Sash windows: out of square, and that is normal

Measuring an old opening

Width at three heights, drop at three widths, plus diagonals to establish the out-of-square. On a shutter, the frame absorbs that discrepancy so the panels themselves stay true and the louvres line up horizontally.

A blind cannot do this — it either shows a tapering gap down one side or has to be fitted narrow enough to clear the tightest point.

Configurations for sashes

Sash proportions suit some layouts far better than others.

• Tier-on-tier — mirrors the two-over-two sash division and gives independent privacy
• Café-style — covers the lower sash only, keeping the upper light clear, ideal on a street frontage
• Full-height with mid-rail set at the meeting rail — cleanest architectural line
• Solid lower panels — for bedrooms facing a lit street

Working sashes and cords

Panels are hinged clear of the sash so you can still raise the lower window. Where a window has box shutters, architrave or a deep sill, we scribe the frame to it rather than covering it.

In conservation areas and listed buildings, internal shutters are generally the least intrusive option — but always check with the local authority before ordering.