The computation of Value at Risk ($VaR$) has long been a problematic issue in commercial real estate. Difficulties mainly arise from the lack of appropriate data, lack of transactions, the non-normality of returns, and the inapplicability of many of the traditional methodologies. In addition, real estate investment is difficult to diversify and specific risk remains latent in investors' portfolio. It follows that risk of the entire market does not correspond to risk an investor bears. Therefore the risk measurements based on index do not represent the specific portfolio risk. As a result, calculation of this risk measure has rarely been done in the Real Estate field. However, following a spate of new regulations such as Basel II, Basel III, NAIC and Solvency II, financial institutions have increasingly been required to estimate and control their exposure to market risk. Hence, financial institutions now commonly use ``internal'' $VaR$ (or Expected Shortfall) models in order to assess their market risk exposure. The purpose of this paper is to propose a model that incorporates real estate portfolio specificities in a real estate VaR model.