​Bill Shorten used his opening address to Labor’s national conference to unveil new subsidies to promote more affordable housing at a cost of $6.6bn over a decade.

Shorten took the opportunity of his opening pitch to the delegates and onlookers gathered in Adelaide for the three-day event to commit to a target of 20,000 houses built in the first term of a Labor government.

The policy, unveiled on Sunday, offers 15-year subsidies of $8,500 a year to investors who build new houses, with the taxpayer support conditional on the dwellings being rented to eligible tenants at 20% below market rent.

The cost of the measure is $102m over the forward estimates to 2021-22, and $6.6 bn over the decade to 2028-29. The program would provide support for 250,000 new units and houses over its lifespan.

Shorten planned to tell conference delegates Labor’s mission between now and the next federal election is not only to secure government, but also “rebuild trust in our democracy” and “restore meaning to the fair go”.

“We must revitalise around the nation what we in this hall hold as an article of faith: the idea that government has the power to bring meaningful progress into people’s lives,” the Labor leader will tell delegates, according to a speech extract circulated ahead of Sunday’s address.

“A hidden struggle in this country is being fought by the hundreds of thousands of our fellow Australians who can’t afford to live anywhere near where they work. They’re spending over a third of their pay packet on rent – and plenty more on petrol each day they travel.

“Rental affordability is a national challenge and it demands national leadership. Building more affordable housing is infrastructure policy. It is cities policy. It is jobs and productivity policy. And it is population policy”.

Shorten says the policy will provide certainty for property investors to build new dwellings knowing that subsidies are available for a decade. The program builds on the existing national rental affordability scheme.

The Australian Housing and Urban Research Institute estimates there is currently a shortfall of more than 525,000 affordable rental properties in Australia.

The Labor leader says access to housing stands as one of the biggest challenges in addressing intergenerational inequality. “There is a persistent and increasing wealth gap which is locking Australians out of the housing market”.

With a federal election looming, and the Morrison government behind in the polls, the three-day conference provides Shorten with an opportunity to rally the base and project a message to voters that Labor is ready for government.

But there have been several policy flash points going into the event, including a debate about whether to commit to an increase in the Newstart payment, and an argument over environmental regulations.

A draft national platform signed off by the ALP national executive in October committed Labor to significant legal reforms as well as an independent national Environment Protection Authority (EPA) and a national environment commission that would act as an environmental watchdog – but the shadow environment minister, Tony Burke, is resisting some of those changes.

There has been intensive work over the past 48 hours to iron out contested positions on refugee policy, trade and workplace relations reform, and well as contentious foreign policy issues, like the recognition of Palestinian statehood. The factional caucuses met in Adelaide on Saturday afternoon in advance of Sunday morning’s kick off.

The Labor leadership has been negotiating with the trade union leadership for months on a range of policies that would strengthen the current regulatory framework, with that dialogue an effort to minimise public confrontation in Adelaide.

The Construction, Forestry, Maritime, Mining and Energy Union, the most influential union on Labor’s left, has signalled it will push to strengthen the party’s stance on labour relations. Ahead of the conference, the CFMMEU national secretary Michael O’Connor said: “Record low wage growth and inequality are hurting our economy and our society.”

“Wages will only improve if we improve the voice and bargaining power of workers through strengthening trade unions and increasing trade union membership.”

It also looks likely there will be a ballot of the conference for positions on the party’s national executive – which is unusual.