Windows: Repair or Replace?

There’s a host of factors to consider when updating your home’s windows – especially if you are dealing with a period property. Chris Bates helps you weigh up the best route for your project
by Chris Bates
14th November 2016

Your home’s windows are a vital part of its character. They work alongside the external cladding and roofing materials to form part of an architectural picture that sets the tone for the rest of the property. So if you’re tackling a renovation project and your fenestration needs attention, deciding on exactly how to proceed is not something to be taken lightly.

In most scenarios, repairing and replacing windows like-for-like is considered permitted development (PD). This means you don’t usually have to apply for specific planning consent, unless your project involves significant changes.

Some councils are more flexible about this than others, so check what’s required. You might be expected to precisely match the design, materials and method of opening of the originals before going ahead.

Note that bay windows are likely to be classed as extensions that require formal permission.

Repairs are usually also permissible in listed buildings – but replacement tends to be a little more strictly controlled are requires listed building consent. Alterations to the style or the insertion of double glazing in such properties will also need specific consent.

Repairing existing windows

If you’re taking on a major project that features tired-looking windows, it can be easy to rush into the idea of switching them out for new products. But this isn’t the only option, as damaged units can often be brought back into service by an experienced joiner or specialist company.

Indeed, you may find that it makes more sense to refurbish what you’ve already got. This is particularly true if you live in a period property, where preserving original examples could be key to maintaining the house’s character and value.

Even units that appear to be rotting (telltale signs include flaking paint, sticking sashes and spongy wood that can be easily dug out with a screwdriver) can be successfully refurbished. Cills and lower rails are notorious weak points but are fairly easy to solve. So depending on the extent of the work, it may prove cheaper to repair rather than replace.

The exact process will depend on the issue at hand and underlying condition of the frame. Typically, any decaying timbers can be cut or routed back to sound wood and new sections (moulded to match the originals) scarfed into the frame. These are then sealed and primed, ready for decoration.

large restored sash window

Developments in glazing allowed the Victorians to fit large one-over-one sash windows that maximise views and light. These versions have been restored by Ventrolla

If necessary, the entire window can be removed, repaired and reinserted – although this has obvious cost implications. If you do wish to upgrade to double glazing, specialist companies such as Sash Window Workshop and Ventrolla can replace the individual sashes within new slimline versions. This allows you to retain much of the original unit, preserve the traditional profile and still get the benefit of improved comfort levels.

Fixing draughty windows

Another common issue that can develop over time is draughts. This is the most common cause of significant heat loss through old windows (even more so than through single glazing). In some cases cracks and gaps might be clearly visible; in others there may be signs of mould or condensation that direct you towards the problem area.

There are two main routes to upgrading. You could insert appropriate draughtproofing strips (most firms will do this as a matter of course while repairing windows). Alternatively, you could fit secondary glazing behind the unit, on the internal side.

Both measures will also help to reduce noise issues and dust ingress. They represent the least intrusive ways to improve comfort levels while preserving a property’s appearance.

Is it worth repairing standard windows?

Generally, significant repair is only really worthwhile on heritage units. There’s rarely much point in trying to salvage a decaying 1980s softwood window, for example, as few products from this era are likely to be of a high enough quality to merit refurbishment.

However, it could still prove cost-effective to replace panes that are misting up with condensation (usually a result of damaged seals) rather than stripping out the entire unit.

Corroded metal windows can also be brought back into good condition via specialist processes, such as acid pickling or flame cleaning (note that rust expands, so it often looks worse than it really is). Steel units suffering from bowing or similar issues can sometimes be repaired with new welded-in sections if necessary.

Replacing windows

It isn’t always cost-effective to repair old units; sometimes getting rid of them and starting again is the only viable course. With period properties, this is particularly true if originals have previously been swapped out for cheap, inappropriate versions. This was unfortunately a commonplace practice in the late 20th century.

In such cases, reinstating more suitable fenestration could actually add value. It’s also a pretty safe bet if you have a property built post-1960 where the windows are no longer offering good service (unless it’s a particularly remarkable building that merits a conservation approach).

Like-for-like replacement will always be the path of least resistance from a planning perspective. Depending on your project, however, you may be able to gain consent for a different material or even a more unusual design (more on this later).

Note that all replacement windows come under the scope of the Building Regulations (whereas repairs are exempt from the rules).

