October, 2017
Inspection News and Views from the American Society of Home Inspectors

Foundations and Wood Structures


Foundation construction has changed radically over the last 50 to 100 years. Stone, brick and, in many locations, concrete masonry units (commonly referred to as concrete or cinder block) are obsolete foundation materials. That does not mean that foundations constructed with these materials are all failing or have failed. 

The performance of these older foundation materials may be quite satisfactory in some areas of the country, but they may be inadequate in other areas, especially if they have been under extreme duress.

Footings under an old stone or brick foundation are usually nonexistent. I have seen concrete block crawl walls built directly on dirt. Piers and columns may or may not have footings. Old brick foundations with lime-based mortars can be almost fluid, like a slow liquid, in the long term. Stone foundations may have dirt or sand between the stones simply to fill the gaps, rather than to provide adhesion between the stones. Gravity may be holding the stones in place, but if the wall is moving or failing, gravity may be helping the wall fail.

Most of these foundations have literally no connection between the wood frame structure and the masonry. This is usually not a problem in the part of Virginia where I live and work, but it may be a significant concern in areas prone to earthquakes or floods.

During inspections here in Virginia, it is fairly common to find foundation walls sitting on nothing but unsupported soil in places where someone has excavated a crawl space into a cellar. The heavy rock and clay soils may appear to be stable, even decades after the excavation was done. If there is loose soil at the base of the excavation or signs of water moving through the soil, I note these as significant concerns that should be evaluated further.

When inspectors find cracks or signs of movement at the foundation, they may wonder: Where is the line between making a recommendation to monitor the foundation for future functionality or movement and making a recommendation to seek a more comprehensive evaluation? It’s important to note that horizontal cracks or bulges, at any level, are an indication of failure. Vertical or stair-step cracks are an indication of movement, but not necessarily failure, unless significant displacement is observed.

In my inspection report, I make a point of indicating that a below-grade, old foundation will be subject to moisture intrusion that will be difficult, if not impossible, to address completely. The moisture may be anywhere between dampness flooding, depending on the weather or a change in the environment. Exterior grading and drainage can make a significant difference in how wet a foundation is, but in places where the soil is wet and the water doesn’t drain, water inside an old foundation is pretty much a given. Interior waterproofing systems, such as French drains, may not be able to be installed in an old cellar because there are no footings under the walls, and many times, the bottom of the wall is at the level of the cellar or crawl space floor. In these cases, the installation of an interior drain may destabilize the foundation.

Foundation materials may deteriorate over time, due to age, deficient components or inadequate design. Bricks may spall or be subject to rising damp. Cinder or concrete blocks may disintegrate. Steel reinforcing, if any have been placed, can rust. Mortar joints can deteriorate. Foundation walls can fail under horizontal or vertical loads.

Evaluating these types of foundation problems generally is based on the inspector’s level of experience and on the observable conditions at the time of the inspection. At times, a recommendation for the foundation to be evaluated by a specialist (that is, a structural engineer) is warranted, but this should not be the standard statement to use every time you observe cracking in an old foundation.

If you inspect a lot of older foundations, you will build up a personal comfort level with typical issues. History is usually an effective way to measure the success of a foundation. If it has functioned successfully for decades, it probably will continue to do so in the future unless changes are made or something happens to the conditions around the foundation. 

If the foundation shows signs of significant structural movement or water penetration, further evaluation by an objective specialist may be warranted.

Some of the greatest changes in residential construction have been related to wood structure and framing techniques. It’s also true, of course, that indoor plumbing, central heating, air conditioning and electric lights have been major changes, but wood construction technology has changed dramatically over the last century. The old, large trees once used for lumber are gone. Now, trees are farmed, harvested, ground up, processed and turned into manufactured wood products that don’t really look like trees any more. George Washington, with his axe, would be shocked.

Wood framing has changed. The oldest wood houses were made from logs. Logs provided a quick way to build a home. The pioneers first had to clear the land to plant crops, so they had large quantities of trees with which to work. A man with an adz could square a log in half an hour, so building a log house was a quick way to create shelter before winter came. Getting a roof over your head was important to stay warm, dry or out of the sun.

