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The specified building products for the new Multi Comfort school building

Multi Comfort Construction

Speller Metcalfe logo

Speller Metcalfe is a national building contractor and family-owned business, founded in 1995 by Steve Speller and Andy Metcalfe - both experienced surveyors who aspired to be at the cutting edge of construction.

Under their leadership our Company has grown to an annual turnover of £125 million, working on projects across the public and private sectors. We deliver a full range of services including new build, design & build, extension, retrofit and regeneration, as well as land acquisition and turnkey schemes, facilities management, restoration and extension services.

May 2015

Ground was broken and the build of the King’s School, Worcester multi-purpose hall got underway. It’s estimated that as much as 30-35% of the heat lost through a building can be lost through the floor. A floor is also the most difficult to improve thermally once the building is complete – so it makes economic sense to get it right now. If the floor is well insulated, as well as the structure, then the possibility of cold spots and uncomfortable temperature differences are reduced, ensuring Thermal Comfort for its occupants.

LECA® Insufill is installed underneath the concrete slab and provides insulation and protection to services entering the building. LECA® is expanded clay lightweight aggregate, which offers good insulation and free-drainage properties. LECA® Insufill replaces the need for standard compacted limestone and for a sand blinding layer – also saving around 2 weeks from the build programme. Due to LECA® Insufill’s thermal qualities the overall floor thickness was reduced with the use of a thinner insulating board prior to the concrete slab. This has the additional environmental and economic benefit of reducing the amount of sub soil to be removed from site. 

July 2015

A polyethylene separating layer was fitted over the top of the LECA® Insufill and then 250mm of Celotex FR5000 installed with staggered joints. FR5000 from Celotex, is manufactured from rigid PIR (polyisocyanurate) and has a lambda value of just 0.021 W/m.K (the lower the number, the better the thermal performance). Multiple layers of insulation were used and the joints of the boards staggered. The insulation is fixed very close and abutting the concrete without any gaps, to maximise the thermal performance. This helps to reduce cold-bridging and improve air-tightness by removing direct paths, between inside and out, where heat and air can escape.

Celotex FR5000 has also been used around the perimeter of the slab. The use of insulation around the perimeter limits heat loss through the junction and minimises the risk of surface condensation forming. The insulation layer in the floor is also in the same line as the wall insulation above, which ensures the design is wrapped like a tea cosy. The u-value for the floor is approx. 0.11 W/m2.K A separating layer was fitted over the top of the Celotex insulation. The reinforced concrete slab was then poured on top. Click here to read more about the benefits of proper insulation.

build-up of floor

build-up of floor

July 2015

The structure of Bartholomew Barn is constructed from glue laminated timbers (Glulams) connected with I-joists Pasquill.

Glulam timber’s tensile characteristics make it suitable for long span, load-bearing widths, such as bridges. It is an exceptionally strong material, used for load-bearing structures where visual appearance is important, which can be shaped, helping to form spacious buildings.

The Glulam timbers were used to mimic the existing aesthetical appeal of a barn – typical of other buildings in the vicinity. This modern method of construction allows for increased structural spans and provides large open multi-use spaces such as the required specification of King’s School multi-purpose hall.

The Glulam timbers were structurally erected in sequence and infill panels created through engineered I-joists. The combination of I-joists and the Glulam timber structure provides a rigid construction, without diagonal bracing, allowing for easy installation of Isover insulation and Vario airtightness barrier at a later stage. 

August 2015

The specification of the main External Building Fabric targeted providing optimum Thermal Comfort and Indoor-Air Comfort. The External roof and wall systems used a combination of high-performance insulation and air-tightness membranes from Isover with internal finish linings from British Gypsum that would also ensure durability plus Acoustic Comfort within in the Barn.

Isover Frame Façade Slab is a low lambda rigid glass mineral wool slab which provided a continuous layer of insulation around the visually stunning glulam frame construction. Giving excellent thermal performance with a thermal conductivity of 0.031 W/mK it provided a continuous layer of insulation around the frame, reducing cold bridging and allowing very low U-values to be achieved, ensuring optimum Thermal Comfort. Both Gyproc SoundBloc and Rigidur H ACTIVair were used to line the external walls offering durability plus improved Indoor-Air Comfort and Acoustic Comfort.

