FENSA Limited is the Fenestration Self-Assessment Scheme for companies
that install windows and doors in dwellings.
FENSA Guidance notes:
In order to assist its member’s interpret various aspects of
the approved documents, FENSA has issued a series of guidance notes.
Special Note: These are
the interpretations being used by "FENSA
registered companies". This is important because some of the
local authorities may interpret some of the building regulations
slightly
differently. If you are not using a FENSA member and are going to
apply to the local
authority for permission rather than use a FENSA company you would
be well advised to seek clarification before an installation commences.
Also worth reading are the FENSA Technical FAQ's at http://www.fensa.org.uk/faqtech.phtml
FENSA Guidance Noates (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 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)
FENSA Guidance Notes (2)
Replacing Vertical Sliding Sashes
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.
FENSA Guidance Notes (2)
Replacing Vertical Sliding Sashes
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
FENSA Guidance Notes (2)
Replacing Vertical Sliding Sashes
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
Our Thanks to FENSA for permission to reproduce these notes here:
http://www.fensa.org.uk FENSA Limited
is the Fenestration Self-Assessment Scheme for companies that install windows
and doors in dwellings.
