Trained Eye


Wood Panelling


I enjoy your questions and answers in the Free Press very much.  My question relates to use of wood for ceiling, walls and floor in an unheated extended season sunroom, which I am planning to build this summer.  The sunroom will be fully insulated but will have no heat.  For occasional use in early spring and late fall we will plug in an electric heater to take out the chill, but during the winter there will be no heat.

My concern relates to expansion and contraction of the materials I plan to use, as relating to extremes in temperature and humidity.  I am planning to use 1/4" x 4" knotty pine on the walls and ceiling, treated with Watco Danish oil.  For the floor I am planning to use laminate flooring, the type that locks together.  Will the changes in temperature and humidity create gaps or warping, depending on the season.


Unheated additions, such as the sunroom you are planning, may indeed be subject to more effects of seasonal changes in temperature than the heated homes they are attached to. There are other issues to consider, as well as choice of wall and floor coverings, and we will explore some of these.

First, to answer your question, the wood panelling and laminate flooring may be affected dramatically by the change in temperature as well as dryness, mainly in the winter. Wood panelling may be one of the best choices for wall coverings in this addition, but not the thin ¼” material you are suggesting. This material if very thin and must be installed over a backing material, such as drywall or plywood to have proper support. I have seen this material, especially pine, shrink as much as 10 to 25% in the first year after installation. It is often dramatic enough that the material has to be removed and reinstalled or becomes loose due to the small tongue disengaging from the groove.

Wood paneling used for wall coverings should be a minimum of approximately 5/8” or 15mm thick. This thicker material was originally designed for use as exterior siding, but has become common in rec-rooms and cottages as interior wall coverings. Cedar and pine are the most common materials used, and both must be properly dried and acclimatized before use. If you want to use this thicker pine panelling, you should ensure that it is either kiln-dried or allowed sit for several months, dry-piled, in the unfinished sunroom. This will allow it to dry sufficiently to prevent excess shrinkage after installation. Danish Oil is an excellent choice of finish as it seals the surface of the wood, but still allows it to “breathe”. I would recommend pre-finishing the siding with one coat of oil, on all surfaces, before installation. This will help prevent uneven drying of the planks, which often causes “cupping” after installation. A final coat or coats of oil may be applied to the surface after installation. If this is done, the wood wall coverings should adapt well to the changing environmental conditions for several years before reapplication of Danish Oil is required.

The floor covering is another matter entirely. Laminate flooring is a manufactured product made from plastic laminate bonded to a wood-fibre base. This base material is often High Density Fibreboard, which is not well suited to changes in moisture levels. This material will often swell or deteriorate badly if it becomes excessively wet. The laminate surface is very durable and may protect this substrate from minor spills and wetting, if dried quickly, but will not protect it against prolonged exposure to dampness. If installed over a concrete surface, or an unheated plywood subfloor, the flooring will be subject to condensation, which may damage the Fibreboard. An alternative flooring that is more moisture resistant is recommended.

An unheated sunroom will be subject to major changes in air moisture level and Relative Humidity, even during a single day, dependent on the direction it faces. If the sunroom faces South or West, it will be subject to major thermal effects from the sun beaming in through the windows. The room may be moderately warm during the middle of the day, even on the coldest winter days, if the windows have a southern exposure. The sun will heat the air inside the addition, and will allow it to absorb a considerable amount of moisture from warm air leaking from the heated house. When the sun goes down the temperature will drop drastically and the moisture in this air will condense rapidly and form on the cool windows, walls, ceiling and floor. This will turn to frost, in the winter, which will melt the next day as the sun again warms the addition. This melted frost will wet the surface of the walls and ceilings and may even drip on the floor, causing moisture damage. This condensation may also happen in the summer if the sunroom stays closed for several days at a time, with little air movement.

Leaving the windows slightly open or installing an exhaust fan or other vents in the sunroom may help to minimize the condensation due to changes in temperature. Installing attic ventilation is critical, as the moisture from the periodically heated air in the addition may rise into the attic and cause damage, if not vented to the exterior. Keeping the attic cool in the winter will also help prevent the wood on the ceiling from warping or cupping due to uneven temperatures on opposite surfaces of the panelling.




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