double glazing

Double glazed windows supply and installations

You can come to the specialists at The Glass Man for double glazing services anywhere in the UK.  Contact us for more information.


Applicable to all orders

The standard adopted in the UK glass industry, is to measure in millimetres (mm). If you measure in Imperial use inches and either one eighth (1/8″) and/or one quarter (1/4″) of an inch. Multiply inches × 25.4 to convert to millimetres. Always give the WIDTH first × HEIGHT second, this is most important for patterned glasses and double glazing units with square/diamond leads, Georgian Grills or Duplex Bars. It also applies to clear glass that is being BS or EN stamped in the corner, if the width is not first, the mark may be in a different corner.

Allowances for glazing
A glazing clearance is normally the tight opening size minus 6mm giving a clearance of 3mm all round. For larger pieces a larger clearance may be necessary. If you are not giving a finished glazing size, you must state this at the time of ordering, unqualified sizes will be taken as the glazing size.

Template and patterns
Use a hard material, hardboard is easy for you to work with. We probe your template on our CNC machine; the more accurate your template the greater the accuracy of the finished article. A template should be the actual size required and need no additions or subtractions to it. Mark the face surface. All templates should be made as viewed from the outside. We do not accept paper or cardboard templates.

Types of Glass

What are the basic types?
  • Annealed – Standard glass as made by the Float or Rolled plant.
  • Horticultural – Annealed glass for use in greenhouses and sheds where optical quality is not important and compliance to BS6206 is not required.
  • Toughened – Annealed glass, arrissed as standard, heat treated and breaks safely into small pieces. Cannot be cut or drilled after toughening.
  • Heat Soaked – A further process after toughening to try and eliminate spontaneous breakage in toughened glass from Nickel Sulphide inclusions. Normally used on thicker glass glazed at high level.
  • Laminated – Two pieces of glass with an EVA, PVB or resin interlayer, breaks safely and normally is retained within the aperture.

Standards and regulations

How do I know if my order must comply with a standard or regulation?
The most common references are as shown below. Please advise us at the time of enquiring or ordering if these are a requirement.
  • Document L & its amendments October 2010 – Building Regulations – Conservation of fuel & power. The key targets are as follows, however, there are variations and exceptions:
  • Replacement Windows – Whole Window U value of 1.6 W/m²K or a minimum WER of C.
  • Replacement Doors – Whole Door U value of 1.8 W/m²K or a minimum WER of C.
  • New Dwellings – Standard government software, SAP, provides the calculations to comply with the predicted rate of emissions from the dwelling (the Dwellings Emission Rate) not being greater than the Target Emissions Rate (based on a notional dwelling). The SAP calculation will be made and the whole window U value calculated on receipt of which we can then provide the specification for the double glazing unit make up.
  • Document N1 & N2 – Building Regulations – Glazing + materials & protection.
  • BS476 Part 22 – EN13501-2 – 1363 – 1364 – 1365 – 1634 – Fire.
  • EN12150 – EN14449 – EN14179 – EN12600 – BS6206 – Safety.
  • BS5544 – EN356 – EN13541 – Anti Bandit Glazing.
  • BS6180 – Barriers & Balustrades.
  • BS8000 – Part 7. Code of practice for glazing.
  • FENSA (BFRC) – The simple method – In UpVC & Timber Frames (timber depth of frame to be a minimum of 70mm from front to back) a double glazing unit constructed with a 4mm Softcoat Low E – 16mm warm edge spacer + 90% Argon – 4mm Float, with a centre pane U value of 1.2 W/m²K will comply and no further evidence to the consumer or FENSA inspector will be necessary.
  • Certass (TRR) – Members of this scheme will have had their products or services evaluated to show compliance with Document L2010.


How do I know where to use a safety glass, laminated to EN14449, toughened to EN12150 or clear wired to EN12600?
Very briefly and not covering all the requirements, Document N1 & N2 of the Building regulations define areas that are deemed to be critical locations and more prone to an accident. In these areas, e.g., glass in a door, either side of a door or within 800mm of the floor, use an appropriate safety glass. Where abnormal behaviour can be expected, e.g., in schools or hospitals, all necessary precautions must be taken to minimise any potential risk.

