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.

DoctorG schrieb:

But the core question is: am I wrong to consider using these seemingly well-insulating materials for this purpose?

Yes, you are. Because you don't want to apply 20cm (8 inches) of carpet just to achieve an insulating effect. Besides, there are much better insulating materials that are just as easy to handle. But as with any insulation, 1cm (0.4 inches) is really not effective.

If anything, just install a better door. There are specifically designed thermal insulation doors that also provide a tight seal.

SaniererNRW123 schrieb:

If needed, just install a better door. There are special thermal insulation doors for that. They also close tightly.

Even considering

DoctorG schrieb:

old exterior door with historical preservation / cannot be replaced with something modern

?

I’m not sure if there is any alternative other than adding a second (modern thermal insulation) door behind it. That would probably require reversing the opening direction of the existing door. That won’t be easy either.

Thank you.

That would actually be quite a lot.
I looked up a thermal insulation door. It seems to be made up of the door itself, the frame, hardware, etc. It looks complicated—but well, that would be something for a professional company anyway.
I stopped totaling the costs somewhere above four figures, without even including labor. 🙁

I’m still hesitant because I have this issue in several places throughout the house.

A thickness of 20 cm (8 inches) would be roughly the amount I wouldn’t even have if I just installed a thermal insulation door on both the inside and outside of my current poor-quality door. Is there no alternative to such a bulky solution, like polyurethane panels or mats?

Does this mean that practically all these hallway doors—at least for now, if you don’t want to heat the hallway—are effectively useless?

If that’s the case, then it is what it is. I’m just trying to get used to it. 😳

Tolentino schrieb:

Even considering


?

I’m not sure if there is an alternative other than installing a second (modern thermal insulation) door behind it. For that, you would probably have to reverse the opening direction of the existing door. That’s not easy either.

That really sounds like proper craftsmanship and quality work.
But it is an interesting idea.

DoctorG schrieb:

That probably includes the door itself, the frame, the hardware, etc. Looks complicated.

That’s simply how a door is constructed. It hasn’t changed much, even over the last hundred years...

You only want to replace the interior door, right? That shouldn’t be such a big job. Leave the exterior door as is (due to heritage preservation).

DoctorG schrieb:

I stopped adding up somewhere above four figures, not counting labor costs.

That shouldn’t really be a surprise, should it?

DoctorG schrieb:

Does that mean that basically all hallway doors — at least today, if you don’t want to heat the hallway — are useless?

I don’t quite understand. There are exterior doors that seal the house from the outside world. Then there are apartment entrance doors, which provide the barrier to a staircase or similar area—they are essentially better interior doors. And finally, there are interior doors that are mainly decorative or separate rooms within the house or apartment.

Are you referring to your old interior door to the entrance area? Yes, if those are that old, they are energy inefficient. That’s why, as a rule, people install an energy-efficient exterior door as the main access to the house. Then the rest inside the house is just decoration (as mentioned above). Or in your case, you keep the exterior door and replace the inner door (similar to an apartment entrance or interior door).

Improving the energy efficiency of a door with minor DIY fixes won’t work. You need to accept that or invest properly. So either spend the money or don’t. Installing an interior door is actually a fairly straightforward task.