Bono Consulting Civil Engineers is the local industry leader in the field of site drainage and grading plans for additions to existing single family houses. Since 1997 we have prepared the site plans for over 1,200 additions to existing single family homes. Some of the additions are simple family room bump-outs and some additions are huge and can double the size of the existing home.
The goal is to design the site grading to protect the owner's house from flooding and have a useable, well draining yard that does not have ponding areas, in a manner that does not impact the neighbors, is compliant with the municipal code, and can be constructed within the allowable construction budget.
Our crews will first perform a detailed topographic survey of the existing property. Depending on the extent of the addition, it may only be necessary to perform a partial topographic survey at the site. This will include surveying grades throughout the property on a grid. This also includes surveying onto the adjacent properties to determine the overall drainage patterns for the property and the immediate neighbors. Park Ridge requires collecting grade shots on a five foot grid along shared property lines. If the property is lower than he neighboring properties, the proposed design will need to continue to accept that water from the neighboring properties. Our survey will also include locating visible utilities including opening manholes and measuring sewer inverts. We will locate significant trees on the property, and if required by the community, we will have the trees identified by an Illinois Licensed Arborist.
After the topographic survey is completed, we will work with the Architect to finalize the design of the addition. Depending on the existing topography, the top of foundation for the addition may be at a different than the existing house. If the rear yard is currently draining towards the back of the existing house, and an addition is proposed for the rear of the house matching the existing top of foundation, this may result in a condition where the yard is above the top of foundation. This has been observed to cause flooding to the crawl space or basement. To fix this after the fact requires significant regrading of the entire site, whereas it could have been avoided if the foundation for the addition was raised to be higher than the yard. We will design the grades for the patios, terraces, driveways and sidewalks. We will design the new utility connections for storm, sanitary and water. We will design the grades around the house including side yard drainage swales that direct the water away from the adjacent properties.
Each community has different requirements for the engineering plans. Some communities including Wilmette, Evanston, Skokie, Lincolnwood, Chicago, Lagrange, Riverside and Western Springs will not allow storm water into their sewer systems. In these cases, the storm water has to be handled by infiltration including dry wells, rain gardens and French drains, and having an overflow that drains to the street. Some communities including Winnetka, Northfield, Deerfield and Glencoe require storm water detention facilities. This is typically accomplished by installing either large diameter pipes under the lawn or driveway, or by installing a surface detention area in the rear or front lawn. Winnetka requires detention if you are increasing the impervious coverage by more than 25%. Northfield requires detention if you are increasing impervious coverage by more than 1000 square feet. In Lagrange, the designs must compensate for the storage of the groundwater displaced by the new basement. In Highland Park, Riverwoods, Deerfield and Elmhurst all the new downspouts must be connected to the Village storm sewer system. In Park Ridge, Glenview, Northbrook, DesPlaines, Niles and Morton Grove yard drainage must be collected by a storm drain and tied into the Village sewer system.