Window sizes

theres no real restriction other than whats mentioned in the relevant regs.
ive bolded the most important ones, but they are all applicable.

The only other restriction is what the window manufacturer can actually make and stand over.

(a) The window should have an openable
section which provides an
unobstructed clear open area of at
least 0.33 m2

The height should be not less than
450 mm. The width should be not less
than 450 mm. The opening section
should be capable of remaining in the
position which provides this minimum
clear open area.

(b) The bottom of the window opening
should be not more than 1100 mm
and in the case of a rooflight not less
than 600 mm above the floor,
immediately inside or beneath the
window or rooflight.

(c) As an exception to the general
guidance in TGD K that guarding be
provided for any window, the cill of
which is less than 800 mm in height
above floor level, (where the external
ground level is below 1.4 m below
floor level), guarding should not be
provided to a rooflight opening
provided in compliance with this
paragraph.

(d) In the case of a dormer window or
rooflight, the distance from the eaves
to the bottom of the opening section
of the rooflight, or, where the window
is vertical, the vertical plane of the
window, should not exceed 1.7 m
measured along the slope of the
roof.

(e) The area beneath the window
externally should be such as to
make escape or rescue practicable.
For example;
(i) where there is a clear drop from a
window in an upper storey or attic
conversion, the ground beneath the
window should be suitable for
supporting a ladder safely and be
accessible for rescue by the fire
services or others.

(ii) Where there is a roof,
conservatory, balcony or canopy
below a window for escape or
rescue, it should be structurally
adequate to support those using
the window.

(f) The opening section of the window
should be secured by means of
fastenings which are readily
openable from the inside. In certain
circumstances safety restrictors may
be fitted to such windows see TGD K
Section 2.7. Lockable handles or
restrictors, which can only be
released by removable keys or other
tools, should not be fitted to window
opening sections for escape or
rescue.