In accordance with British Standards the glass will be marked as required in one corner of each piece.

Our glazing units

For glazing to timber windows where the overall thickness of the unit needs to be as thin as possible for use in joinery of a traditional size or conservation work.

The units can be constructed with a non–rigid silicone foam based black spacer as narrow as 4mm where the overall size does not exceed 600mm x 600mm. The sightline is 8mm from the edge of the glass to the top of the spacer. A clearance for glazing must have already been allowed when submitting your order.

When utilising a unit make up of 4mm Float, 4mm gas filled cavity and an inner leaf of 4mm Softcoat Low Emissivity Float (Patterned, Sandblasted, Low Iron or Conservation Glass can be substituted for the 4mm Float), the centre pane U value will be 1.5 W/m²K for Xenon gas, 1.9 W/m²K for Krypton gas, and 2.6 W/m²K for Argon gas.

Units have been tested by the manufacturer of the spacer to EN1279 – 6, including EN1279 – 3 for gas retention and are manufactured in our own factory where we have obtained EN1279 1 – 6 for units with conventional spacer bars and are manufactured utilising the same quality control systems.

Care must be taken to ensure compliance is not required to Document L of the Building Regulations 2010. Check with your Conservation or Building Control Officer at the appropriate Council Department for exemption. Should compliance be required you must produce a whole window U value simulation. We can assist you in the calculation on receipt of the frame construction details.

If the units are being glazed without beads (which is contrary to BS8000 & GGF recommendations) they must not be glazed with putties containing linseed oil. Please contact us for a glazing method data sheet for suitable glazing materials for glazing with or without beads. To ensure the best adhesion of glazing tapes, compounds & silicones, Thinlite units are not edge taped.

Double glazing services

1. What is U-value?
The rate of heat loss per square metre for a temperature difference of 1 degree Kelvin, or Celsius, between the interior and exterior.

2. What is the “greenhouse” effect?
Clear glass will allow heat from the sun to enter the building, contributing significantly to internal temperatures.

3. What standard are the units made to?
EN 1279 Parts 1 to 6

4. Is there a date from which all units must be made to EN 1279?
April 2007

5. How can I improve the U-value?
  By using either a hard or softcoat low-e glass with Argon Gas in the cavity if necessary.

6. Can heat be kept out?
Solar heat gain can be reduced by using a solar control glass.

7. Does the thickness of glass improve the insulation value?
Very little.

8. Is there a self cleaning glass?
There are clear and tinted self cleaning glasses produced by the glass manufacturers with a hard hydrophilic coating to help the removal of dirt when it rains or hosed down. There are other applications available that are applied to the surface of the glass prior to installation, the life of which should be checked with the manufacturers.

9. How should my frames be constructed?
A frame needs the U-value or WER (the Architect, Specifier or Frame Maker will give you the U-value or WER for the frame); from this information we can give you the required makeup of the double glazing unit. Make clear if your U-value is a centre pane U-value for the glass alone or a combined frame & glass U-value. The size of the rebate in timber frames especially, is critical, the height of the rebate must be at least 15mm & the width, thickness of the unit, plus 6mm for glazing materials, plus the width of the timber bead (normally a minimum of 12mm).

10. What cavity widths (1) are available and what colours (2)?
  • 4mm, 6mm, 8mm, 10mm, 12mm, 14mm, 16mm, 18mm & 20mm.
  • Warm Edge Spacer GREY or BLACK. Aluminium spacer SILVER, WHITE, BRONZE, BLACK & GOLD. Some cavities and colours are only available on request.

11. If I do not specify a spacer colour, what will I get?
Default spacer colours are silver for aluminium & black for warm edge.

12. Are there inserts available to go into the cavity?
  • Georgian Bar – Straight or curved in White or Brown, 25mm/18mm × 8mm.
  • Gold Victorian Grill – Please submit your enquiry.
  • Duplex Bars – The pitch, the dimension of the flat of the bar to be applied is required. Duplex bars are only incorporated in units that are constructed toughened glass to minimise the risk of thermal fracture.

