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TDC101 Putting the Pieces Together

Example: Boulder County, Colorado

As early as 1973 the county recognized a loss of agricultural land to residential development and began instituting planning tools to reduce this affect. Originally a clustering technique called Non-Urban Planned Unit Development (NUPUD) was adopted where any property larger than 35 acres could have 2 units with an additional developed unit per 17.5 acres conserved. A maximum of 25% can be developed and a conservation easement is to be placed on the remainder. The intention of NUPUDs, to allow farm families building sites, did not stop the trend of agricultural land loss as developers were purchasing 35 or greater acre properties and using the NUPUD program to develop country estates.

Twenty years later the county increased the land required to do a NUPUD to 320 acres and adopted a TDR program where densities could be moved to non-contiguous parcel under different ownership. The county also has a Purchase of Development Rights program. Not all PDRs are extinguished upon purchase as they are in some other programs. They may be sold as TDRs after public review with the proceeds going to further open space and conservation easement acquisitions by the county.

The Program

Boulder County is 2/3 mountainous and 1/3 plains. The Transferable Development Rights program is currently only used in the Plains portion of the county, although the county is in the process of designing a program in the mountainous parts. The purpose of the program is to protect lands with productive agricultural value or environmentally sensitive areas such as wetlands, rare plants or wildlife habitat. It is not specific to one geographic area.

Under the TDR program 2 TDR units per 35 acres can be transferred with an extra unit per 35 acres if an undivided interest in water rights stay used on the land is deeded to the county.

With very limited opportunities, no subdivision developments can currently occur in the county without the use of TDRs. Receiving sites are not designated in this program with two exceptions – Longmont and Niwot. Other receiving sites are approved by assessing “performance” driven factors; for example if the site is near a major transportation artery and water and sewer is available it is a likely candidate as a receiving site.

In the unincorporated areas around Longmont TDR sending and receiving developments can be permitted pursuant to an intergovernmental agreement between the city and the county. The county uses development standards that match those of the city since once the development is complete it will be annexed into the city at some future point. Platted TDR receiving site densities range from 0.75 – 2.0 acres per unit. Without TDRs, these same lands could only be developed at much lower densities of one unit per parcel (i.e. any parcels under 70 acres in size and which are legal buildable sites cannot be subdivided further and can therefore only be developed with a single residential dwelling). The conservation easements acquired as a requirement of the TDR program are held jointly by the county and the city.

Niwot is an unincorporated community with about 4,500 people. With county assistance the community designated a number of TDR sending areas in their buffer and four receiving sites within the Community Service Area. The county has sold some of the PDRs they had acquired from eligible buffer area properties to developers around Niwot. Currently each TDR costs between $60,000 and $90,000 on the free market.

Public support for programs that preserve open space is considered very high in Boulder County. Very few people attended open houses or filed any type of complaint in response to the TDR program. The “Open Space Sales Tax” has been reauthorized repeatedly in Boulder County since initial voter approval in 1993.

Key Lessons

A very positive feature of this program, especially to the development community, is that  the County Commissioners (akin to Alberta’s municipal Councillors) will provide the developer an opportunity to present and have a review or “pre-screen” of their draft plans at an earlier stage than if developing without TDUs. This saves up-front resources and provides some indicator to the proponents about whether or not they have a viable proposal before they make significant expenditures in time, finances, and specific site design/layout work.

Another positive feature is that effort to encourage a healthy matrix of land uses in the receiving areas. In Boulder County, up to 5% of receiving areas may be used for non-residential purposes such as office parks, industrial or public uses (e.g. schools). The use of TDUs is not required to build these kinds of facilities.


Boulder County’s land conservation programs (e.g. PDR, open space, TDR, NUPUD) are considered very successful. However with success sometimes comes criticism. The county estimates that perhaps less than 20% of private unincorporated lands are unencumbered and vacant or undeveloped. Following basic supply and demand rules this means the remaining land can be quite expensive to develop. This has caused some people who work in Boulder County to live in surrounding counties where they can buy land and accommodations for less money. As a result, quality of life issues associated with a fairly large commuter population have become an increasing concern to residents in both the municipalities and county.

As this program has evolved naturally there have been changes made to the “rules”. As a result there was caution expressed from a public support perspective that the program needs to be very clear in its purpose and function. The developer and the landowner really need to understand what they can and cannot do on the land once the TDRs have been transferred. It was suggested that when changes are made that there needs to be very clear communications around those changes and about their implications on the old rules, restrictions or guidelines.



What is a TDC Program?

The Why, What, How and Who's of TDCs

Miistakis Reports

Government of Alberta


Papers and Reports

Web Resources



Support Organizations and Consultants

American Examples

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Also, check out our full list of TDC Resources.