Windows are rarely the first topic in a renovation conversation, yet they often have the greatest influence on comfort and heating costs. They are also one of the few decisions that shape both the appearance of the façade and the indoor climate. The question is therefore seldom whether something needs to happen, but how far to go: new glazing only, or the complete frame.
When is new glazing enough?
Replacing only the glazing is the least invasive route. The frame stays in place, the façade is not opened up and the work is completed quickly.
This option comes into play when:
- the frame is still structurally sound
- the timber is free of rot
- the hinges and locking hardware function properly
- the rebate is deep enough for the new glazing unit
- the connection between frame and façade is still airtight
- the property still has single or outdated double glazing
Rebate depth is the key detail. Modern insulating glass is thicker and heavier than the glass older frames were designed for. If the new unit does not fit, the rebate must be adapted or frame replacement comes into the picture after all. Hardware deserves attention too: heavier glass requires hinges capable of carrying that weight.
When should the whole frame be replaced?
Once the frame itself no longer performs, new glazing delivers only half a solution. The glass insulates better, but heat and draughts continue to escape through the frame and its connection to the wall.
Full replacement is generally appropriate in cases of:
- rot in stiles, sills or bottom rails
- frames that have warped or dropped
- windows that no longer close properly after adjustment
- deteriorated or missing sills
- a poor connection to the masonry that cannot be repaired
- a desired change in layout, dimensions or opening direction
- combining the work with façade insulation or a new façade finish
That last point is frequently underestimated. Insulating a façade changes the depth of the wall build-up. The frame then has to be repositioned within the insulation plane, and that is rarely achievable with an existing frame.
Timber, aluminium or PVC: choosing the material
No single material is best in every situation. The choice follows from the type of property, the desired appearance, the acceptable level of maintenance and any heritage status.
| Material | Appearance | Maintenance | Often suited to |
| Timber | traditional, slim profiles | periodic repainting | listed and 1930s properties |
| PVC | flat and modern | limited | post-war and terraced housing |
| Aluminium | sharp, very slim profiles | limited | modern extensions, large glazed areas |
| Timber-aluminium | timber inside, aluminium outside | limited externally | properties with demands on both sides |
For a listed building or a home within a protected townscape, the choice is not free. Requirements may apply to material, profile subdivision, colour and detailing. Timber is usually preferred in those cases, and prior consultation with the municipality is necessary.
As for thermal performance, the complete frame counts, not just the glass. A good glazing unit in a poor profile performs less well than the glass specification suggests.
Air sealing: why the connection matters more than the frame
A new frame with excellent specifications can still disappoint when the connection to the façade is wrong. Heat and moisture find the weakest point, and that is almost always the joint between frame and structure.
Correct installation gives attention to:
- an airtight seal on the inside
- a vapour-open, water-resistant seal on the outside
- filling the gap between frame and wall with insulation
- the connection of the sill to the water-shedding surface
- limiting thermal bridging around the frame
- the position of the frame within the insulation layer of the façade
The order within that seal is not negotiable: airtight inside, weather-resistant but vapour-open outside. Reverse it, and moisture can enter the structure but no longer leave it.
“With windows, the sequence of work often matters more than the product choice. If the frames come out after the plastering is finished, you can schedule the interior finish all over again. And if you fit the frames first and only then decide to insulate the façade, the frame sits at the wrong depth. That is why we fix the sequence before anything is ordered.” — Robert Siutkowski, CEO Renoverend
Sequencing façade and interior work
Windows sit exactly on the boundary between outside and inside. As a result, scheduling them touches almost every other trade.
A logical sequence is usually:
- establishing whether the façade will be insulated or refinished
- determining the frame position within the wall build-up
- measuring and ordering, allowing for lead times
- removing the old frames
- installing and sealing the new frames
- façade repair and external finishing
- interior finishing, plastering and painting
- fitting window sills and trim
Reversing this order almost always means paying twice for the same finish. Installing new frames in a freshly plastered and painted room inevitably creates internal remedial work.
Lead times matter too. Frames are made to measure, and production runs to several weeks with many suppliers. That period belongs inside the programme, not outside it.
Documentation with possible support schemes in mind
Where the replacement of glazing or frames may fall within a national or local scheme, the paperwork matters as much as the work itself. An invoice stating only that new frames were installed often contains too little information.
Record from the outset:
- the type of glazing and its thermal performance
- the number of square metres replaced
- whether frames, doors or panels were included
- product data for the materials used
- the quotation, invoice and proof of payment
- photographs before, during and after the work
Conditions differ per scheme and can change. Always check them before entering into commitments, and agree with the contractor which details must appear on the final invoices.
A window never insulates better than the joint around it – the installation determines what the glazing actually delivers.
FAQ
1. Can I replace only the glazing?
Yes, when the frame is structurally sound, the hardware works and the rebate suits the new glazing unit.
2. How long does a timber frame last?
That depends largely on maintenance, detailing and exposure to weather.
3. Are PVC frames less attractive than timber?
That is a question of appearance and context. For listed and historic façades, timber is generally considered more appropriate.
4. Do I need permission for new window frames?
Often not when the façade is unchanged, but a listed property, a protected townscape or a change in dimensions may create obligations. Check this in advance.
5. When should frames be fitted during a renovation?
Before the interior finish, and coordinated with any façade insulation so the frame sits at the correct depth.
6. Why do I still feel a draught after new windows?
Usually the window is not the cause. The connection to the façade or the adjustment of the hardware is the more common culprit.
