BedZED: Construction Materials Report. Contents:
- Credits, background and introduction
- Summary
- Materials in construction
- Measuring the environmental impacts of materials
- Material selection (examples): Window frames, reclaimed steel and recyled sand.
Material selection (examples)
Example case studies
This chapter describes the main components that make up a ZED building
and the reason for each material choice. Numbers in boxed brackets indicate
a case study number, eg [6]. More details on that material can be found
in its case study in chapter 6.
Chapter 5 gave an overview of all the materials used at BedZED. This chapter
6 provides details of some of the more unusual materials. It compares
the BedZED material with conventional alternatives and describes design,
quality and sourcing issues, contractual arrangements and cost implications.
Each of the 15 case studies quantifies the environmental impact of the
material and compares with the conventional choice. The case studies are
graded according to:
• How easy it was to acheive..
• Cost-effectiveness.
• The significance of the environmental benefits.
All gradings are relative to the conventional material choice for that purpose.
The Case Studies included in the complete report
are: (linked examples are in blue)
| 1 LOCAL TIMBER | 6 KITCHEN FITTINGS |
| _ Oak weatherboarding | 7 RECLAIMED DOORS |
| _ Ash floor boards | 8 RECLAIMED STEEL |
| 2 RECLAIMED TIMBER | 9 RECLAIMED PAVING SLABS |
| _ Internal studwork | 10 CONCRETE FLOOR SLABS |
| _ External studwork | 11 RECYCLED AGGREGATE |
| _ Bollards | 12 RECYCLED SAND |
| _ Floor boards | 13 LOCAL CONCRETE BLOCKS |
| 3 FSC CERTIFIED TIMBER | 14 LOCAL BRICKS |
| 4 PLYWOOD | 15 INSULATION |
| 5 WINDOW FRAMES |
case study 5: window frames
The BedZED Design Team sought to avoid high impact materials such as uPVC and aluminium. So when it came to selecting window frames, timber was the obvious choice.
Options explored
The Design Team explored the best environmental
option -frames made from locally sourced hardwood. This long life and
low maintenance material has lower life cycle costs than softwood alternatives
which would require a £14,000/year maintenance programme and more
frequent replacement. Using a locally distinctive product adds character
to a development; whilst creating a demand for locally grown timber products
brings neglected UK woodlands into economically viable management.
However, local joinery companies were reluctant
to work with local chestnut, when their experience lay in producing softwood
frames. There was little local expertise in manufacturing high performance,
triple glazed, airtight windows. Also, the scale of the contract was too
large for the companies operating locally. These factors led to prohibitively
high quotes.
The geographical net had to be spread wider. Danish window specialist
Rationel were able to meet both stringent performance demands and cost
criteria. Rationel source 40% of their timber from FSC certified sources.
Cost comparison
Timber windows are typically cheaper than
aluminium or uPVC but can attract higher maintenance costs. The Rationel
windows on BedZED are high specification in terms of air tightness, thermal
performance and also durability. Their costs are higher than most timber
windows but maintenance costs are lower.
The supply cost of Rationel windows on BedZED (excluding installation)
for double and triple glazed ranged between £130/m 2 and £300/m
2 . Equivalent aluminium frame windows from Alcoplan ranged from £185/m
2 to £275/m 2 . uPVC windows from Ankers & Sons in the same
price range only achieved U-values of 1.9W/m 2 , as compared with 1.0-1.6W/m
2 for Rationel's timber windows.
Quantified environmental benefits
BRE have compared the BedZED softwood timber
framed windows from Denmark with the conventional choice of uPVC windows
manufactured in the UK and with aluminium framed windows (all double glazed).
BRE are aware that better quality LCA data on uPVC is now available and
they are hoping to work with the British Plastics Federation in the near
future to update this data.
Saving from using BedZED Specification
| uPVC windows | Aluminium windows | |
| Ecopoints | 4,800 | 4,500 |
| Embodied CO2 (kg 100 yr eq) | 793,900 | 838,000 |
| Embodied Energy (GJ) | 12,000 | 9,750 |
| Eco-footprint (ha years) | 176 | 186 |
case study 8: reclaimed steel
98 tonnes of reclaimed structural steel has been used on BedZED. This amounts to 95% of the structural steel on the scheme and is mainly used in the steel frames in the workspaces. The sections are retrieved from demolition sites within the 35 mile radius.
Design
The engineers specified a range of section
sizes that could be used for each piece. Connection details were designed
to accommodate this range of sizes. This approach, at an early design
stage, allowed for flexibility in sourcing the reclaimed sections.
Once reclaimed steel sections had been identified, The Historic Sections
Book was used to obtain allowable stresses.
