Foundation drainage is a complex topic of high importance, to avoid wet basements and foundations. We could probably dedicate an entire book to just this topic because there are many facets and different details to proper Foundation drainage, grading, what are diversion, and waterproofing. All of these things sound separate and different, but they’re all really part of the same sub topic of proper Foundation drainage and waterproofing. In recent past blogs, we talked about and looked at particular photographs of a nearby concrete foundation for a new construction building on an old existing lot. The particular construction is very interesting because we can learn a lot from looking at these details even as the new construction is very different than historic construction, there are similar principles. Most historic buildings in Washington DC are built with brick masonry Foundation walls and the footings are also built with brick masonry but set generally in a corbel. Some of the foundation walls here in Washington DC are actually also alternatively built with a stone foundation. Many of those down foundations predate the majority of the buildings in the city.
The picture below shows the entirety of the foundation wall from top to bottom. The window that leads to a silo looking type of thing is a egress well. This window will be set below the required maximum seal height so that it can comply with standard egress requirements in habitable spaces of a finished part of a residence.
Foundation drainage is an associate yet critically interrelated aspect of concrete foundations and below-grade basements, especially when those basements are intended to be finished living spaces. The primary objective of this drainage system is to divert water away from the foundation, preventing moisture intrusion which maintains the integrity of the footing / supporting subgrade earth while keeping the interior dry.
This corrugated retaining barrier works similar to a retaining wall but because it has a very limited size it can be self-supporting, using the corrugations to create a structural resistance to the lateral forces of the adjacent retained earth. If you look closely in the photo below you can see that although there is a dirt floor to this well, there is also a corrugated drainage pipe stamped upwards which will likely be terminated to a slot drain or area wage drain in the access well. The mesh cover could allow someone to step on top of this without falling into the pit.
The corrugated metal, which creates the sidewalls of the well, has an interesting set of structural resistance or structural engineering properties. The bends in corrugated materials enhance their structural resistance primarily through increased moment of inertia and the creation of multiple strength axes. Moment of inertia is a measure of an object’s resistance to bending; it increases when more material is positioned further from the neutral axis, which is the centerline of the material where bending stress is zero. In corrugated materials, the ridges and grooves move material away from this axis, making the structure stiffer and more resistant to bending. Additionally, the corrugations create multiple axes of strength by forming ridges that run perpendicular to the main plane, providing additional paths for load distribution and making deformation more difficult. The three-dimensional structure resulting from the corrugation pattern offers out-of-plane support, enhancing stability and resistance to vertical forces. Furthermore, the alternating peaks and valleys create counterposed strength axes, allowing the material to effectively handle complex loads and stresses in various directions. This combination of factors makes corrugated materials significantly stronger and more durable compared to flat sheets.
At the heart of the overall drainage system relies on a dimple board, an impermeable high-density polyethylene sheet characterized by its raised dimples. This waterproofing membrane is applied directly to the exterior of the foundation walls, creating an interconnected barrier against water and water vapor. There are multiple different positions under configurations of both dimple board, against foundations and integrated with filter fabric which can work to facilitate an expedite the flow of water against the foundation but allow for it to be diverted away. The dimples, facing inward towards the foundation, form a channel that guides water downward, towards a collection pipe at the base of the foundation. This design not only prevents direct contact between water and the concrete but also establishes an air gap that facilitates the smooth flow of water towards the foundation’s base.
This dimple board system runs down the exterior wall and essentially creates a separation or space so the impermeable sheet doesn’t stick directly to the foundation wall and the interstitial space allows room for water to pass down through without clogging as easily.
In the coming week, we will continue looking at the foundation drain system and explore some of the details related to the passive collection of water around the foundation and also waterproofing at the side walls of the foundation.
We can Help
Our company focuses on historic restoration more than modern building upkeep, maintenance, and construction, but our company understands both types of construction very well and a full picture well-rounded approach is needed in any niche in the construction industry. Although we focus on historic restoration, repointing, tuckpointing and historic brick repair, our company also has technical knowledge and competencies in the areas of modern and contemporary construction as well as we become one of the leaders in that area of the market today. Understanding both historic and modern or contemporary construction is useful because both aspects help understand the challenges and potential solutions for challenges in building science and construction.
We can help with a variety of historic masonry restoration needs and upkeep, from modest tuckpointing and or repointing to complicated and extensive historic masonry restoration. Infinity Design Solutions is a historic restoration specialist contractor specializing in both historic masonry restoration such as tuckpointing our repointing, and brick repair. If you have questions about the architectural details or facade of your historic building in Washington DC, reach out and say hello and if we can help we’ll be glad to assist you. You can email us or call us on the telephone at the following link: contact us here.
