Haberdashers’ Boys’ Pre-Preparatory School

Bauder Total Green Roof System (BTGRS) waterproofing with BauderGREEN XF 301 Sedum Blanket extensive green roof finish


Haberdashers’ Boys’ Pre-Prep School is one of the largest independent schools in the country, based in Hertfordshire. The project involved the design and new build of an education facility, as the pre-preparatory school was previously based at a different location. The project delivered a single-storey pre-prep school to enable Haberdashers’ to create a lower-school complex on a single site providing a high-quality educational facility to maximise learning for pupils in reception to year 2.

Bauder Building Board

Project Haberdashers’ Boys' Pre-Preparatory School
Location Borehamwood, Hertfordshire
Project type New build
Roof size 630m2
Specifier VolkerFitzpatrick
Approved contractor Ryan Roofing
Environmental focus Extensive green roof

The specification

The new development involved the construction of a cross laminated timber (CLT) frame. The building was designed to be a single-storey, earth sheltered structure to blend successfully into the surrounding landscape.
The roof specification was designed to meet the client’s requirements of a lightweight solution. To deliver a high-quality waterproofing system, with a green roof finish to match the surrounding vegetated areas, the Bauder Total Green Roof System (BTGRS) was specified with an extensive sedum system finish.
A Bauder green roof combines the finished planting scheme and all its supportive components with a secure waterproofing system. BTRGS waterproofing was specified for its strength and durability. Bauder Green Roof Sedum Blanket finish was chosen due to being a versatile, lightweight green roof solution that provides instant vegetation cover for the roof.

Products applied

The root-resistant capping sheet used in a multi-layer flat roof system with a green roof landscaping finish.

BauderGREEN XF 301 sedum blanket
Designed to be a lightweight, single layer, green roof product. It enables green roofs to be installed on structures with very low weight loadings.

Project challenges

Due to the unusual shape of the roof with numerous steeply pitched areas of up to 45 degrees of slope, the roof was designed to ensure the living green roof was securely fixed onto the roof slopes. The BauderGREEN XF 301 sedum system uses a nylon carrier which hooked onto the retention strips to hold the sedum blanket in place and prevent the green roof from slipping down the roof slopes. There was also a bespoke irrigation system designed to prevent the vegetation from drying out in hot dry spells.
During installation the Ryan Roofing construction team had to work around certain challenges including access requirements. The school remained open throughout the project. Therefore, access was restricted at school drop off and pick up times and noisy works had to be carried out appropriate times around the school’s timetable. To protect the fragile sedum plants the project team used a permit to work system, so that only the Ryan Roofing team were able to access the roof.
There were areas of the roof which were too steep for the operatives to walk on. Therefore, sections of the roofing works had to be carried out via access equipment including platforms and ladders for both the waterproofing and green roof installation.

System installed / system build up

1 BauderGREEN XF 301 sedum blanket A single layer sedum system, GRO compliant substrate is held within a nylon mesh with attached moisture mat. The sedum blanket is grown for circa 12 months and contains up to 17 species of sedum.
2 BauderGREEN AL 40 A bespoke edge trim which retains the XF 301 system at its perimeter and secures the system to the underlying waterproofing.
3 BauderGREEN RS 22 Bespoke stainless-steel teeth which grip the XF 301 blanket and hold it in position. The strips are fixed in place by strips of the waterproofing membrane.
4 BauderPLANT E Root-resistant capping sheet used in a multi-layer flat roof system with a green roof landscaping finish.

The result

By working closely with all stakeholders involved, including VolkerFitzpatrick, Ryan Roofing and the client, the project successfully delivered a watertight and aesthetically pleasing green roof. The project has enabled Haberdashers’ to create a lower-school complex on a single site with the primary school. The completed project offered a 25-year fully comprehensive guarantee covering all elements of product, design, and installation of the Bauder system.


Ben Walker, Project Manager, VolkerFitzpatrick:
“Bauder played a key role in the waterproofing installation on this project. Bauder’s ongoing support in detailing and working closely with VolkerFiztpatrick on the delivery and logistics was invaluable, ensuring our client’s project was handed over on time and within budget. The sloped green roofs look fantastic, thanks to the Bauder staff for their hard work and dedication in getting this project completed on time and to an exceptionally high standard.”