Warm roof upgrade to 1930’s mansion blocks

Leviat’s unique Helifix InSkew helical fixings provide a bespoke solution for highly insulated warm roof upgrade to 1930’s mansion blocks.

Built in the 1930’s to provide much needed affordable housing away from London’s busy city centre, these three imposing 4-storey mansion blocks provide a total of 110, largely 2- and 3-bedroom, residential apartments.

Over the years, wind and weather had taken their toll on the buildings’ expansive pitched tiled roofs, and the decision was taken to undertake a total replacement and upgrade of the roof areas, plus associated dormers, to both improve weathertightness and bring thermal performance up to modern day standards, improving living conditions and reducing energy costs for residents.

The Challenge

Involving a total of 5000m² of roof area, this was the largest project of its type ever undertaken by specialist roofing contractor, Ashton Roofing & Maintenance, who, on stripping the old roofs, discovered a non-standard construction with an external rafter lining of 22mm hardwood close boarding in place of the expected 15mm softwood sarking. As the boarding was providing lateral support for the roof structure, it could not be removed, adding significantly to the complexity of the project.

Meeting the upgraded thermal performance targets for the new warm roofs required 140mm of high performance rigid thermoset insulation board, in two connected 70mm layers, to be incorporated within the structure. This now had to be installed above the rafters, between the sarking board and the counter battens which would support the new heavy roof tiles and tile battens.

The weight and depth of the new roof, hardwood layer, split insulation and requirement for a minimum of 40mm fixing penetration into the existing rafters, created a major challenge for Ashton, in finding a reliable fixing method to support and stabilise the complex structure.

The Solution

As traditional nail fixing was not an option, Ashton approached Leviat, who proposed a solution using their Helifix InSkew, a high performance helical fixing specifically designed for securing counter battens through insulation in pitched warm roof constructions. The self-tapping design would avoid splitting of battens and would not pull out, providing resistance to both wind and sliding loads, whilst its small cross-section area and no-head design would also help to optimise the thermal performance of the warm roof structure, making it perfect for this project.

Taking into consideration all of the roof parameters, including Wind zone and exposure, the height and weight of structure and the total depth, Leviat’s technical support engineers produced a bespoke design specification using special 230mm long Helifix InSkew Super6, a

6mm profile 304 Grade Stainless Steel fixing with extra strong core. This unique fixing could be simply installed using a standard hammer drill and power driver attachment, fully meeting all elements of the client’s specification, as well as providing a secure 43mm penetration into the supporting rafters.

In view of the complexities of this project, Ashton worked with Leviat to create an on-site mock-up and trial to prove the solution prior to commencement of work.

The Outcome

Whilst installing the screws through the dense hardwood sarking boards did initially present a challenge to Ashton, who had not previously used InSkews in such a complex roof construction, the Leviat technical team were able to suggest a technique using pre-drilled pilot holes, which considerably improved the speed and efficiency of the installation process.

To ease congestion on site, a total of 58,000 of the special fixings were manufactured and delivered in batches to meet Ashton’s work schedule which, thanks to the simplified installation process, was completed without problems, comfortably within the project timeline.

The Managing Director of Ashton Roofing and Maintenance, Michael Ashton, was grateful for the service and support he received from Leviat throughout the project. “This was the largest and most complex reroofing project ever undertaken by either Ashton, or our client. Thanks to excellent support from the Helifix team, however, we were able to complete the upgrade to all roofs and dormers ahead of schedule, installing the full 58,000 special InSkews throughout the 5000m2 roof area, all whilst the buildings remained fully occupied.

“Despite this being one of the biggest single orders to date for its Helifix InSkews, Leviat supplied the high performance fixings in 5000 to 10,000 lots, at short notice, to meet our installation programme, and answered all of our queries promptly, preventing unnecessary delays on site.

“This project will now provide a template for similar jobs in the future. Everyone involved is delighted with the outcome of this outstanding project, which is now being entered for a national roofing award”.