Despite the ongoing stagnation in the property market, housebuilders looking for cost re-ductions on current developments can achieve “significant” savings using Bridgestop – a Robust Details-approved system from the Monarfloor Acoustic Systems division of Icopal that also offers maximum credits under the Code for Sustainable Homes.
Developed by a joint venture between Monarfloor/Icopal and the Building Performance Centre at Edinburgh Napier University, Bridgestop was launched as a response to the growing number of new-build homes now being constructed on brownfield sites where ground conditions may require raft foundations or gas barriers.
The high-performance Bridgestop membrane reduces flanking transmission while the Bridgestop quilt prevents acoustic bridging commonly caused by a mortar build-up at the base of the cavity within separating party-cavity walls. The membrane can also act as methane and radon barriers or protect such barriers from the damage that can occur when site operatives remove the mortar from the base of the walls.
It does this by isolating both masonry leaves of the cavity party wall from mortar collecting on the raft or continual foundation. Where the slab has been split and a gas barrier in-stalled, the Bridgestop membrane ensures the integrity of the gas membrane from poten-tial damage.
Research by Icopal has already shown cost savings can be made in materials and labour because the party walls only require plasterboard of 8kg/m²instead of 12.5kg² for solid Part E solution walls, saving 4.5kg/m² of gypsum-based board per m². Time is also saved through easier detailing for step and stagger constructions.
Now the Roger Bullivant Group, one of the largest foundation engineering companies in the UK, has demonstrated additional benefits when clients specify the Bridgestop system along separating walls used in conjunction with their precast foundation system.
The isolation of the separating wall at ground floor level allows the foundation to be in-stalled higher out of the ground than that for a separating wall being built to the Robust De-tail alternative with a 225mm cavity below ground floor.
Roger Bullivant chief engineer (house foundations) Nigel Rake said: "When the developer is using Bridgestop, the savings alone from the supply and installation of the reduced un-derbuild, which can be as much as £22 per metre, would more than cover the cost of the Bridgestop system at £15 per metre.
“Also, depending on the number of separating walls, there can be significant additional cost and time savings from less excavation and spoil, and being able to offer a less com-plicated foundation solution."
Bridgestop is laid in the cavity between the separating walls and folded around to bridge the gap at the base. Acoustically-resilient wall ties hold it in place with a special cap on the first course of brickwork. A second layer is then held in place by new wall ties on the sec-ond course of brickwork.
Bridgestop’s properties have high acoustic damping to absorb more sound energy and re-duce structural flanking, performing approximately 4-5dB better than solid walls and 8dB better than standard Robust Detail E-WM-4 walls. National housebuilder Gladedale have achieved 53dB (mean value) – a four-credit solution – on one of their sites via this method.