"Joe Egginton" wrote:

I was watching a building program yesterday, and the builder said it was
12c constantly 2 metres underground. They was building a house in
Maidstone, Kent.

I know builders are known for telling porkies, but is it true that just 2
metres underground the temperature is constant?
--

I found this:

"The range of temperature diminishes quickly below the soil surface.
The day-night and summer-winter fluctuations are still evident but
there is a delay in the time of maxima (and minima) because the
conduction of heat downwards continues after the time of maximum
heating by the sun. In lowland Britain, at 8cm (3in) below the surface
the extreme temperature are around 24°C and -4°C, and 30cm (1ft)
down 21°C and 0°C. Thus only in the very coldest winters does frost
penetrate to a depth greater than one foot.

By the time we get 60cm (2ft) down the temperature variation
between day and night is very small, less than 2degC, warmest
early-evening and coldest mid-morning. Once we reach 90cm
(3ft) - the precise depth varies with soil type - the diurnal
fluctuation disappears altogether.

And at 1.2m (4ft) the highest reading, typically 17°C, occurs in
early-September while the lowest reading, about 4°C is usually
obtained in early-March. Day-to-day temperature changes at
this depth are always very small, measured in fractions of a degree.

Measurements at greater depths are not normally made, but a
series of observations were taken by a Colonel H.S. Knight at
Harestock, near Winchester, in the 1890s. His records showed
that at 3m (10ft) the temperature ranged from 7.9C in April to
11.7C in October, and at 6m (20ft) the warmest month was
December with 10.4°C and the coldest July with 9.5°C.

At 9m (30ft) there was no evident annual cycle and all months fell
between 9.6°C and 10.2°C. At 20m (66ft) the temperature appeared
to be constant at exactly 10.0°C."

Philip