13. Can units be leaded?
A self adhesive lead strip is applied to the inner and outer surfaces of the outer leaf of the double glazing unit. In squares, diamonds and colour film designs, details with any necessary drawings and colour references are required. Standard designs are available.

14. How should units be glazed?
Glazing should be in accordance with BS8000. 
Are there special requirements for glazing glass in a roof?
  • The outer leaf is normally toughened to resist thermal fracture.
  • The inner leaf can be toughened or laminated depending on the application. If laminated it must be stepped back to be within the building.
  • If the bottom edge of the double glazing unit is exposed, the edge should be encapsulated by a U-channel or the top leaf should be longer than the bottom leaf to run water clear of the seal.
  • Both top and bottom leaves must be “stopped” in the rebate to prevent the glass sliding down.

15. Can I have a cat flap in a double glazing unit?
Yes, buy a cat flap with a round hole for fitting into glass.

16. After glazing what maintenance is required?
Follow the maintenance instructions below for all types of installation:
– Flush Edge Units
Inspections should be carried out after about one year and periodically, thereafter, as deterioration could take place as a result of incorrect application or vandalism.
Damaged sealant should be cut out and replaced in the affected areas. The Sealant Manufacturers’ recommendations should be followed.
Where gaskets have been displaced or damaged, or where there are gaps, they should be re-fitted or cut back and capped with silicone sealant.
With vented glazing methods, checks should be made to ensure the drainage or ventilation holes or slots, have not become blocked with dirt. While checking these, it is also advisable to examine the effectiveness of the seal of the exposed frame joints, which may determine the weather tightness of the rebates.

– Stepped Edge Units
Routine maintenance is similar to that required for single glazing with the putty fronting. i.e. ensure that painting is carried out regularly to provide protection for the putty. The paint line to extend onto the glass inside and out.

– Micro Porous Frames and Stained Frames
Special care must be given to the inspection of treated and stained softwood frames. Lack of routine maintenance causes the finish to flake off and joints in the frame to open up. This may allow water to permeate the seal and cause failure of the unit.

Visual quality standard for installed double glazing units constructed from flat transparent glass.
It is necessary to apply a viewing standard when it is deemed a double glazing unit may have a fault. The glass manufactures apply a standard to their glass for imperfections in the main body of the glass and any coatings they may apply to it during their manufacturing processes. The quality of glass used in the manufacture of double glazing units is the same as that for single glazing. Working with the materials supplied to us to the relevant EN standards in turn dictates the quality of the double glazing units supplied to you and has to be taken into account for the finished product.
The viewing standard will be as follows: Annealed glass will be viewed at 2 metres. Toughened, laminated or low e glasses will be viewed at 3 metres. Other coated glasses will be viewed from 3 metres. The viewing will be at 90 degrees, in natural daylight, imperfections may not be marked to highlight their presence and will only be visible to the naked eye. A band 50mm wide around the perimeter of the double glazing unit is excluded as an area to be viewed. The double glazing unit will be looked through, not at the surfaces.
Flat transparent glass, including laminated and toughened shall be deemed acceptable if the following phenomena are neither obtrusive nor bunched: totally enclosed seeds, bubbles or blisters; hairlines or blobs: fine scratches not more than 25mm long: minute embedded particles.
Due to the manufacturing process seeds and bubbles are deemed acceptable in patterned glass.

Duplex and Back to Back Bars
The method of construction compounds tolerances and allowance should be made for this when determining the width of the bar to be applied to the surface of the glass. The width of the bar should be the pitch of the Duplex or Back to back bar plus 3mm. Deviation from parallel along the bar lines is acceptable.

Double glazing units

Heat will migrate from a warmer surface to a cooler surface when there is a difference in temperature between two surfaces.

A transparent glazed surface is subject to solar radiation, G Factor, resulting in heat gain.

Double glazing will give better thermal insulation than single glazing. The dry, still air between the two sheets of glass improves the thermal insulation. Heat exchange by convection is reduced and the low thermal conductivity of the still air limits heat loss by conduction.

