Stormwater Management is a pervasive issue in Alexandria and across the DC Metropolitan Region. It should not be a surprise though. The DMV is after all located within the watershed of our nation’s largest estuary, the Chesapeake Bay. Beneath our feet, under our sidewalks, through our lawns, and against our basement walls, water flows. Along the Potomac River, water makes it to the Chesapeake Bay and ultimately, the Atlantic ocean.
Living in this watershed is a source of pride for many ecological stewards, such as myself, but it also results in a host of issues for property owners if proper steps to protect your home or property against water damage are not taken. Through the course of this article, I will share information about several options that exist for most properties in Alexandria and across the DMV. It is important to keep in mind, however, that solutions related to water are never permanent, and it is important to consider that routine maintenance is essential to your water solution’s effectiveness.
The first type of water you’ll often encounter if you have a basement is groundwater. Depending on where your home is, your basement is likely below the water table. This is important to keep in mind because it means that groundwater is likely to pool or migrate to your basement walls via ‘capillary action’. Most basement walls are built from concrete masonry units (CMUs) or cinder blocks. Cinder blocks are used because they are inexpensive and strong, but they are also very porous, meaning that they can absorb groundwater, ultimately leading to a damp basement or crawlspace. Newer construction projects address this concern by applying a waterproofing membrane on top of the cinder blocks, but older ones rarely included these materials. Therefore, it is important to note, whether you have a basement or are considering digging out a crawl space to make one, exterior waterproofing is a must.
As property values continue to increase, the economics of digging down to extend usable square footage through converting crawlspaces to basements makes sense. But we shouldn’t assume that it is as simple as moving the dirt out. Properly waterproofing outside is critical, and though many products that are applied inside claim to solve the problem, they are only temporary bandaids if you have an active leak, or underground water abutting a basement wall. In a region such as ours, where the water table is often above the basement floor, this means having extremely effective outdoor waterproofing membranes, and applicable exterior drainage solutions.
Some contractors and material vendors may recommend that applying a paint sealant, such as DryLok, on the inside of a basement wall will be sufficient to address moisture concerns, but this is ineffective, and should only be considered as a supplementary installation to exterior waterproofing. It is best to address groundwater at its source. To avoid water entering your basement living spaces, the only reliable solution is waterproofing the foundation from the outside. This should include installing an adhesive waterproofing membrane. Whether it be rolled, painted, or sprayed on, an impermeable membrane must be applied to your porous exterior walls. On our waterproofing projects associated with permeable hardscape installation, we generally install a 40 mil PVC liner against the underground portion of the wall to prevent direct contact between block or brick. In situations where there is a permeable hardscape abutting an exterior wall, we utilize this liner to serve as a subterranean eave extending several feet away from the house to ensure that percolating water dissipates away from the wall. In other types of installations, this can be coupled with waterproofing tar membrane and/or drainage tile. Otherwise, water will find its way into your home.
But even these solutions are considered by some to be only the last line of defense after a redirection or collection system is installed. A prime example of such a system is drain tile or dimple boards adhered to the exterior wall to allow water to flow downwards into a perimeter French drain. When drainage tile is installed, the intent is not just to defend against water incursion into basements and crawl spaces, it is intended to redirect down the wall and into a French drain to direct the water away. When correctly installed, a French drain utilizes a perforated PVC pipe, rather than a black corrugated pipe, that will generally be installed in at least a 12-inch depth gravel at the base of the foundation near the footer. These drainage systems will collect and redirect water. But this doesn’t work for all properties, since the water will need gravity to flow elsewhere towards a lower grade area. Where this is not possible, some contractors will suggest that water be piped into the interior footprint below-grade and into a sump pump basin, (more on this later). Generally, these are costly retrofit installations, since it requires a substantial amount of excavation to dig down below the basement floor. Given the dynamics of the installation, they are generally only plausible for single-family homes, and not possible for townhomes unless systems are installed for the entire block face or contiguous section of homes.
Stay tuned for next week’s article where we continue the conversation of how to best waterproof your home and properly protect your investment.
Patrick Moran | CEO Tactical Land Care
Patrick utilizes his passion for the outdoors along with his professional skills as a licensed Landscape and Home Improvement contractor in Virginia, DC, and Maryland, as well as a Project Management Professional (PMP) and LEED Green Associate. Patrick has a BA from Yale University, where he studied climate change and its impact on society.