Bay Window Heat Loss: The Worst Geometry in the House
A bay projects out of the heated envelope, presents glass on three planes, carries three times the frame perimeter of an equivalent flat window and usually sits above an uninsulated bay roof or floor void. It is the coldest part of nearly every Victorian and Edwardian front room we survey.
Four separate heat paths, not one
The glass itself is the obvious one. Less obvious are the mullions between the bay lights, which are often a single thickness of timber; the bay roof or canopy, which in a terrace is frequently a lead or felt deck with nothing under it; and the floor of the bay, which projects beyond the joist run and is regularly uninsulated. A window-only upgrade addresses one of four.
- Three planes of single glazing
- Slim uninsulated mullions
- Uninsulated bay roof or canopy
- Cold floor projecting beyond the joist line
How we glaze a bay
We template each facet individually and fit a matched set of panels rather than trying to force one unit around the angle. Corner posts are colour-matched and kept as slim as structurally sensible so the bay reads as a bay from inside. Where a window seat exists we set the panel line to preserve the sill depth.
Do the cheap wins at the same time
If the bay roof is accessible from the room above or from a loft void, insulating it is inexpensive and makes a bigger difference than most owners expect. We will point it out at survey. Our job is the glazing, but we would rather you got a warm bay than a well-glazed cold one.
Frequently asked questions
Yes. Splayed and square bays are templated facet by facet. True curved bays are handled with a faceted approximation, which we will show you on the survey drawing before ordering.
Ready for a free, no-obligation quote?
South Yorkshire's specialists in secondary glazing — survey, measure, manufacture and install.