| Various Lot Contours to Build On - Issue #3 |
How would you classify your lot?
In describing the contour of a lot to build ones' home, there are three classifications, namely a flat lot, a depressed lot, or an elevated lot. Building a house on any one of these contours would offer advantages and disadvantages. This piece of advice is intended to help the lot buyer in choosing the right contour for his future home. And for the lot owner ready to build his house, these are advice to ensure the safety of your homes and also to reduce the cost of construction.
Lot shape - the lot you have or are considering can either be regular (usually rectangular in shape) or irregular. It is a lot easier to plan and construct on a regular shaped lot. Space is also used more efficiently in a regular shaped lot. For an irregular shaped lot, space can easily be wasted but some designers however can use these spaces very efficiently and creatively. A corner lot can give your house a very good perspective since your house can be viewed from two different angles (you can also have two entrances). However, you need to pay a little more for a corner lot.
Lot Contour - the contour of the lot can either be flat, depressed or elevated.
Building on a Flat (Level) Lot
A flat lot would give you the lowest cost of site development since no additional backfill or excess material to be disposed is to be handled. Designers usually balance cut and fill (this simply means that the soil excavated in one area is backfilled in another area). Handling of materials within the project site also becomes easy on a level lot. Access to a flat lot is generally easier than on the other types. Construction materials can also be handled with ease if construction in on this type of lot.
From the point of view of cost of site development including foundation works for a home, building on level ground can be the cheapest.
Houses on elevated or depressed lots usually give a good view of nearby areas, but it has its own disadvantages.Slope stability analysis is important to ensure the safety of the house.
Building on a Depressed (Sloping Downwards) Lot
If the property is depressed (sloping downwards), you may consider constructing a basement. Constructing a basement can increase your construction cost due to additional foundation works, backfilling, waterproofing and extra provision for drainage not to mention the additional cost of labor. Some locations may even require a drainage pump on your basement in order to pump out excess water into the drainage line found at street level. If you do plan to put up a basement, check if a drainage line is available at the back portion of your lot to ensure that you can dispose of excess water easily without the aid of a pump. Do not assume that a drainage line is available at the back portion of your lot for some subdivisions do not have this utility.
Slope stability analysis is important to ensure the safety of the house.
Houses constructed on depressed lots usually give a good view of nearby areas. Homes built on these contours can be planned very well to give a multi level home that offers a breathtaking view of adjacent lower areas. However, houses built on slopes need extra attention and precaution since the slopes can be de-stabilized and can slide (remember Cherry Hills?) during a very heavy rain or worse - during an earthquake. Yes, a house can still be built safely on a slope but engineering and geologic studies have to be done to fully assess the safety of slopes. The effect of the weight and other loads induced by the house is compared with the strength of the soil. In the analysis, soil samples have to be retrieved from the sites thru soil drilling. These samples are then brought to the soils laboratory for analysis and testing. The design consultant, called the geotechnical engineer certifies the safety of the slope.
If the slope is unsafe, engineering solutions have to be implemented. These solutions include the construction of retaining walls, driving of rock anchors or soil nails, using a different type of foundations system, ground improvement, benching, etc. A house on a slope therefore can indeed become more expensive but the rewards of a good view can well offset the additional costs. To ensure your peace of mind, consult your design professional regarding this matter.
If your lot is only slightly depressed, you may choose to just simply fill it up with well-compacted soil in order to convert your lot into a flat lot. When we say well-compacted soil - engineering procedures and quality control have to be followed. The additional backfill soil needs to be confined by a retaining wall - a structure that would ensure that the soil within the property boundary is properly contained.
Building a structure on a depressed lot implies that there are added costs for backfill material, larger foundations, additional costs for concrete, construction of retaining walls and design fees. A multi-level house with a good view of lower lying areas offsets the additional costs of development.
Building on an Elevated (Sloping Upwards) Lot
If the lot that you have is elevated, you may have to face the additional burden of extra excavation and disposal of excess soil materials. If the disposal site is far, the high costs of hauling out excess materials have to be considered. Just imagine if your construction site is in San Juan and your disposal site is in Antipolo. But again, an elevated home can be very attractive to view from the street level. A split-level home can be adapted to an elevated type of lot.
The risks of slope instability on a depressed lot also apply for an elevated lot so it would be wise to consult your design professional regarding this matter. Since the house would be higher than street level, the drainage problem that one would have in a depressed lot would not be present in an elevated lot.
Final Note
The depressed or elevated lot contours on where to build ones property can offer advantages, as well as disadvantages in terms of additional safety requirements and design/construction costs. The additional costs however would offset the benefits that one would get by building on an elevated or depressed lot. In buying a property prior to actual development (pre-sold properties), it is best to make sure that one sees the actual location of the lot prior to purchase. Relying simply on marketing maps is not advised since 'everything is flat' on a marketing map. Developers usually have a scale model of a development project and they would be happy to show you where the lot you are interested in is. Topographic maps show all the contours of the entire property and one can easily see where the lot is relative to the other contours of the entire subdivision development.
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