The U-value of a double glazing unit can be improved by reducing the heat transfer by conduction, convection and radiation. This is achieved by reducing the heat exchange between the glasses incorporated in the double glazing unit.

A low-emissivity (low-e) coating will reduce the radiated heat transfer.

Argon gas filling of the cavity will reduce heat loss by conduction.

A solar control glass towards the exterior, with high solar radiant heat absorption or reflectance, will reduce solar energy heat gain.

For our services anywhere in the UK, contact us today.

Toughened glass - Stamping

In order to comply with the relevant BS or EN standard the glass will be stamped in the corner.

Please state at the time of ordering if you require the stamp to be the full size mark or a line mark on the face close to the edge. Line marks will not be visible once glazed and may be rejected by Building Control, FENSA, or similar bodies.

It is not possible to always align the stamps in a double glazing unit; the glass may bow during the toughening process and they will be paired as best they can for sealing of the double glazing unit.

1. Viewing
  • The glass shall be viewed from the room side standing at a distance of not less than 3 metres in natural daylight and not in direct sunlight. The area to be viewed is the normal vision area with the exception of a 50mm wide band around the perimeter of the unit.
  • The glass shall be deemed acceptable if the following phenomena are neither obtrusive nor bunched: totally enclosed seeds, bubbles or blisters; hairlines or blobs; fine scratches not more than 25mm long; minute embedded particles. Obtrusiveness of blemishes shall be judged by looking through the glass, not at it, under lighting conditions as described in 1.
  • When toughened glass is viewed by reflection, the effect of the toughening process may be seen under certain lighting conditions. The visibility of surface colouration or patterns does not indicate deterioration in the physical performance of the toughened glass. Because of the nature of the toughening process, distortion can be introduced. Such distortion will be accentuated when glass is viewed in reflection or incorporated in double glazing units.

2. Bow
The nature of the toughening process, heating the glass to approximately 700 degrees centigrade and cooling rapidly whilst the heated glass is rolled over a series of rollers, induces bow into the glass. This is an inevitable part of the process and is unpredictable, being dependent on a combination of factors and the type of furnace being used. If you require the full technical details of bowing during the toughening process, please contact us to request a full copy of the standard.

Thinlite double glazing units

Ideal in conjunction with joinery of a traditional size or in instances of conservation work, in which timber window units need to be as thin as possible.

In instances where the unit does not exceed 600mm x 600 mm, a flexible foam-based black spacer as narrow as 4mm can be fitted. The sightline is 8mm from the glass edge to the spacer top. When submitting your order, the glazing clearance must have been accounted for.

In any unit consisting of a 4mm float, 4mm gas-filled cavity and a 4mm inner leaf of Softcoat Low Emissivity Float, the centre pane U-value will be: 1.5 W/m²K for Xenon gas, 1.9 W/m²K for Krypton gas, and 2.6 W/m²K for Argon gas. The 4mm float can be substituted for patterned, sandblasted, low iron or conservation glass.

All units have been tested by the spacer’s manufacturer to EN1279 – 6. This includes EN1279-3 for gas retention. We’ve obtained EN1279 1 – 6 within our factory and all units are manufactured here in accordance with the same quality control systems. This includes units with conventional spacer bars.

Ensure that compliance to Document L of the Building Regulations 2010 is in effect where necessary. When pursuing exemption, you should liaise with your conversation or building control officer where necessary. If so, you must produce a whole window U-value simulation. We can help with this once you receive frame construction details.

Where units are glazed without beads, putties containing linseed oil must not be used. A glazing method data sheet can be supplied where glazing materials are listed for glazing with or without beads. Thinlite units are not edge taped for optimum adhesion with glazing tapes, silicones and compounds.


1. What are the basic edge finishes to a piece of glass?
  • Arrissed Edge – The sharp edges are machined, not a finished edge, suitable for glazing or handling purposes or to reduce the risk of thermal fracture in annealed glass.
  • Smoothed Edge – The edge of the glass is machined flat and the edges arrissed but not polished.
  • Polished Edge – The edge of the glass is machined flat, the edges arrissed and the edge is polished.
  • Bevel – The face surface of the glass is ground way and polished to various widths and thickness at the edge. Unless the thickness at the edge is specified, it will be to our normal setting.
2. What diameter hole can be put into a piece of glass?
Virtually any diameter of hole can be drilled or cut. The internal finish to a hole is generally a smooth one. In toughened glass there are limitations as to how close to the edge the holes can be positioned.

