Last week I wrote about what causes flooding and what we can do to help prevent it. For some communities, both in the UK and abroad living on water, or near water is a fact of life. To avoid being flooded these buildings might be built on stilts or float and adapt as water levels rise. Today’s blog explores these designs.
Floating buildings – Expanded polystyrene is a key component to ensure the house stays afloat. it can either be used to create a slab on the water: or by creating a composite material with concrete:Presumably there are longevity issues with bare polystyrene and that the composite hull will be much longer wearing.
An alternative to polystyrene is to use a reinforced concrete hull: The hull is often left as a void, perhaps filled with polystyrene, with the house constructed above. It is possible though to use the hull as a basement though, as was shown on grand designs: The building is connected to four columns, and can slide up and down these as required by the flood water. This ensures the house stays level as it rises and falls and it obviously means it doesn’t float off during a flood. Much of the design inspiration for these has come across from the Netherlands. In Amsterdam there are entire communities floating on the water, such as the IJburg estate: All of the houses and walkways are connected to steel mooring poles to ensure they stay in place, floating up and down, as the water dictates.
Building on stilts – It may be very obvious how this design works in the floods, but let’s not knock the simplicity. Here are two UK build houses on stilts: Architecturally, building on stilts can be very effective. The top building appears to levitate above the ground due to the slender and dark columns. In contrast the bottom design emphasizes the columns locations with the glazing and wall panels breaking at these points, leaving clear vertical lines through the design. This is accentuated further by the horizontal lines at each floor level, and by the roof line.
All of the buildings featured in this blog have clear architectural / structural overlaps within the design work and must be the culmination of great collaborative working. As more developments creep onto existing floodplains I hope design strategies such as these are utilized and that rather than feeling threatened by more, unpredictable weather and the associated higher flood risks, we actually use it to inspire us. Perhaps we too will create floating communities like those in the Netherlands.
All civil engineers will be aware of CEM1 concrete. It’s a standard concrete mixture using cement to cure and harden. CEMFree has been created by the David Ball Group to entirely replace the cement requirement in concrete.
What’s wrong with using cement?
Portland cement (OPC) is a mined material. It is therefore a finite resource, and has an environmental impact in its creation. During the curing process of cement / concrete large quantities of carbon dioxide is released into the atmosphere (0.95 tonnes / tonne concrete) which has a knock on effect on global warming and climate change.
What is CEMFree?
CEMFree is high performing cementicious binder that can entirely replace the need for cement. It consists of ground granulated blast-furnace slag (GGBS) and pulverised fuel ash (PFA) plus an admixture (kept very secret!?) so uses a large quantity of waste products in its creation.
CEMFree technical comparison to CEM1
- Better chloride protection
- 0% permeability
- Lower embodied energy (<1.5GJ/tonne vs. 5GJ/tonne)
- 95% less CO2 emissions (0.09tonne/tonne vs. 0.95 tonne/tonne)
- Reduction in thermal expansion so no expansion gap requirements
- No requirement for crack control so reduction in steel usage
- Equal strength at 28 days with a greater strength from then onwards
Publicly available specification is available: PAS 8820:2016
All in all it seems to be a miracle product to help revolutionise the industry into a climate friendly industry. This could presumably also use recycled aggregate to further reduce its environmental impact. It does make you wonder what the admixture is though?
I had heard of Passivhaus prior to attending the conference, but not many details in what it was and how it affected structural engineering. Put simply Passivhaus is design focussed on minimising energy use during it’s lifetime. (This links quite nicely with Peter Head’s talk focussing on performance focussed, rather than financially focussed tenders written about here.) Passivhaus, as a basis, tends to ensure the following in its design:
- good levels of insulation with minimal thermal bridges
- passive solar gains and internal heat sources
- excellent level of airtightness
- good indoor air quality, provided by a whole house mechanical ventilation system with highly efficient heat recovery (more info)
There is also a very similar set of standards for retrofitting properties called EnerPHit, since we obviously can’t solve poor building design by simply starting again. The EnerPHit standard is a slightly more relaxed version to Passivhaus due to the difficulties in renovating properties and because there needs to be an element of value for money. I live in a draughty, Victorian terrace, solid wall construction. Making it anywhere close to Passivhaus standards would be incredibly difficult.
Why follow Passivhaus design?
In an average building there is a 60-80% increase on heating costs compared to its design expectations.
78% of homes do not achieve the required air change rate rising high humidity levels, condensation, mould growth and associated health issues.
How does it affect structural engineering?
Thermal bridging: Make sure the structural framework of a building is enveloped within a thermal, insulating layer (and preferably a thick one). In professional work ensure a masonry column supporting a steel beam doesn’t penetrate through the cavity, ensure appropriate construction notes ensure all displace insulation is re-inserted.
Airtightness: During construction a building should have continuous plastic sheeting within the external structure. How do you fix this without using nails or staples? How do you ensure a building’s structure doesn’t penetrate through this?
Communication: Both of the above topics cannot be resolved without considerable communication between architects and engineers. Personally I have a great interest in sustainable design. Unusually I also have a degree in Architecture, as well as currently studying in Civil / Structural engineering. I hope in the future I am able to work on projects that combine both my personal interests, and also combine my skill sets.
The Bosco Verticale in Milan are literally green tower blocks. The two tower blocks are home to over 700 trees, of which there are 90 species of plant! There are sooo many benefits to this, but these are the key ones:
Passive solar / thermal design – A deciduous tree during the summer has thick foliage, providing shading. If designed well, and integrated into the overall building’s design the trees could reduce strong glare and overheating during the summer months. Equally during the winter months, when the weather tends to be more overcast the lack of leaves allows much more light and heat to enter a building. This ultimately reduces the need for lighting and air conditioning / heating.
Water use – If there is a cohesive building wide strategy for water use, including biodegradable shower and cleaning products then…
So much more to read about…