Glazing methods of Double Glazed Sealed Units: (Timber frames).

To ensure that your Unit performs as it should will only be achieved if it is glazed into a well designed frame, using appropriate durable glazing materials, and following the correct glazing proceedures.

Prior to glazing. An edge clearance is necessary to prevent frame-to-glass contact, and to prevent water from bridging between the rebate and edge seal of the Unit. The edge clearance should be sufficient to allow for thermal movement also, so, when measuring the frame you should allow 6mm on the width and 6mm on the height (3mm all around the Unit).

If the frame is in-situ and exposed to the weather before glazing commences, the frame must be kept adequately covered to keep the rebates and glazing beads as clean and dry as possible.

Glazing conditions are much better improved when there are no obstacles, such as scaffolding, around the frames to be glazed.

Glazing to timber frames. 1  Firstly ensure the rebates, beads and Unit are clean. Run a continuous seal of silicone around the back of the rebate and place two glazing blocks on the bottom rebate. The glazing blocks should be of a resillient, non-absorbing, rot-proof, compatible material; of which can be obtained from our factory sales counter.

Please Note: Silicone has to be of a 'Low Modulus Neutral Cure' type and of high quality. If you are unsure of your silicone type or quality, bring a sample to our office for a test for compatibility.

2  Sit the Unit on the glazing blocks and push gently against the back rebate and centralize, making sure not to push silicone out from the rebate. There should be a 3mm gap all around between the Unit edge and the timber, to allow for thermal movement and to prevent water from bridging between the rebate and edge seal of the Unit.  (see fig 1)

3  Next fix the glazing beads around the Unit. The beads should be a snug fit, and fixed using suitable non-corrosive material (sheradized and brass glazing pins are available at our factory sales counter). 

4  With a fine nozzle, run a neat continuous seal of silicone sealant between the face of the glass and the glazing bead.  (see fig 2)

5  Again, with a fine nozzle, run a neat continuous seal of silicone sealant between the face of the glass on the inside and the back rebate as in section 4, thus forming a water tight seal on the edge seal of the Unit from any moisture which may occur. Make sure any residual voids are filled. (see fig 3)

6  Do not work on or around the fixed Unit for 24 hours to allow the silicone sealant to set.

 

 

Frequently Asked Questions

Applying to all orders.

Q. Measuring.
A. The standard adopted in the UK glass industry, is to measure in millimetres. If you measure in Imperial, use inches and either, one eighth (1/8”) and/or one quarter (1/4”) of an inch. Multiply inches x 25.4 to convert to millimetres.  Always give the WIDTH first x 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 badge marked in the corner, if the width is not first, the mark may be in a different corner.

Q. Allowances for glazing.
A. 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.

Q. Template and patterns.
A. Use a hard material, hardboard is easy to work with. Paper is not very good as it tends to crease and is hard to find the edge on to work accurately to. A template should be the actual size required and need no additions or subtractions to it. Mark the face surface. Templates for double glazing units are made as viewed from the outside.

Q. Tolerances.
A. Plus 2mm minus 2mm. Thick Float and thick constructions have larger tolerances.

Types of Glass.

Q. What are the basic types?

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

Standards & Regulations

Q. How do I know if my order must comply with a standard or regulation?
A. The most common references are, advise at the time of enquiring or ordering, if these are a requirement,

1. Document L – Building Regulations – Conservation of fuel & power.
2. Document N1 & N2 – Building Regulations – Glazing + materials & protection.
3. BS476 Part 22 – BSEN1363 – 1364 – 1365 – 1634 -12600 – Fire
4. BS6206 – Safety
5. BS5544 – EN356 – Anti Bandit Glazing.
6. BS6180 – Barriers & Balustrades.
7. BS8000 – Part 7. Code of practice for glazing.
8. British Fenestration Rating Council (BFRC) - Window Energy Rating (WER) A, B, C, D, or E.

Safety

Q. How do I know where to use a safety glass, laminated, toughened or wired?
A. Very briefly and not covering all the requirements, BS6206 and 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, eg., 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, eg., in schools or hospitals, all necessary precautions must be taken to minimise any potential risk.

Double Glazing Units

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

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

Q. What standard are the units made to?
A. BS EN 1276 – 3. All our units have the standard printed on the spacer bar.

Q. Is there a date from which all units must be made to BS EN 1276?
A. April 2007

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

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

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

 Q. Is there a self cleaning glass?
A. There are clear and tinted self cleaning glasses produced by the glass manufacturers with a hard hydrophyllic 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. 

