Pilkington K Glass gives optimum thermal performance keeping the cold out and the warmth in
Choose a company who cannot only install a product but ensures it looks good too, eg:
In-line gaskets set within the window prevent a black lined appearance between the frame and glass
Frame widths can vary. 70mm frames not only improve the overall appearance of the installation but also decreases loss of heat
Full removal roofline might be slightly more expensive but "cap-over" means simply attaching new product to the old decaying product. Warping will occur sooner, and the lifespan of the new product will be reduced to that which it is attached to. Full removal removes all existing product first and is guaranteed for 10 years.
Bird-comb should be fitted as standard (where allowed) to prevent under-eaves intrusion for birds and insects.
Non-zinc materials should always be used to avoid rusting