Insulating an internal door

[Canuk]

So my son is coming back to stay for a few months (I hope!). His room was always cold, he was forever complaining about it, but we never had the time, nor the inclination to fix it! It's on the other side of the house into the prevailing wind, too far from the wood burner to get any benefit. All that's in the room for heating is a single oil filled electric wall heater.

So I've put in a (second hand) double glazed window and sealed off all the potential gaps and leaks, but the big problem is a flimsy door which is only really plywood and a middle section (probably a metre square) 5mm thick at the thinnest.

I priced an insulated internal plastic door, and it's ridiculous expensive at 500 quid. He might not stay stay that long, so I'm looking for cheaper alternatives to insulate this door. It's the only weak link in the room. Ideas?

 

[101]

Is the space heated the other side of the door?
If so all you will be doing is keeping the heat out of the room.
If not then you need quite a bit of insulation to make a difference.
If the door is really flimsy then polystyrene core or offcuts of Kingspan type material and ply on the polystyrene/Kingspan.

However if the door is a fire door (for a 3 storey house it is required) then you have another problem, fire integrity which ply and polystyrene would compromise.

If it's an old house I would suspect the external walls are more of an issue. Insulated plasterboard could help here.

 

[Mike Muz]

I want to keep a training room cold and not have the heat from the rest of the house escaping into it!
Hoping that having the back door open will help with this

 

[Canuk]

Is the space heated the other side of the door?
If so all you will be doing is keeping the heat out of the room.
If not then you need quite a bit of insulation to make a difference.
If the door is really flimsy then polystyrene core or offcuts of Kingspan type material and ply on the polystyrene/Kingspan.

However if the door is a fire door (for a 3 storey house it is required) then you have another problem, fire integrity which ply and polystyrene would compromise.

If it's an old house I would suspect the external walls are more of an issue. Insulated plasterboard could help here.

The other side of the door is very cold and unheated. I have a load of offcuts from insulation of the loft. It's 50mm expanded polystyrene. The cheap stuff. But how to fix it to the door? Ideally I would not want to glue it...

 

[101]

That's going to make the door very thick, and it may end up not fitting the recess, architraves or even frame.
Plus consider fire risk. And you'd have to edge it, it's going to be quite a task.

It is unusual to insulate internal doors, I realise you have a cold house but insulating external walls and heating the room is probably best.
But then be wary of condensation and mould.