Most of the permanent winter quarters were constructed with red cedar planking. The sleeping areas were down the two sides of the longhouse, and the cooking fires were down the center. Each cooking fire would accommodate two families, one family on each side of the longhouse; hence, a five fire longhouse could accommodate ten families, and a nine fire longhouse could accommodate eighteen families. The size of a longhouse was known by its number of fires. Each longhouse may accommodate 80-100 people. It was not uncommon for these longhouses to be 100 feet long. One on the northwest coast was known to be 900 feet in length and nearly 100 feet wide. Each longhouse sheltered all of the living members of an extended family of several generations.
The apartments for the different households were laid out with poles laid along the earthen floor, and held in place with short stakes. An aisle was made by first laying two poles parallel down the center. Poles were laid out on the ground at right angles on either side, forming squares. These were the apartments. There were no partitions. Beds were placed along the outside walls of the house. They were double-deck affairs, made of boards which somewhat resembled a Pullman’s berth. There was usually a space between the bed and the outer wall where the sleeper kept his/her valuables in a box or woven basket. Their clothing was also kept in these boxes or woven baskets. The bed "springs" consisted of split planks. These were softened by the use of numerous furs laid on top of these boards. Furs were also used for blankets. These furs were softly tanned and were taken from the mountain lion, the bear, and other animals of the forest. The wealthy could afford the furs of the sea otter. These furs were a great nesting place for fleas and other insects, but the Cowlitz had the powerful hellebore root which kept their beds free from these pests.
The smoke from the numerous family cooking fires would fill the longhouse, but it was no problem, for they would simply take a pole which was kept for that purpose and push aside one of the roof planks, which then created a great roof vent for the smoke to escape.
A giant cedar tree was required to provide the ridge pole that held up the roof. The ridge pole was held up with house posts that were carved with the totems of the longhouse.
The summer temporary gathering stations (for berries, roots, bark, etc.) were lightly framed structures covered with matting. Occasionally, hunting parties constructed temporary cedar bark lean-tos at favorite game sites. Their residence was patrilocal.
The permanent winter villages contained the great cedar-planked longhouses. About the first of May they abandoned these permanent winter villages and erected mat lodges on the prairies of the same type as their cedar-plank longhouses. Two months later, having harvested and either cooked or dried their roots, they moved up into the hills where the berries grew abundantly. These summer camps were occupied for weeks at a time at the major resource locations with hundreds of people gathering for short periods of time.
Governor George Simpson reported in 1829 regarding natives living on the northern bank of the Columbia: "The country is densely inhabited … much greater than any other part of North America I have visited … the shores are actually lined with Indian lodges." It is possible that Simpson saw Chinook villages, because the Chinook lived on the north bank of the Columbia, while the Cowlitz lived back from the Columbia River about a half-mile or so. It was reported that there were approximately 50,000 Cowlitz Indians living at that time.