3. Can you polish or bevel shapes?
Shapes can be bevelled and polished. Internal radii must exceed the minimum radius for the type of machine the glass is being worked on. Submit details of the shape required.

4. Can you cut a shape from a .dxf file emailed to you?
Yes. We have CNC machines for glass cutting and processing.

5. Can stencils be cut for sandblasting designs onto glass?
Stencils can be cut from your drawing, after being entered into our graphics computer, a copy will need approving before being put in hand or from your computer generated file.

6. Can “cut outs” or “notches” for plug sockets or other items be incorporated in the glass?
Yes, normally in toughened glass to increase the strength of the finished piece so there are rules as to how close to the edge or corner they can be, submit a dimensioned drawing for approval.

7. What sort of glass can be used in a barrier or a balustrade?
BS6180 defines the type of glass depending on the type of framework and building it is used in. Your Architect, Specifier or Building Control will specify the Uniformly Distributed Load (UDL) in kN/m² and/or the Point Load in kN. On receipt the type of building, eg domestic or commercial and the loadings, we can make a recommendation as to the type of glass to be used.

8. Glass floors, is there a maximum area and special frame?
We have data for the appropriate thickness up to 1m². Submit the UDL in kN/m² and Point Load in kN and advise if a domestic floor, dance floor, corridor, or stair tread, for our recommendations.

9. What is “Cracked Ice”?
An EVA or resin multi laminate where one of the glasses used is a toughened one which after laminating, is broken and gives a “crazed” appearance. At the time of enquiring we need to know if the piece is four edge glazed, clear, or tinted, and any processing that may be necessary.

10. Mirrors, how do I determine the, thickness, edgework, number of holes and whether safety backing is required?
We have tables to help determine the thickness. If the edge is exposed or tiled up to, the edge should be polished. A mirror will normally hang on the screws put in first, so 4 or 6 holes in the right position with the correct fixings, will be sufficient.

11. What thickness should I use for a shelf?
Again, we have tables and can advise you.

12. Is there such a thing as, “One-way Mirror”?
Yes, 6.4mm Laminated One Way. The glass has a grey body tint with a reflective surface coating. The glass is installed with the surface coating facing the observed area. The glass has low light transmittance and high reflectance. When the glass is installed with a lighting ratio of 7:1, the dark side being the side where the observer is (the observer should also wear dark clothing), the reflection will look like a mirror to the observed.

13. What is the mirror with stripes on?
“Venetian Stripe Silvered” deceives the eye by reflecting light from the bands of silvered glass, but is obviously not a secret viewing mirror.

14. Safety or Foil Backing
A mirror or painted glass can be safety backed with a white woven film to give impact resistance on one face to BS6206 Class Bo. Glass with a white woven safety backing cannot be fixed with a mirror mastic or low modulus silicone. The film is coated with a release agent to enable the roll to be unwound and consequently no manufacturer of safety backing has approved their film to be fixed with an adhesive and conversely no manufacturer of mastic or silicones has approved their products to be used with a safety backing.

A mirror or painted glass can be backed with an aluminium foil,; it does not have an impact resistance classification. Foil protects the painted surface of a mirror or painted glass and as it has no release agent it can be fixed with mirror mastic or low modulus silicone; with this method the bottom edge of the glass must be supported to take the weight of the glass.

If desired a mirror or painted glass can be fixed directly to the substrate with mirror mastic or low modulus silicone provided there is an ample covering to ensure, in the event of breakage, no large and dangerous pieces are able to break off and fall or cause injury. Support along the bottom edge is essential.

Fire resistant glazing

1. How do I know the type of fire resistant glass I need?
  • Your Architect or Specifer will advise you or Building Control will stipulate what you need to comply with in the Building Regulations.
  • Advise us of the specification as follows and we will advise of a suitable glass for your requirements:
a. Integrity only – 30 minutes or 60 minutes
b. Integrity plus Insulation – 30 minutes or 60 minutes
Example: 60 minutes Integrity plus 30 Minutes Insulation.

