Zips, slots and flows
A breath of fresh air With the clamour to make buildings more airtight and conform to higher insulation standards, there is a worry that they may become less healthy places than they already are. It is widely accepted that the rise in asthma is significantly due to the headlong rush to draughtseal properties after the energy shocks of the '70s and '80s, without consideration of the need for ventilation.
It is important to learn from the problems of the past - to remember that airtight detailing must include adequate 'controlled' ventilation which will ensure that we do not suffer from the hazards of stale air. Illthought-out Part L compliance could lead to an increase in detrimental health impacts. However, the problem of draughts caused by ventilation gaps is something which has the potential to spoil user comfort and undermine thermal improvements.
Local authority and housing association tenants especially do not have to have very long memories to remember the days when the answer to domestic condensation was to 'open the window'.
The Martin Centre at Cambridge University is engaged in a research programme to try to address many of these concerns, investigating the energy-saving potential of 'supply-air windows'.
Effectively, the window unit draws air in at sill level, which passes between the panes of a double-glazed unit before being trickle vented into the interior at the head of the frame. The system has been shown to operate on the principle that air - provided that it is travelling at a suitable speed of flow - will pick up heat within the plenum between the panes, which would otherwise be lost to the outside, and reintroduce it into the interior.
Dr Mike McEvoy of the Martin Centre notes that 'not only is the insulation of the window increased but background ventilation is supplied pre-warmed into the house', hopefully reducing the perception of draughts. The pressure differential can be enabled by standard passive stack ventilators and the unit contains dampers to ensure regulated constant flows. Following tests in Canada and Finland, the 'whole house low energy' system has achieved effective U-values of as low as 0.4W/m2K.
For further information e-mail Dr Mike McEvoy at m366@cam. ac. uk Faster foundations RMC Readymix has just launched a new product aimed at simplifying and speeding up substructure work on site.
Generally, construction sites are hardly places of innovative practices. Strip foundations are laid as they have been for many years, with several labourers in wellies, up to their knees in concrete, shovelling, raking and tamping the mix along the trench. Now, however, RMC's Foundation Flow should make that a thing of the past, as the concrete is a selflevelling mix poured directly from the mixer.
In normal circumstances, readymix concrete arrives on site on the back of a mixer, is loaded into digger buckets, carried to the trench and deposited in manageable batches while the labourers do their work. A non-scientific test carried out by the manufacturer indicated that the trenches for a standard domestic house would be completed in 30 minutes using three men; trenches laid in the new way take two minutes! And the system involves only minimal use of heavy labour.
Foundation Flow arrives on site in the conventional way.The chute is lowered into place and the mix is deposited directly into the trench, where it begins to work its way along in a self-levelling way.Due to a special viscous additive, the mix does not need additional water to aid flow, and nominal finishing is required.Visually, it has the appearance of slow-moving lava.Because it is poured from a single location, it will be particularly beneficial on awkward, tight sites.
The new mix has excellent early strength, enabling bricks to be laid within 24 hours of pour.The manufacturer confirms that the concrete does not segregate or settle out in the trench and contains entrained air to increase its resistance to frost.With the claim that 'foundation integrity is therefore improved', this material could make a real difference to construction site performance.
Details from Anna Southern on 01932 568833
It's a wrap
Aspen Systems of Massachusetts, US, manufactures low-cost aerogel insulation products which it describes as 'the best insulation material ever invented'. The company is currently looking for industrial partners to optimise the potential applications for the material.
Aerogels are gels dried at a temperature and pressure higher than the critical point of the pore fluid. Through avoidance of capillary stress, this supercritical drying process largely replaces the original pore fluid with air with little associated shrinkage, resulting in a highly porous but brittle material. After treatment the pores are measured in billionths of metres.
Originally discovered more than 60 years ago, aerogels have extremely high porosity and extremely low density and conductivity (average 0.017W/mK). Looking like translucent foam, silica aerogels are effectively a highly porous and lightweight glass which, because of its extreme fragility, is remarkably difficult to handle. Normally sheets have to be transported in vacuum-sealed bags to avoid any pressure on the material which could cause it to shatter.
Recent cost reductions mean that aerogels may now have a realistic chance of getting into the mainstream insulation market. The product is not yet readily processable for everyday insulation requirements, such as injecting into wall cavities, for example, but could be developed with glass manufacturers (see Airglass on www. airglass. se), heating and ventilation or refrigeration products, etc, to produce something highly energy saving.
Although it is currently still more suited to the space race than the commercial building industry, we may yet have a super-insulant material playing an important role in mainstream construction very soon.
For more details contact Aspen Systems on 01 (925) 422 3735 There are many great inventions out there that we do not hear enough about, if anything at all. If readers have heard of any technological breakthroughs or know of specific advances in materials, please e-mail Austin Williams at austin. williams@construct. emap. com
Zip up warm
Composite roof panels have fortunately moved on from the days when architects argued that they should be made up on site. In those days, not so long ago, it was commonplace to try to keep costs down by specifying the bottom tray, the separating purlins, the integral insulant and the top sheeting layer from different sources. Apart from the hassle, it often led to a minefield of litigation between manufacturers, installers and specifiers when things went wrong.
The composite board, comprising internal and external skins containing 'hermetically'sealed insulation, has meant that individual layer specifications are a thing of the past.
However, the lap joints and secret fixing details of composites are potential weak points in the system.
Standing seam sheeting has the benefit of raising the seal above the normal run of water.But this lacks the benefit of integral insulation.
The next generation of roofing is Rigidal's standing seam composite roofing system, which zips the joint to form a tight water seal, and includes continuous insulation with half-lap joints for continuity of thermal performance.An insulant thickness of 85mm gives a standard U-value of 0.25W/m2K.
For more details contact Rigidal on 01905 750500
Slotting into place
When Frank Hornby patented his first set of Meccano in 1901 he could not have imagined that 100 years later we would be imitating his classic simplicity in actual construction practices.
A new concept in steel erection is being developed by Mike Byfield of Cranfield University and the Steel Construction Institute.The difficulties of working at high level using traditional bolt fixings and welded connections are well known.The new idea is based on a slotted connector fixed to the stanchion (or beam, for beam to beam connections), so that a beam, with pre-positioned shoulder bolts, can be attached with relative ease.
The slotted connector is an idea with Meccano simplicity, having a flange and an integral web with a number of spaced slots along its length.The slots are shaped to allow the shoulder bolts to fit through the wider portion and the shank to slot into the narrow portion by self-weight, locking the beam in its final position.
The main test will be the accuracy of the fabrication to ensure that the slots are tied together uniformly.With luck, this could be the beginning of kit-building, albeit with the use of heavy lifting gear.
For more information contact the Steel Construction Institute on 01344 623345