48 Inches of New Hampshire Frost. Build Under It or Rebuild It.

Where to start on your project

Start with the structure that holds back the most weight or carries the most traffic. In New Hampshire, that is usually a retaining wall or a gravel driveway. Both have to deal with deep frost and the glacial till underneath.

• Retaining walls that hold back soil and stay plumb through the freeze-thaw cycle.
• Gravel driveways built on a 3/4 inch crushed gravel base that sheds water instead of trapping it.
• Paver patios off a dooryard or a walkout that stay level.
• Walkways and steps that connect a mudroom entry to the driveway.
• Paver driveways for a front approach that needs to carry a plow.
• Grading and drainage to move water away from the foundation before it freezes.

The part before the shovel

You get a written price before any ground is opened. The quote covers the dig, the base, the material, and the machine time the site demands. You know what the job costs before you commit.

From there, the work follows a set order. The site is marked, the dig goes to depth, the 3/4 inch crushed gravel goes in and gets compacted in lifts, and the surface goes down last. You need to be present for the start to confirm the layout. You do not need to be there for the compaction passes or the surface work. You can follow the whole sequence on the process page and see what drives the price on the cost guide.

Why the dig is the whole job in New Hampshire

Frost does not push down. It pulls up. When water in the soil freezes, it expands and lifts whatever sits above it. A patio slab that was laid on top of the ground will heave unevenly by spring. A wall that was not tied back will go out of plumb as the soil behind it freezes and thaws.

The depth changes across the state. In the Seacoast and around Manchester and Nashua, plan for about 48 inches. In Concord and the Lakes Region, the line stays similar. In the White Mountains and North Country, frost runs 60 inches or more. A base that works in Nashua may not work in Littleton.

The second problem is the soil itself. Glacial till with boulders and ledge sits under much of the state. Sand and gravel fill the Merrimack valley, and clay sits in the seacoast lowlands. Each one behaves differently when it freezes. Clay holds water and heaves the most. Till and ledge make the dig harder but drain better once they are opened.

Where the base has to start

The base has to start below the frost line. For most of New Hampshire, that means the bottom of the excavation sits at roughly 48 inches. In the North Country, it sits deeper. The 3/4 inch crushed gravel goes in from that point up, compacted in lifts so it locks together and cannot shift.

Under NHDOT Item 304, crushed gravel is the specified base material for this kind of work. In the yard, it is called 3/4 inch crushed gravel. The name does not change what it does: it drains, it locks, and it does not hold water the way clay does.

Drainage is part of the base. A retaining wall gets free-draining backfill behind it so water does not build up and freeze behind the face. A patio gets a drainage layer below the gravel so water moves out to the edge instead of pooling under the pavers. Taller walls get geogrid to tie the wall back into the slope behind it.

The season window runs from roughly April to November. Mud season slows the start, and frozen ground stops compaction in winter. That window sets the pace for the work.

What makes a New Hampshire job cost what it costs

Three things drive the price. Deep frost sets the excavation depth, which means more material moved and more gravel placed. Ledge and boulders in the dig add machine time, and that time is unpredictable until the ground is open. The short season means the work has to happen in a tight window, and that affects scheduling.

Granite is local, which keeps the cost of wall stone and steps down. The cost is in the ground, not the surface.