2. Can it be clear?
Wired was the traditional fire resistant glass but the latest fire resistant glasses are clear.

3. Are there different types for glazing internally & externally?
Wired is for internal or external use; specify if it is to comply with EN12600. Most types of clear have an internal and external grade apart from 7mm & 11mm Pyroguard and some modified toughened glasses.

4. Do I need special frames?
Yes, the frame must be constructed from the correct material to give the fire rating required.

5. Do I need special glazing materials and glazing methods?
Yes, Intumescent, compounds, strips or sealants are needed depending on the type of glass and the rating. When you specify the glass required we will advise on the necessary materials and glazing method.

6. Can you provide test evidence if required?
Yes, we have manufacturers’ reports available on request.

Newton's Rings

When a plano-convex lens with its convex surface is placed on a plane glass sheet, an air film of gradually increasing outward thickness is formed between the lens and the sheet. The thickness of the film at the point of contact is zero. If monochromatic light is allowed to fall normally on the lens, and the film is viewed in reflected light, alternate bright and dark concentric rings are seen around the point of contact. These rings were first discovered by Newton - that’s why they are called NEWTON’S RINGS .

Newton’s rings are formed due to interference between the light waves reflected from the top and bottom surfaces of the air film formed between the lens and the glass sheet.

The phenomenon of the formation of Newton’s rings can be explained via the wave theory of light.

* An air film of varying thickness is formed between the lens and the glass sheet.
* When a light ray is incident on the upper surface of the lens, it is reflected as well as refracted.
* When the refracted ray strikes the glass sheet, it undergoes a phase change of 180O on reflection.
* Interference occurs between the two waves - this works constructively if the path difference between them is (m+1/2) and destructively if the path difference between them is m, producing alternate bright and dark rings.

Let the radius of the curvature of the convex lens be R and the radius of ring be ‘r’. Consider light of wave length ‘l’ falls on the lens. After refraction and reflection, two rays - 1 and 2 - are obtained. These rays interfere with each other producing alternate bright and dark rings. At the point of contact, the thickness of the air film
is zero and the path difference is also zero; and as a 180O path difference occurs, they cancel each other and
a dark ring is obtained at the centre.
As we move away from the central point, the path difference is also changed and alternate dark and bright rings are obtained.
Suppose that the thickness of air film is ‘t’.  By using the theorem of geometry,

r2 = 2Rt………….. (1)
In thin films, path difference for constructive interference is:
2nt = (m+1/2) l
Where n= refractive index
For air n = 1
2t = (m+1/2) l ………….. (2)
For first bright ring m = 0
For second bright ring m = 1
For third bright ring m = 2
For Nth bright ring m = N-1
Putting the value of m in equation (2)
2t = (N-1+1/2) l
2t = (N-1/2)l
t =1/2 (N-1/2) l ………….. (3)
Putting the value of ‘t’ in equation (1)
r2 = 2Rt
r2 = 2R . 1/2 (N-1/2) l
r2 = R (N-1/2) l

This is the expression for the radius of Nth bright ring where
rn = radius of Nth bright ring
N = Ring number
R = radius of curvature of lens
l = Wave length of light

Brewster's Fringes

The appearance of the optical phenomenon known as Brewster;s Fringes is not a defect of the glass and can occur with any glass of high optical and surface quality. This phenomenon is a result of the high quality now being achieved worldwide by modern methods of glass manufacture. Brewster's Fringes occur if wavelengths of light meet up with each other when they are exactly 180 degrees out of phase – an example of the phenomenon known to physicists as the interference of light. The effect is similar to, although usually much smaller than, the interference fringes which can sometimes be seen on toughened glass windscreens.

Brewster’s Fringes occur when the surfaces of the glass are flat and the two panes of glass are parallel to each other - i.e. when the light transmission properties of the installation are of a very high order. This phenomenon is not a defect of the product, being dependent on the laws of physics and not on the quality of the insulating glass. In fact it arises because modern glass made by the float process is flat and therefore free of the distortion inherent in sheet glass.

