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Question DetailsAsked on 8/8/2014

Which contractors will dig basement under existing house

We are thinking about putting a new basement under our 1729 sq. ft. existing manufactured home. We would like to know who does this kind of work, and how to find them. We are in the Lakebay, WA area.

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2 Answers


Here is a prior similar question with answers that should help you:

Answered 5 years ago by LCD


Search basement dig out and you will see my educational videos on this subject, user name njstoll on youtube. My dig out videos are rated #1. I promise you will learn something.

There are so many variables when considering a basement dig out. Access, soil type, water table, parking if you are in a city setting, engineering, permits, where to discard soil / rock. condition of existing foundation walls, condition of existing beams, structural condition of home, property value. Your first step is to consider if your property value will support the cost to lower a basement and liberate the space.

If you live in an area that has depressed home values, I do not recommend a dig out, unless you are dead set on remaining in your current area for a long time. If the current value of your living space (excluding the basement) is less than $165 per square foot, it may be best to look for another home that suits your needs. Basement dig outs are a huge commitment. If your property value will support an basement dig out project, design is especially important. Basement dig outs can be designed many different ways. Over engineering can put your project over budget. The design should be suited to the structure. For example, If you have a 2 story framed home and you engineer the new foundation underpin for a 3 strory masonry home, you will elevate the cost of your project. The engineering design should be structurally sound for your specific project. I have videos that will give you an idea on engineering an beasement dig out.

Consider what is beneath your home. If you live in an area that is known to have rock outcrop, the costs of your basement dig out will increase. Drive around the neighborhood. Do you see any huge rocks, boulders or bluffs next to the road? If so, your costs will increase. I am currently on a project that has an immense amount of basalt that needs to be removed. Basalt / granite removal requires 10 times more energy to remove than sticking a shovel in the ground. You should know what needs excavated BEFORE you start a basement dig out.

Consider water management. The last thing you need is water problems in your new basement. If you are in a low lying area, water will be an issue. Even homes on a hill will require water management. If someone tells you that water will not be a problem, you are getting poor advise. Every dig out MUST have water management. Ground water is something every basement dig out will be subject to. If your new basement will be below grade of the surrounding homes near your home, you will be the water magnet. Water management is not expensive once the basement is dug out. It makes no sense to exclude water management. It is also important to design proper discharge. The best way is to remove the water from the property by discharging to a storm sewer. If you do not have a storm sewer on the property, then drywells should be included in your design. Be sure to keep drywells on the low side of the lot and a minimum of 20 feet from the foundation. Tie in all downspout leaders. You do not want to dump roof water into the backfills. Watch my videos on this subject (Youtube: njstoll user name)

Consider your basement floor plan and lighting. I always recommend egress wells when doing a basement dig out. Egress wells will qualify the liberated space for bedrooms. Even if you do not want a bedroom in the basement, egress wells are well worth the investment. Basements are very dark if you do not have natural light entering through windows. Natural lighting gives the appearance that you are not living in a dungeon. The more natural light, the better. Egress wells also provide an escape route in the event of fire or other emergency.

Consider benching your mechanical area. Most basements have a furnace, boiler, water heater, etc. If your mechanicals are in the basement, you can bench that area. There is no need to spend the money removing and re-enginnerering all your mechanicals, unless you are replacing or redesigning. Consider heated floors. Your new basement floor will remain ambient (about 55 degrees). Before pouring a new slab floor consider the flooring. If you are using porcelain tile, it will be cold. If you plan on carpet, be sure to use a high quality anti-microbial pad below.

Basement dig out vs. a new addition. If you live in an area where property taxes are high, or your lot will violate zoning code by adding an addition, a basement dig out will make sense. Say you have a 2 story 2000 sf home and you need 1000 sf of extra living space. An addition will cost more than a basement dig out. The addition will increase your property taxes much more than a dig out, as the addition expands the footprint of the home and the city will tax the new addition accordingly.


Answered 2 years ago by njstoll

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