Mapping Your Home’s Exterior Elevation to Your Topography

Three Types of Exterior Elevation Detail

I mentioned in my last post that before you authorize the modular dealer to build your home you need to see a complete exterior elevation plan that shows what your home will look like, taking into account your property’s slopes and contours after your GC completes his button-up work and site-built structures. To provide this plan, someone must integrate three types of detail. The first shows how the home will look after the GC completes his button-up work.  The purpose of this detail is to show what the modular manufacturer is building. It assumes the GC is not building any other structures on site and that your property is perfectly flat. The second type of detail adds all of the GC’s site-built structures, such as a garage, porch or deck, along with any extra finishes he’s applying to the home. The third level of detail depicts how the property’s grades and landscaping will integrate with the first two levels to more accurately depict what will be built.

The Topography Detail for a Complete Exterior Elevation

Few builders, modular or stick, provide the third set of details, those that capture the property’s topography. This is not important if the land is perfectly flat. It is important, however, when the exterior elevation plans depict the home on a flat lot but the property actually slopes front to back or side to side. For instance, if the finished grade varies more than a couple of feet around your home, more of the foundation will be exposed at the low points. Once you see an accurate plan showing a large section of the foundation above the finished grade on one side, you may want to consider replacing that section with wood-framed kneewalls or walk-out walls. This may in turn lead you to relocate the furnace and water heater to maximize the benefits that the added windows will provide. To accomplish this, you may have to modify the house plan to move the chimney closer to the new furnace location. If you do not discover this situation until after the excavation work has begun, it may be too late to change the house plan and relocate the chimney, which could mean that the furnace is stuck in the middle of what could have been a very useful and affordable basement family room or office.

An accurate exterior elevation plan may also make you aware that the slope in your backyard is so steep it will require a few additional steps to the rear porch. You may prefer to avoid a long set of stairs. Learning of this potential situation in advance will allow you to eliminate the problem by purchasing additional fill for the low spot. Since the fill will cost a bit of money, however, you may not be able to afford it unless you omit something from your modular contract, which you will only be able to do if you make the decision when you review the exterior elevation plans. Waiting until the GC begins the excavation will be too late, since you will have already signed-off on the plans and specifications. Another situation that is often revealed by an exterior elevation plan with topographical detail is when there needs to be a step down or up between parts of your home. For example, you might need three steps to enter the home from the garage because of a gentle slope across the front of the property. One way to avoid the steps is to build a retaining wall on the side of the garage so that additional fill can raise the garage floor without the threat of erosion. You will want to know about this condition while you are still in the planning stages so that you can budget the additional funds required.

Planning Issues Revealed by a Complete Exterior Elevation

As these examples illustrate, the natural contours of your land can significantly affect how you build your home. The more you know before construction begins, the more options you can consider and factor into your design and budget. Consequently, ask the dealer to show the property’s topography when he draws your home and site-built structures. Your GC or a surveyor, however, will need to provide the dealer with this information. The most accurate topographical detail comes from using a transit or its equivalent. The GC may suggest that he can come close enough by walking the property, but line-of-site judgments made with the naked eye are often inaccurate, especially when a property is heavily wooded or covered with thick vegetation. The only way to accurately determine the topography is for someone to take detailed site measurements with the appropriate equipment. You will have to pay for this service, but unless your property is perfectly flat, it will be worth the expense. Keep in mind that even if you receive exterior elevation plans that conform to your property’s grades, they may not represent exactly how your home will sit on the lot after it is built. That’s because the actual finished grade will depend on how deep the foundation is installed, which will partly depend on the soil and groundwater conditions discovered after the basement hole is dug. Groundwater and ledge can require the house to be raised substantially higher than what was drawn on the proposed exterior elevation plan. The finished grade will also depend on how much fill, if any, is brought to or removed from the site to compensate for these conditions. Unless you dig some test holes on the property before finalizing the decisions on your home, you will not be able to anticipate and plan for these exterior elevation changes. Only after your property is finish-graded and landscaped will you truly see what it is going to look like. For more information about how to get an accurate exterior elevation of how your home will look when finished, see Designing a Modular Home, Modular Home Specifications and Features, and The General Contractor’s Responsibilities for Building a Modular Home in my book The Modular Home.