The occurrence of Brewster's Fringes is in its nature rather like (though very much more than) the fact that under certain conditions, the observer will see a reflection of himself in any window or door and no-one could claim that this was a defect of glass.

Cleaning Glass

When it comes to cleaning your glass product from the Glass Man, it's recommended that you use our specialist Glass Man Glass Cleaner for optimal results.

Regular cleaning of glass is important to ensure that there is no discolouration and deterioration at the glass surface. Indeed it may be necessary according to the atmospheric conditions prevailing in the area to determine the frequency for regular cleaning, particularly where infrequent cleaning could result in obstinate dirt having to be removed by methods and labour at greater cost. Again the usual effect of dirt on glass is to reduce the light transmittance, which was probably one of the reasons for the glass being installed in the first place.

Generally, cleaning of glass as a routine operation is by the use of warm water with soap or mild liquid detergent, followed by rinsing with clean water. Washleather or cloth is suitable to use for transparent glass but certain types of washleather or imitation washleather have been know to cause streaking if the glass has not been initially polished with a cloth. For glass having a textured surface into which it may not be possible to clean off with a cloth, a stiff plastic or bristle brush is effective. Obstinate dirt in such cases can usually be removed by using either whiting in water or methylated spirits.

If dirt, contamination, staining and the like are not overcome by these normal methods, then other means may be adopted but before choosing a particular form of treatment it is advisable to determine wherever possible the actual cause of the trouble. If the cause is an on-going one, the first step should be to prevent further trouble at source. The remedy perhaps could be in the sealing of concrete lintels or the provision of drip channels so that the rain will not run down the glass surface. However, where obstinate staining is present, the answer may be in the use of a specialist cleaning and polishing process by experts.

Self cleaning glass must be cleaned as soon as possible after the building work is completed by rinsing with water to remove all traces of dust, abrasives etc. Then either spray on or apply by a saturated cloth a cleaning solution (a mild detergent and water solution is recommended) onto the coated surface. Gently rub the wetted coated surface with a clean, lint-free towel or cloth. Rinse with water and wipe nearly dry with a dry, clean, lint-free towel or cloth. The use of a squeegee on the coated surface is not recommended. If it is absolutely necessary to use a squeegee then particular care must be taken to prevent any metal parts from contacting the coating or dirt particles becoming trapped under the blade and dragged across the coating. If the water quality is particularly hard (i.e. greater than 180ppm combined content of calcium carbonate CaCO2 and magnesium carbonate MgCO3) then rinsing water should be softened through a domestic water softener or through the addition of a couple of drops of detergent (dishwashing detergent suffices) to litre of water.

Double glazing units should be cleaned in accordance with the types of glass used in the construction of the unit, as described for clear and self cleaning glasses. Body tinted glasses and surface coated glasses should be cleaned carefully to avoid surface scratching. When cleaning excess water from the surface of any unit, no water or cleaning agents should be allowed to come into permanent contact with the edge seal due to poor perimeter seals or blocked draining holes in drained and ventilated frames, they may attack the edge seal of the unit.

Fire resistant glasses constructed in a laminated form must not have water in contact with the edge of the glass. The special materials used in the lamination of the glass will be affected by contact with water.

The information provided in this document provides general guidance as to best practice with regard to glass cleaning.

It does not, however, constitute any representation or warranty with respect to the products, their suitability for any application.

Under no circumstances must a metal scraper ever be used to remove excess paint from the surface of glass, it will result in surface scratching.

External Condensation

xternal condensation (dew) can occasionally occur on highly insulating glass units in temperate climates. Such occurrences will only happen on cloud-free nights when there is little or no wind and usually when a warm front follows a dry spell.

The combination of several factors, namely external air temperature, localised micro climate and thermal transmittance of the glazing itself may contribute to the formation of external condensation. As a consequence of variable temperatures and localised conditions, it is possible to experience a situation whereby both clear and ‘misted’ windows exist at the same time in the same development.

