Labour's Budget failed to address the big issues on an RIBA 'wishlist' including taxing greenfield developments and levelling out VAT on new-build and refurbishments.
The RIBA said the 'biggest shake-up of tax for a generation' was a let-down for the profession.
However, it welcomed the additional £500 million on public transport over the next three years and £50 million extra into public transport in rural areas.
The RIBA supports the cut in VAT on energysaving materials from 17.5 per cent to 5 per cent, and the exemption from landfill tax where material is used to restore land.
'As most architectural firms are small businesses we welcome the reduction in small business tax to 20 per cent, ' RIBA said. The £500 million extra for hospitals and £250 million for schools will also be welcomed.