Keeping Wood Siding on Historic Buildings
by Andrew Powter

We think of siding as a modern phenomenon, but it has been used in one form or another for centuries. Preserving the historic character of traditional siding on older buildings can be a challenge for heritage professionals.

Siding is typically used to cover vertical (or nearly vertical) wall surfaces. Its usual function is to protect the building from weather, but it can also be decorative.

Siding appears on buildings in a wide variety of materials, shapes and sizes. One type of siding is sometimes used in combination with another. Types include horizontal or vertical boards, shingles, asphalt materials like insulbrick, asbestos cement shingles, and sheet and panel metal.

Like any component of a building, siding is subject to various natural forces that cause it to deteriorate, requiring periodic maintenance and repair. Many owners want to avoid the expense and trouble of maintaining siding, so it’s covered with lower maintenance materials like vinyl or aluminium. What are the pros and cons of this controversial approach to siding historic buildings?

Wood Siding and Heritage Character

Siding is a product of its period of construction, available technology, materials and skills, and reflects stylistic trends, fashion, climate and industrial development. More recently, the choice of siding has been influenced by marketing and available transportation. For example, in 19th-century Canada, western red cedar shingles from British Columbia substantially replaced others after the construction of the railway.

Siding choices on historic buildings are therefore major contributors to establishing their place in a community,region and time period, and consequently their heritage character. For example, surviving pre-World War I residential buildings in the west end of Vancouver are among the few reminders of Vancouver’s earlier timberbased economy.

Maintaining and Repairing Authentic Wood Siding

Siding “Systems”

A wood siding “system” usually consists of a weather-shedding surface (the siding itself) that is attached to a surface (such as planks, battens or girts) with fasteners (usually nails). The siding is usually coated with a protective coating such as oil, stain, limewash or paint. Some form of wind protection (bark, kraft paper, Tyvek, etc.) is often installed behind the siding. Putty covers and protects fasteners. Wood siding is usually installed horizontally (such as bevelled, riven, short plank, long plank, edge profiled, cove, drop and shiplap), vertically (such as plain board, board-andbatten, tongue-and-groove) or as shingles.

Threats and Forms of Deterioration

Siding deteriorates because of trapped moisture and lack of ventilation, leading to decay and insect attack. Vertical siding is particularly susceptible if the bottom end grain is not sealed. If siding is not protected by a well-maintained coating such as paint, it deteriorates from weathering (cycles of wetting and drying, ultra-violet light and windborne abrasives). It slowly changes from the colour of fresh wood to the warm grey of barn boards.

Other forces, such as impact, are far less damaging.

Perhaps the most problematic agent of deterioration is paint. Paint accumulates over time to form a thick, impermeable, inflexible layer that can prevent the natural expansion and contraction of the siding, causing it to split and crack. Alternately, a thick paint layer itself may crack and split (called alligatoring) as it expands and contracts at a different rate than the wood below. If a building has been painted too frequently or improperly prepared for new paint, the time comes, possibly after 100 years or more, when the excessive accumulations of paint must be removed to start from bare wood. Repainting, let alone stripping to bare wood and repainting, can itself present a threat. At this point, many owners resort to calling the aluminium or vinyl siding contractor.

Repair and Conservation

A siding repair program gives owners an opportunity to get up close and personal with their building and check for splits, reset popped nails, reputty over nail heads or carry out other maintenance. Although small repairs can be performed with the siding board in place, it is often advisable to repair the board on a bench to effect a better fit and clamping.

Siding board units can be spot repaired by removing deteriorated material back to a sound, straight edge and patching using Dutchmen and other insert repairs. Always use wood of similar species, density and grain direction. Be sure to use moisture-resistant adhesives for the most enduring repairs.

If a siding board is loose, nail it to its stud with a fastener similar in size to the old fastener. Remove the old fastener and fill the hole. Be careful of nailing slightly cupped boards too tightly as they may split.

Remove siding boards by removing exposed fasteners and using a hacksaw blade to reach behind to cut concealed nails. Do this gently to avoid damaging adjacent boards.

This is easier with bevelled siding than with coved or tongue-and-groove siding. With these more complex profiles, in situ repairs may be best. To make a number of repairs, it may be necessary to demolish a short length of board below to gain the necessary manoeuvring space for the boards above. Also, the inside of the groove may have to be sacrificed to install the final new board. Once the board is repaired or the new board made, it can be slipped up behind the board above and fastened into place. Stick with one nail per stud to allow for movement. Remember, siding should always be back-primed before being installed.

Refinishing

When painting exterior woodwork, preparation is the most important step. Scrape loose paint and sand the surface to give the new coat a “tooth.” Wipe away dust. Apply a top quality knot sealer to exposed knots. Even a 100-year-old knot will bleed through, so be sure to seal it. Apply an oil-based primer and then two coats of oil-based or latex finish.

