[Yana]

My OH is building me  a cold frame and it is going to be sitting on paving slabs. I know that this is not ideal but it is going alongside the beautiful shed/greenhouse combo he bought me last year so I can't complain.
I've been thinking that it needs something as a base as the pots/trays will sit directly in the paving slabs and get cold?? Drainage isn't a problem as we didn't get the slabs concreted all round but instead left the smallest gap and filled this with sand. I thinking a sheet of polystyrene insulating type stuff with holes drilled to allow any water through. Or maybe pallets to allow drainage?
Do I need to insulate the side, front and rear panels as well to improve the temp inside?
Any ideas, thoughts most welcome.
Ta 

[RichardA]

polystyrene should help or for a  quick fix just put an upturned tray under each tray as an air trapping layer. I don't insulate the sides of mine but I don't have stuff out in extreme low temps as I have greenhouse and polytunnel so have spaces for most things through till about March to May when hardening off is the main use of the cold frames for me and I don't want cold frames to be too air tight for fear of mould etc.  Depends of how well built the cold frames are, I guess.
R

[Goosegirl]

I would use polystyrene on the base (cheapest suggestion - wall insulation on a roll which you can cut up and put down in layers) or other similar stuff. Then, use upturned seed trays with drainage holes to allow water to drain from your pots stood on them. I would think you need to insulate all the sides, then just use a removeable cover over the top panel as added protection depending on the temperature. It's a delicate balance between keeping any warmth in and preventing mould, so lift the lid to allow air to circulate but close it up at night.

[fatcat1955]

I would do away with the paving and use gravel in the coldframe.

[Yana]

I would do away with the paving and use gravel in the coldframe.

Thanks for the suggestion, but no can do fat cat. it's taken all my power of persuasion to get the cold frame built so can't ask for the slabs to be removed.

[Goosegirl]

Unless the frame is sealed somehow onto the slabs, you could still use gravel inside for drainage?

[Yana]

Ah I get it now. The come frame will be sitting on the slabs but not attached as such or sealed to the slabs so gravel inside would work.
Would the gravel also act as an insulator?

[Goosegirl]

No, I don't think it would as it is composed of stone like your slabs. A layer of polystyrene on top of gravel will insulate - perhaps those that look like Quavers that would allow any water to escape?

[Yana]

No, I don't think it would as it is composed of stone like your slabs. A layer of polystyrene on top of gravel will insulate - perhaps those that look like Quavers that would allow any water to escape?

I know exactly the ones you mean GG and I have loads of them. I save them from parcels and just knew someday they would be needed. Thanks 

[gypsy]

I use the polystyrene trays that B&Q sell 30 plug plants in to line my cold frame. I turn them upside down and stand my plants on them.

[Yana]

Some great ideas being suggested. Thanks everyone. 

[RJR_38]

What are you building your cold frame from? I am thinking that I might build one this year....

[Yana]

OH loves to design and build things so he was in charge. It has a wooden frame and is 'cladded' on the outside. There are two  windows that are polycarbonate, with wooden frames that are hinged and have a catch in the front to secure them down. Not sure how they are being held open as that is being added this weekend as it gets put together in the garden. It's designed to be easily dismantled and stored when not needed (I'm sure it will be used all the time). It's sitting on a base of paving slabs and the internal walls will be insulated with silver lining stuff from B and Q.

[RJR_38]

Very high- technical sounding and a bit beyond my capabilities lol! I wish my partner was 'handy' on the DIY front lol

[Yana]

Very high- technical sounding and a bit beyond my capabilities lol! I wish my partner was 'handy' on the DIY front lol

It's not always a blessing RJR. 
He is great at building things but he does get carried away sometimes.
I've got a beautiful shed at the lottie that he built and I get a lot of stick about it believe me. It withstood all the gales and rain, some weren't so lucky so I musnt complain.