Plasterboard lining generally provides the most common resistance to fire in timber frame construction. This is the same for the construction of timber frame party walls. To achieve a 1-hour fire resistance rating (as required in the building regulations), two layers of plasterboard are fixed to the timber frame party walls.
The two most common types of plasterboard used are:
15 mm wallboard, which is mounted vertically.
19 mm plank type plasterboard, which is mounted horizontally.
The following are plasterboard requirements:
It must have an overall 30 mm min. thickness.
Each layer of plasterboard should be fixed independently to support around the edges entirely by timber. This does not apply to plank type board mounted horizontally unless it is along a cut edge.
Joints between layers of plaster board are required to be staggered
It must be of the correct type, thickness and fixing method to provide adequate fire resistance.
Plasterboard between party walls at roof level may have a reduced thickness below the 30 mm minimum (Typically two layers of 12.5 mm).
Party wall and roof junctions
Typically, 9 mm non-combustible building board is used to close the gap at the junctions of the roof wall and the top of the party wall. The roofing underlay is carried over the top of the party wall and the spaces between the tiling/slating battens filled with mortar bedding or rock fiber.
TGD B also allows any other system that has been shown by test to be equally effective in restricting the spread of fire at the party wall/roof junction.
Services are not allow pass through the party wall or allowed run in the cavity located between the party wall structures; to run services, a special service cavity should be constructed in front of the party wall.
Cavities and roof junctions
Vertical cavity barriers should be used to close the cavity between the timber party wall and the masonry outer leaf. In addition to the vertical barriers, additional fire stopping may be required between party wall frames.
At the junction between the fascia, soffit and the slope of the roof, the fire stopping should be tightly positioned to ensure that the gap is sealed.
At the junction between the slope of roof rafters and the horizontal soffit board, 9 mm non-combustible building board must be used to protect against the spread of fire between party wall locations.
Non-combustible boards and battens
Non-combustible boards should have appropriate third party accreditation, e.g. Irish Agrement Board (IAB) certification, British Board of Agrement (BBA) certification, or in some instances, European Technical Approval (ETA), and be suitable for external use.
The battens (and counter battens as required) and batten fixings should be designed by the building designer and typically fixed through the non-combustible board and sheathing into the studs (typical batten centres 400 mm). Battens should typically be fixed with smooth or annular ring shank nails at 150 to 200 mm centres depending on nail type, diameter and length.