The previous owners of our house built a conservatory, then removed one window and one door of the house, so that the conservatory is now open through to the kitchen.

As this makes the house quite cold in winter, we are considering to replace both the window and the door and are wondering which materials we have to use to comply with Building Regulations?

- window: we would like to fit a horizontal sliding window, the ones often used as secondary glazing, rather than 'normal' external windows, to keep the feeling that the conservatory (which we use as dining room) is part of the house. Is this acceptable for Building Regultions in terms of the insulation they provide?

- door: could we fit an internal wooden door, maybe partially glazed or do we have to fit a patio door?

- Would a window company usually provide a certificate that the alterations comply with Building Regulations?