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  How to Measure for your new uPVC window Frames


Your existing upvs home windows will usually have been fitted in one of two different methods.

How to measure for aluminium and pvc windows in cavity wall constructions

The first method is for cavity wall construction, the frames are fitted between the outer skin of brickwork. If your property is of this type of construction then:-     




cavity wall construction

Take your measurements from the outside, take three width measurements from top, middle and bottom of the existing brickwork opening. From the average reading deduct 10 mm. Do the same for the height and again deduct 10 mm. if external cills are required, quote the overall frame size including the cill. If measuring to fit frames in stonework that has very irregular shapes, make suitable allowances.


The Reason for the 10mm deduction in the height & width is:- it allows for manufacturing tolerances and for the minor expansion that may occur in hot weather, it also allows for minor deviations in brickwork and makes for easier fitting. If you find for any reason that your new frame is tight, you may plane down the frame up to the depth of the ribs, this will give you some tolerance and can get you out of trouble but is no substitute for careful measuring in the first place.


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 allowing for reducing the frame size. Sometimes the tiling or plasterwork is so close to obscuring the frame that you may have to request add-on frame extenders to both sides and sometimes top and bottom, especially if the internal cill has been built up.

This situation most commonly occurs in bathrooms & kitchens. If you need to order add-ons, just quote the overall window dimensions and state where you require the add-ons to go, we will automatically reduce the frame size to suit the add-ons.

It is Particularly important to check for plaster thickness 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 486 6049 we are here to help?

Older properties and most terraced houses have there original frames fitted behind the outer skin of brickwork, this requires a different approach and you may decide to fit the frames between the outer brickwork and make good inside, in this case take the measurements as for ?Typical Cavity Wall Construction?.


The second method in which your existing windows may have been fitted is behind the outer skin of brickwork and this 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 10 mm. 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 the extra 10mm width to the frames? is 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. The good bit is you will  save a small fortune by doing it yourself as window installation companies charge a lot for this type of time consuming labour.

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




If in doubt.. Do not hesitate to call us on 0161 486 6049 we are here to help?


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