HOW TO BUILD YOUR OWN IGLOO

OUR EXPERT: SNOW ENGINEER

1. CUT BLOCKS OF SNOW Grab an old carpenter's wood saw. Find a large patch of tightly packed snow—similar to the density of a snowball— and cut about 50 blocks that measure 18 inches long, 9 inches thick and 12 inches tall.

2. PREPARE YOUR BASE Create a ring of blocks in the snow. Then cut a gradual rise across the tops of half the blocks, starting from the base of one and rising through adjacent blocks to the top of the block positioned directly across the ring. Cut the interior edges of all the blocks so they slant slightly down toward the inside of the igloo.

3. STACK THE BLOCKS Layer blocks on the base, cutting the sides of each so they fit tightly together. Enlist a friend to stand inside and support the walls as you stack. Cut the ceiling block slightly larger than the space it will fill, then taper the sides so it fits like a cork in the dome.

4. MAKE A DOOR To get inside your igloo—and free your friend now trapped inside—cut a door. Find a header—a block that sits on top of two other blocks—and make an arch-shaped cut from its center all the way to the ground. Remove the snow cutout, then come and go as you please.

Yankielun, who lives inMaine, isthe author of How to Build an Igloo (W.W.Norton,2oo7)andruns www.doctorwhy.com. Hemajored in engineering.