Thread: Render or insulation?

Hi All,
Block walls are going up on my new build, and I'm trying to decide what to do on the inside before fibreglassing. I'm not going to be heating the pond, and I can't really imagine ever doing so other than to stop it freezing, but I could put a layer of 25mm Kingspan on the inside before fibreglassing, It's either that or put on a coat of render. Anyone got any advice? I'm rendering the bottom of the pond to bench it towards the centre anyway.
Pros/Cons of each I can see:
Insulation:
+Some insulation if I ever decide to heat
-Lose some pond volume
-Will be awkward to fit around window, skimmer etc.
-Makes walls wider so need wider coping stones
Render:
+Fairly cheap and easy (I'll do it myself)

Anyone got any other points? If I'm not heating, render seems sensible.
Thanks,
Matt

ponds above ground lose a lot of heat when it's sub zero temps.
insulation slows the loss of heat if you ever intend to cover your pond.
if not it make little difference as the vast majority is lost from the water surface.

covering the pond can hold temps 5-10C above ambient, as the ground gives up a little heat and covers help hold it in.
rather than immediately losing it if not covered.