Closing a Tahoe Second Home for Winter

The U.S. Department of Energy’s consumer guide to home heating puts the case for a setback plainly: you can save 1 percent on heating bills for each degree Fahrenheit you set it back during an eight-hour period, and as much as 10 percent on heating and cooling costs by setting back when you are not at home. Nothing in this guide argues against it; the cabinetry does not care what the number on the thermostat is.

What the cabinetry does care about is relative humidity, and relative humidity changes when temperature does. The Forest Products Laboratory’s Wood Handbook tabulates the moisture content wood settles at for a given temperature and relative humidity, and the table shows that temperature alone does almost nothing: at 30 percent relative humidity, wood equilibrates at 6.3 percent moisture content at 30 degrees Fahrenheit and 6.2 percent at 70. Relative humidity is the whole story. At 70 degrees the same table runs from 4.5 percent moisture content at 20 percent relative humidity to 9.2 percent at 50 percent and 11.0 percent at 60. A door pushed from the middle of that range to the bottom of it in an afternoon is being asked to shrink across every wide piece of solid wood in it.

That is exactly what a rapid warm-up does. The air in a cold house holds a certain quantity of vapour; heat the same air quickly and its relative humidity falls, so the wood begins chasing a drier room than the one it sat in all week. Thin door skins and the faces of panels follow the air within hours. The core of a thick solid panel follows over days. In between, the two are at different moisture contents, and a panel in that state cups. The checklist consequence is one line: program the rise, not just the setback. A thermostat told to begin warming the house a day or two before arrival turns a one-hour swing into one the wood can follow evenly.

The Wood Handbook’s recommended moisture content for interior woodwork, flooring and furniture at the time of installation is an average of 8 percent for most areas of the United States, 6 percent for the dry southwestern area, and 11 percent for the damp, warm coastal area, with individual pieces allowed a range on either side. A Sierra house in the heating season sits toward the dry end of that spread. Cabinetry built in Rocklin and acclimatised in the conditioned house, as the mountain home guide describes, arrives at the right starting point; the closing routine is about not driving it past the low end faster than it can follow.

An unheated, winterised house does the opposite. With no furnace running, the interior tracks outdoor humidity through the winter, and the Wood Handbook’s outdoor equilibrium table for Reno, the nearest station it lists to the lake, runs from 12.3 percent in January down to 7.7 percent in July. The wood in a cold, closed house spends the winter at the top of its annual range, not the bottom, and the moment of risk is the day the house is reopened and heated, when the drying described in the setback section happens from a higher starting point and all at once. The checklist consequence is the same instruction read in reverse: reopen slowly. Heat the house over a day before the first big meal is cooked, and open the cabinet doors before the furnace comes on rather than after.

This guide does not recommend a humidity target for an empty house or a humidifier in one; an unattended humidifier is a water source nobody is watching, and the Department of Energy’s caution to keep a summer system running to avoid moisture build-up that could produce mould is a reminder that an unoccupied house fails damp as often as dry. A hygrometer left on the counter and read on arrival tells you which regime yours is in.

Pantry pests — the moths, beetles and weevils in flour, cereal, pet food and birdseed — arrive in the food itself and breed in what is left behind. The UC Statewide Integrated Pest Management Program’s pest note on the subject is direct: store food and bulk goods like pet food in containers with tight-fitting lids, not plastic bags; throw away any food that has evidence of infestation; vacuum corners and crevices of cupboards to get rid of insects and wash shelves with soap and water. It is equally direct that insecticides are not recommended for controlling pantry pests, and that spraying pesticides on or near food may cause greater harm to a household than the pests would. For a house being closed: everything in a bag or box leaves with you or goes in the bin, what stays goes into sealed containers, and the shelves and corners are vacuumed with the crevice tool before the door is left ajar.

Mice are a construction problem more than a cleaning one. The same program’s note on the house mouse states that mice can enter through openings as small as a quarter inch, and that plastic screening, rubber, vinyl, insulating foam, wood and other gnawable materials are ineffective for plugging holes. Wire screen or coarse steel wool that mice cannot chew through are the materials it recommends, with the caution that steel wool may rust over time. In a kitchen the openings that matter are the ones a cabinetmaker leaves on purpose — the cut-outs around supply lines and drains in the sink base, the gap behind a dishwasher, the hole for a range cord — and they close easily with mesh once you know to look. Droppings, fresh gnaw marks and a musky odour are the signs to check for on reopening day.