Engel & Völkers Private Office > Blog > House conversions or extensions to create more space

House conversions or extensions to create more space

Sometimes the living space requirements of a house can change. Then it's time to convert the interior of the house, change the function of a room or even expand the exterior. This creates space for the new home office, an additional children's room, a wellness area or a fitness room. With a little deliberation and planning, as well as appropriate construction measures, a house that has become too cramped can once again become a perfectly sized dream home.

 

Converting the interior to create new living space

If you own a detached house with several floors, there is often still potential for expansion in the basement or attic. Converting the attic may ultimately yield a new office, a quiet library or even an apartment with a bathroom for the younger or older generation. Converting a basement, on the other hand, allows for the installation of a sauna, a spacious party room or a fascinating home cinema. As a rule, converting the interior is cheaper than adding new living space or usable outdoor space. Another advantage is that the size of the garden is maintained even though the living space increases. No matter how you choose to expand your home, there are a few things to keep in mind.

 

What to consider before converting an attic

Before converting an attic, it is important to check the statics and the condition of the roof structure, especially in old buildings. This is because the required thermal insulation and formwork add quite a bit of weight. Moreover, the roof must be tight or must be renovated before the conversion. This work is cumbersome and costly to implement later on. Another factor is the floor slab, which has to withstand the load of flooring, furniture and people. If in doubt, it is advisable to consult a structural engineer or architect.

 

Planning and calculating the attic conversion

How much an attic conversion costs depends on the size of the attic and its condition before the conversion. Are there already electrical connections, heating and water pipes or do they still need to be installed? Is there sufficient thermal insulation and does it meet the requirements of the Building Energy Act? Does the attic already have proper windows or is window renovation or even the purchase of new windows necessary? If the attic is improved in terms of energy efficiency through insulation, windows or heating, the costs can be significantly reduced with the help of government renovation subsidies such as the Federal Subsidy for Efficient Buildings (BEG). These subsidies must always be applied for before starting or commissioning the conversion measure.

 

What are the legal requirements for attic conversions?

It may be necessary to obtain planning permission for the attic conversion. However, this depends on the reason for the attic conversion. Will the roof only be remodelled on the inside or also on the outside and in which federal state is the house located? Some federal states already demand planning permission if living space is to be created in the attic. In some German regions, a planning permission is only required if a separate living space is to be built under the roof. As soon as the state building code classifies the attic conversion as a change of use or major interventions in the statics are required, the building measure is subject to approval. If in doubt, it is therefore advisable to talk to the responsible building authority and an architect before starting the attic conversion.

The following may require building permission, depending on the state building code:

  • Changing the roof pitch or height
  • Major changes to the statics
  • Change of use: Conversion of utility space to self-contained flat, living space to commercial space or utility space to living space
  • First-time installation of roof windows
  • Installation of a dormer window
  • Construction of a roof terrace
  • New staircase to the roof required
  • Change of floor plan and removal of walls
  • Change in the cubature of the house


Not subject to approval:

  • Interior only without static or visual changes on the outside
  • Window renovation: Replacement of already existing roof windows of the same size
  • Renewal of the building technology
  • Installation of drywalls
  • New roofing while keeping the same dimensions
  • Better insulation of the gable
  • Cosmetic repairs
  • Measures to improve thermal insulation, sound insulation and fire protection


Whether or not planning permission is required, there are other requirements and regulations that must be met, such as:

  • Fire protection
  • Sound insulation
  • Thermal insulation
  • Building energy
  • Monument protection


Basement conversion and its huge potential

The basement is often the stepchild in a single-family home. It offers space for heating, for drying laundry and for storage. Basement rooms often have a lot of potential for creating beautiful living space or a pleasant wellness area. Teenagers are generally delighted to have their own space in the basement, which offers them a place to retreat. Even an atrium, an indoor swimming pool with sauna or a relaxation zone connecting to the outdoor pool can be realised by a basement conversion. For sports enthusiasts, a fitness studio is the highlight of the house. Because with an appealing design, training is even more fun. For many people, a party cellar is a dream come true. And this can be implemented relatively easily. A chic bar, bar stools or lounge furniture, the right lighting and appropriate decoration quickly transform the former storage room into a trendy party zone. In any case, a basement conversion brings with it an increase in living comfort, more space in the house and an increase in the value of the property when it is sold. Other basement conversion ideas include:

  • Wine cellar
  • Guest room
  • Dressing room
  • Home cinema
  • Table tennis room
  • Billiard room
  • Hobby room
  • Game room
  • Utility room
  • Music room
  • Home office
  • Bathroom with bathtub or whirlpool
  • Apartment for multi-generation house or for rent

 

What is important to bear in mind when converting a basement?