Q. How should my frames be constructed?
A. A frame needs the U-value or WER, the Architect, Specifer or Frame Maker, will give you the U-value or WER for the frame, from this information, we can give you the required make up 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). 

Q. What cavity widths (1) are available and what colours (2)?

1. 6MM, 8MM, 10MM,12MM,14MM,16MM,18MM & 20MM.
2. SILVER, WHITE, BRONZE, BLACK & GOLD. Some cavities and colours are only available on request.

Q. If I do not specify a spacer colour, what will I get?
A. Silver Spacer.

Q. Are there inserts available to go into the cavity?
A. Georgian Bar - Straight or curved in White or Brown, 25MM/18MM X 8mm.

Q. Can units be leaded?
A. 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, full details with any necessary drawings and colour references are required. Standard designs are available.

Q. How should units be glazed?
A. Glazing should be in accordance with BS8000. Open the attachments below for the basic method, contact us for other types of glazing and glazing of self cleaning glass.                       
 

Q. After glazing what maintenance is required?
A. Follow the maintenance instructions below for all types of installation.

 MAINTENANCE INSTRUCTIONS FOR DOUBLE GLAZING UNITS

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 that the drainage of ventilation holes or slots, has 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 regulary to provide protection for the putty. The paint line to extend onto the glass inside & out.

MICRO POROUS FRAMES & 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.

Q. How do I clean the glass?
A. In accordance with BS8000 4.1, “Cleaning & Protection”.
     Do not use tools or abrasive materials on the finished faces of the glass. After preparation for cleaning, wash with warm soapy water, rinse thoroughly and wipe dry with a clean soft cloth.

Q. Are there special requirements for glazing glass in a roof?

1. The outer leaf is normally toughened to resist thermal fracture.
2. The inner leaf can be toughened or laminated depending on the application. If laminated it must be stepped back to be within the building to resist thermal fracture.
3. 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.
4. Both top and bottom leaves must be “stopped” in the rebate to prevent the glass sliding down.

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

Processing

Q. What are the basic edge finishes to a piece of glass?

1. 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.
2. Smoothed Edge – The edge of the glass is machined flat and the edges arrissed but not polished.
3. Polished Edge – The edge of the glass is machined flat, the edges arrissed and the edge is polished.
4. 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.

Q. What diameter hole can be put into a piece of glass?
A. Virtually any diameter of hole can be drilled or cut. The internal finish to a hole is generally a smooth one.

Q. Can you polish or bevel shapes?
A. 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. 

Q. Can “cut outs” or “notches” for plug sockets or other items be incorporated in the glass?
A. 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.  

Q. What sort of glass can be used in a barrier or a balustrade?
A. 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, Uniformley Distributed Load (UDL) in kN/m and/or Point Load in k/N. 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.

Q. Glass floors, is there a maximum area and special frame?
A. We have data for the appropriate thickness up to 1M2. Submit the UDL in k/M and Point Load in k/N and advise if, a domestic floor, dance floor, corridor or stairtread, for our recommendations.

Q. What is, “Cracked Ice”?
A. A 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.

Q. Mirrors, how do I determine the, thickness, edgework, number of holes and whether safety backing is required?
A. We have tables to help determine the thickness. If the edge is exposed it 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.

 Q. What thickness should I use for a shelf?
A.  Again, we have tables and will advise.

Q. Is there such a thing as, “Oneway Mirror”?
A. Yes, 7.4MM 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, who should also wear dark clothing, the reflection will be look like a mirror to the observed.

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

Fire Resistant Glazing
 
Q. How do I know the type of fire resistant glass I need?

1. Your Architect or Specifer will advise you or Building Control will stipulate what you need to comply with Building Regulations.
2. Advise us of the specification as follows and we will advise of a suitable glass for your requirements,

 i. Integrity only – 30 minutes or 60 minutes.
ii. Integrity plus Insulation – 30 minutes or 60 minutes.
Example of type – 60 minutes Integrity – 30 Minutes Insulation.

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

Q. Are there different types for glazing internally & externally?
A. Wired is for internal or external use, specify if it is to comply with BS6206. Most types of clear have an internal and external grade apart from Pyroguard and some modified toughened glasses.

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

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

Q. Can you provide test evidence if required?
A. We have manufacturers’ reports available on request.

http://www.hockleys.net/Glass_Safety.pdf