Secondary Glazing in Church Buildings

Leaded windows
Leaded church windows often offer one of the main opportunities for fabric thermal upgrades in a church building. If the walls are plastered “on the hard”, the roof is exposed and is a significant architectural feature of the building and the floor is hard to insulate, then this may leave the windows as the main opportunity for upgrading.

Leaded windows are often protected from damage (malicious or accidental) externally by metal grills and sometimes by glass or plastic sheeting. External secondary glazing is suboptimal as it invariably goes hard against the leaded glazing so there is no cavity and little improvement in thermal performance. In addition it is hard to remove for maintenance purposes and sealing the glazing to the walls can be difficult to achieve neatly or permanently.

Internally, secondary glazing may be set in frames. There are manufacturers who sell the components for this, but they can be unsightly. Bespoke proprietary systems, like those provided by Glaze and Save (Cocoon) based in Perth, which are fixed magnetically have been successfully used in historic churches but can be expensive. To spread the cost, churches could consider doing just one or two each year.

Glass used for secondary glazing is very heavy to handle on large windows and requires substantial frames to hold it while acrylics and polycarbonates are easier to handle. Acrylic is less workable and weaker than polycarbonate but is more durable while polycarbonate is less expensive.

Secondary double glazing will mainly work by reducing draughts and so improving comfort and reduce noise, but while it will also help to prevent heat loss it is not as efficient as purpose-made sealed unit double glazing. Unfortunately it will reduce ventilation as it will rarely be possible to open hoppers or sashes when it is in place. Fixings can be by mechanical clips or magnetic strips. High-grade well-designed systems are available but so too are much lower cost systems that are neat and may not impede the operation of shutters. Secondary double glazing should be readily removable for inspection and maintenance of the stained glass.

It is important to have leaded glass examined by an expert in stained glass. While stained glass windows are often fitted with drainage channels and weep holes to drain condensation to the outside, if there is any likelihood of condensation in the cavity this will put the leaded glazing at risk.
It is important to consider in detail how it will fit with the mouldings around windows. Large scale sectional drawings through the reveals are vital and should be provided when Canon 35 is applied for. Any additional astragals ((glazing bars) within the secondary glazing should be carefully worked out to align with the timber or masonry of the stained glass so as not to spoil the appearance of the windows.

Sash and case windows
In assessing sash and case windows attention should be given to the glazing. Thin historic Crown glass can add immensely to the character of a building. It is irreplaceable (modern equivalents never quite achieve the same appearance) and its removal should not be seen as a trivial matter.
Decayed or worn timbers can very often be repaired. Nineteenth century or earlier timber is invariably of a quality unobtainable today. Again, it should not be discarded lightly.

If sills are decayed and it is decided to repair them with “half sills” then it is vital to form a watertight bond between new and old. This can be achieved using resin such as the RepairCare System which can also be used to repair other sorts of decay. Replacing “whole sills” is often a better option.
It is sometimes possible to replace single glazing with thin double glazing units. Care should be taken in their selection as there is no standard governing their manufacture and their performance may be questionable. Units made with a vacuum between the glass sheets by a reputable manufacturer could be a better option.

Double glazing (secondary or sealed unit) tends to have a poor “payback” compared with draught stripping. A leading company doing draught stripping is Ventrolla but they have many competitors.

If sash and case windows are replaced entirely very great care should be taken to ensure that they conform with the size and pattern of the originals. Sash and case window manufacturers typically work to sloppy tolerances suited to them which reduce the daylight area and spoil the appearance of the replacement windows. Meeting rails in the centre of windows are often thicker and more visually intrusive than their historic counterparts. Astragals are moulded to suit the convenience of the manufacturer rather than to match the original.

Steel windows
Typically dating from around 1930s these are often treated with disdain. Where excessive accumulations of paint have thrown opening lights out of alignment, often silicon sealant has been applied that only compounds the problem. They are rarely if ever irreparable. Although they do not have the sophisticated thermal breaks of contemporary equivalent windows, repairing and refurbishing them is invariably much more economical. Slim double glazing units may be an option but the glass fixing clips (“sprigs” as they would be in a timber sash) may no longer fit and this should be given some thought.

Wherever possible consideration should be given to reviving shutters and, indeed, to fitting them for the first time where it is appropriate to do so (see illustration).

Funding
Information on sources for funding can be found on the SEC’s Net Zero website and on the SEC website.

For rectories the Home Energy Scotland Loan is an interest-free loan administered by the Energy Saving Trust that helps homeowners make energy and money-saving improvements to their home. All homeowners are eligible to apply, subject to a credit check. Funding is available for a range of energy efficiency improvements, including up to £4,500 for glazing and £500 for draught proofing. To request an application form please speak to Home Energy Scotland free on 0808 808 2282.

Business Energy Scotland’s energy assessments are a good way of reducing project costs through the 75% cashback options and the reports produced can help shape ideas around other net zero steps.

Further information about stained glass can be found on the Scottish Stained Glass Trust’s website.

Finally
Secondary Glazing should be assessed along with all other factors (Items 1 to 5 in the SEC Guidance on Insulation) with the intention of improving insulation values and establishing if this affects the performance of the building fabric. This would enable an optimum overall balance to achieve the best possible outcome towards a net zero solution. Professionals, such as Building Services Consultants, Conservation Architects and/or Conservation Building Surveyors are the only parties that can embody this overall concept.

When thinking about replacing your windows it’s good to check if there are any restrictions on the changes you can make to your property. A good starting point is your local authority’s office for building standards.

There are also likely to be limits on what you can do with your windows if you are in a conservation area or the building is listed. In conservation areas, any changes to your windows might need to be in keeping with the look of the building or the locality. If the building is listed, you may not be allowed to replace the windows. In either case, secondary glazing is often an option.

In addition to Canon 35 approval, Listed Building Consent will be required for alterations to the windows if the building is protected or located in a conservation area.

The mygov.scot website has a helpful tool that can help you determine whether you are in a conservation area or the building is listed. It also tells you who you’ll need to contact for different types of planning permission.