Umbau GmbH Logo von Umbau GmbH – Vectorgrafik

Bauträger und Baubetreuer

Specialists in redeveloping existing buildings

Our Business


UM Bau GmbH helps its clients to successfully and profitably develop real estate property in Austria. We offer our clients a single point of contact for all project-related matters, managing all necessary relations and work with municipalities, engineers, construction workers, and more. In short, contracting our services brings our clients a stress-free building experience with 100% peace of mind.

We offer our services in the following 2 ways:

Full Suite

We run the entire (re)development project from “A to Z” managing all day-to-day construction management operations.

Pick and Choose

We run specific project tasks only.

We work for private individuals, commercial investors, businesses and government agencies. As a trusted partner, we are contracted by our clients to provide independent expertise and hands-on organisational support in areas of real estate acquisition, planning & design, construction supervision, interior design, and more. Clients also buy into our tested and trusted network of partner companies and craftsmen. These partners provide professional skilled labour, quality products, industry standard warranties and, of course, competitive prices.


We are specialised in REdeveloping existing buildings into apartment buildings, private homes or boutique hotels. We take an old building and give it a valuable second life, often with a new function. Our first point of departure is to assess the remaining economic value of any given building. We cleverly REuse as many of the existing structures (e.g. walls, basement, roof) as possible, as part of a new design. In doing so, we do not compromise on floor plan layout or structural design. It is a complex puzzle to solve and requires significant conceptual vision and technical insight.

Our specialism provides our clients with three major benefits:

  1. It allows our clients to significantly reduce construction costs by cleverly reusing existing building structures that still have substantial value.
  2. It allows our clients to preserve any structural building elements that hold historical, artistic and/or sentimental value.
  3. It allows our clients to adopt an eco-friendly approach to construction by limiting unnecessary material waste and debris.


Our approach to any real estate development or redevelopment project is about spending a lot more time on-site than behind our office desk. We do so before and during the entire project life cycle.

Our committed on-site presence allows us to collect all the essential technical and environmental data required to prepare a solid and fitting building concept. Once construction starts, we are able to properly supervise and coordinate work by third parties and deal with all daily questions and issues that arise. Being on-site also allows us to make last-minute decisions on design details, achieving the best overall results.

Our Work














Free to choose

Our expenses are usually offset against the savings we bring our clients. We successfully mitigate the risk of budget overruns. We ensure our clients pay a fair market price for materials and labour procured. Not to mention the time and money our clients save by outsourcing work to us.

We always offer upfront fixed pricing. We don’t like hidden or variable costs. We have three pricing models from which our clients can choose:

Fixed Price per Project
We calculate a fee between 7.5% and 10%, based on total project cost.
This model is designed for clients who wish to contract a Full Suite service. They want no direct operational involvement in the project and are seeking to outsource work to a strong partner. They value their own time and desire 100% peace of mind.
Fixed Price per Assigned Task
We agree to a fixed lump sum to complete a specific task.
This model is designed for clients who want a Pick and Choose service. They want an expert team to jointly develop the project with them. As such, they only outsource cer-tain tasks (e.g. develop an interior design plan or supervise all construction work).
Fixed Price per Hour
We charge an hourly fee of 125 € per hour.
This model is designed for clients who intend to run the project themselves but are seeking occasional on-demand expert advice or organisational support. They value a professional second opinion on their project.

The Team

Urban van Stralendorff

Owner / Technical Lead

Urban was born in Sweden, the son of a Dutch architect. He lived and worked in Stockholm, Copenhagen and Amsterdam, and was constantly active in the field of construction. He spent over 20 years personally rebuilding houses, historical ships and decorating film sets. His 100% hands-on building experience allows him to fully understand the nature and challenges of any given building project.

Urban is an accredited and certified real estate developer registered with the Austrian Chamber of Commerce.

Martijn Bos

Owner / Commercial Lead

Martijn was born in Holland, the son of a Dutch family of entrepreneurs. He has lived in 9 countries and travelled to more than 50, and now speaks 6 languages. His extensive travel in life has exposed him to many buildings, interior designs and living concepts. Martijn’s broad expertise adds a strong creative touch to each project.

Martijn holds a degree in Business Administration (BBA) from Amsterdam Poly-technic.

Elisabeth van Stralendorff

Creative Advisor

Elisabeth was born in Austria to a family of musical artists. She graduated from Goldsmiths, University of London, where she completed a degree in fine art. She specialised in textile art and established a name for herself in Japan as an inde-pendent artist.

Danielle Koole

Interior Design Consultant

Danielle was born in Holland to a Dutch family who owned a business in interior design. She subsequently graduated from the Dutch Wood and Furniture Col-lege and later completed a graduate degree programme in Cologne as an interi-or designer. Over the years, she has worked for several renowned home & life-style stores representing famous international designer brands. Her career has taken her from Amsterdam to Rotterdam and Düsseldorf and, most recently, Dubai, where she spent five years working as a senior interior design consultant, completing turnkey projects.

Our Principles

Social Responsibility


We regionally source skilled labour from small and mid-sized family-run companies that truly understand the craft of building. By providing them with work, we directly contribute to their livelihood and help to preserve their valuable know-how for future generations.


In all our building designs, we promote the use of ecological building materials of lasting quality. We also encourage the use of smart technology to efficiently manage energy and water consumption. This includes the use of modern BIO heating installations generating energy from sources such as solar power or wood pellets.


A building has an exceptionally long life. That is why we put so much emphasis on a building’s design. It can enhance the look and feel of a neighbourhood and contribute to the well-being of its owner and the community. We feel a collective responsibility to give any new or re-developed building more than just four walls and a roof.


Independent & Transparent

We strive to be 100% independent when advising our clients and work solely to serve their best interests. We have no financial or contractual ties to any third party suppliers or stakeholders who could cloud our judgement or create a con-flict of interest. We guarantee full transparency of our business operations.

Contact Us

UM Bau GmbH
Rössing 10

8972, Ramsau am Dachstein


Phone: +43-664-7503 2454


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