They are an iconic part of Glasgow's landscape and a popular choice for first and second time buyers.

However the tenements are a blot on the city's green credentials. With significant amounts of heat lost through sandstone walls, sash windows, roofs and floors they are high carbon emitters.

Now, a major project is underway at an empty social housing block to try to create a blueprint for improving the energy efficiency of the distinctive buildings.

Eight one bedroomed flats have been stripped back to their bare bones to allow construction workers to put in place "21st century energy efficiency solutions".

The mammoth retrofitting project has involved air sealing the entire building with the internal and external walls, floor and loft areas insulated and windows triple glazed.

A mechanical ventilation system  delivering a continual supply of fresh air aims to reduce the need for tenants to open windows.

A plan to create 'green' tenements in the south side of Glasgow could be replicated across the city

Air source heat pumps are also being installed in four of the flats, on Niddrie Road, which are owned by Southside Housing Association, with a control group using gas boilers.

The green changes do not come cheap - there is an estimated cost of up to £30,000 per flat but the team estimates the measures will lead to an 80% reduction in fuel bills.

Chris Morgan, Director of John Gilbert Architects, which is involved in the project, said: "Someone that was spending around £100 a month on heating will move into here and broadly speaking will be spending £10 to £15 a month.

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"That's a huge difference.  Ideally what we want to do is put insulation round the outside of the building like a tea cosy.

"But we all know, that we don't want to cover all the beautiful stone buildings in Scotland in insulation and render so where it matters that we can see the stone walls on the outside, we put the insulation on the inside.

A plan to create 'green' tenements in the south side of Glasgow could be replicated across the city

Mr Morgan says owners will often "half-heartedly" put in a bit of insulation or  leave gaps between it.

"About 40% of your heat loss is draughts," he said. 

"What we find is that the windows are almost always the weak point. We put a huge amount of time and trouble into getting the best possible windows and installing them in the best possible way.

"When you close off a building like this, people intuitively think it's going to be stuffy but that isn't the case because what we do is install high quality ventilation and so you have a nice fresh atmosphere in the house without losing all the heat."

A plan to create 'green' tenements in the south side of Glasgow could be replicated across the city

Housing is responsible for around 20% of carbon emissions.

There are more than 75,000 pre-1919 sandstone tenements in Glasgow and they make up around a fifth of the city's housing stock.

However, it's not all bad news for tenement dwellers who are more likely to live closer to shops and amenities with less reliance on cars, helping contribute to the climate-friendly 20-minute neighbourhood.

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Ken Gibb, a professor of housing economics at the University of Glasgow, is involved in the evaluation of the project, which has been funded by Glasgow City Council, the Scottish Government and Southside Housing Association.

"This is a huge issue for Glasgow as it is for Edinburgh.

"It's a unique project in that the block is empty so there are no issues with other owners.

"We are going to monitor the performance of the building once it's finished, which will be around January.

A plan to create 'green' tenements in the south side of Glasgow could be replicated across the city

"Then the tenants will come in and we will find out their experience of living in what will be quite a different property.

"Our assumption is that the air tightness and insulation and triple glazing will effectively greatly reduce the need for heating."

Retrofitting works have been carried out a multi-storey block in the north of Glasgow owned by Queen's Cross Housing Association.

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"Triple glazing is amazing...to tell you the truth, my heating is never on," says George McGavigan, a tenant at the block. "I've got the ventilation system and the only time I open my windows is to wash them."

Housing leaders at Glasgow City Council say "lessons will be learned" from the project and it is hoped elements of it will be replicated.

A council spokesman said: “The retrofitting of homes in Glasgow offers the chance to deliver economic, environmental and social benefits to the people of the city through reduced energy bills and carbon emissions, the creation of thousands of new jobs, and improved living standards and significantly reduced energy poverty. 

"In addition, this will play a key role in meeting our 2030 Net Zero targets, as outlined in our proposals for both the Glasgow Green Deal and the Greenprint prospectus.”