Matéo Moglia*, Henri Wöhleke**

*What are the housing supply costs in dense areas? Levering a unique dataset, linking development costs, building permits, and precise land occupation, I provide precise estimates of the housing construction costs by project type. I embed those cost estimates in an optionvalue forward-looking model of land (re)development, calibrated on the Paris area. Thanks to model estimation, I am able to precisely separate regulation, construction, and land costs in the local housing supply elasticity computations. Counterfactual exercises highlight the importance of targeted subsidies and loans to address the current housing supply crisis.

**Under a post-2008 floor system, central banks set the policy rate by paying interest on abundant reserves rather than by rationing their supply, raising the question of how monetary policy still reaches the real economy. I extend the floor-banking model of Piazzesi, Rogers and Schneider (2022) by closing the loop between the policy rate and bank balance sheets: bank holdings of non-reserve securities A_t are tied to a stock price index q_t via A_t = P_t , q_t, with q_t responding endogenously to the policy rate through the household stochastic discount factor. The resulting New Keynesian DSGE model embeds three transmission channels: the standard NK channel through the household Euler equation, a reserve-side bank channel operating through the central bank's reserve-supply rule, and an endogenous bank collateral channel arising from the closure. Calibrating to U.S. quarterly data, a four-way decomposition of the deposit response to a contractionary monetary shock shows that endogenous collateral amplifies the deposit response 3.5-fold relative to a model in which it is shut off, while output amplification is only 2.9 percent: the channel changes how monetary policy reaches the economy more than how much. The reserve channel provides modest dampening (3.4 percent of the total banking effect on deposits) that is structural to the floor regime and vanishes when the reserve-supply rule is muted. A robustness test in which households are made near-indifferent to deposit liquidity confirms the result is structural to the bank balance sheet, not driven by household preferences.