Building Regulations
Rescue Windows
A window should be set on the front of the roof to be used as a means of escape the most commonly used window is an M08 Velux (see Velux post for sizes).
The size of the window when open should be at least 550mm wide x 800mm high. And this needs to be in the new room NOT on the landing, this is because it is meant as a means of escape if the stairs and landings become filled with smoke.
There should be enough space for the fire brigades ladder direct from the ground and pitched at a 3 in 1 angle.
Smoke Alarms
Smoke alarms should be fitted in the stairway, one in the hallway, one in the landing and one in the new loft conversion, this is the minimum standard. They should be mains powered, and they can be connected to the lighting circuits, that way there are no batteries to replace.
Staircases
The stairs are where most accidents happen in the home, so it’s important that the new stairs are safe, and the existing stairs are not made unsafe. At least 2.0m headroom is needed over the exsiting stairs. The new stairs headroom can be reduced which might allow the flight to fit under a hipped roof.
The landing should be the same width as the stairs, and there is no minimum width for the stairs, a width of 750-800mm works well, and doors must open away from the stairs.
The New Loft
If the dormer is less than 1.0m from the party wall the side of the dormer must provide 1/2 hour fire resistance from inside and outside
Eaves ventilation, at least 25000mm squared per linear metre, equivalent to a continiuos 25mm ventilation gap.
Ridge ventilation, at least 5000mm squared per linear metre, equivalent to a continious 5mm ventilation gap.
A 50mm air gap must be left above the insulation, so the roof joists need to be at least 150mm deep, and because rafters are usually 100mm deep, they need 50mm battening under them. This is because water vapour rises through the ceilings and can condense out, above the insulation which can cause structural damage and unsightly stains.