Home inspectors in New Jersey often inspect properties with wood retaining walls. As home inspectors we often find problems with these wood tie walls such as wood rot, water damage, insect damage and inadequate construction. Often these walls are built over masonry, pavers, or stone walls because they are lower in cost, however we find more problems with these wood walls than we do with the more expensive masonry, rock or paver retaining walls.
There are several mechanisms of failure that NJ home inspectors should be aware of and look out for as they’re doing their exterior home inspection. One of the most common reasons for a wood retaining wall to fail is simply wood rot and wood decay. A wood retaining wall will simply break down over time especially because it has direct contact with the soil. A wood retaining wall has a typical life expectancy of about 20 years. As the wood wall degrades over time it will lose its structural integrity and its ability to hold back the soil behind it. Wood by its very nature will deteriorate when it’s touching grade due to high moisture conditions. A failing retaining wall is not only unsightly but the earth behind it can slip and slide causing injury, damage to property and other hazards.
Another mechanism of failure of a wood retaining wall is inadequate drainage. If water cannot drain effectively when it collects behind a wall hydraulic pressure will begin pushing on the wall especially during times of freezing. This pressure on the wall generally exceeds the wall design capacity causing the retaining wall to lean and possibly give way. One of the significant drawbacks of a wood tie wall is that they are not constructed with drain holes. Masonry walls are generally constructed with a means to drain water from behind the wall which relieves this hydraulic pressure. Wood retaining walls rely on the perforated pipe drain and gravel which over time gets obstructed and typically fails.
Many of the wood walls that New Jersey home inspectors inspect have been installed by a nonprofessional and are not properly engineered to hold back the soil loads behind them. Retaining walls are important pieces of structure that should be professionally engineered so that they will adequately hold back the soil loads. Often these walls are installed as weekend projects without any engineering being performed at all. A wood retaining wall that is not properly engineered will be prone to premature failure.
In regions like the Northeast with temperatures that fluctuate and that have cycles of thaw and freezing wood walls in this environment face even greater challenges. When moisture within the wood freezes it expands and this leads to cracking and warping. This repetition of freeze and thaw cycles hastens the deterioration of the wood tie wall and significantly reduces its lifespan in the Northeast environment. It is imperative to choose a retaining wall composition that can hold up during these freeze and thaw cycles. As home inspectors in New Jersey, we often find that wood walls just don’t hold up long term. A more resilient long-term option would be to install masonry, concrete, rock, or paving stone wall.
Often wood walls lack proper anchoring. If a wood retaining wall is not anchored, it will be vulnerable to soil pressures and eventually lean and fail. Deadman anchoring is a simple system that is used to anchor wood walls to the soil. A Deadman anchor consists of a wood tie installed perpendicular to the retaining wall with a cross brass. The dead man is anchored to both the retaining wall and the cross bracing. The length of the Deadman anchor should be the same height as the retaining wall. For example, a five-foot-high retaining wall will have a five-foot long dead man anchor. These important anchors are spaced about 8 feet apart.
As New Jersey home inspectors we can see that a wall has dead man anchors but what we will not be able to see is if they are properly installed or long enough because they are buried in the soil behind the wall. A retaining wall over three feet with no anchoring is a defect that should be reported because it is likely that the wood wall will experience a premature failure.
Wood retaining walls should also have a perforated pipe drainage system. Water will not be able to flow through the wood like it can for a block, paving stone, or a concrete retaining wall with weep holes. It is especially important that water does not build up behind the wood walls. This is accomplished by installing a drainage pipe at the foot of the wall on the side of soil retention that is pitched to a low area so gravity can drain water from behind the wall. At least a foot of gravel should be placed behind the retaining wall around the pipe. The pipe should be wrapped with landscaping fabric to help avoid it getting obstructed with sediment. This will help in drainage and hopefully allow most of the water to drain from behind the wall. The wall should also have a gravel bed under it as a base. Home inspectors in NJ will not be able to see this, however we will be able to look for signs of failure.
Sometimes we will come across brand new retaining walls. If there is a brand new or newly build wall the home inspector should ask their client to request information from the seller regarding any warranties from the installing contactor as well as the engineering plans to make sure that the wood wall has a system of drainage and anchoring.
NJ home inspectors should look for defects in retaining walls such as wood rot which can be found by probing areas of the wood walls. Home inspectors should also look for leaning walls or damaged walls because this is an indication of poor construction, a failed drainage system or inadequate sized wall materials. Any retaining wall defects should be explained to the client and reported on.