Q: Are Shari’ah compliant home purchase plans considered a debt for zakāh purposes?
الجواب حامدًا و مصليًا و منه الصدق و الصواب
A: Under the Murabaha home purchase plan the client purchases the desired property on a deferred payment basis from the financier. Ownership of the property is vested in the client at the time of contract and in return the client incurs a debt for the balance of the purchase price payable to the financier according to an agreed schedule. Under the Ijarah and Diminishing Musharakah home purchase plans the only debt incurred by the client is that of the outstanding monthly rental payments subsequent to his use of the property. This debt is then settled on a monthly basis by virtue of the rental payments. 
For a detailed breakdown, please see the Zakāh on Islamic Home Purchase Plans research paper on the Al Qalam website.