The biggest ‘Grand Design’ project to go way over budget on the popular Channel 4 show was Pembrokeshire’s ‘Low Impact House’ in Glandwr, which exceeded its original cost by a massive 5,300 per cent.

House designers Simon and Jasmine Dale set out to hand-build their ecological home with just £500 in the bank. 

But during the six years it took to build the sustainable property in the Lammas eco community of north Pembrokeshire, the final total had risen to £27,000 which represented a massive 5,300 per cent increase over the initial starting sum.

The findings were published this week by the Been Let Down Professional Negligence team who claim that 77 per cent of all the projects featured in Kevin McCloud’s popular tv programme exceeded their original estimation. 

According to research, many of the projects which ended up massively exceeding their initial cost estimates experienced issues or delays during the construction process although sometimes the additional spend was the result of incorrect structural surveys, groundwork problems or in-experienced DIY project management.

Others, however, simply miscalculated the total costs at the planning stage and were left with no other option than to overspend.

When Grand Designs first highlighted the ‘Low Impact House’, it was promoted as the cheapest house ever to be built in the western hemisphere. 

Work on the three-bedroomed property, situated in Tir y Gafael near Glandwr, began in 2012. 

The main building and roof were made from larch, with lime rendered straw bales filling the gaps and sheepswool was used for insulation.

Around 300 volunteers helped with the construction of the property and it took six years to complete.

Sadly, on New Year’s Day, 2018, the house was destroyed by fire as a result of an electrical fault.

The report states that of the 212 properties featured in Grand Designs, only 16 per cent stayed perfectly within budget. 

Only 4 per cent ended up costing less than originally planned.

The second highest costing property was a 16th century farmhouse, originally estimated at £70,000 but which went on to cost £30,000.

This represented a 328 per cent mark-up on the original estimation.