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How to Measure for Secondary Windows

How to measure your existing opening.

To measure for secondary windows you’ll need paper and a pencil. Measure from the inside, always width by height in millimetres. A spirit level with both horizontal and vertical bubbles. If you have a plumb-bob, it’ll be useful. A metal tape measure, use the builders’ type that pulls out of a case and usually has a spring return … don’t use a fabric measure as they shrink and grow.

Have Bay Windows?

Contact us for more information on how to measure and install for bay window.

Establish that the cill is level. You may be lucky although settlement makes them at least a little bit out! If the window is less than 1800mm wide and the “out of level” is minimal, -3mm, you may decide not to consider it.  If it is more, then note which side is the highest. Now check the window head for level. Note which side is the lowest. Again if minimal, you may ignore it. Your new window can only be made in a perfect rectangle so these points need to be established. It’s best to draw a straight and level pencil line across both head and cill to give you the level lines to measure up to.

Establish, with the spirit level that the jambs are plumb. Again, a pencil line as you did at the head and cill, to use next.

Measure the width to the nearest millimetre, between the pencil lines at the jambs. Take THREE widths at the top, middle and bottom and use the smallest one and take a note of it.

Measure the height as above. Again, take THREE heights, left, middle and right and use the smallest one and take a note of it.

If you’ve used the pencilled lines to measure the opening, your new window, that will be perfectly rectangular, DEDUCT 12mm from the sizes you’ve noted down – these will be the MANUFACTURING size.

If you’ve noted the smallest width and height after measuring a NOT rectangular window, the rectangular NEW window going in has to be able to fit, so DEDUCT 14mm from the sizes you’ve noted down – these will be the MANUFACTURING size. CHECK the manufacturing size WILL FIT BEFORE ORDERING!

UNEQUAL PANES IN SLIDING HORIZONTAL WINDOWS. From the inside, left to right, divide sliding panes to align with the exterior, primary window mullions. 

VERTICAL SLIDING SLIDING WINDOWS need to be split at the meeting rails. Measure from the top down to the midpoint of the rail. DEDUCT HALF of the tolerance allowance, either 6 mm or 7 mm. That will be the manufacturing break-point for the new meeting rails. Note these dimensions on your paper or sketch to add to your order form that will be sent to you, after placing your order.

PLEASE CHECK YOUR MANUFACTURING SIZE WILL FIT YOUR EXISTING WINDOW. The windows are bespoke and can’t be altered, once made!

Last, check the window will fit through your home. The twists and turns from room to room, up stairs and into the room you’re fitting it into.