With high prices of property in Israel, many homeowners find it more cost-effective to extend their homes rather than move to a bigger place. Some people choose to build upward into attic space in order to gain an additional bedroom or two.  Others close off a porch, open up “challal” space or extend the main floor. A common trend in Israel is to build a basement beneath a house.

While the addition of a basement to an existing property can provide the owner with a large amount of extra living space, a basement in Israel can also add significantly to the value of the property. However, basement excavations and conversions, carry many regulations and permissions with them. Each is unique and very much depends upon the condition and structural ability of the existing property.

There are a few important considerations and steps to be taken before initiating the addition of a basement to an existing structure in Israel:

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1. Rights and permits: Check with the Town Engineer in the local municipality what building rights, permits, and conditions exist, if at all, to add an additional structure to the particular property.
2. Select contractors: You will need to hire a range of different professionals and experts at various stages of the project. Before choosing any contractors or professionals, engage in market research, put up a tender, and ask for recommendations in order to increase the chances of satisfaction.
3. Cost-estimate: Make sure that the size of the basement is designed and built in such a way that it will justify the cost.  Cost-estimate should be done in advance together with the architect and engineer, and all the other consultants involved in the project. Take into consideration all the fees that must be paid to the local authority (e.g. permits), as well as the “improvement tax” (Hetel Hashbacha), a payment to the Israel land authorities (Minhal Mekarkaey Israel), and additional fees due to the various consultants and experts – architect, surveyor, structural engineers, soil engineer, specific lab test by the Israeli Standards Inst. etc.   Additional costs of all the finishes must also be taken into consideration such as floor and walls tiles, plaster, paint, windows, plumbing, electricity, etc.
4. Architect’s plans: According to the instructions from the local authority’s building department and the rights that are applied to the particular property, an architect should submit to the local authorities a suggested plan together with the structural engineer’s calculation of the proposed additional basement structure, while taking into consideration the existing structure.
5. Analysis of soil: It is important to hire a soil engineer (Mehandes Beesus/Karka) who will take sample/s and analyze the soil underneath the existing house in order to determine what kind of foundations the new structure should have.
6. Structural support and connection: Due to the fact that basements are built while there is already an existing structure above them, special care should be taken with structural support, and precautions must be taken in order not to cause any structural damage to the existing foundations in the process of the excavation.  One also has to take into consideration the kind of the existing house structure, in order to connect the new structure of the basement to the existing structure, in the appropriate structural way.
7. Excavation effects: It is very important to take into consideration the influence of the excavation on the existing house and neighboring properties.
8. Ventilation: It is recommended that the basement will be naturally ventilated in order to avoid condensation and mold or dampness.  In order to achieve natural ventilation (e.g. windows), it is recommended to design the basement in such a way that its ceiling will be a level higher than the level of the ground outside.  This may be achieved by lowering the existing ground level.
9. Insulation: Special care should be taken for waterproofing and insulation, because the external part of the walls is underground, and increases the risk of water penetrating the property.
10. Floor: The design must also ensure that the floor slab of the basement will be done with dampproof membrane.
11. Relocation of existing plumbing and electricity: It must be checked whether pipes and sewage, electrical wiring, and plumbing are located under the existing structure, in which case, these may need to be relocated.
12. Radon testing: Check for Radon gas, which is a naturally occurring radioactive gas common in some parts of Israel, and must be taken into consideration when building a basement.  A simple test will measure the level of radon.  If radon gas exists, it can be collected by buried drain lines and vented to the outside, much like excess water.

It is important to note that in some homes in Israel, there may already be an open space which was excavated in advance underneath the structure during the time that it was originally built, with a future view to have an option to extend the house and use that space as a basement in Israel. However, for legal reasons, the access to that open space underneath the house was blocked by brick walls or similar partitions.  In order to find out whether or not a pre-prepared space exists underneath the house, the original plans of the property should be checked.  Alternatively, one could break down some of the partitions in order to examine beyond. However, it must be emphasized that no demolition should be undertaken without the consultation and supervision of a structural engineer, as some of those partitions could be structural load-bearing walls.

In the case where there is an open space that has been already excavated and can be used as a basement, then the cost will drop dramatically and will consist only of the finishes such as floors and tiles, plaster, paint, electricity, plumbing etc., without the added cost of the structural aspects.

Each of these steps, considerations, and decisions is extremely important and no stage should be skipped.  Due to the complexities and potential issues that can arise in building a basement in an existing home, it is highly recommended to hire a professional and experienced project manager from the outset who will supervise the planning and construction and oversee the various stages of development of your new basement in Israel.