BUILDING FABRIC 49 OPEN TO ALTERNATIVES
Kevan Woolf of Velfac questions whether the introduction of Part O to mitigate overheating means inward opening windows are the only solution.
FOR HOUSEBUILDERS AND DEVELOPERS,
UNDERSTANDING THE
FULL IMPACT OF PART O IS CRUCIAL
T
he recent introduction of Part O of the Building Regulations has prompted designers to seek effective solutions to meet ventilation requirements, with many turning to inward opening windows as a primary option. But is this the only solution? Not necessarily. While inward opening windows address the key requirement that “window handles on windows that open outwards are not more than 650 mm from the inside face of the wall,” they also present several considerations that housebuilders and developers must account for.
ne of the most signifi cant factors is the impact on internal space. Inward opening windows require suffi cient clearance to swing open, restricting where furniture can be placed and limiting design exibility. nlike outward opening windows, which allow for clear, unobstructed use of internal space,
inward-opening designs can interfere with room layouts, particularly in compact or high-density developments where every square metre counts. Additionally, window cill boards – often used for decorative items, storage, or plants – become less functional, as they must remain clear to allow the window to open fully.
These practical limitations mean housebuilders must rethink internal layouts, potentially increasing design complexity and reducing usable space. Another key consideration is cost. Inward opening windows often require more complex tilt-and-turn ironmongery, making them more expensive than traditional outward-opening alternatives. This additional cost, when applied across an entire development, can signifi cantly impact budgets something developers must factor in when specifying window solutions.
Beyond ventilation, another crucial aspect of Part O is the control of solar gain. Excessive heat from facade glazing can lead to overheating in modern homes, making it essential for architects and developers to carefully design window confi gurations that balance ventilation with thermal comfort. A key strategy is to minimise large fi xed glazing elements and increase the proportion of openable windows to encourage natural air ow while limiting solar heat build-up. This means developers must be more strategic in their window selections, ensuring they meet both regulatory requirements and occupant comfort needs.
There are also additional design and usability factors to consider when choosing between inward and outward opening windows. Flexibility in ventilation is essential, and outward opening windows often provide a greater range of options, including lockable night
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