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Standards and Guidelines for the Conservation of Historic Places in Canada

Additional Guidelines for Rehabilitation Projects

Within this section:

Exterior Wood

Clapboard, weatherboard, shingles, logs and other wooden elements

Recommended	Not Recommended
PRESERVING exterior wood features — such as siding, corner boards, brackets, columns, window and door surrounds or architraves, cornices, pediments and balustrades; and their paints, finishes and colours — that are important in defining the overall heritage value of the building.	Removing or radically changing exterior wood elements that are important in defining the overall heritage value of the building.
*Documenting* the form, type and colour of coatings such as paint; and the condition of exterior wood features prior to beginning project work.	Undertaking project work that will have an impact on character-defining exterior wood elements without first documenting their existing character and condition.
*Protecting and maintaining* exterior wood elements by preventing water penetration and by maintaining proper drainage so that water or organic matter is not allowed to stand on flat, horizontal surfaces or accumulate in decorative features.	Failing to identify, evaluate and treat the causes of exterior wood deterioration, including faulty flashing, leaking gutters, cracks and holes in siding, deteriorated caulking in joints and seams, plant material growing too close to wood surfaces, or insect or fungus infestation.
Inspecting painted exterior wood surfaces to determine whether repainting is necessary or if cleaning is all that is required.	Removing paint that is firmly adhering to and thus protecting exterior wood surfaces.
Retaining coatings such as paint that help protect the exterior wood from moisture and ultraviolet light. Paint removal should be considered only where there is paint surface deterioration and as part of an overall maintenance program that involves repainting or applying other protective coatings in kind.	Stripping paint or other coatings to reveal bare wood, thus exposing historically coated surfaces to the effects of accelerated weathering.
Removing damaged or deteriorated paint to the next sound layer using the gentlest method possible (scraping and sanding by hand), then repainting in kind.	Using destructive paint removal methods such as propane or butane torches, sandblasting or water-blasting. These methods can irreversibly damage exterior woodwork or cause catastrophic fires.
Using electric hot-air guns carefully on decorative wood elements and electric heat plates on flat wood surfaces when paint is so deteriorated or so thick that total removal is necessary prior to repainting.	Using thermal devices improperly so that the woodwork is scorched. Failing to have a fire extinguisher nearby when using thermal devices.
Using chemical strippers primarily to supplement other methods such as hand scraping, hand sanding and the thermal devices recommended above. Detachable wooden elements such as shutters, doors and columns may be chemically dip-stripped if proper safeguards are taken.	Failing to neutralize the wood thoroughly after using chemicals so that new paint does not adhere. Allowing detachable wood elements to soak too long in a caustic solution so that the wood grain is raised and the surface roughened. Stripping character-defining painted exterior wood surfaces to bare wood, then applying clear finishes or stains in order to create a “natural” look. Stripping paint or varnish to bare wood rather than repairing or reapplying the same finish (e.g., a grained finish) to an exterior wood element such as a front door.
Creating conditions that are unfavourable to the growth of fungus, such as eliminating unintentional entry points for water, drying out the structure by opening vents, removing piled up earth resting against the building and applying a chemical preservative treatment using recognized preservation methods.
Applying compatible paint coating systems following proper surface preparation, such as washing with trisodium phosphate.	Failing to follow the manufacturer’s product and application instructions when repainting exterior woodwork.
Repainting with colours that are appropriate to the building and district.	Using new colours that are inappropriate to the building or district.
Applying chemical preservatives to exterior wood elements such as beam ends or outriggers that are exposed to decay hazards and are traditionally unpainted. Inspecting buildings to determine the reason(s) for any damage or degradation, such as abrasion, animal gnawing (e.g., rodents), fungal decay or insect infestation (e.g., beetles, horntails, wood borers, carpenter ants, carpenter bees, wasps, termites and weevils).	Using chemical preservatives such as creosote or copper napthanate, because if they have not been used historically, they can change the appearance of exterior wood elements. Undertaking remedial project work on log buildings without first identifying the actual cause(s) of damage or degradation.
Treating the deterioration of log buildings from abrasion or animals by isolating, insofar as possible, the building from the source of deterioration, such as blocking wind-borne sand and grit with a windbreak, or putting a wire mesh screen over floor joists in a crawlspace to thwart rodents.	Neglecting to treat known conditions that threaten buildings, such as abrasion, animal gnawing, fungal decay or insect infestation, thus putting them at risk of further deterioration.
Treating active infestations of insects by first identifying the type of insect and then implementing a program of elimination appropriate to that insect. If using pesticides, confirm that the chemical is registered for the intended purpose with Agriculture and Agri-Food Canada and follow the manufacturer’s product and application instructions. Fumigation should be done only by a licensed applicator.
Taking into account the settlement rate of a building when augmenting or reinforcing its structural components, so that the new components settle at the same rate.	Structurally augmenting or reinforcing a building with components that do not have a similar rate of settlement.
*Retaining* sound exterior wood or deteriorated exterior wood that can be repaired.	Replacing wood elements that can be repaired.
*Repairing and stabilizing* deteriorated exterior wood elements by structural reinforcement, weather protection, or correcting unsafe conditions, as required, until any additional work is undertaken. Repairs should be physically and visually compatible.	Removing deteriorated exterior wood elements that could be stabilized, repaired and conserved; or using untested consolidants and untrained personnel, thus causing further damage to fragile elements.
*Replacing in kind* extensively deteriorated or missing parts of exterior wood elements where there are surviving prototypes. The new work should match the old in form and detailing.	Replacing an entire wood element such as a cornice when limited replacement of deteriorated and missing components is appropriate. Using replacement material that does not match the historic wood element.
Evaluating the overall condition of the exterior wood to determine whether more than protection, maintenance and limited repair or replacement in kind are required; in other words, if more extensive repairs to wood elements will be necessary.	Failing to undertake adequate measures to protect exterior wood elements.

