Malbern Trade Windows

Supply Only PVC-u Windows, Doors & Conservatories Throughout the North West of England

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Building strong and loyal professional relationships with local trades people is what's built Malbern into what it is today - Norths West's leading supplier of UPVC Conservatories, Windows, Doors and Double Glazing to the Trade Installer keen DIY'er and construction industry.

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How to Measure

Your existing windows will usually have been fitted in one of two different ways.

Fitting Standard Windows

Method 1

Method 1 is where the frames are fitted from the outside and sit between the outer skin of brickwork. If your property is of this type of construction then:-

Take your measurements from the outside and measure brick face to brick face. Take three width measurements, top, middle and bottom. Deduct 10mm From the average reading. Repeat this process for the height, don't forget to deduct 10mm. If you require external cills, quote the overall frame size including the cill and we will incorporate this allowance during manufacture. If measuring to fit frames in stonework that has very irregular shapes, make suitable allowances to ensure that any opening windows can pass the obstructions.

The reason for the 10mm deduction in the height & width is to allow for any irregularities in the squareness of the brickwork and for the minor expansion that may occur in hot weather, it also makes for easier fitting if the frame is a loose fit. If you find for any reason that your new frame is too tight, ribs are provided on the outside edge of the frame that can be planed down up to the depth of the ribs, this will give you some tolerance and can get you out of trouble however there is no substitute for careful and accurate measuring during your survey.


Fitting with Tiles or Plaster

Deep Plasterline and/or Internal Tiles

Take note of the plaster thickness inside, are there any tiles fitted to the reveals etc. if you can’t see much of the existing timber frame and the surrounding internal structure is almost obscuring the frame then you may need to consider using add-on frame extenders to both sides and sometimes top and bottom, especially if the internal cill has been built up.

It is Particularly important to check for these deep plasterlines for doors and Tilt & Turn windows because the hinges are fitted close to the inside edge of the frame and if your plaster is anything other than the normal 15/20 mm thickness you need to take this into consideration to prevent hinge fouling.
Doors often have to have frame add-ons to ensure the door hinges are not fouled by the internal plasterwork or to clear decorative fitments such as skirting boards and dado rails.

If in doubt….. Do not hesitate to call us on 0161 320 2068 we are here to help


Method 2

Older properties and most terraced houses have their original frames fitted behind the outer skin of brickwork, this requires a different approach but you may choose to fit the new frames between the outer brickwork just like method 1 and then make good inside, in this case, adopt the same approach as method 1.

Fitting Windows Behind Brickwork

To replace like for like, the second method will often necessitate a box sash replacement, this applies to all frames that are fitted behind the outer skin of brickwork. If your property is of this type of construction then:

Measuring from the outside, take three different width measurements of the outer brickwork from top middle and bottom of the existing brickwork opening. From the narrowest reading, add 10mm. If measuring to fit frames in stonework that has irregular shapes, make suitable allowances so that any openers will pass any irregularity of the stonework.

The Reason for adding extra the 10mm width to the frames is so that the frames are fitted from the inside and the extra width allows the frame to fit up behind the outer skin of brickwork.
You would not normally require external cills for this type of installation, the frames would sit onto the original stone cills, remember to state “No Cills” when ordering.
If you are removing the original box sash windows, this type of installation is quite time consuming and can be a very dirty job that involves considerable making good.

These instructions also apply to doors, patio doors and French doors.


If in doubt….. Do not hesitate to call us on 0161 320 2068 we are here to help


For a more detailed insight, please see our downloadable Measuring Guide