Nicola Harrison, General Manager of Bereco Timber Windows & Doors answers the most common questions she's asked by homeowners - 'How often will I have to decorate my windows?' and 'How long is the paint actually going to last?'.
The reality is that there is no definitive answer to these questions as many factors need to be considered, such as house design, fitting method, exposure, finish type and colour. But there are things that both homeowner and manufacturer can do to ensure that the interval between redecoration periods is significantly extended. The homeowner's choice of species and coatings, as well as their maintenance regime will have a big effect, but the longevity of any timber window or door relies heavily on the manufacturer's adoption of best practices in the selection of timber, design, construction and in factory finishing of timber windows and doors.
Timber types used in the manufacture of timber windows and doors not only affect the total service life of the joinery but also the paint system and its durability. There are so many types of timber on offer, which one do you choose?
Timber windows and doors in the UK are generally manufactured from slow growth pine, typically from Scandinavia, engineered to remove knots and defects. Pine takes preservative treatment well, and sustainably grown, certified timber is widely available. A study by Heriot Watt University shows that a factory-finished pine frame made to Wood Window Alliance standards can be expected to last around 60 years.
Hardwoods are often chosen for their decorative appearance when a translucent or stained finish is specified. They are more expensive and certified timber is less readily available. Hardwoods and modified timber, such as Accoya™, will have an even longer service life than pine, but care needs to be taken with coatings and hardware as some are more acidic than pine. You should always ask for FSC or PEFC chain of custody certification.
Design features, such as sufficiently sized glazing rebates appropriate to the type of glazing, carefully designed drained and vented glazing systems that prevent water accumulation, rounded frame edges (min 3mm radius), sloping cills (min 7 degree fall) and glazing beads designed with water drain off in mind are all key to the service life of any timber window or door. The British Standard BS644 (Fully Finished Factory Assembled Windows – Specification) defines these design features and a manufacturer that can prove compliance through third party certification or, at a minimum, by test to BS644 is a must.
Construction of the windows and doors is key to the longevity of external joinery. All joints must be appropriately and robustly constructed with any fixings concealed below the surface of the timber. Where separate drips and cills are not part of the main frame construction, they should be fixed using screws on a concealed part of the cill - not through its face.
A manufacturer that preservative treats its timber and controls the moisture content of its timber will also enhance durability and longevity of their product over those that don’t. Keep it simple and ask to see samples as evidence of robust construction methods and ask about preservative treatment and moisture control.
Factory Finishing is now common practice for many manufacturers of timber windows and doors. The painting or staining process is fully incorporated into the production facilities where windows and doors are made. Long gone are the days of windows being supplied with just a basecoat for on-site coats of paint; the cost of factory applied coatings from a manufacturer with fully integrated paint facilities is now comparable if not cheaper to that of employing decorators to hand paint your windows.
With factory coatings you get a finish applied in controlled conditions, no damp, no humidity, no brick dust, no dirt, just a clean smooth defect-free finish.
Modern paint systems are also highly flexible. They allow timber to expand and contract, and are resistant to direct weathering; so always choose a paint system designed for external joinery and ensure your chosen manufacture is using one.
Modern paint systems are always applied in stages, with most following a similar process of:
1. Preservative Treatment: Penetrating deep into the timber, the preservative treatment offers protection against rot and fungal decay, stabilises the timber against the risk of twist and warp and promotes even colour on final application.
2. Primer: Ensures the perfect surface for application of subsequent coats, even colour and deeper translucent stain colours on final coat application.
3. Intermediate Coat & Join/Grain Protection: Coating and sealing of end grain and v joints provides the timber with all-important protection from the elements. Flexible joint sealants allows the timber to breathe, whilst leaving the coating unaffected by cracking.
4. Final Coat: Providing the products with their final weather resistant coating, and featuring UV absorbers to prolong the durability of the finish.
Another key consideration is the choice of colour of the finish of your windows as this will have a direct impact on their service life. Dark colours absorb UV and heat and can degrade quicker than pale colours, or white.
Stained finishes - especially paler shades - contain less pigmentation and less UV protection than opaque colours and will need recoating more often.
Post Installation Maintenance
All windows and doors need maintenance, not just timber. Whilst many claim to be ‘maintenance free’, read the small print and you will find a maintenance requirement of some form or another.
Timber windows and doors have had a bad reputation when it comes to needing painting, and no-one wants to be faced with the daunting task of repainting windows and doors every summer but advances in the manufacturing process that I have already discussed as well as those in the quality of the factory applied paint and stain systems today are already offering extended service lives for timber windows and doors.
So what can I expect to be doing in reality after installation? You can expect from a timber window and doors supplier today to have an annual or bi-annual cleaning routine, with top coat redecoration not being required until between 8-10 years (opaque finishes) from delivery followed by a 5-7 year cycle from first redecoration and thereafter. See the WWA Maintenance Guidance for more information.
It's important to note that factory-finished coatings will need little preparation. As long as you have repaired any damged areas with primer and topcoat when the damage occurred, the frames should just need a light rub with abrasive paper, followed by two top coats. See the WWA redecoration video for more information.
I would strongly urge the use of the care sets provided. Most suppliers now offer a care set that should be used during routine maintenance - some yearly, some twice a year. These paint care sets revive dulled paint, restore the water repellent properties of the finish and enhance its UV protection. You wouldn’t sit in the sun for hours without sun cream with a suitable SPF factor, so you shouldn’t expect your windows to do the same if you want them to last.
So how do I ensure my windows will be low maintenance?
My advice is to do your homework before any purchase. Don’t be afraid to ask for evidence of performance and to see the maintenance and redecoration cycles during your supplier selection process; it is, after all, a big investment and one that you that will have to live with long after all the suppliers and builders have gone from your home. So:
1. Choose a supplier that is a member of a trade organisation, such as the British Woodworking Federation (BWF) and the Wood Window Alliance (WWA), whose strict membership requirements and quality standards are higher than those of the timber window and doors industry in general and have to be achieved and proven in order to gain membership
2. Choose a supplier that uses durable timber types such as engineered, preservative treated European pine and who has PEFC or FSC Chain of Custody certification
3. Choose a supplier that can prove compliance with the British Standards (BS644) for peace of mind that your windows have been designed with longevity and perofrmance in mind.
4. Choose a supplier that can offer evidence of a controlled, measured and documented paint application process or even better that can provide independent third party accreditation.
5. Ensure you have reviewed all the post installation and maintenance information from your chosen supplier so you fully understand what needs to be done after the windows are in and the builders are gone.
6. Ensure you get a warranty from your supplier; one where action has to be taken i.e. repair or replacement should the coating show defects within the defined warranty period.
Finally; follow the suppliers and or paint manufacturers guidance for maintenance and redecoration after installation it will make your windows look better and last longer.
Heriot Watt Service Life Study
The Specifiers Guide to Timber Windows, Wood Window Alliance
WWA Maintenance Advice Note
Teknos Technical Manual – single pack joinery coating systems
British Standards BS644 – Fully Finished Factory Assembled Windows – Specification