County Durham and Darlington Fire and Rescue crews were called to Beech Close, Brasside, on Monday evening. The street is in the Framwellgate Moor area of the city.
The man was pronounced dead at the scene.
A joint investigation between the fire service and Durham Police has been launched, a fire service spokesman said.

25 November 2016 Last updated at 07:57 GMT
It was given to the London museum in 1905 by a rich business man and the giant skeleton has been amazing visitors for many years as they enter the museum's main hall.
It isn't a real dinosaur but a life size plaster replica of the skeleton of a Diplodocus.
Now Dippy is on the move on a trip around the UK, watch this video to find out more.

Matthew Gordon said he never "cut corners" when it came to maintenance and spent more than Â£6,000 in a year on repairs to the truck.
He told Bristol Crown Court if the lorry had been unsafe he "would have done something about it".
Mr Gordon, 30, of Dauntsey, Wiltshire, denies 14 charges against him.
Mr Gordon, the owner of Grittenham Haulage, is defending himself following the crash on Lansdown Lane on 9 February last year.
Mitzi Steady, four, Robert Parker, 59, Philip Allen, 52, and Stephen Vaughan, 34, died in the crash in 2015.
The lorry hit several pedestrians, including Mitzi, from Bath, and a car containing Mr Allen and Mr Vaughan, both from Swansea, and Mr Parker, from Cwmbran, south Wales.
Driver Phillip Potter, 20, also of Dauntsey, denies causing the deaths by dangerous and careless driving. He is also charged with causing serious injuries to Karla Brennan and Margaret Rogers - Mitzi's grandmother - by dangerous driving.
He denies a total of 10 charges against him.
Peter Wood, 55, from Brinkworth, Wiltshire, a mechanic who carried out safety checks on the truck, denies four charges against him.
The trial continues.

Grand leaves along with club hero Jason Walker, both aged 32, teenage defender Brad Carroll and 17-year-old goalkeeper Dan Eccles.
Midfielders Mo Fafana, 28, Dan Pilkington, 25, Paddy Lacey, 23, and Alex Newby, 20, also exit.
Four players have been offered contract renewals, including Newby's brother, 20-year-old Elliot.
Fellow midfielders Alex Ray Harvey, 26, Andy Parry, 24 and 17-year-old defender Steve Williams make up the quartet who have been offered a new deal following an 11th-placed finish in the National League.
Grand helped to captain the side to promotion to the fifth tier of English football, while Walker was the game-winning goalscorer as Barrow lifted the FA Trophy in 2010.
Barrow have also said that talks are on-going to renew the contract of striker Andy Cook, 25, who scored 24 goals in 45 appearances for The Bluebirds this season, despite his willingness to pursue a career in the Football League.
BBC Cumbria Sport understands that Barrow have offered to make the talisman - and third highest goalscorer in the National League this season - the highest paid player in the club's history.

The would-be thieves - four men dressed in black - struck at a service station in East Delph, Whittlesey at 02:55 BST.
Cambridgeshire Police said the cash machine was left at the scene and it was not clear whether cash or anything else was stolen.
Fire crews closed the petrol station on safety grounds.
Two other trucks were also used in the raid.
A red car - possibly an Audi - was seen leaving in the direction of the Dog In A Doublet pub and Thorney, Cambridgeshire Police said.
On Saturday, a JCB was used to steal a cash machine from a newsagent's in Harlow in Essex.
A police spokesman said it was "too early to say whether it [the Whittlesey raid] is being linked to others, but we are keeping an open mind".
A man has died in a house fire in County Durham.
[NEXT_CONCEPT]
Dippy the Diplodocus is one of the Natural History Museum's most recognisable residents.
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The owner of a lorry that crashed on a steep hill in Bath killing four people has told a jury he did not think the vehicle was unsafe that day.
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Captain Simon Grand will leave Barrow as eight players fail to have their contracts renewed.
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Ram-raiders using a JCB digger and a forklift truck destroyed a petrol station building in a bid to steal a cash machine.