Tunnel in a tunnel

[roitelet]

I am contemplating constructing a tunnel within a tunnel so that I can heat it early in the year. Up until now I have insulated one end of the tunnel with bubble wrap and screened it off from the rest of the tunnel and this is where the heater is placed. It's not ideal as the tunnel has bottom rails so the cover is not tight to the ground.

The vague idea is to construct the tunnel over the center bed on a frame and covered with white geotextile membrane. This is because it is stronger than fleece and not biodegradable.

The question I have are 1 What are the insulating properties of the membrane? 2 Even though it is white will the light levels be too reduced to grow decent plants? 3 Would I be better using bubble wrap?

I will be interested in your thoughts, thanks

[bramble]

Roitelet, sounds a great idea in theory but cant help as I dont know anything sbout the light levels of the particular membrane you intend using.
I will watch the answers with interest.

[Bigmallly]

I don't know how much bubblewrap is but I've just re-covered my tunnel with this:

Heavy Duty Clear Polythene Plastic Sheeting 4M Wide DPM Rolls 250Mu,1000 Gauge | eBay

Could this be used as an inner tunnel?

[veggiechicken]

After gogling "white geotextile membrane" it looks opaque. I'm curious about why you've thought about using this instead another layer of polytunnel plastic.
I've used blowaways inside GHs in winter.

[roitelet]

It because I have got lots of the membrane and it's tough. ALso I could make a cover that I could remove easily and replace it as needed.

[veggiechicken]

How much light gets through it?

[roitelet]

I'll do a bit of testing and let you know

[Nicos]

No idea about the membrane, but are you intending growing in the ground or pots?

I was just thinking back to summer camping holidays when I didn't have a decent mat to sleep on, I got absolutely frozzed from underneath...the ground sucking the heat out of me.

If you are intending to grow in pots I'd suggest a layer of some sort of insulation on the floor as an extra.

[marchogaeth]

There is a thread on here somewhere which shows people's experiments with tunnel inside a tunnel and there is absolutely no benefit from doing it in terms of increased heat over the single skin. If it's just for frost protection that is a different issue. I think Martin H was one of the contributors.