Doors and windows have two purposes: they open to provide access or let in air, and they shut to keep out rain, draughts and sound. So they must open easily and shut firmly, which means that they must be fitted very accurately into their frames. Hanging doors and windows is not particularly difficult, and there are only a few facts and procedures you need to know about to get it right every time. The most important part of the job is getting the door or window to fit properly into its frame. They do not fit exactly; there has to be a clearance all round to allow for expansion in wet weather, and to keep the door from scraping against its frame when it is opened and shut.
Doors do not open straight as if they were being lifted out of their frame. They swing slightly outwards as they pivot on their hinges, and the lock side of the door, opposite the hinge, has to be cut away to allow for this movement. Different kinds of hinges cause the door to move in different ways, and you have to know how a particular type of hinge will make the door behave. The hinges themselves have to be installed strongly but accurately, so that the door does not sag or hang at an angle. It is not hard to put them in correctly when you know how.
Doors (and wood-framed windows) invariably expand slightly when the humidity rises. If they are painted, or sealed in some other way, it slows down the rate at which the humidity affects them, but they still change size. Outside doors are obviously more affected than inside ones, but even so, inside doors in a house that is centrally heated during the winter or air-conditioned during the summer, may change their size quite noticeably from season to season, perhaps by as much as 1.6mm.
Panelled doors made of solid timber move more than modern ones made from man made boards. Softwood ones move more than hardwood ones. And of course, wide doors move more than narrow ones (in actual distance, not in proportion to their width). The way to estimate the right clearance is to leave a minimum of 1.6mm round the top three sides of the door, and at least 3mm at the bottom (but more about clearance under doors later). Then you can add to this figure 0.8mm for each factor that might make the door expand an extra amount-for example it if is an outside door, in a centrally heated house, or if it is made of solid timber panels. The average clearance for an inside door is about 3mm on the top three sides, and 6mm at the bottom. There used to be a British joiner’s and carpenters rule of thumb that you should be able to get an old penny (just over 1.6mm thick) between a door and its frame all round. This was before central heating, however, and the gap is a bit small by today’s standards. But it is a good way of measuring if you can find a coin of the right thickness for the clearance you need. The method for fitting a standard-sized door into a standard-sized frame is as follows: first, buy a door of the correct size and leave it in the room where it is to be fitted for a couple of days to let it adjust to the prevailing humidity.
New doors with solid timber rails and stiles (this includes many flush doors) often have the top and bottom ends of the stiles (vertical side pieces) left uncut, and these projecting horns, as they are called, should be sawn off and planed smooth. When the door has acclimatized itself, offer it up to the hinge side of the door-frame and examine the edge of door and frame to see if they are parallel. Many frames are leaning or curved, even in new houses. If the frame is really irregular you may have to scribe the door to it, but otherwise an ordinary plane and your own judgement should be enough to make it fit.
Make sure that you don’t remove so much more wood from one end than the other that the door is no longer vertical; an occasional check with a spirit level should guard against this. If the door is not too tall to fit into the door frame at this stage, hold it up with a couple of wedges underneath it while you check it against the frame. If it is too tall, rest it on the floor and put wedges under it only when it begins to take on the right size and shape. After the hanging edge of the door is cut to shape, do the same with the top, then the bottom (remembering to remove more wood than for the sizes).
Then raise it to its correct height on wedges. and shape the last side, which is the side with the lock. Finally run a coin around the top three edges of the door to check that there are no tight spots.
Most door frames in houses less than about a century old are in standard sizes, and you can buy doors that only need a little planing to fit into them. If however, you are unlucky enough to have a door frame in a non-standard size, you are going to have to alter your new door more drastically, than merely planing it. Nearly all doors, including flush (flat surfaced) modern doors have some kind of supporting framework of stiles and rails to strengthen them and keep them from sagging or warping. This is held together by mortise and tenon or dowelled joints. If you remove more than say, l3mm from any side of the door, there is a danger of cutting into one of these joints, and this could seriously weaken it.
One way round this problem is to order a specially-made door, but this might turn out to be expensive. Ask a builders’ merchant and see if you think the job is worth the money.
The best solution is to dismantle a door and re-cut the joints to alter the size-if you can be bothered to do it. It is a laborious job. however, for door manufacturers use good glue and strong joints deliberately to stop their doors from coming apart. Altering the size of window frames in this way is nearly impossible for the amateur carpenter. They will almost certainly have lo be made to measure by a professional joinery and carpentry company.