Frame design
Multi chambered frames, are thermally more efficient than single chambered frames. Many modern frames are 3 chambered, some 5 or even 6. the greater number of chambers increase the thermal efficiency, but reduce the ability to insert reinforcing. Reinforcing (usually steel or aluminium) has always been needed to reduce distortion under load or increase stability for wood grained profiles and improve screw retention for security furniture.

Recent Frame developments
Thermal Inserts have recently been introduced. These effectively increase the number of “thermal chambers” in the main profile to 8 chambers. At the same time, rigidity of the frame is enhanced, so that usually, no further reinforcement is required. In some circumstances, such as woodgrain profiles, additional steel reinforcement is applied. But as this is fitted within the Thermal inserts, then thermal losses due to conductivity of steel are minimised. Tests have shown that Furniture screws, into the Thermal Inserts give similar screw retention properties as steel. Another advantage is that screws will have less tendency to corrode when applied to thermal inserts, rather than steel (as the screws are fitted, they leave swarf which corrodes and breaks down the screw coating). Overall the frames with thermal inserts are the most cost.

Our Frames
Synseal “Shield” 70mm system, internally beaded For Standard windows, to achieve equivalent “B Rating”, we use the following:

• Thermal inserts in frames (plus reinforcing for wood grains)
• Glass units with “Soft coat Low E” plus Argon 90% fill.

For C rating we use a slightly cheaper urethane foam frame insulation.

Upgrade to A
Specification as for C, but with Swiss V Spacer Bar(insulating Spacer Bar)

We recommend the upgrade option A
Because Fensa & Building control have indicated that they will accept the glass label as sufficient evidence that the window complies to (at least) the new minimum requirements. (Without having to produce complex individual reports for each frame).

Glass Units
Generally, the larger airspace the better the thermal efficiency (up to 20mm airspace) The addition of Argon gas (90% by volume) also improves the thermal efficiency. “K” glass (hard coat Low emissivity glass) on the inner (room side) improves thermal efficiency by reflecting radiated (infra red) energy back into the room. Soft Coat “Low E” glass does the same as “K”, but much more efficiently. Aluminium spacer bar is less thermally efficient than the new “Swiss V” composite spacer Bar.