Ecophon sound absorbing ceiling Ecophon Master SQ XL was installed to the ceiling in conjunction with Akusto Wall C Super G wall absorbers to ensure complete Acoustic Comfort for the users of Bartholomew Barn. These high-performance Ecophon products are suitable for schools, open plan offices or other premises where strict demands are made on good acoustics and speech intelligibility. The tiles were bonded directly to the soffit surface. Ecophon Master SQ is installed with a gap between each tile, creating a ceiling with a smooth appearance. Akusto TM Wall C was also installed for use as wall absorbers, to achieve excellent acoustic properties in the room. 

build-up of wall and sloping roof

build-up of internal wall

November 2015

Thermal comfort can only be achieved if the temperature being controlled by the high levels of insulation isn’t allowed to disappear through unwanted gaps in the building fabric. A disproportionate amount of heat can be lost through the smallest of gaps. The Multi Comfort criterion for non-residential new-build, for air-tightness, is 0.6 V/h @ 50Pa (N50 standard). That is 0.6 air changes, by volume, per hour when the building is subjected to a pressure of 50 Pascal. This is roughly equivalent to 1m3/m2.hr@50Pa for the UK Q50 standard.

In order to carry out the test, the building was sealed and blowers attached. The blowers work in two directions. The blowers push air in (pressurisation) and draw air out (depressurisation) up to a pressure of 50 Pascal. The amount of energy required to keep the pressure/depressurisation at 50 Pascal is then recorded. From this you can work out how air-tight the structure is.

The test result for the King’s School in Worcester was 0.48 V/h @ 50Pa for the fabric airtightness test. With this level of air-tightness uncontrolled air infiltration is minimised and the introduction of mechanical ventilation provides controlled air circulation. The system extracts stale air from inside the building and replaces it with filtered fresh air. Seminal research links significant gains in productivity with indoor air comfort from delivered fresh air and reduced pollutants. 

January 2016

The mechanical and electrical services installation included installing pipework for the underfloor heating system, domestic water distribution, ventilation equipment and distribution ductwork, lighting and electrical cabling for power sockets etc. Multi Comfort buildings require a high level of insulation and building fabric air-tightness resulting in little or no requirement for a heating system.

In the case of the new multi-purpose hall at King’s School, it was decided, as the building was frequently unoccupied, just a small system would be required to efficiently prepare the space, prior to occupants and equipment taking the bulk of the heating load requirements. The system will supply hot water for use in the underfloor heating circuits located around the perimeter of the building. The design of the building and the high-performance fabric specified in conjunction with the heat generated by the occupants will mean that the heating system will only be required during the very coldest periods of the year.

A Mechanical Ventilation Heat Recovery (MVHR) system was installed to serve the main hall space. This will maintain the Indoor Air Comfort by supplying fresh air from outside. Stale air, containing CO2, heat and other pollutants, will be extracted and passed through a plate heat exchanger, in the MVHR unit, which will warm the incoming fresh air, minimising any additional heat which will need to be provided by the heating system.

Throughout most of the year, the heat generated by the occupants and equipment in the building, in conjunction with the MVHR system will be sufficient to maintain a comfortable indoor temperature and excellent air-quality. Minimising the time which the heating system is required to run is a particular advantage to this site as the rural location of the school means that there is no mains gas supply. Therefore, a new oil boiler will be installed, connected to the existing oil tanks – the low requirement for heating negated the requirement for any infrastructure upgrade. Reducing the time which the boiler will run means that fewer oil deliveries will be required and running costs can be minimised.

CLIMAVER® Pre-insulated Ductwork System, from Isover, was installed to provide the air distribution network for the MVHR system. The use of this system also reduces any system noise from entering the main hall space.

Electrical cabling was also installed for the lighting system. The design, with its high levels of glazing, will deliver sufficient natural daylighting to minimise the amount of time electric lighting is required and maximising exposure to natural light throughout the school day giving great levels of Visual Comfort for the occupants.

April 2016

The final air pressurisation test delivered a result of 0.50 V/h @ 50 Pa. That’s a difference of just 0.02, from the test undertaken in November 2015 – but we could have got a better result! The opening roof-lights have a two stage seal in order to deliver the required performance requirements. The second seal delivers Passive House levels of air-tightness. When the final air-tightness test was carried out, the windows were only sealed to the first stage.

Many potential air-tightness pitfalls were designed out early in the project by choosing to mount services to the internal surfaces rather than having them penetrate the structure and air-tightness membrane. Although the project was tendered in the usual way, Speller Metcalfe ensured all trades worked together, Toolbox talks were held and an air-tightness champion appointed. Each trade involved in the project knew of the impact their activity could have on the previous and following trades. Like any project, changes were made along the way, but by working together the end goal, an air-tight building, was achieved ensuring Thermal Comfort for the occupants.

photo of completed barn