If the wood has lost most of its paint and is heavily weathered, sand well to remove loose wood fibres. Brush the surface clean, and then apply a coat of 50/50 boiled linseed and thinner to condition the wood.

The paint you are removing may contain lead, so test it to ensure you comply with health, safety, containment and disposal requirements.

Owners may apply new siding directly over old. Stucco, insulbrick and fibre cement tiles have all had their periods of popularity. Indeed, some of these materials have begun to be appreciated on their own merits. Since the 1960s, vinyl and aluminium siding have been frequently considered to maintain historic material. The vinyl siding industry markets extensively to the owners of heritage properties (see www.vinylsiding.org).

This trend is controversial. What are some factors to consider?

Maintenance and Cost

Preparing and painting a wooden house can appear daunting, but spot repainting after five years with general repainting after seven years or longer can mitigate this.

Vinyl or aluminium siding lasts about 20-25 years, equal to two to four paint jobs. Figures from the U.S. indicate that vinyl siding costs about the same as two and a half paint jobs.

Furthermore, vinyl and aluminium are not maintenance-free, especially on heritage buildings that were not designed for these materials. Mould may grow under the siding. Many owners try to deal with this by using pressure washers to clean it out. However, siding is designed to shed water from above, and washing from below can force water up behind it, leading to wood decay.

Physical Impact

Opponents of vinyl and aluminium siding often say these materials are susceptible to impact and difficult to repair. While replacing siding is extremely difficult, the need to do so is probably rare.

Environmental Considerations

Paint, vinyl and aluminium are manufactured from non-renewable resources. How does the embodied energy required to manufacture and ship paint compare to producing aluminium and vinyl? That’s hard to say, but we know wood that was cut and installed 100 years ago uses no energy or non-renewable resources. Aluminium and vinyl siding will not reduce your heating bill. The R-value of siding with backing ranges from R-0 to R-2.5 at best. This is about the same as a pane of glass.

There is no energy payback on these materials. Aluminium can be recycled. Vinyl cannot. Vinyl also emits toxic fumes and carcinogens when it burns.

Protection

Some say that oversiding products protect historic materials, but this is a red herring. Installing oversiding is very damaging due to the number of fasteners and the blocking, trimming and removal of detail necessary for a decent fit.

Concealment

Oversiding a historic building conceals damage that should be repaired. Oversiding requires many non-standard fittings and connections. Often, caulking plays an important role in the new finish. Eventually, these details will fail, admit water and contribute to deterioration underneath. I once found a failed porch beam and column beneath a 20-year-old aluminium job.

Heritage Character

Oversiding a historic building means the building’s heritage character will be affected for the next 20-30 years. This occurs in several ways.

Aluminium and vinyl siding are manufactured in a wide range of widths and colours, but historically accurate profiles are rarely available. The optional grained finish is more characteristic of sandblasted wood than historic siding. The doubleboard profile is an inaccurate detail no craftsman would replicate.

The biggest concern is the dramatic effect these materials have on the details of a building. If sufficient care is not taken, the board width will change to nonregional dimensions or will reduce window and door trim projections and force the blurring of historic mouldings and removal of inconvenient projections.

For more information on the vinyl siding issue, see Vinyl Siding: The Real Issues by the Connecticut Trust for Historic Preservation at www.cttrust.org.

In 2007, the Heritage Canada Foundation is carrying out a project to repair the siding on the historic Runciman House in Annapolis Royal, Nova Scotia. The building is clad with wood shingles on two sides and the rear, and with beadedged cove siding on the front, including two curved bays. A follow-up article will report on the full range of repairs described in this article.

Andrew Powter has been involved in national and international heritage programs and projects. His main areas of interest include historic wood structures, building envelope performance and sustainable heritage conservation practice.

References

Fram, Mark. Well-Preserved: The Ontario Heritage Foundation’s Manual of Principles and Practice for Architectural Conservation. Boston Mills Press, 1992.

Cunningham, Jan. Vinyl Siding: the real issues. Connecticut Trust for Historic Preservation, 2001.

Information Brief: Maintaining Vinyl Siding. Washington, Vinyl Siding Institute, 1994.

Information Brief: Vinyl Siding and Historic Restoration. Washington, Vinyl Siding Institute, 1994. Online at www.vinylsiding. org/vsic/historic/index.htm

Meyers, John H. Revised by Gary L. Hume. Preservation Briefs Volume 8, Aluminium and Vinyl Siding on Historic Buildings, The Appropriateness of Substitute Materials for Resurfacing Historic Wood Frame Buildings. U.S. Department of the Interior, National Park Service, Washington, D.C., 20402, Oct. 1984.

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