicular to wind direction, with your entrance on the sheltered side.

Sun path: Stand on your proposed site at midday. Note where shadows fall. In winter, the sun is lower — ensure your site gets direct sunlight from the south during the coldest months.

Clearing the Site

Once you have chosen your location:

1. Remove all vegetation within your building footprint plus 1 meter (3 feet) on each side. Pull roots — do not just cut them at ground level. Roots left in the ground will rot, creating voids beneath your foundation.

2. Remove the topsoil layer. The dark, organic top layer (usually 15-30 cm / 6-12 inches) is too soft and compressible for building. Scrape it away down to the subsoil — the lighter-colored, firmer layer beneath. Save the topsoil for gardens.

3. Remove any large rocks that sit partially buried. They create uneven support points and can channel water toward your foundation.

Save Your Materials

Cleared timber becomes building material. Removed topsoil goes to garden beds. Dug stones become foundation material. Nothing should be wasted.

Leveling the Ground

A level building site is critical. Even a few centimeters of unevenness across a foundation creates problems that worsen under load.

The Water Level Method

You do not need modern tools. Fill a length of hollow reed, bamboo tube, or animal intestine with water, leaving both ends open. Hold one end at your reference point and the other at the point you want to check. Water seeks its own level — when the water surface is at the same height at both ends, those two points are level.

Step-by-Step Leveling

1. Set a reference stake at the highest corner of your site. Mark it at the height you want your finished ground level.

2. Check all other corners against this reference using your water level. Mark the difference on each stake.

3. Cut high spots by scraping away soil with a flat stone or wooden blade. Move this soil to low spots.

4. Compact filled areas by tamping — use a heavy flat stone on a handle or a thick log stood on end. Drop it repeatedly across the filled area. Loose fill will settle under your building if not compacted.

5. Re-check level after compacting. Filled areas always sink slightly.

Error	Consequence	How to Prevent
Fill not compacted	Foundation settles unevenly over months	Tamp in 10 cm layers, water each layer
Organic material in fill	Decomposes, creates voids	Use only mineral subsoil for fill
Leveled too large an area	Wasted effort, disturbed drainage	Level only the building footprint plus 1 m margin

Establishing Drainage

Water must flow away from your structure, not toward it or under it.

Surface Grading

The ground around your building should slope away at a minimum grade of 5% — meaning a drop of 5 cm for every 1 meter of distance (about 1/2 inch per foot). This applies for at least 2 meters (6 feet) out from your walls in all directions.

Drainage Channels

If your site has water flowing toward it from uphill, dig a diversion channel (swale) upslope of your building:

1. Dig a trench 30-45 cm deep (12-18 inches) and 30 cm wide across the uphill side of your site, angled to divert water around the building.
2. Line the bottom with gravel or small stones if available.
3. Direct both ends of the channel to natural drainage paths that lead away from your site.

The French Drain

For persistent ground moisture, dig a trench alongside your foundation, fill the bottom half with gravel, and lay a channel of overlapping flat stones on top. Cover with more gravel, then soil. This invisible drain pulls water away from your foundation underground.

Understanding the Frost Line

In cold climates, water in the soil freezes and expands during winter. This expansion — frost heave — can lift foundations, crack walls, and destroy a structure in a single season.

The frost line is the maximum depth to which soil freezes in your area. Any foundation must extend below this depth, or it will be pushed upward by freezing soil.

Frost Line Depths by Climate

Climate	Typical Frost Line Depth
Tropical / subtropical	0 cm — frost is not a concern
Mild temperate	30-45 cm (12-18 inches)
Cold temperate	60-90 cm (24-36 inches)
Severe continental	90-150 cm (36-60 inches)
Subarctic	150-250 cm (60-100 inches)

Determining Your Local Frost Line

If you do not know your climate zone, observe:

• How deep does ice form on ponds? Multiply by 3-4 for approximate soil frost depth.
• Where do plant roots survive winter? Perennial roots that survive give you a minimum frost-safe depth.
• Ask locals if any remain — traditional builders always know frost depth.

Digging Below the Frost Line

1. Dig your foundation trenches or pier holes to at least 15 cm (6 inches) below the frost line.
2. Fill the bottom with gravel — this drains water away from the base, reducing the amount of moisture available to freeze.
3. In extremely cold areas, insulate the outside of your foundation with dry materials (straw, bark, dry leaves packed against the wall) to slow heat loss from the ground.

Frost Heave Destroys Gradually

Frost heave does not happen all at once. Each freeze-thaw cycle lifts the foundation a small amount, but it rarely settles back to its original position. After several winters, a foundation placed above the frost line can be 10-15 cm higher on one side than the other.

Final Site Checklist

Before laying any foundation, confirm:

• Topsoil removed down to subsoil across entire footprint
• Ground level checked at all corners and center points
• Fill areas compacted in layers
• Ground slopes away from building on all sides (5% minimum)
• Uphill drainage diverted around the site
• Foundation depth planned below frost line (cold climates)
• No standing water within 3 meters of the building footprint after rain

Key Takeaways

• Site selection is the most important construction decision — no amount of building skill overcomes a bad location.
• Remove all topsoil — organic soil compresses and decays, undermining anything built on it.
• Level carefully and compact thoroughly — uneven settling is the most common cause of structural failure.
• Slope everything away from the building — 5% grade for at least 2 meters in all directions.
• Dig below the frost line in any climate with freezing winters, or frost heave will destroy your foundation.
• Observe before you build — watch water flow, wind direction, and sun patterns before committing to a site.