Keeping a watertight roof on a barn is probably the number one maintenance task. Water from a leaky roof will rot roof boards, rafters, framing, and floors and damage what is stored in the barn.

Historically roof coverings on agricultural buildings range from the earliest wooden shingles (generally prior to 1850) through slate and early metal (from about 1850 to 1940) to the asphalt shingles and modern metal of today. Each has different requirements for maintenance and repair, but all provide a watertight roof, and slate and metal will last for generations if properly maintained. (Corrugated fiberglass sheets are not compatible with the historic character of old barns.)

Check your roof at least once a year to see that it is watertight. Use binoculars to scan the outside, systematically following the rows where roofing overlaps and all flashing. Pay particular attention to potential problem areas where roofing or flashing may fail, such as the ridges, eaves, valleys, around cupolas, along intersecting walls, and anywhere snow and ice can drop down from a higher roof. Inspect the roof from the inside, looking for pinholes of daylight or walk through during a heavy rain or after a snowstorm watching for drips or dark stains. Repair any damaged flashing. Do not use tar to repair leaks because it is only temporary, may make the problem worse, and will make correcting the problem even more expensive.

Wood shingle roofs rarely date from the time a barn was built, though you may find shingles under another layer of roofing. Once a wood shingle roof begins to fail, it is usually necessary to replace all of it. If you choose to do so, select edge-grain red cedar shingles that match the existing size and thickness. A wood shingle roof requires wood strapping underneath the shingles for ventilation and drying. The shingles will cup if laid directly over asphalt roofing or tar paper.

Slate roofs will last up to several hundred years, and it is usually more economical to repair them than to replace them with other materials. Every few years you will have to replace several broken or missing slates. A roofing contractor familiar with slate roof repairs will give you the best price and be able to match the size and color of existing slates. Be wary of offers by contractors to remove your slate for salvage and install a new material; they may simply be selling you what they know how to do rather than what is your best and most economical option. Be sure to use adequate staging during repairs to slate and flashing. Slates will crack and need replacement if the roof is walked on. Hang replacement and new slates with stainless steel or copper nails and hooks, which will not rust through.

Metal roofing, including early galvanized metal, standing seam, and corrugated roofing, is very durable, but may need painting to prevent rust after its original coating wears off. Coatings range in increasing cost and durability from galvanized to a baked (usually colored) finish to lead-coated, which is used for jobs that must last fifty years or more. Beyond rust, the most serious threat to these roofs is wind damage. Wind may lift sheets along the outside edges of the roof and the ridge cap. Nails in corrugated roofing tend to work loose slowly, so they should occasionally be hammered back down to prevent wind damage. Sheets may be single or double-locked where they join; double locking is both more secure and expensive. Make sure gaskets or grommets are used on the nails or screws that fasten down the roof to avoid leaks.

Asphalt roofing is less durable than slate or metal, typically lasting between ten and twenty-five years. Although you can repair small holes or replace blown-off shingles, may be done, once asphalt begins to leak the whole roof generally must be replaced. Sunlight on the south side or moisture on the north side of roofs may lead to one side wearing out before the other. If possible use a ladder to inspect an asphalt roof, since detecting the areas where the mineral surface has worn away may be difficult from the ground. Tab shingles often wear through between the tabs first. When you replace an asphalt roof, if the roof boards are solid, it is acceptable to install a second layer of shingles over a worn first layer. If there are already two layers, remove all the shingles and repair the roof boards before installing new roofing.

Decide to replace a roof only after exploring the repair options discussed above. As you choose the type of new roof you will buy, consider durability as well as cost. If possible the new roofing material should match the existing material or that of a known earlier roof covering. Since proper flashing is very important and varies with different materials and conditions, make sure that you or your contractor know which flashing materials and techniques are right for your roof.

© 1995 Vermont Division for Historic Preservation and Vermont Housing and Conservation Board. All rights reserved.

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