Why is affordable housing a public good?

If by " Affordable Housing" you mean, the Low Income Housing Tax Credit Program (LIHTC)and by " Public Good" you mean financed by taxaition, then actually LIHTC program is not a " Public Good" Sinced it is not financed by tax payers. The owner that developes a LIHTC projects receives a reduction to his tax liability. That is what makes the LIHTC such a great program, it provides decent, safe and sanitary housing with affordable rents to those whom need it most and tax payers are not paying for it.