Updating an old door without replacing it

This nice door was made for The Old Brewhouse when it was a farm service building where nobody lived.

It has thin planks with cracks between, and is a heat sink in the house during winter, no matter how much draft proofing is stuffed in and around it.

As a listed building, we’re supposed to make a formal application to the council heritage department and pay a fee if we wish to replace it. Our solution was to leave the old door untouched, apart from a few new screw holes, and build an identical door on the inside of it to double the thickness, cover the cracks and improve its thermal performance. It should make a noticeable difference to the warmth of the room in midwinter.

Above is the near completed inner lining, showing some of the second layer of planks screwed down, and with the old top cross piece still showing. And below is a new plank being screwed on top of the cross piece.

The result is an inner door that looks exactly like the inside of the old door, apart from the untreated freshness of the wood.

This is the finished door, with a third hinge in the middle to help take the extra weight. With a thicker door, the hinges and bolt had to be remounted on spacers made from oak offcuts to get the level right, but that was straightforward to do.

The whole operation was done with the door in place, which saved a lot of bother, especially with the wild weather of the last few days.

When the hinges were off, spacers were put under the door to keep it a few millimetres away from the bottom, so the hinges could be re-fixed at the correct level.

The inside of the old door had three coats of a combined anti-fungus liquid and woodworm controller applied, followed by two coats of boiled linseed oil. The new wood was similarly treated on both sides before being fixed.

Next, the screwholes were filled and the door was painted with a traditional linseed oil-based paint, the same as used on the outside.

Linseed oil paint, from Ingilby’s as always, is very slow drying, with a minimum overcoating time of 24 hours. We keep the room quite cool and that lengthens touch dry to 24 hours and overcoating to 48. Outside in cold weather it can be even longer. The key is to keep dust and insects down and to have time to space out the job properly: if you’re in a rush or painting a door kids have to use a lot, you might think again.

But otherwise it is lovely to paint with. The best primer is linseed oil and if you need to dilute for a first coat, real turpentine is advised, which scents the house. Bare wood, especially old wood, benefit because the paint soaks into it, as well as forming a hard surface later. The consistency is extremely good for applying smoothly, though you need to lay off well and avoid runs.

If you do make a mistake or put on a messy coat, you have a day to put it right because of the slow drying. The brush stays soft for many hours so you can pause for a while without cleaning it or coming back to a solid mess. The brush cleans easily with white spirit.

Before making the inner door, we considered placing a sandwich of insulating material between the old and new wood, but it was not clear that the gain in heat efficiency would be worth it, and the door would probably end up too bulky. Doubling the thickness is a good compromise.