There are a lot of creative ways that homeowners and potential home owners come up with ways to help pay for expensive bay area mortgages.
Renting a room in your home may not only save some money on a large mortgage payment but can also have some added tax savings as well.
Here is an article that we found from Home-Real-Estate.com that discusses tax advantages of renting a room.

Tax Advantages to Renting a RoomIf you are a homeowner that rents out part of your home, you getthe tax benefit of deducting a portion of your home ownership expenses. People that do not rent out a room do not receive thistax break! By renting a room in your house you are reducing your income taxes which means you are increasing your after-tax income!If you rent part of your property (a room or a floor), you must dividecertain expenses between the part of the property used for rentalpurposes and the part of the property used for personal purposes,as though you actually had two pieces of property.Tax Deductions for Renting a RoomWhen you rent a room in your personal residence you can deductexpenses related to part of the property used for rental purposes. These deductions include the following:
Real Estate Taxes and Home Mortgage Interest
General Maintenance Expenses such as electricity, gas,HOA fees, general repairs to appliances that are availableto the whole house (ie over, refrigerator, water heater, etc..)
Expenses tied directly to the room itself. Examples wouldbe installing a phone line or cable line directly into the room.
Depreciation on the part of your residence used for rentalpurposes
Dividing ExpensesIf an expense is for both rental use and personal use, such ashome mortgage interest or electricity for the entire house, you mustdivide the expenses between rental and personal use. You can use any method for dividing expenses. The two most common methods for dividing an expense are one based on the number ofrooms in your home and one based on the square footage of yourhome. Example: Eric rents out a room in his 3 bedroom house to Johnson. The room is 20 x 10 feet, or 200 square feet. Eric's entirehouse is 2000 square feet. Eric can deduct as a rental expense 10% of any expense that must be divided between rental use andpersonal use. If Eric's electrical bill was $800 for the entire house in2005, he can deduct $80 ($800 x 10%) as a rental expense. Thebalance, $720, is a personal expense that he cannot deduct.If Eric has a home office, he can claim a greater deduction. Let'sassume Eric 's 3rd room is an office. The office is 15 x 10 feet, or150 square feet. This is 7.5% of his house (150 square feet / 2000square feet). Eric can deduct $140 of the electrical bill for the year($800 x 7.5% as a business expense and $800 x 10% as a rentalexpense). Note that you do not have to divide expenses that belong only tothe rental part of your property. For example, if you paint a room that you rent, of if you pay premiums for liability insurance in connection with renting a room in your home, your entire cost is arental expense. Expenses That Can be Fully DeductedThere are expenses that can be fully deducted and do not have tobe divided between personal and rental use. This would includethe installation of a separate phone line running into the rental room the installation of a cable line. In these cases, you can deduct100% of the cost as a rental expense