The basement conversion should create pleasant living spaces or a practical utility area. In order to create a healthy indoor climate and at the same time meet the legal requirements, the basement must have a number of different features. Dry walls for one as well as a certain ceiling height. Plenty of light and fresh air, provided by appropriate lighting and the installation of suitable windows or lighting panels, make it easy to forget that the rooms are underground. With a heating system and appropriate insulation, the basement is transformed into a feel-good living space or a relaxing wellness oasis. By the way, the government supports basement conversions with subsidies if they improve the energy efficiency of the house. In order to maintain good living comfort in the converted basement and at the same time fulfil the legal requirements, the following points must be observed:

  • Minimum size of the window area (10% of the room area)
  • Minimum requirement for the clear room height (from 2.2 metres depending on the federal state)
  • Fire protection requirements such as fire protection door and wall to the utility cellar
  • Second escape route for the living rooms e.g. via an external staircase
  • Good insulation of the basement and the floor
  • Impact sound insulation on the ceiling to the living space above
  • Installation of a heating system or extension by (electric) additional heaters
  • Installation of a sewage lifting unit when installing a shower or bath
  • Power connection for the sauna
  • Requirements for renting out a converted apartment

 

Legal requirements for basement conversions

If a part of the basement is converted into living space, the authorities assume that this is a change of use. This means that in some federal states building permission is required. In most German regions, however, basement conversions for owner occupation purposes do not require approval. The conversion to a granny flat in the basement is always subject to approval and may even require an additional parking space for a vehicle.

 

Extending the house upwards by adding storeys

Attic or basement conversion is only possible if the house has a basement or an unused attic suitable for conversion. If the roof truss is too low, or if there is limited space on the property, adding a storey can be the best solution for bungalows or houses with a flat roof. A flat roof is usually the ideal prerequisite for adding a storey. Because not only can the living space be extended upwards, but a roof terrace can also be added, for example.

If the house has a relatively new pitched roof or another roof with a slope, this can be raised to fit the new storey or, alternatively, a knee wall can be added underneath. The labour costs are higher though, as the roof has to be removed and put back on again. If a new roof is needed anyway, then the right time to do it is when adding an extra storey to your house. Since a new roof usually improves the energy efficiency of the house, subsidies can be claimed for the renovation measure. Adding a storey is more cost-intensive than a mere interior conversion, but depending on the structural conditions, it is cheaper than a new building or the addition of a living space with foundation slab. This is because the heating system and the hot water supply can almost always be extended to the upper floor, as can the other house connections.

 

Prerequisite for adding a storey to a house: Statics, development plan and building permit

However, adding an additional storey requires that the statics of the house are suitable for this and that the local development plan permits this. This is because the walls, the storey ceiling and the foundation slab all have to be able to support the weight of an additional storey. Instead of using concrete or brick, adding another storey made of wood can be a more lightweight alternative. A structural engineer can make the necessary calculations and an architect can help with the application for planning permission. Because this must always be obtained before adding a storey to the house. The interior finish of the added storey is then subject to the energy efficiency compliance regulations.

 

Annex for a conservatory or as a house extension

If the property is large enough, a house extension is another option for expanding the living or utility space. One way is to inconspicuously expand the living space by one or more rooms on one or more floors. The visual appearance of the existing house facade is continued in the extension. However, a house extension can also add impressive architectural accents. A stylish flat-roof extension, for example, skilfully contrasts the classic design of a detached house with a hipped roof. By choosing a different material or an eye-catching colour for the facade, the extension also enhances the visual appearance of the house. A conservatory is an attractive extension of the house into the garden. It extends the garden season and brings nature indoors at the same time. The glass extension is therefore one of the popular ways of extending the area of a house. A ground-level extension of an office or several offices with separate entrances may become necessary for business reasons. The cost of an extension depends on its design. It is cheaper to create utility space than to extend the living space, because this requires a solid foundation slab and a roof. Neither of these are required in interior conversions. If an existing roof is used and the statics are appropriate, adding a storey to the house is often cheaper to implement than a new extension.

 

DIY when converting or extending the house

If you have the necessary DIY skills, you can save a lot of money when converting or extending your house. A dry basement is relatively easy to convert into a party room or hobby room, even for non-professionals. Installing a shower or a bathroom is already more challenging, as is laying tiles or insulating the walls and roof. When installing a sauna, an electrician must be consulted for legal reasons, at least for the high-voltage connection. The extension of the heating system may be carried out by homeowners themselves. However, this work is subject to the inspection and approval of the chimney sweeper. The same applies to measures for sound insulation or fire protection. Depending on your skills and your time at hand, the costs for an extension, an additional storey or a house conversion can be significantly reduced by doing some of the work yourself. Applying for a building permit, on the other hand, always requires the cooperation of an architect. You need to factor in an average of 0.5 percent of the total construction costs for this. If subsidies are claimed for simultaneous renovations, the permitted personal contribution may be limited depending on the programme. No specialists are required by law for the following work:

  • Bricklaying
  • Drywall
  • Installing PVC, laminate or tiles
  • Plastering, wallpapering and painting work
  • Window and door installation
  • Installation of heating system
  • Sanitary installation
  • Electrical installation without connection to the fuse box
  • Installation of a sauna, but without the power connection


Increasing the value of the property by converting, extending or adding a storey to the house

Extending your own house inside or out creates new living space or spacious utility areas. But it is not only the floor plan that changes, but also the quality of living. A quiet office in the attic or a playroom in the basement provide harmony in the home, while a fitness studio or sauna increase the recreational value of the home. Adding another storey enlarges the house without reducing the plot area. The addition of a glass conservatory extends the house outwards and connects it with the garden. House extensions offer the opportunity to improve the energy efficiency of the property. All these extension measures have one thing in common: They expand the living or usable space and increase the attractiveness of the house for its residents. Furthermore, a house extension increases the value of the property.

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