Maximizing the retention of character-defining materials and features is the primary goal of Preservation, as demonstrated in this photograph. Work on this wooden warehouse consisted primarily of minor repairs to the foundation skirting and limited replacement of deteriorated material. The new wood will be left to weather to the same appearance as the old.

Additional Guidelines for Rehabilitation Projects

Recommended	Not Recommended
REHABILITATING an exterior wood element, if an evaluation of its overall condition determines that more than preservation is required.	Failing to evaluate the overall condition of an exterior wood element in order to determine the appropriate method of conservation.
*Repairing* exterior wood elements by patching, piecing-in, consolidating or otherwise reinforcing the wood using recognized preservation methods. Repair may also include the limited replacement in kind — or with a compatible substitute material — of those extensively deteriorated or missing parts of elements where there are surviving prototypes such as brackets, moulding or sections of siding.	Replacing an entire wood element such as a cornice or wall when repair of the wood and limited replacement of deteriorated or missing parts are appropriate. Using a substitute material for the replacement part that neither conveys the same appearance as the surviving parts of the wood element nor is physically or chemically compatible.
*Replacing in kind* an entire exterior wood element that is too deteriorated to repair — if the overall form and detailing are still evident — using the physical evidence as a model to reproduce the element. Examples of wood elements include a cornice, entablature or balustrade. If using the same kind of material is not technically or economically feasible, then a compatible substitute material may be considered.	Removing an entire exterior wood element that is irreparable and not replacing it; or replacing it with a new element that does not convey the same appearance.

It is important to identify the cause of any damage to a wooden building element before beginning a Preservation treatment. In the case of the former machine shop of the North Pacific Cannery, exposure to marine conditions led to deterioration of the exterior wood cladding.

The following REHABILITATION work has been highlighted to indicate that it involves a particularly complex technical or design aspect and should only be considered after the Preservation and Rehabilitation concerns listed above have been addressed.

Recommended

Not Recommended

Designing for the Replacement of Missing Historic Features

Designing and installing a new exterior wood feature such as a cornice or doorway when the historic feature is completely missing. It may be a new design that is compatible with the style, era and character of the historic place; or a replica based on physical and documentary evidence.

Introducing a new exterior wood feature that is incompatible in size, scale, material, style and colour.

Creating a false historical appearance because the replaced wood feature is based on insufficient physical and documentary evidence.

Additional Guidelines for Restoration Projects

Recommended	Not Recommended
RESTORING an exterior wood element, if an evaluation of its overall condition determines that more than preservation is required; in other words, if repairs to wood features from the restoration period will be necessary.	Failing to evaluate the overall condition of an exterior wood element in order to determine the appropriate method of conservation.
*Repairing, stabilizing and conserving* fragile wood from the restoration period using well-tested consolidants, when appropriate. Repairs should be physically and visually compatible and identifiable upon close inspection for future research.	Removing wood from the restoration period that could be stabilized and conserved; or using untested consolidants and untrained personnel, thus causing further damage to fragile historic materials.
Repairing exterior wood elements from the restoration period by patching, piecing-in or otherwise reinforcing the wood using recognized preservation methods. Repair may also include the limited replacement — preferably in kind — of those extensively deteriorated or missing parts of elements from the restoration period where there are surviving prototypes such as brackets, moulding or sections of siding. The new work should be unobtrusively dated to guide future research and treatment.	Replacing an entire exterior wood element from the restoration period such as a cornice or wall when repair of the wood and limited replacement of deteriorated or missing parts are appropriate. Using substitute material for the replacement part, which neither conveys the same appearance as the surviving parts of the wood element, nor is physically or chemically compatible.
*Replacing in kind* an entire exterior wood element from the restoration period that is too deteriorated to repair — if the overall form and detailing are still evident — using the physical evidence as a model to reproduce the element. Examples of exterior wood elements include a cornice, entablature or balustrade. The new work should be unobtrusively dated to guide future research and treatment.	Removing an entire exterior wood element from the restoration period that is irreparable and not replacing it.

The extensively deteriorated wood siding on the exposed side of this building was replaced in kind. The new wood siding matches the surviving siding in form and detailing.

The following RESTORATION work has been highlighted to indicate that it involves the removal or alteration of existing wood features from periods other than the accepted restoration period; and the replacement of missing wood features from the restoration period with all new materials. This work should only be considered after the Preservation and Restoration concerns listed above have been addressed.

Recommended	Not Recommended
Removing Existing Features from Other Periods
Removing or altering wood features, such as a later doorway, porch or steps, dating from other periods.	Failing to remove a wood feature from another period, thus confusing the depiction of the building’s significance.
Documenting materials and features dating from other periods prior to their alteration or removal. If possible, selected examples of these features or materials should be stored to facilitate future research.	Failing to document wood features from other periods (which results in the loss of a valuable portion of the historic record) prior to removing them from the building.
Recreating Missing Features from the Restoration Period
Recreating a missing wood feature that existed during the restoration period based on physical or documentary evidence; for example, duplicating a roof dormer or porch.	Constructing a wood feature that was part of the original design of the building, but was never actually built; or constructing a feature that was thought to have existed during the restoration period, but for which there is insufficient documentation.