This phenomenon is influenced by the thermal insulation of the glazing. Single glazing offers poor thermal insulation therefore heat escaping from inside a room readily passes through the glass to the outside environment. Consequently, the external surface temperature of single glazing is generally higher then the ‘dew-point’ temperature of the outside air, thus prohibiting the formation of condensation on that surface.

With conventional double glazing the thermal insulation is improved, but sufficient heat still escapes through the glass so as to warm the external surface of the outermost glass, thereby precluding the formation of condensation in most circumstances.

In common with other low emissivity glasses, Low E reflects heat back into the room and as such the quantity of the heat passing through the glazing is reduced. Consequently the external pane of low emissivity double glazing is not warmed by escaping heat (which instead is retained within the room) and therefore presents a colder surface to the outside environment.

In such cases, and in situations where the external glass surface temperature is lower then the ‘dew-point’ of the air, (and when weather conditions are comparable to those mentioned previously) condensation can form on the external glass surface.

However, the combination of these contributing factors is largely unpredictable and therefore it is not possible to quantify the number of occasions when external condensation will occur. Instances of external condensation are relatively rare and in all cases it will be a transient effect. Upon any one of the climatological variables changing, the condensation on the glazing will usually dissipate within a short period of time in much the same way as morning dew.

Information and instructions for applied window film

1. Installed film has a discrete time for full adhesion to be effected since installation utilises a detergent solution in the water to float the film onto the glass.  The excess water will remain between the film and the glass. The time to achieve full adhesion is often referred to as “the adhesive cure time”. Visual and adhesive cure time is related to the thickness of the film and the type of metallic coating.

2. The inspection for optical quality can be made before the full visual cure is attained. It should be noted that effects during cure, such as water bubbles, water distortion, and water haze are not to be regarded as defects.

3. The glass with applied film shall be viewed at right angles to the glass from the room side, at a distance of not less than 6 feet (2 meters). Viewing shall be carried out in natural daylight, not in direct sunlight, and shall assess the normal vision area with the exceptions of a 2 inch (50mm) wide band around the perimeter of the unit.

4. The installation shall be deemed acceptable if any of the following are unobtrusive (effects during visual cure should be disregarded): Dirt Particles, Hair and Fibers, Adhesive Gels, Fingerprints, Air Bubbles, Water Haze, Scores and Scratches, Film Distortion, Creases, Edge Life, Nicks and Tears.

5. The inch (50mm) wide band around the perimeter shall be assessed by a similar procedure to that in 3 and 4, but a small number of particles is considered acceptable where poor frame condition mitigates against the high quality standards normally achieved.

6. Edge gapes will normally be 1/32-1/16 inch (1-4mm). This allows for the water used in the installation to be squeegeed out. This ensures that film edges are not raised up by contact with frame margin. Contact with the frame margin could lead to peeling of the film.

7. For thicker safety films the edge gap will normally be 1/32-1/16 inch (1-4mm), with 1/32-1/8 inch (1-5mm) being acceptable for films of > 7 mil (175μ). Combination solar control safety films will also fall within this standard.

8. An edge gap of up to 1/16 inch (2mm) is recommended, especially for darker (tinted, metallized, tinted/metallized, and sputtered) films, to minimize the light line around the edge of the installed film.

9. Splicing of films is necessary when larger panels of glass are treated, where both length and width of the glass exceed the maximum width of film. This line should be straight and should be parallel to one edge of the frame margin. Film may be overlapped, spliced or butt jointed.

10. Certain films with special high performance coating may have lengthened cure times. Consult the manufacturer for cure times of these films.

The Energy Surcharge – Updated (02.09.09)

The Energy Surcharge (ESC) is a variable rate introduced by the European Glass manufacturers to reflect the increase in the energy costs, associated with the manufacture and distribution of glass, it is not a delivery charge and applies to all sales whether delivered or collected, after November 2004.

The amount is charged per Kilogram weight of glass supplied and is set once a quarter based on the IPE Brent Crude Oil Price Index in London. The energy surcharge will now also include a currency exchange rate factor in the November 2008 and subsequent calculations.

We have no control over the setting of the rate, which goes down as well as up.
For double glazed windows across the UK, 
call The Glass Man on 01698 33 45 45

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