More funding plus regulations to establish embodied carbon targets are needed, they say.
RIBA president Simon Allford said the proposals are "overshadowed by the lack of adequate funding and the absence of vital embodied carbon targets for new buildings."
The plans "fall far short of the action needed to realise the objective of net-zero" added James Rixon of Architects Climate Action Network (ACAN).
"The approach that the UK government is taking involves doing enough to persuade the population that they are taking the problem seriously while, in reality, not doing anywhere near enough to prevent collapse," Pawlyn told Dezeen.
"We need to rethink the fundamental purpose driving our economy, our relationship with the rest of the living world and the way we design, plan and operate our built environment."
Growing calls for embodied emission regulation
The document outlines how the country aims to reach its goal of becoming net-zero by 2050 in line with Paris Agreement targets, at which point it hopes to no longer contribute any additional carbon dioxide into the atmosphere.
But architects have critiqued the UK's approach for focusing solely on operational emissions from electricity and heating while failing to set rules around the embodied carbon footprint derived from material sourcing and construction, which accounts for around half of a building's lifecycle emissions.
"After over a year of waiting, this strategy does not go far enough," said RIBA's Allford in reference to the Heat and Buildings Strategy, which forms part of the UK's wider net-zero roadmap.
"Positive references to 'fabric first' and 'whole building' approaches are overshadowed by the lack of adequate funding and the absence of vital embodied carbon targets for new buildings."
"Moving ahead, we hope for tighter regulation, substantial and sustained funding and adaptation of tax mechanisms to encourage 'able to pay' homeowners to retrofit their homes," he added.
RIBA is among a growing number of industry voices that are calling for mandates around calculating and reducing the embodied carbon footprint of a building including architect Andrew Waugh and advocacy group Part Z.
Green heating strategy could leave "people living in cold homes"
The government's roadmap set out plans to cut down operational emissions by having the entire country run on renewable energy and aiming to install only low-carbon heating systems such as heat pumps come 2035.
These absorb the warmth stored in the ground or air around a building rather than relying on natural gas but are generally more expensive.
To make the technology affordable, the government will be giving 90,000 households across the country a £5,000 grant over the next three years, in the hope that this will increase demand and ultimately drive down the price for the wider population through economies of scale.
However, the UK's independent Climate Change Committee has forecast that around five times as many heat pumps would need to be installed by 2025 to hit emissions targets.
"Bolting on a new heat pump or hydrogen boiler will not resolve the issues of heat and thermal inefficiency that are present in our existing housing stock," argued Rixon of ACAN.
"While heat pumps use less energy to provide the same amount of heat as gas boilers, electricity currently costs about three times more than gas," he continued.
"Without significant improvements in energy efficiency, householders with newly installed heat pumps will face significantly higher bills for heating, increasing rather than reducing the risk of unaffordable energy prices, leaving people living in cold homes."
While the net-zero strategy sets out aims for all UK households to reach a medium energy efficiency rating in the
next 14 years, Rixon argues that the policy offers little financial support for achieving these improvements.
"The government's target of achieving an energy performance rating of EPC C by 2035, caveated 'cost-effective, practical and affordable', is totally lacking in ambition," he said.
"It is providing some additional funding for improving the energy efficiency of social housing and low-income households but no support for homeowners. The government should introduce fiscal changes, including reducing VAT on home improvements, to incentivise investment in upgrading homes."
Regenerative approach needed to restore nature
Pawlyn from Architects Declare added that more systems-level changes are required to avoid runaway climate change, as we need to fundamentally need to redesign buildings to regenerate the natural environment rather than simply reducing the amount of harm they do.
"We need change at a systemic level if we are to rise to the challenges of the planetary emergency," he said. "We need to urgently shift from a sustainable mindset to a regenerative one and that requires much bolder thinking than is currently evident."
Currently, the government considers efforts to restore the UK's natural ecosystems as separate from its built environment strategy, with £625 million designated for planting trees and restoring peatlands so they can serve as natural carbon sinks.
The roadmap also sets out aims to engage 75 per cent of UK farmers in regenerative farming practices come 2030 to cut down emissions from agriculture and help lock away atmospheric carbon in soil.
At the same time, a billion-pound carbon capture and storage infrastructure fund will be established with the aim to pull 20 to 30 million tonnes of carbon dioxide from the atmosphere every year by 2030.
Globally, an estimated 10 billion tonnes of CO2 would need to be removed from the atmosphere annually by 2050 through technologies such as direct air capture and mineral carbonation to stabilise global warming as close to the crucial 1.5-degree threshold as possible.
Main image is of ACAN members at the Global Climate Strike in 2019. Photography by Joe Giddings.