Conservatories, orangeries and any glass extension need to be designed to deal with the extremes of temperature that they will need to endure in both Winter and Summer. It is therefore vital that sufficient ventilation is incorporated into each and every design to ensure a pleasant living environment all year long. Consequently it is wise to invest in sufficient opening roof vents and lots of top hung and/or side hung opening vents when building a conservatory, orangery or extension of glass, as retro-fitting them is extremely expensive, disruptive and not always possible.
Modern day double glazed conservatories or orangeries, along with all double glazed windows, doors and roofs should be specified with Low E Argon filled sealed units with warm edge spacers and soft coat glass or equivalent to deliver the highest possible thermal efficiency during the Winter. In Summer double glazing that has been treated with a decent reflective coating or tint will significantly reduce the amount of solar gain, particularly on south facing glass structures. In addition each double glazed conservatory and orangery, whether made of aluminium, hardwood or UPVC should be fitted with plenty of opening vents to deal with the hotter days.
The current Building Regulations in Approved Document F: Ventilation, require that “There shall be adequate means of ventilation provided for people in the building” and “For new dwellings, a target of four air changes per hour is required to ensure suitable ventilation.”
When it comes to the fundamental principles of replacing existing windows in a dwelling house “The installation of replacement windows should ideally achieve the requirements for new buildings. However, if this is not possible the replacement windows should not make the existing capability worse.” Primarily there are 2 different types of ventilation that is required within a building under current Building Regulations:
1) Background Ventilation
Background ventilation helps protect the fabric of any building from the harmful effects of condensation and mould etc. Consequently, where existing windows provided background ventilation, any replacement windows should also provide background ventilation. However alternative ventilation can be provided to so window designs can be amended without “breaking the rules”, such as mechanical ventilation or high level air bricks fitted ideally at least 1.7 metres above the finished floor level to avoid discomfort from draughts.
Where trickle ventilators are fitted to existing windows and/or doors an appropriately sized trickle vent or air brick etc. should be installed in the new windows/doors or existing wall. The golden rule is that whatever replaces existing must not lessen ventilation in a legal sense.
2) Purge Ventilation
Purge ventilation is supposed to improve thermal comfort and reduce overheating during the summer months as well as being primarily required to remove high levels of pollutants and water vapours.
For hinged or pivot windows that open 30 degrees or more, or for vertical sliding sash windows, the area of the opening should be at least one twentieth of the floor area of the room. For hinged or or pivot windows that open less than 30 degrees, the area of the opening should be at least one tenth of the floor area of the room.
In summary, when replacing windows with new ones or an existing structure with a new one, ventilation must never, never be reduced. For example, if an existing casement window has two side hung opening sashes, each opening 50% of the total area of the window, property owners are not permitted to reduce this area without installing additional ventilation to that room that complies with the current England and Wales Building Regulations. It is therefore essential when designing glass extensions such as conservatories and orangeries that sufficient manual or electric opening roof vents are installed as these act like chimneys, taking away the hot air, as well as having opening vents fitted all along the walls of any double glazed glass extension to allow a constant air-flow on warmer days.
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