The main thrust of the regs is to ensure good thermal performance (via Part L1B) and minimum security standards (Part Q). When it comes to efficiency, the headline figures are that units should achieve a minimum Window Energy Rating (WER) of Band C, or hit a threshold U-value (a measure of heat loss) of 1.6 W/m2K.

Properly-installed factory-made double glazed products will always perform to the required standard. If you need a one-off bespoke unit, any specialist firm or joiner worth their salt should know the ins-and-outs of how to achieve your performance requirements.

new sliding sash windows

Sash Window Workshop fitted new sliding sashes in the existing window frames of this manor house. Manufactured in Accoya, the units are double glazed and painted in standard white

Materials options for replacement windows

One big question when replacing windows is the classic debate of which frame material to go for. The leading contenders are timber, PVCu and metal – and each has its merits when it comes to renovation projects.

Timber windows

Timber is a natural choice for many schemes, especially where conservation issues are involved or you have the budget to swap like-with-like. Few materials can match the innate charm or durability of wood – whether painted or stained, softwood or hardwood.

Modern factory-painted versions tend to come with guarantees of at least 10 years on the finish. Provided they’re maintained properly they should last in excess of 60 years before replacement is required. Timber can be used to achieve a variety of styles and finishes, with the flexibility to deliver the thin glazing bars that tend to suit period properties.

Timber is also a natural insulator, so typically offers a slightly improved whole-unit U-value compared to other materials. It doesn’t come cheap, however: expect to pay at least £200 per m2 for untreated softwood units. Pre-painted timber windows start from around £300 per m2, whilst hardwood versions can cost significantly more.

PVCu windows

PVCu windows are always going to be a strong contender for budget-conscious renovators (prices start from around £150 per m2). But these days there’s much more to recommend them than just the price tag. “High-quality modern units offer a cost-effective and virtually maintenance-free solution,” says Tom Swallow from Quickslide, which sells both PVCu and timber products.

Design-wise, these advances also mean plastic frames can be a much better fit in period properties than they were a decade ago. This is largely due to the fact that profiles are getting thinner. That said, they still can’t quite match timber and aluminium.

Metal windows

Metal products are also extremely low-maintenance, with options including galvanised steel, bronze and powder-coated aluminium. They offer the slimmest sightlines of all, which can look fantastic in both traditional and contemporary settings. This will also maximise the amount of natural light that filters into your home’s interiors.

You’ll pay for the privilege (prices start from around £300 per m2), but you’ll get the benefit of a high-quality product with a service life of at least 45 years.

“Don’t make getting a low price your main consideration,” says Stuart Judging, managing director at Crittall. “Cheap installations can look poor and wipe thousands of pounds off your property’s value.”

You can also buy composite windows that combine timber with aluminium cladding. This offers the best of both worlds: warmth internally and a low-maintenance external finish.

replacement steel windows

Replacement steel windows from Crittall, complete with slimline glazing bars, have restored this house’s early 20th century character

Changing configurations

If you’re replacing windows anyway, you might want to rethink the form and function of your fenestration. PD rights can allow you to alter, enlarge and insert new units in an existing building – provided they look similar to those in the main house.

Check with your local council how far you can go, and whether a formal planning application might be needed. This is likely to be required if you plan to change the style significantly. Remember you will need separate consent for this kind of project if you’re dealing with a listed property.

Changes such as adding floor-to-ceiling glazing at the rear of an existing house could transform the way you interact with your living space. Key goals include allowing more natural light to flood the interiors and creating a better connection with the garden.

If you’re embarking on a period renovation, bear in mind significant intervention can affect the fabric of the building. Tackle the works carefully to ensure heritage finishes are preserved, for instance.

A note on ventilation

Historic buildings were constructed as ‘breathable’ entities, allowing moisture to wick through the structural fabric and, ultimately, evaporate. Good ventilation is critical to preserving this situation.

Draughtproofing or switching to sealed modern units can cut out a potential source of air infiltration. However, in isolation, upgrading windows is very unlikely to prevent the building breathing effectively.

Provided you take simple precautions – such as avoiding modern impermeable paints and ensuring suitable natural or artificial sources of ventilation are present in kitchens, bathrooms and similar zones – there should be no issues.

Main image: Replacement PVCu windows by Quickslide

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