Log framing: A log structure is a series of beams stacked on top of each other. The beauty of this structure is that if one log rots, the log that sits immediately above it will take over structurally. So, you can have considerable damage to some logs in a house, and although it can be very difficult and potentially expensive to repair or replace them, the structure is not necessarily compromised.

The material used to seal the gaps between the logs is called chinking. It was made from mud, manure, tree branches or whatever was at hand. The logs were green when cut and assembled, and they shrank considerably over the first year or two. The shrinking compressed the chinking tightly between the logs and increased the weather-resistance of the walls. The log walls usually were covered with siding as soon as possible. Siding provided an additional layer of weather-resistance and protection for the exterior structure. The current practice of exposing the logs is actually not historically accurate after the first year or two of an old log home’s life. 

When I stop to think about how people and animals (the main power sources) managed to lift the logs to stack them and raise the stones for chimneys, it amazes me.

Logs or trees also were used for light framing. It is not unusual to find logs flattened on one side and used for joists and rafters. Sometimes, especially for rafters, the logs weren’t even flattened or debarked. Remember, winter was coming or enemies were attacking. People must have thought, “Let’s get this home, shelter or defensible positon up!” Even when time wasn’t critical or when everything was manufactured with limited machine power, sawing logs into boards was (and still is) labor-intensive.

Determining if a structure is made of logs is sometimes necessary when there are finishes inside and out. The thickness of the wall is a significant clue. A log wall is much thicker than a frame wall and doesn’t sound like masonry when tapped. When inspecting a log structure, probing the logs inside and out to discover damage is essential. Looking for obvious damage and directing your investigation from there is a good way to go. If a log with a dimension of 8-in. or 10-in. has about 1-in. of deterioration on the exterior, there is still a lot of wood remaining for the structure.
If your probe starts to go farther into the logs, however, that’s reason for concern, but still not necessarily a serious structural problem. 

Timber framing: Timber frame structure is another previously common wood construction technique. A large frame of wood posts and beams was assembled, and the infill and cover of the timber frame made up the walls, floors, ceilings and roofs. This type of construction may be difficult to determine in the field. Examination of the structure in the attic, cellar and crawl spaces may yield some information. Hand-hewn, large timber sills with logs or joists notched into the sills is a possible clue. Large beams under the rafters in the attic is another. Infill between the timber frame parts is usually similar to light frame construction, with vertical studs, floor and ceiling joists and rafters.

Balloon framing: The earliest light framing construction is known as balloon framing, which was popular between about 1880 and 1930. This framing was entirely sawn lumber. A sill was placed (not necessarily attached) on the foundation walls. Vertical studs ran from the sill up to the top plate under the rafters unless there was an opening for a door or window. The first-floor joists were usually set on the sill next to the studs. The second-floor joists were supported on a 1-in. x 6-in. ribbon let into the studs. The joists also were nailed to the studs. Interior bearing and nonbearing walls were framed within the floor framing and did not run two stories.

Balloon framing makes it easy for an electrician to fish wiring up and down the exterior walls, but the vertical spaces are all little chimneys for fire. Blocking can be installed in the cellar or crawl space between the joists to close off the vertical openings and limit the ability of fire to rise up the walls. Openings in balloon framing may or may not have headers. Large openings for stairs can have unusual or inadequate support, usually single joists for the sides and headers. This can explain why the floors around stairways can be significantly “unlevel.” Bay windows may not have had adequate support of the cantilever.

Platform framing: Another type of construction is platform framing. This became popular in California in the 1920s and spread through the rest of the country. As the virgin forests disappeared, the 20-ft. long studs needed for balloon framing were no longer available. Building became much more standardized. Headers at wall and floor openings became typical.

In my next article of this “Old House” series, I will provide more details about types of wood construction and offer insights about how the systems worked, or in some cases, didn’t work.

If you have any questions about inspecting old homes, please contact me at ABLE Building Inspection, ableinsp@centurylink.net or 540-636-6200.