Skilled Fixes for a Log House

A variety of materials and methods work together in the structural repair of an 1850s building.

By Gordon Bock and Douglass C. Reed

Houses from the 1850s represent an interesting era of buildings. Not only were they built across the full expanse of North America, but they often bridge a variety of styles and technologies, making them a challenge to restore. Because they are neither totally handmade, nor completely the products of steam-powered sawmills and millworks, they require a mixed bag of techniques and approaches, especially for addressing the realities of time, money, and modern lifestyles.

This is certainly the case for the Noah Rohrbach House. Though the house appears from the road to be stud-frame construction, it is actually a log house held up by immense oak timbers hand mortise-and-tenoned together in a heavy skeleton (see sidebar). Moreover, this log skeleton is actually recycled and relocated from a much earlier structure. Clearly the complex mix of skills and techniques needed to repair such a building required the experience of specialists in the restoration of log houses, such as the folks at Preservation Associates, Inc. When we caught up with Douglass Reed and his crew on a frosty day last December, we got a quick education in several restoration methods they are using--both traditional and state of the art--that can be applied to solve a variety of problems in many 19th century houses.

A Surprising House
What makes the Noah Rohrbach house such an interesting and challenging building is its surprising history and construction. Located within the environs of the Antietam National Battlefield, the house was already a fixture in the valley when Gen. George Mead stayed there in the 1860s. Studies of the building hardware, such as the bevel-sided, cast-iron rim locks, suggested a date of about 1850 for the current appearance. However, once the failing plaster was removed indoors, the wall revealed a remarkable earlier life. Inspection of the 12''-thick walls showed the skeleton to be vertical-post log construction, a system where the horizontal logs are let into posts at corners and intermediate points in the wall, rather than, say, lapped with notches. This sophisticated system, which uses carefully constructed mortise-and-tenon joints, was common from the 1820s to the 1860s and represents some 5% of the log houses built in western Maryland. What is even more unusual about the house is that there is no evidence of chinking or daubing in the spaces between logs. Typically, the timbers for a log house were cut, shaped, and erected while the logs were green, and the spaces between them filled with chinking of wood, stones, or mortar. Then, as the logs dried to their final dimensions over about two years, they shrank slightly, compressing the chinking. It was only after the frame had reached this stable dimension that the builders could add interior plaster and exterior siding. Since the Rohrbach House never had chinking, the logical conclusion is that builders applied the plaster and siding as soon as the frame was complete because the frame was already stable. Moreover, it was stable because it was fully dried, and it was dried, because these immense logs had been recycled from an earlier structure--judging by the evidence, an 18th-century log house.

Tackling Termites
Given the log construction of the Rohrbach House and its unique history, one of the challenges the project presented was how to repair parts of the timber frame without removing large sections of the basically sound exterior cladding. And repairs were indeed required. Though the house had been occupied up to the 1970s, since then termites had established major colonies in four areas of the house leading to severe damage to two vertical corner posts and two sets of foundation sills. To correct these conditions, the crew turned to modern materials and techniques.

The massive post in the northwest corner is a good example of one set of techniques. Since replacing this key member with a new piece of timber would have meant disturbing all of the framing connected to it, as well as peeling off exterior siding, the crew decided to leave the post in place, but relieve it of its job. To do this, they added sections of 2x8 lumber on two inside faces of the post in such a way that it took over the load-bearing work. Where the tenons of the mating horizontal logs were in good condition, they supported them with 2' sections of lumber that, when stacked one over another, carried the loads of the corner down to the foundation. Where the horizontal timbers and tenons were in bad shape, they either reinforced them with epoxy consolidants or, in cases too far gone to revive, replaced them with a built-up assembly of 2x lumber. Doug and his crew use modern pressure-treated structural lumber for this kind of repair but, surprisingly, not primarily for it's rot-resistant qualities. Pressure-treated lumber is made from southern yellow pine--one of the strongest, densest woods--and is a good choice for the structural needs of this relatively heavy, nearly three-storey house.

Modern pressure-treated lumber was also the material of choice for repairing the foundation sills on the southeast corner of the building. As is a common scenario with old houses, sections of original solid-timber sills supporting the Rohrbach House had to be completely replaced. While it was relatively easy, and minimally intrusive, to remove a few courses of the horizontal lapped siding to expose the sills, jacking up the walls to remove the deteriorated sill and introduce a new solid timber was not a good option for this log-frame building. Instead, Doug and his crew chose to build up a new sill by laminating several lengths of 2x pressure-treated lumber laid up on edge (see photo above). Using this method allowed them to remove and replace the old material a section at a time, without the work and disruption of temporarily supporting large sections of the house.

Once the four or five plies of 2x are in place, they are bolted, rather than nailed, together to form an integral member. With built-up beams and sills alike, the positioning of these bolts is important. They are located in the middle 1/3 of the planks--or about 3 in from the edges of a 2x8--and spaced roughly 18 apart in a staggered pattern. Such a pattern keeps the bolt holes out of the areas of the boards that do the load-carrying work of being in tension and compression, and the staggering reduces the chances of in-line bolts that might cause the wood to split.

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