TL;DR Support building more (subsidized) affordable housing in Cambridge by signing this petition: https://docs.google.com/forms/d/e/1FAIpQLSf9zDU-qYFHvMoumIc_uWV8IUJu893WkRre_QINhB_HMGRETg/viewform

The Longer Explanation

Housing in Cambridge is way too expensive, and it really needs to be cheaper. How should this be solved?

Subsidized housing can help people...

There are a long list of ways to improve the situation, but here we're discussing a particular kind of subsidized affordable housing. Here's how it works:

1. A real-estate developer (usually, but not necessarily, a non-profit) gets a bunch of grants from the state, the city, and so on.
2. The money is used to buy land and construct a new building. The funding agencies make sure the result is decent.
3. The apartments are then rented at below-market rates to people with low incomes.
4. If this is a for-profit developer, there are caps on how much money they can make, again supervised by the granting agencies.

Basically, by subsidizing land purchase and construction, rent only needs to cover maintenance, instead of the mortgage a normal real-estate developer would have taken out.

The Cambridge Housing Authority, for context, has 21,000 people on the waitlist for subsidized affordable housing. That's a lot of people.

... but land is expensive!

1. Cambridge has limited land, and it's expensive land.
2. The more units you build, the more you can amortize the cost of land acquisition across units.
3. The more units you build, the more affordable housing you have.

So ideally you'd like build as many units as possible.

... and Cambridge has height construction limits!

Except—you can't just build a 6 story building necessarily. Cambridge has zoning rules that limit building height, to the point where many perfectly lovely existing buildings would be impossible to build today.

The (almost) solution: The Affordable Housing Overlay

So Cambridge passed a law saying "if you build affordable housing, it can be taller." It still had height limits, though... and they turned out to be too low in some cases.

Consider 2072 Mass Ave: it was supposed to be an 8-story affordable housing building, on Mass Ave. There is an 8-story building a block away. But! AHO zoning only allows 6 stories, so it need approval by the Board of Zoning Appeals.

A bunch of neighbors showed up and said "this will mean competition for our street parking" and "tall buildings are so ugly" and "this is too tall for this area" and so on, and the BZA made clear they would never approve it.

The proposed solution: increase height limits for affordable housing

Along main roads across Cambridge (but not side streets), affordable housing buildings would be allowed to be taller. Returning to our example, 2072 Mass Ave could be built without NIMBY neighbors being able to kill it.

There would also be some more flexibility if green space is added, which would've allowed some current projects to have more units and more green space.

Potential questions you may have

"I don't qualify for this sort of housing, how does this help me?"

The proposed law would make it easier to build subsidized housing for people with low incomes. You might not qualify and still have too-high rent. And sadly this particular proposal won't help with that.

But the people organizing the petition, A Better Cambridge, as well as supportive City Council members, have a bunch of additional proposals to increase the housing supply so your landlord has less of a monopoly. This isn't the answer, but it's part of the answer.

"I like this proposal, but I think building more regular housing is bad"

That's a different discussion, but that's fine: you can still sign this petition, which is just about the AHO extension, and when other proposals come up that won't stop you from arguing against them.

More questions? I'm not an expert, but I'll try to answer any (or find someone more informed than me)