ᐅ Insulation / Thermal Insulation for Old Interior Doors in a Detached Historic House

Hello everyone,

The current energy situation has also led us to the need to optimize insulation.

Situation: An old interior door with a glass panel (1970s style) separates the hallway from an anteroom. The anteroom (approx. 1.5 m² (16 sq ft)) is unheated (in front of it is an old exterior door with heritage protection/not replaceable with something modern and shows the typical warping of wood after 100 years). Naturally, this creates an unfavorable thermal bridge—and there is a noticeable temperature zone in the hallway area/around this interior door.

I would like to improve thermal insulation on both doors. While researching thermal resistance values, I noticed that cork, laminate, and carpet provide very good insulation under underfloor heating systems. For that reason, these materials are often undesirable there. So my idea was to use this effect to insulate the doors. Especially with carpet, I think it would be convenient to work with simple tools like a utility knife or scissors (instead of routers, circular saws, etc.).

Has anyone had experience with such retrofitted “interior cladding” covering the whole surface of doors? Permission is not an issue since the house is privately owned. Of course, fasteners like glue, adhesive tape, or screws (I’m still undecided) will leave traces if you decide to remove them later.

But the core question is: Is my idea unreasonable—to use these apparently well-insulating materials for this purpose?

Personally, I have not seen this done anywhere before. The only similar solutions are heavy draft-proof curtains. But I would prefer something that moves with the door rather than a curtain that I can only access while standing on one side. There is a product on Amazon that goes somewhat in this direction—pre-cut to a certain extent (it looks a bit like a mix between a padded psychiatric door and a Chippendale sofa)—but there is basically no information about the material. I haven’t found any other ready-made kits or solutions either.

Also, all the adhesive sealing tapes only solve the joint problem—the thermal bridge caused by the textured glass cannot be solved with these household remedies, in my opinion. My experience with sealing the gaps has been mixed, too. In the end, these old doors always end up sticking somehow. Perfectly fitting seals, which you can buy precisely to size—like refrigerator gaskets—would be ideal, of course. But as far as I can see, you need corresponding new doors for that. Ours are probably older than the word “order number.”

So for the gaps, I would probably also prefer a piece of carpet or rolled cork that simply overlaps the gap on one side instead of some “gap stopper” that causes sticking.

Again: Is this just an idea—or from a professional point of view like trying to weld wood?

... I would be happy to hear any ideas or solutions that have worked for others. I am not a carpenter or joiner who has already seen everything.

Thanks for any feedback.