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Measuring the back door – the correct procedure

Before installing a new back door, you first have to measure it correctly. Obviously, if you order a new door having measured by guesswork, by chance or based on old measurements, you will quickly face the problem that the door does not fit and cannot be installed.

Even if the measurement methodology appears complicated at first glance, determining the correct order size is anything but rocket science. The following instructions explain the materials required and the correct procedure for both old and new buildings.

1. The Preparation – this is required

To determine the correct size for the new back door, the width and height of the frames must be measured. Before measuring, a drawing of the old back door should be made, in which the values measured on the frames are subsequently entered. The positions of the door handle and lock should also be sketched here. A few simple tools can make this work much easier.

If a blueprint of the present door is available, using this may also prove to be beneficial. The dimensions of the existing door are often already noted on it, but it can happen that these are no longer correct due to subsequent conversion work and modifications to the building. Therefore, doors should always be remeasured during renovation and the dimensions should be entered on the blueprint together with the date – this saves a lot of time if further renovations are made at a later date.

a) General tips for measuring doors

Regardless of what type of door is to be measured, the measurement is always taken looking from the inside of the door to the outside. The measured width and height of the frames is also referred to as the opening dimension. These values are always given in millimetres. Incidentally, once the opening dimension has been determined correctly, this can also make it much easier to adapt accessories, such as insect screen doors, later on.

The measurement procedure is the same regardless of whether the new back door is made from wood, uPVC or aluminium. However, it makes a difference whether the measurement is to be carried out in a new building or during a renovation. As with all manual work, the greatest possible care must be taken when measuring the back door. Especially when the doors are ordered in a custom-made special size, even a small measurement error can quickly result in high costs and a delay in the construction project (Fig. 1).

Incidentally, once the opening dimension has been determined correctly, this can also make it much easier to adapt accessories, such as insect screen doors, later on.

2. Measuring the back door during renovation

Due to structural and technical reasons, the procedure for measuring doors in existing buildings must be different than in a new building. The steps described below should therefore be carried out to determine the correct order height and width for new doors.

a) Measuring the height of the back door

Firstly, the frame is measured on the left and right in the inside from the upper edge of the door to the floor. If there is a difference in the dimensions between the two sides, the smaller measured value is used to calculate the order height. 10 mm are then subtracted from the measured value – this is the order height for the back door. The space is necessary in order to be able to use seals and similar accessories later on.

Example table for the correct order height

Measurement on the left (in mm) Measurement on the right (in mm) Order size (in mm)
1990 2000 1980
2000 1990 1980
2000 2000 1990

Normally, the order height is calculated by measuring the inner edge of the frame. However, if there is a difference in height at the threshold between the inside and outside of the back door, taking the measurement is a bit more complicated, because a detailed cross-sectional view must be made in order to ensure a perfectly fitting door.

b) Measuring the width of the back door

The order width for the back door is then determined by measuring the width of the wall rebate. This is the distance between the embrasure on the right and the embrasure on the left. As with the height, the width should also be measured twice – once in the upper area of the door, once in the lower area. 20 mm should then be subtracted from the smaller value in each case in order to be able to place the order correctly and, ultimately, fit the door into the wall opening.

3. Measuring the back door in a new building

Measuring the back door in a new building is much easier than when renovating, because the clear dimension is taken as the basis. The clear dimension is the measurement of the existing opening in the wall. There is only one special aspect to consider when measuring the height since, depending on the degree of completion of the building, the floor structure may have to be taken into account.

a) Measuring the door height in a new building

With new builds, measurements are also taken on the right and left of the wall opening, and here, too, the smaller of the two values is used to calculate the order size. 20 mm should be subtracted from the smaller value. In addition, a desired or existing floor structure may have to be included in the calculation, from which 10 mm is deducted. This is the only way to achieve a flush finish between the threshold and the floor structure. Depending on the design, the dimensions should always be recalculated.

With floor constructions 140 mm in height, a frame extension of 130 mm must be taken into account for the door.

b) Measuring the width of the back door

For a back door that fits as precisely as possible, the width of the wall opening should again be measured at a minimum of two different points, preferably at the top and bottom. As usual, in the event of deviations, 20 mm will be deducted from the smaller of the determined values in order to establish the order size.

4. Measuring the back door correctly – also possible for do-it-yourselfers

You don't have to be a professional to correctly measure the height and width of a back door. With good instructions and the necessary care, which is the basis for all manual work, do-it-yourselfers and amateurs can quickly determine the exact order size for the new back door. Sketches, precise documentation of the measured values in the blueprint and the help of measuring aids and – in more complicated cases – detailed cross-sectional views make this work easier. After measuring, the new back door can then be conveniently ordered and configured at windows24.com.

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