Timber Windows – What’s the Difference?

September 17, 2019

I recently priced a job for some Clients comprising a large number of windows and several doors including some oversize bifolding doors.

The total cost was higher than their preferred budget, and so they approached two other companies for quotes. Both came in cheaper, at more than £200 per unit.

Now, such a difference is not to be sniffed at. But, as mentioned in our previous blog ‘What Are The Elements Of Quality?‘ there is a world of difference between one timber window and another.

Below are photos of two installed products. On the left is a casement window from a local non-specialist joinery company, and on the right is a window from our preferred specialist fenestration manufacturer. Below the photos are lists of the differences, all of which impact on price, longevity, performance, security and durability.



One of the principal benefits of high quality timber fenestration is how it looks. Designs vary considerably. Cheaper products, whether from non-specialist local companies or re-sellers of imports, simply do not look as good.

Differences include profiles, beadings, drip bars, glazing bars, how the glazing is fixed (i.e. unsightly silicone?), weatherbars etc.

If the product is well designed, why spoil it with poor finishes? One local joinery company we visited had the spray bay open to the main factory. This meant that all the products had dust in the paintwork!

New products: dust and dints (left); bubbling paint (centre); dints and poor jointing (right)

The photos above show new products which are nothing short of tatty. Note the rough edge of the door on the left. The cling film, when removed, apparently left imprints on the paint work which hadn’t dried properly! Below shows how it should be done.

Envy of the industry: our preferred timber partner’s beautiful jointing and finishing


When replacing single glazed windows with modern, thicker and heavier thermally efficient double glazed units, the window and casement frames must be robust enough to resist movement and warping over time. Many cheaper products have simple flat window and casement frame rebates which are less resistant to warping, less weatherproof and in flush casements can render the hinges and lock keeps visible.

Left: a flat rebate = visible hardware; Right: stepped rebate, no visible hardware

The flush style window above left has less substantial frames, whilst the window on the right is a stronger casement frame, with a tighter fit in the frame. The stepped rebate also promotes better weatherproofing (see below).

Our preferred timber partner: sophisticated rebate. Note the strong branded lock keep


If required by Building Regulations, these can be really ugly – surface mounted and intrusive. Or not (see below).

Our preferred timber partner: discreet trickle vent – almost invisible if colour-coded


Engineered timbers (lengths of which are made up of severals layers) reduce the natural movement in the wood. Solid timber is more prone to twisting and warping.

Softwood: we’re not fans of softwood. Even well-sourced engineered softwood will require more maintenance than a decent hardwood. Some joinery companies still use solid knotty pine – avoid! Only the best knot-free European Redwood or Larch should be used. These will be cheaper than hardwoods but expect to re-decorate in 10 years or so.

Hardwood: more expensive than softwood, solid Red Grandis is quite common. Engineered is better but we still wouldn’t recommend it. Just because it’s a hardwood doesn’t make it durable – so is balsa!

Red Grandis is much cheaper than engineered Sapele Mahogany, but this is the hardwood we recommend. Naturally rot resistant with a 30 year guarantee.

For those who want to see the grain, European Oak is best, but as oak is the worst for movement, it MUST be engineered.

Accoya wood: this is our favourite timber, which is the most stable timber available, and because of this does not need to be engineered. But it is the most expensive.

Finally, no matter how good the timber, if a product is only as good as the design and the skill of the manufacturer.


Window manufacturer’s should use glazing which allows their product to comply with the minimum Building Regulations U-Value requirement of 1.6Wm2K (see our blog ‘What Are U-Values?’ for info). But it’s important to understand that this is the WHOLE WINDOW value, not just the glass. The use of cheaper glazing units can make a difference to your home’s overall comfort and heat retention. Also, the spacer bar, which separates the glass, should be ‘warm edge’, not metal (which conducts heat). Our preferred timber partner uses a 1.0 U-value glazing with warm edge spacer bars as standard which usually achieves whole unit values of 1.2-1.4, depending on the window style. Make sure that you get a whole unit U-value in writing for each unit.


Windows used to have single point catches on the side of the casement and stays on the bottom to hold the window in position when open. Cheaper windows often still use these. However, even with locking catches and stays, which are extremely fiddly, usually requiring keys, they are relatively insecure.

Left/Centre: secure multi-point locks, with ‘easy clean’ hinge; Right: cheap catch and stay

Modern espagnolette systems lock the casement in several places. This is more secure. However, cheaper alloy metals can bend and break if forced, so products with solid stainless steel branded hardware should be sought. On these systems, stays are not required. Friction hinges are used which can be adjusted for stiffness and can hold a window in place when open. ‘Easy clean’ hinges allow the windows to be cleaned from the inside.


Many companies use silicone sealant to fix their glazing (see below). This is a problem for three reasons: 1) it usually looks terrible, 2) it gets dirty and 3) it degrades over time and can compromise the seal around the unit.

Competitor’s show product: 2-3mm sealant – dirty even indoors! Note the metal spacer bar

The best fixing method is to use glazing tape (see below). It’s hardly visible and doesn’t degrade.

