Insulation for a better tomorrow

Party Wall Thermal Bypass Solutions




URSA has a range of products for masonry and timber frame party cavity walls to prevent party wall thermal bypass.


URSA Cavity Batts and URSA Party Wall Rolls 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 TF Roll/Slabs 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 Cavity Batt 35 - thermal conductivity 0.035 W/mK.

Density 19.5 kg/m³.


URSA Cavity Batt 32 - thermal conductivity 0.032 W/mK.

Density 29 kg/m³.


URSA Party Wall Roll, URSA Acoustic Roll & URSA TF Roll/Slab - thermal conductivity 0.035 W/mK.

Density 22 kg/m³.


Traditionally the heat loss through separating/party cavity walls in semi detached and terraced properties was assumed to be zero as, in theory, 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.

·      Installing adequate edge sealing at all exposed edges and contiguous with the insulation in adjacent elements. 


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


For optimum performance the party cavity 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 these 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.


URSA TF Roll/Slab, URSA Acoustic Roll, URSA Cavity Batts and URSA Party Wall Rolls are all classed as non-combustible and will not prejudice the fire resistance properties of the wall.