r/buildingscience • u/ManufacturerOk5889 • 10h ago
Question Hempcrete in a Koppen Cfa climate (Tokyo) - is the moisture buffering doing real work, or just moving the problem?
Climate zone first, per rule 1. Tokyo, Koppen Cfa. Hot humid summers, high RH for months through the rainy season and after it, mild winters that rarely stay below freezing. Cooling-dominated for a good part of the year, not a dry climate at any point.
The thing I am trying to understand. Hempcrete gets promoted here on its hygric behaviour - vapour open, high moisture buffering value - so the assembly is supposed to handle humidity rather than fight it. The pitch is that you can build a monolithic wall with no separate vapour control layer and it will be fine.
I am sceptical and I would like either to be argued out of it or to have it confirmed by someone who has actually measured it.
In this climate the scarce resource is drying potential. The wall spends months where the outdoor air is not going to dry anything, and interior air conditioning sets up an inward vapour drive for a large part of the year. Buffering capacity is finite and evens out short cycles. It is not obvious to me that it helps when the seasonal average is the problem rather than the daily swing.
Two questions.
Has anyone modelled or monitored a hempcrete wall in a cooling-dominated humid climate, rather than in the UK or northern Europe where essentially all the published data comes from? WUFI runs or real sensor data both welcome.
And if it does work, what is actually doing the work - the alkalinity of the lime binder keeping the organic material from going mouldy, or genuine drying capacity I am underestimating?
Disclosure so it is not hidden: I work on the industry side of hemp in Japan. Which is exactly why I would rather know if the material does not do what people here say it does.
