The firm said increasing the maximum LTV, along with its manual underwriting, means brokers with complex cases will be assisted.
Complex cases include expat, new-build, later life and intergenerational lending.
Suffolk Building Society said it was also removing its requirement for later life borrowers to show a minimum income of £20,000.
Charlotte Grimshaw, head of intermediaries at Suffolk Building Society, said: “Having recently enhanced our loan-to-income ratios for applicants with rental history, it’s great to offer new-build flats and JBSP for those with smaller deposits.
“JBSP is already proving very popular with our brokers. As well as boosting affordability, there are tax planning advantages when it comes to liability for second home stamp duty surcharge, and first-time buyers retaining their stamp duty discount.
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“We hope first-time buyers, people starting over, and some downsizers, will also welcome the ability to borrow up to 90% on new-build flats. Apartment living can help to address the UK’s housing needs, particularly for those purchasing in urban areas.”
Earlier this year, Suffolk Building Society said it will offer up to 5.49 times applicants’ income for those with a rental track record to support first-time buyers.
