On this website, Vidrotorre will try to answer frequently asked questions made by our customers and visitors. Nevertheless, if you cannot find here the answer to your question, Vidrotorre will gladly help you clarify all your doubts. Send your questions through this form.

What is the influence of the butyral thickness of a laminated glass in its mechanical strength?

The strength to breakage does not change, but if it happens, the butyral holds it and reduces the risk of intrusion.

The strength of a laminated glass is the same as a simple glass?

The bending strength of a monolithic glass is higher than a laminated glass with the same overall thickness. The advantage of a laminated glass is that in case of breakage, the butyral keeps the fragments connected, which gives more safety.

What kind of stress a window glass can bear?

Basically the wind pressure. The method for calculating these values is indicated in the Technical Building Code (TBC) and it depends basically on the geographic situation, altitude and exposure.

How does the chamber thickness affects the thermal insulation?

The thermal transmittance (U-value) has a reverse connection with thickness. By increasing thickness, the transmission by radiation weakens, so the U-value decreases. That is valid for a chamber thickness up to 14-18mm, when the air flows created inside the chamber increase the energy transmission.

How to select the chamber thickness in a double glazed unit?

Regardless the chamber thickness incidence on the U-value (see previous note), this value must be related to the glass thickness, dimensions and areas, in order to ensure a minimum distance between glasses, at any moment.

What is the advantage in using cover glasses?

They allow a higher control over energy and light which gives more comfort and savings. They basically can be divided into solar control (they reflect energy), low emittance (they reduce transmission/energy loss) and selective glasses which have both functions. To reach the low emittance effect, these glasses must be always incorporated in a double glazed unit.

Why there is some advertising with U-values in Kcal/m² ºC and in W/m² ºK?

The only reason is that Kcal value is lower than the W value, so it can give the impression of higher performances, but it is not true. The European Standards consider the U-value (the equivalent to the K value) in W/m² ºK.

Is it true that a glass with low emittance keeps houses cooler in Summer and warmer in Winter?

A low emittance glass alone is not able to keep houses cooler in Summer and warmer in Winter. Its main function is to prevent the energy created indoor (either cold or hot) to escape outdoor, so being energy efficient and resulting in financial saving.

Is the glasses position important in a double glazed unit?

Only if we put cover glasses (solar control, low emittance, etc.) Although there are not many differences, the correct position gives more efficiency and under any circumstance the cover can be exposed outside the double glazed unit. The position is also important if the double glazed unit has safety glasses (laminated or tempered).

How to avoid condensation?

Condensation is a physical phenomenon that depends on the atmospheric humidity and the glass temperature, so circumstances can make it possible to happen. In order to reduce the risk, we can use low emittance glass to enable the inner glass in the double glazed unit to keep higher temperatures. It is only possible with double or triple glazed systems.

How to avoid sun discolouration?

Laminated glass reduces in over 95% the incidence of ultra-violet rays, which cause discolouration. If you want 100% protection, you must use laminated glass with thickest PVB and double or triple glazed systems.

When is necessary to temper a glass?

A glass with a high range of energy absorption, under solar exposure, can reach high temperatures. When the heating is not equal - which happens frequently - the differences in expansion can break the glass. Tempered glass supports higher thermal differences between closer points, which helps in this situation, especially when the absorption is over 40%. Polishing glass edges reduces the risk of breakage, especially in these situations: partial shadows over the glass, with nearby curtains, labels, blind spots, cold drafts, etc.

What is the effect of humidity on glass?

Glass in general has a very high resistance to the action of water and atmosphere. Nevertheless, under certain conditions, glass can be attacked, namely by alkaline solutions. In groups of glass panes, water can infiltrate by capillarity, slightly attacking the surface with a sodium solution that will damage the glass. Therefore, glass with humidity spots must be washed and dried before storing it in a dry place.

What is light transmittance?

It is the percentage of light energy transmitted through the glass, coming from the existing light flux.

What is light reflectance?

It is the percentage of reflective light coming from the existing light flux.

What is the solar factor?

It is the relation between the total quantity of energy that enters through the glass, coming from the existing flux. It is the sum of the direct solar transmittance, the solar transmittance absorbed by the glass and the one radiated to the interior.

What is energy absorption?

It is the percentage of solar energy absorbed by the glass and creates a temperature increasing on the glass. This value indicates the risk of cracks by thermal shock.

Considering the existence of more than 25 trademarks for double glazing with Seal of Approval, is there any difference between their features and/or performances?

It is true that equal compositions give identical performances and trademarks follow the same quality standards because they are exclusive responsibility of the manufacturers and belong to them. For example, when a manufacturer decides to change trademark, the quality of his products is not affected.

Is it possible to establish comparisons when measuring acoustic attenuations?

Laboratory tests are performed under the UNE EN ISO 140-3 Standard for airborne noise insulation (transmitted through the air). The global values for acoustic insulation index are calculated under the UNE EN ISO 717 Standard. The results are calculated as follows:

  • The index for airborne noise insulation in Rw.
  • Weighted index for noise reduction in Rw (C; Ctr), being:
  • Rw + C = Weighted index for noise reduction to pink noise
    Rw + Ctr = Weighted index for noise reduction to traffic noise

Following the mentioned above we can say these results can be compared to its global values. Nevertheless, depending on the frequency (Hz) issued to mitigate noise, the indexes are variable and behaviors of different materials and compositions depend on the mentioned frequencies.

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