Party Wall Thermal Bypass Solutions

URSA CAVITY BATTS and URSA PARTY WALL ROLL are suitable for use in fully filling the party wall cavity to prevent party wall thermal bypass in masonry walls.

URSA ACOUSTIC ROLL and URSA FRAMETEC are suitable for use in fully filling the inter stud and inter frame cavities to prevent party wall thermal bypass in timber framed walls.

URSA FRAMETEC SLAB 35, URSA ACOUSTIC ROLL and URSA HOMETEC ROLL 35 are suitable for use in fully filling the inter stud and inter frame cavities to prevent party wall thermal bypass in light steel framed walls.

URSA CAVITY BATT 35 - thermal conductivity 0.035 W/mK.
Density 22 kg/m³. 

URSA CAVITY BATT 32 - thermal conductivity 0.032 W/mK.
Density 32 kg/m³.

URSA PARTY WALL ROLL - thermal conductivity 0.035 W/mK.
Density 22 kg/m³.

URSA ACOUSTIC ROLL - thermal conductivity 0.035 W/mK.
Density 22 kg/m³.

URSA HOMETEC ROLL 35 - thermal conductivity 0.035 W/mK.
Density 22 kg/m³.

URSA FRAMETEC 35 & FRAMETEC SLAB 35 - thermal conductivity 0.035 W/mK.
Density 22 kg/m³.

Design

Traditionally the heat loss through separating/party cavity walls in semi detached and terraced properties was assumed to be zero as there is no temperature differential across the wall. Studies have shown however that air movement within this cavity (with further infiltration from the front and rear external cavity walls) means the separating wall can have an equivalent U-value as high as 0.70 W/m²K. The Building Regulations now recognise the importance of the party wall thermal bypass and measures must be taken to reduce its effect. The studies have identified two important measures;

• Fully filling the cavity with glass wool, with a minimum density of 18 kg/m³.
• Installing adequate edge sealing at all exposed edges and contiguous with the insulation in adjacent elements. 

Further detailed information is available from the Mineral Wool Manufacturers Association (MIMA) in their document 'Preventing Thermal Bypassess in Party Separating Walls'.

For optimum performance the party cavity wall insulation and the edge sealing must be contiguous. These measures will reduce the heat flow through, across and along the separating wall and reduce air movement into and within the wall. Done correctly this will reduce the U-value of the wall to zero. Effective edge sealing alone will only reduce the U-value to 0.20 W/m²K.

Masonry cavity and timber frame separating walls must provide suitable sound insulation between dwellings as outlined in Approved Document E of the Building Regulations (Section 5 in Scotland). Suitable details have been used successfully for many years; adding further layers of insulation into the walls must not degrade this performance. Extensive testing has been undertaken to show that the use of glass mineral wool fully filling any cavities does not degrade the performance.

The above products are covered by a range of acoustic solutions under the Robust Details for parged and unparged masonry walls and timber framed walls. See below for more details.

URSA FRAMETEC, URSA ACOUSTIC ROLL, URSA CAVITY BATT and URSA PARTY WALL ROLL are all classed as non-combustible and will not prejudice the fire resistance properties of the wall.

Installation

Download the detailed installation guide here

Robust Details

This range of URSA products is approved for use in a number of Robust Details for masonry and timber frame walls. Check the Robust Details handbook (link below) for the exact specification in each detail.

*Note that some Robust Details may not give zero U-value for party wall thermal bypass, check the details carefully.

Masonry Separating (Party) Walls

Timber Separating (Party) Walls

For further information see our technical brochure in the Documents section. Alternatively please contact URSA Technical Department.

Industry information

Sources of useful additional information