Chiefs at UCATT have written to the major house builders demanding the introduction of extreme weather health and safety guidelines for construction workers.
The National House Building Council publishes minimum temperature guidance to protect materials on site.
Now UCATT wants to see similar recommendations to protect workers.
It said: “The NHBC makes it clear mortar should not be used below 2 degrees C, whilst construction workers should put their gloves on, get out there and suffer.”
The union also hit out at an “institutionalised” macho culture which prevents workers from complaining about the cold.
UCATT Acting General Secretary, Brian Rye, said: “It’s a complete indictment of an industry that has temperature guidelines to safeguard materials but none whatsoever for the workers. This must now change.
“We have written to the NHBC to ask them to inject some humanity into the industry and provide clear temperature and extreme weather guidelines for constructors to apply to workers.
“In an age when we no longer send young children up chimneys to clean them, we should equally not be forcing construction workers to work in inhuman conditions.
“If it’s too cold for mortar – it’s too cold for mortals!”
There is no current legal minimum or maximum temperature for working outside.
Unions are currently negotiating to have rules or guidance on working in extreme weather included in the Construction Industry Joint Council agreement.