U-value of a thatched roof

We came across thatching in progress and were amazed at how thick it is. I'd never seen a cross-section of thatch before. U-values are used to measure the effectiveness of an insulation material. The rate of heat loss = area x u-value of insulation x temperature difference between inside and outside. Thus u-value is measured in Watts per square metre  per degree Celsius and the lower the u-value, the better the insulation because the fewer the Watts are lost. According to one website, the maximum allowed u-value is 0.15 https://www.thegreenage.co.uk/getting-to-grips-with-u-values/ I found a site with values for thatch https://www.uttlesford.gov.uk/CHttpHandler.ashx?id=2139&p=0 which gives 0.29 and 0.23 depending on the reed used. So a thatched roof on its own does not meet current regulations and would need internal insulation. But it's not far off. The trapped air between the reeds acts a good insulator.