Our preferred timber partner: glazing tape used as standard


The bane of timber windows, in our opinion, is when beadings and glazing bars warp, dislodge and come off. Especially if you have Georgian style windows. The majority are individually stuck on, as below:

Major competitor: separately applied glazing bars. Note the horizontal bar here does not line up with the beading (secured with a line of silicone). This unit is only 5 years old.

But when they are fully jointed and fixed as a matrix, this cannot happen (see below). This method of manufacture adds hours and materials to the production of the unit. But it’s well worth it.

Our preferred timber manufacturer: jointed beadings and bars

The image above shows a window which is part of a whole house installation made in stages from 2002-2004. Still in perfect condition.


It is vital that Clients are fully aware of what is included in their supply and installation contract. These need to be considered as follows:

Certification – Building Regulations

It is a legal requirement that your installation complies with building regulations and you are issued with a certificate that confirms this. If you sell your home, you will be required to present this certificate to the purchaser’s solicitor. There are three main routes to certification:

  1. the installation is carried out by a Certass or Fensa registered company or installation team. These are self-certification schemes whereby your installer registers the works with the local authority and arranges for your certification,
  2. the installer or Client engages an independent Building Control Consultant (such as ASK in Harrogate), who carries out inspections of the works, or
  3. the installer or Client engages a local authority Building Control Officer who carries out the inspection

Whilst TV ads will give you the impression that Fensa is the only method to ensure you get a professional service, this is not the only route. Indeed, self-certification does not always guarantee that your works will be done well. It depends on the company, and standards vary considerably. Whilst members of Fensa and Certass are periodically inspected, the benchmarks with regard quality is, in our opinion, quite low. A product may pass the fitting criteria, but there is no consideration of aesthetics. Using an independent BCO can work in your favour as the works are independent of the installer and they are working for you.


These vary considerably from company to company and you must get full written details of what is guaranteed, what is not, and how long each aspect is guaranteed for. We recently found a local manufacturer whose small print guarantees their installation and products for only 2 years, and only 12 months for supply only!

10 year guarantees are the most common, but they may not be comprehensive. For example, you might find that the small print excludes glazing units and hardware. One company we know gives a guarantee of only 5 years on glazing units and 12 months on handles.

We know another company whose marketing makes much of their 15 year glazing units guarantee, and another who offer a ‘lifetime’ guarantee. But looking at the small print you find out that what you have to do to comply with the terms of the guarantee are somewhat onerous.

In addition to a general product and installation guarantee, the timber itself should carry a 30 year guarantee against rot, whilst Accoya should carry a 50 year guarantee against rot, fungal and insect attack.

But even then you can come unstuck. The image below shows a unit, part of a whole house of windows and doors, showing signs of severe rot. The installation was less than 6 years old. The guarantee was 30 years, but when the Client complained the installer blamed the supplier, the supplier blamed the (overseas) manufacturer…..you get the idea.

The Client in this case got no redress and the whole thing needed doing again. If only she hadn’t gone for the cheapest quote in the first place.

There’s alot of poor quality imported product about, although we know some companies with pretty showrooms won’t tell you they don’t manufacture themselves.

We recommend sticking to UK manufactured products, so ask to visit the workshop. If they prevaricate, walk away. And if you’re getting several quotes, research all the companies and visit every workshop!

Deposit Protection

It’s now fairly standard for companies to take 90-95% of your money before your installation in several instalments – at point of order, after survey, prior to delivery/installation. This has come about because a significant minority of Clients have a habit of not paying. This has caused serious difficulties for some and has put others out of business. It’s worth bearing in mind in an industry where 100s of companies go in and out of business every month.

The exceptions to this are the big nationals or smaller companies run by people who don’t have good business heads. The nationals put considerably high mark-ups on their rather average products, making large profits, so they can afford to take much smaller deposits and have big legal departments!

So when you pay your hard-earned cash in the form of a deposit, you need to ensure it’s covered. Find out if they’re registered with a scheme such as the Double Glazing and Conservatory Ombudsman Scheme (DGCOS) or the Consumer Protection Association (CPA)

What is important to understand is that these schemes only cover a proportion of your total contract price (up to 25%). So there is no such thing as total protection. All the more reason to ensure you do your research and have enough information to feel you can fully trust the company.

But, also bear in mind the company is also taking a risk. Specialist timber manufacturing costs, labour and materials, are high. If you paid your second deposit, but unforeseen circumstances prevented you from paying any more, the company will still have made a loss and be lumbered with a whole load of product that cannot be used elsewhere.

Insurance-Backed Warranty

Companies go in and out of business all the time. An insurance-backed warranty protects you in the event that something goes wrong with your installation after completion and the company goes out of business. Having this will give you peace of mind, but it usually only covers the installation itself, not the product, as this is usually covered by the manufacturer themselves.

To be fair, this should not be a concern, as a decent product (see above!) will last much longer than the 10 years the warranty covers. These warranties are usually supplied by the same company that covers the deposits.


Robert Goldsbrough

Robert Goldsbrough

Robert has been developing and building period & contemporary homes since 1995, and has installed all types of external home improvement products.