FENSA Guidance Notes

FENSA Guidance Notes (2) - Replacing Vertical Sliding Sashes

When replacing vertical sliding windows it is important that the compliance to Approved Documents F (Ventilation), N (Safety) and B (Fire Egress) is either maintained, or that the replacement windows are not worse than those being removed.

Example
The surveyor is called to a house fitted with a wooden vertical sliding sash window in a room measuring 4m by 4m.


Diagram 1 - The sizes and position of the original vertical sliding sash (mm)
The customer requires the external appearance of the window to be fundamentally the same and requests a PVC-U top hung vent over a fixed light.


Diagram 2 - This solution will fail (Fire Egress)
Approved Document F - Ventilation

1. Rapid Ventilation

The original window provided 0.45m2 of rapid ventilation (less than required for new build regulations 4m x 4m x 1/120 = 0.8m2) however a portion of the opening sash set out in Diagram 2 is 1750mm above floor level and therefore, does not make the situation worse and is acceptable in this respect.

Note: Rapid ventilation needs some part of the ventilation opening above 1750mm.


2. Background Ventilation

As the original window did not contain trickle vents, nor was it capable of being locked in the open position, it did not provide background ventilation. The design of the window in Diagram 2 is acceptable in this respect. If a background ventilation facility was available then the replacement window would need to be fitted with either trickle vents or a lockable night vent so compliance would be maintained.
Approved Document N - Safety Glazing

The replacement window is less than 800mm from floor level and therefore the lower sash needs to be fitted with safety glass to BS 6206.

(Diagram 3 - window on a staircase).

Note: Diagram 3 shows how the distance from a staircase to the bottom of the window is to be measured.

Diagram 3 - Window on a staircase showing how the distance from a staircase to the bottom of the window is to be measured
Approved Document B - Fire Egress

1. Fire Egress

The original window provided a clear opening 600mm high and 750mm wide at height of 600mm from the floor. This more than satisfied the size requirement for a fire egress window in a new build situation (i.e. 0.33m2 with a minimum dimension of 450mm). The replacement window (Diagram 2) can, dependent upon the type of hinge used, maintain the size of opening required for egress (taking into account an external stone cill if in place). However because symmetry is required the transom height will be above the 1100mm level. (This height is the maximum required for a fire egress window to comply with the legislation.) Therefore the window in Diagram 2 fails fire egress compliance (it makes matters worse).


Options available:

• Revert to vertical sash design.
• Lower the height of the middle transom to below 1100mm (top opener becomes a fire egress window)
• Redesign the window to be two top opening vents, one above the other. (Diagram 4)
• Redesign the window to be one single top hung opening, measuring 1200mm x 750mm, if suitable hinges are available.

Diagram 4 - Redesign the window to be two top opening vents, one above the other