Drying old Historic Norcross structures

Drying modern drywall quickly does little harm. Drying old wood quickly can crack, split and twist it. Many of the 194 contributing buildings in the Norcross Historic District have aged timber, trim and floors that have reached a stable moisture level over generations. ^[1] A sudden drop in humidity around a wet area puts stress on them, so a skilled operator may hold humidity at a moderate level and take longer over the job. That is a reasonable choice as long as moisture readings keep moving the right way.

Measuring old walls takes care too. A pin meter reads the surface, and plaster can feel dry while the lath behind it remains damp. Readings at several depths and over several days are more reliable than one, and a dry reference point from an unaffected room in the same house is especially valuable because old materials vary so much.

Some older houses were built with stud bays running from the sill to the attic. Moisture can travel up those bays, and water from an upper floor can reappear lower down in places you would not expect. For drying, the open bay can help: dry air fed in at the bottom can move upward through the wall without much opening up. A small hole behind a baseboard, patched afterward, may do the job of a far larger cut. Ask if this has been considered before anyone proposes removing large areas of plaster.

Do check for insulation first. Blown-in material added at a later date can fill those cavities and hold water. If you are unsure what is in the walls, a small inspection hole answers the question, and older loose-fill should be tested before it is disturbed.

In a house on piers, the floor above can dry only as fast as the air beneath allows. If the soil below is damp, joists and floorboards keep drawing moisture from it. Modern practice often starts with covering the ground, removing any wet insulation and using a dehumidifier in the crawl space if it can be enclosed well enough. ^[3] Open foundations cannot be closed in the same way without consequences for appearance and airflow. Have that discussion with someone who understands older buildings, and check with the city first about anything visible from outside. ^[4]

Expect it to take longer than the typical three to five days often quoted for an ordinary clean-water job. Old plaster, thick timber and damp crawl spaces can take more time, and you should plan accordingly. Keep the equipment running as advised and resist the urge to repaint early. After the equipment leaves, keep an eye on the readings for a couple of weeks if you can, particularly on floors, because old wood can continue to move as seasonal humidity changes. A hygrometer in the room is a useful companion for that.

An old house is affected by the season in which it gets wet. In a humid Georgia summer, the challenge is getting the air dry enough while the building leaks at every window sash, so temporary sealing of a contained room can matter more than extra machines. Single-pane windows may run with condensation next to a dehumidifier, and it is worth wiping them so that sills and old paint stay dry. In winter, cold rooms slow evaporation, and a modest amount of heat may help, provided it is raised gradually. Whatever the season, watch doors and windows as drying continues, because wood that has swollen will shrink back and may bind or gap in the process. Do not plane or trim a sticking door until the building has settled, since the problem often disappears on its own. Take a few photographs of joints in trim and floor at the start of the job and at the end. They will help you see what moved, and whether it has settled.

That record is also useful for later owners.