Quality
The engineers specified a range of section
sizes that could be used for each piece. Connection details were designed
to accommodate this range of sizes. This approach, at an early design
stage, allowed for flexibility in sourcing the reclaimed sections.
Once reclaimed steel sections had been identified, The Historic Sections
Book was used to obtain allowable stresses.
Reclamation process
Sand blasting, fabrication and painting of all new and reclaimed structural steel took place in the steelwork contractor's workshop. The reclaimed steel required an extra pass through the sand blaster and treatment with a zinc-rich coating.
Curved steel sections
It was not possible to use reclaimed steel for the curved sections on BedZED. The local section bender was unwilling to pass reclaimed steel through their machine. Due to time and programme pressures, the contractors proceeded with new steel for these pieces rather than finding an alternative company. There is no technical reason why reclaimed steel should not be curved on future projects.
Cost comparison
On BedZED, using reclaimed steel was 4% cheaper
than using new. The cost average was £300/tonne, although this price
varied considerably according to the source. The comparative tender price
for new steel was £313/tonne.
The cost of additional staff time in sourcing reclaimed steel and the
visual inspection has been estimated at £1,000, making the use of
reclaimed steel effectively cost neutral.
Construction contract
The steelwork package was tendered competitively on the basis of new steel. Tenderers were then asked for a rate reduction for the free issue of reclaimed steel. Cut off dates for the placements of orders for new steel were agreed and responsibility for sourcing and delivering the reclaimed steel was with the construction managers.
Sourcing / Availability
There are not vast quantities of good quality
reclaimed structural steel stored in reclamation yards. It requires active
searching and probably some luck to find the right materials. For this
reason, it is important to build in as much flexibility as possible and
to allow for long lead times.
In the absence of sourcing from a yard, the ideal situation is to identify
a steel source in a building that is about to be demolished and to have
it extracted carefully.
Risk allocation
The Construction Manager purchased the reclaimed steel on behalf of the Client. There was a risk to the Client as with any free-issue materials. The structural engineer, Ellis & Moore held the risk associated with the structural integrity of the steel.
Quantified environmental benefits
BRE have compared the impacts of the recalaimed steel with new. They have allowed for one additional grit blasting prior to use. Overspecification of the reclaimed beams was very small (<0.5%), as most of the reclaimed beams were in good condition, and were standard sizes. The environmental impacts of new steel are based on the typical mix of steel sections manufactured from virgin (BOF) and recycled (EAF) steel consumed in the UK.
| Ecopoints | 1,000 |
| Embodied CO2 (kg 100 yr eq) | 81,500 |
| Embodied Energy (GJ) | 2,580 |
| Eco-footprint (ha years) | 137 |
These savings reduce BedZED's total eco-footprint by approximately 3.8%.
In addition
The Construction Manager purchased the reclaimed steel on behalf of the Client. There was a risk to the Client as with any free-issue materials. The structural engineer, Ellis & Moore held the risk associated with the structural integrity of the steel.
As a spin off from BedZED, 11.5 tonnes of
reclaimed structural steel was also used on the entrance building to the
Earth Centre, resulting in 303GJ embodied energy savings, 21 tonnes of
CO2 saved and an eco-footprint reduction of 12.6 hectares.
case study 8: recycled sand
BedZED used 279 tonnes of recycled crushed green glass. It was used in the hard landscaping as bed-ding for paving slabs and replaced the same quantity of virgin sand.
Procurement
The recycled product was bought direct from Day Aggregates by the groundworks contractor, Edenway Contractors Ltd. It is an off-the-shelf product. Product Datasheets are available from Day.
Aggregates
Edenway is now suggesting this product to other Clients and using it whenever possible. They experienced no difficulties in obtaining or using this product and it brings them a cost saving. Day Aggregates say that sales have increased since the introduction of the Aggregates Tax in April 2002.
Safety
Risk assessments and COSSH statements were prepared by the suppliers. The finely ground glass is similar to sand in con-sistency but may be slightly sharper to touch. Gloves can be worn while handling. No safety issues arose on site at BedZED.
Cost camparison
Recycled crushed glass sand cost £10.75/tonne from Day Aggregates. This was approximately £2/tonne cheaper than virgin material, saving the project £558 (~ 15% of the material cost). The aggregates tax implemented in April 2002 (since BedZED construction) has increased the price of virgin aggregate by a further £1.60/tonne, making potential cost savings even greater.
Quantified environmental benefits
The environmental impact of the recycled glass
sand used on BedZED has been compared with virgin sand typically sourced
in the UK.
| Ecopoints | 320 |
| Embodied CO2 (kg 100 yr eq) | 1,330 |
| Embodied Energy (GJ) | 17 |
| Eco-footprint (ha years) | 1 |
Further information
• The full report can be obtained from Bioregional: www.bioregional.com
