05 Jan 2018

Five top tips for specifying glass on a self-build

Here UK-leading architectural glazing specialist, IQ Glass, advises on glazing specification for that sought-after all-glass aesthetic.


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Recognised nationwide as one of the leading experts in windows and glass door systems, IQ Glass is the perfect source for some top tips on specifying glass on a self-build.

Get an idea of design early on

Considering and narrowing down your choice for glazing at an early stage will limit the amount of compromises you have to make on the design.

Deciding between large sliding doors and bi-folding doors can help you choose the positioning of steel supports. Choosing whether you want a steel, timber or aluminium window frame can help narrow the choice for wall cladding. Do you want glazing bars on your patio doors? If so, how will they line up with surrounding cabinetry or wall details?

If you do this it will also help your resulting self-build feel more cohesive and well-thought-through.

Beware of the U-values

The U-value of a material denotes its thermal insulation. The lower the U-value of a material, the better the thermal performance.

When it comes to the U-values of glass there are actually three different types of U-values you need to know about. The Ug value is the thermal performance of the glass, this is sometimes known as the ‘centre pane’ thermal performance. The Uf value is the thermal performance of the frame. The Uw value is the overall thermal performance of the window/door installation. This is calculated using the Ug value and the Uf value as well as the configuration and size of the glazing installation.

For example, a sliding door system may use a glass unit with Ug value of 1.1 W/m2K. When installed into a thermally broken frame the overall thermal performance (Uw) is likely to be about 1.6 W/m2K.

It is the Uw value that is the important factor. This is the thermal performance value that is governed by Building Regulations and other building regulatory bodies.

In some cases, glazing companies will advertise their systems stating a ‘U-value’ performance that looks too good to be true. That is normally because it is and what they are actually quoting is the Ug value (centre pane thermal performance through the glass). Watch out and make sure your glazier specifies what U-value they are talking about.

Check the glass specification

Glass is the main element of a window or glazed door so it is important that the right glass is chosen.

Insulated glass should have a Ug value of at least 1.1 W/m2K in order to give you a good level of thermal insulation. But there are other areas of performance to consider.

Is any roof glazing designed for maintenance loading? This allows the glass to be walked on for access, maintenance, cleaning and allows the glass roof to be walked on in cases of emergency escape.

Is the glass exposed to a lot of sunlight? If so, you should specify that the glass includes a solar control coating. This reduces the amount of solar radiation that can come through it and reduces overheating.

Any overhead glass should be made with a toughened laminated inner pane. This protects internal spaces and people in the case of glass breakage or accidents.

Other areas of performance like acoustic insulation, fire protection and wind loading should also be addressed.

Compare like-for-like quotes

It is only natural that you would want to get multiple quotes from a few different suppliers. The quotation process will help you narrow down to your chosen supplier and different companies may give you a different idea as to what you want on the build.

But when it comes to comparing quotations make sure that you are comparing like-for-like.

If one company has quoted for a true steel door frame and one has quoted for a steel-look frame then of course the costs are going to be different. Some glazing companies will include installation as standard whereas others won’t. Some quotes will exclude essential services like site surveys which you will have to pay for later.

If you are in doubt about what is included in your quotation or what the difference between two quotations are, just ask. Your glazing company will be able to explain exactly why their quote is more or less than their competitor's and will also be able to tell you exactly what is included and excluded. There is nothing worse than thinking you are getting a bargain only to be hit with hidden costs down the line.

Make sure you understand the drawings

When you place an order your architectural glazing company will issue you with drawings to approve prior to manufacture. Make sure that you check the drawings properly and understand what you are looking at. Some of the high-end glaziers will produce quite detailed and technical drawings.

It is from these design drawings that your glazier will place all the orders for the materials. If anything on the drawings is incorrect or they have misinterpreted what you want then what ends up on site will also be wrong.

Things to watch out for are handle locations, opening configurations, glazing bar designs (if applicable), glass specification and colour choice. When looking at the drawings take a note of whether the window/door you are being shown is from an internal or external view. Some companies draw things from an internal view, some from an external view. This will be clearly labelled on the drawing but can trip some people up.

If you are unsure about reading technical drawings you can employ your architect, builder or project manager to do it for you.

The best advice is to speak to a selection of glazing companies and don’t be driven solely on cost. Remember, if something is cheap there is normally a reason. If you are investing in the glass on a project make sure you visit the showroom and see the glazing installed outside in a true building environment, not propped up in frames in a warehouse.

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