Undersoil insulation: any thoughts?

[quanglewangle]

Summary
We successfully start tomatoes and aubergines early January, and now thinking about bringing start forward to November.

Detail
West Cornwall location with winter night time lows of 4"C, very occasional air frosts.

We use under bed heating and LED lights to successfully grow tomatoes from New Year's Day sowings. Looking at our climate records that means we already are growing through the two coldest months of the winter. Some nights do need 200W space heating but fleece usually work.

I have read about some commercial greenhouses that use under bed insulation. Since our greenhouse is quite small it is quite feasible to set a slab of 75mm foam 200mm below floor level before putting heating wires back and backfilling with growing medium.

May have to cut into tiles to allow drainage.

Is this a mad scheme?

[burnie]

There's only one way to find out................................go for it, though not too sure how long foam would last in an environment like that.

[quanglewangle]

.... though not too sure how long foam would last in an environment like that.

Hope it lasts because the builders put loads under our floor when we renovated our cottage.

[burnie]

Ah, if its XPS then it should be no problem

[goosander]

Why not just us builders quality polythene. A layer of gravel on top layer of sand and then the cables Plus more sand / compost.
Bob.

[quanglewangle]

Having done some more research it seems that the place to insulate is around the outside of the greenhouse - Google "Swedish skirt greenhouse insulation"

Turns out that the ground beneath the greenhouse is a store of heat but the ground around the outside loses heat to the cold air in winter so that is what the Swedish skirt is meant to do.