Earthquake Resistant Homes
On this page: Walls, Roofing, Claddings, Things to Avoid, Rainwater Tanks, Emergency Generator, Solar Water Heating, Photovoltaic Cells with a Battery Storage Pack, Sensible Design, New Technologies, Cross Laminated Timber, MagRoc Insulated Building System, How do I Begin?
The following recommendations are based on Dean’s personal observations of where houses failed during the Canterbury earthquakes of 2010/2011.
Experience is a great teacher and as we are all blessed with 20-20 hindsight, so we must use that experience to adapt and survive future events. My goal is that we should learn from the experiences that we have had and rebuild our houses better.
Nobody wants to dwell on what we have been through but geologists advise that both the Alpine Fault and the Hope Fault each have a 50% probability of rupturing within the next 50 years so I believe that it is wise to prepare for the worst but hope for the best.
There are many factors that few of us really comprehended prior to all of this, the first being that it actually could happen here. Prior to September last year, if you were to talk about earthquake risk everybody automatically assumed that it would be Wellington or the Alpine Fault, but not Christchurch.
Now obviously that assumption of low risk proved to be wrong in September and we got a pretty good shake, in fact GNS Science have defined that 7.1 quake as a major earthquake by world standards. But we also got very lucky and while plenty of buildings and houses were damaged and a few people were injured, nobody was killed, and the whole event for most people was more of an inconvenience than a disaster. Unreinforced masonry buildings in particular were damaged, and some came down, but most of the newer buildings survived, there was liquefaction silt to clean up, some water supplies, drains and roads to repair, but generally we were pretty happy and felt that we had got off pretty lightly considering the size of the event.
The earthquake that hit us on February 22nd had the highest peak ground accelerations recorded anywhere, until the Japanese earthquake in March. This was the event that has changed all of our perceptions about how an earthquake could affect us. It was the event that really brought home to us the reality that we live in an active seismic zone. We now understand that there doesn’t need to be a known fault line under us for one to be there, so the likelihood is that there are others out there. And I think that the message that we need to be giving people outside of Christchurch is that if it could happen here under the conditions that it did, then there is a good chance it could happen anywhere in New Zealand.
The second major item that few people realised is that the New Zealand building code standards are set around surviving the initial earthquake event, and that catastrophic failure of a building is acceptable under the code as long as the occupants can escape the building unharmed.
For the vast majority of us, our buildings and homes achieved this, although there can’t have been many people who would have imagined having to abseil down the side of a relatively modern office block to escape. But having escaped our buildings, few of us would have planned for how we cope in a broken home, in a damaged neighbourhood in a destroyed city, with no power, no water, and no sewer.
And the last thing that nobody ever anticipated is the reaction speed of insurance companies and EQC to fulfilling their obligations under the insurance contracts that you and I have been paying our premiums on year after year.
So with all of this background knowledge, I believe it makes a lot of sense to build a house that won’t just survive the earthquake or any other type of event that knocks out basic services for a period of time, but one that will stand a much greater chance of surviving the aftermath also. The Japanese do it admirably as far as earthquakes are concerned. As I understand it, the majority of the damage done in their recent event was caused by the tsunami and there was actually very little damage done to buildings by the earthquake itself. They had a nine on the day and have had regular 6+ events since, which are still occurring
The Japanese have developed many building techniques to cope with seismic events and they build this way because earthquake insurance is so expensive that it is more cost-effective to build to withstand the earthquake and, particularly for housing, it’s really not that difficult.
That way you don’t need business interruption insurance and your staff can still get to work because their homes are intact and the entire infrastructure is still in place. We haven’t built that way here in New Zealand because it has been more cost-effective to build cheap while insurance is cheap and easy to get, and if it all falls down, build it again.
When it all boils down to it, the fundamental requirements of a house are to provide you with shelter, security and safety. A big part of that security is peace of mind, and living in a house that is built to survive a major earthquake plus continue to function to the maximum extent possible after the event is going to help that no end.
So how do we go about building an earthquake resistant home?
Firstly we must know the ground that we are to build on. A geotechnical engineer is the only appropriately qualified person with the knowledge and ability to undertake an examination of your site. Ideally this would happen before you purchase the site, or you could make it a condition of purchase that the test results be to your satisfaction. Once we understand the characteristics of the ground then we can decide on an appropriate foundation system.
Concrete slab on ground with perimeter foundation systems have been the predominant form of foundation for the last 20 years or so, but these have failed where there has been significant lateral displacement of the land. Where the foundation is keyed into the ground, and the ground moves, the foundation goes with it and the floor slab has been unable to cope with the side loads imposed and have failed. They are almost impossible to repair while the building over is still in place resulting in demolition.
Waffle slabs such as the Allied Waffle slab, Firth RibRaft and Max Raft systems all performed well. The foundations are integral with the floor so there is no separation, and the floor is effectively a lattice of reinforced concrete beams. Each floor is specifically designed by a structural engineer for the site conditions.
Many people are interested again in piled foundations, believing that if a building settles in an earthquake event it is easier to re-level the house, and that the separation between the house and the ground will reduce some of the shock to the house. The problem in February was that houses were literally thrown up into the air and if piles separate from the floor structure the house could come down off the piles.
Commercial buildings, particularly in Japan, the east coast of the US and Italy, use base isolation foundations. Despite being originally invented here at the University of Canterbury, Christchurch Women’s hospital is one of a few examples of this in Christchurch and the seven-storey building survived unscathed.
Walls
In most cases for wall systems we will build lightweight timber frames. The physics of lightweight construction means that when the walls start moving in an earthquake they don’t gain as much momentum as a heavier wall, which makes the bracing far more effective because it does not have to work as hard to restrain the wall’s movement. This means that walls won’t accelerate so quickly, so they won’t move as far or as fast or for as long, so the shaking and damage internally will be reduced.
To achieve this, I recommend external walls that are built up with 140 x 45 mm framing and sheathed with plywood from the top plate to bottom plate. Plywood has performed brilliantly as a bracing material by comparison with rigid sheet bracing materials. Rigid sheet materials have all performed as they should have during the initial quakes but in many cases sustained damage in doing so and have continued to degrade during aftershocks, where plywood in general has retained its bracing ability extremely well.
Bracing is the key to keeping your home intact. I recommend that bracing be designed to provide 200% of the lateral bracing requirement of the new NZBC Standards, this will we are told be sufficient to withstand a 1 in 2,500 year earthquake event.
An additional benefit of the plywood is that it acts as a rigid air barrier with all of the joints taped and sealed, reducing air movement through the walls of the house. Combined with 140 mm walls allowing for extra depth of insulation, this provides significantly better airtightness and insulation than standard construction, giving you a warmer and more comfortable house with lower energy costs, so the marginal additional cost will pay for itself.
Another new option for lightweight framing originally from Japan is to introduce shock absorbers into the walls. These are commonly used in Japan and reduce the amount of building movement occurring in an earthquake by about 50 %, turning the absorbed energy into heat.
Steel can be used in two different methods. Structural steel can be used as a post and beam system with in-filled walls and cladding. This is common in commercial construction for warehouses or where large open spans are required, but rare in homes. Steel frame systems use steel in a manner that is similar to timber framing. All of the bracing is provided by the wall systems themselves and is designed by the manufacturer’s engineers. Some steel frame manufacturers claim to produce walls that are one-fifth of the weight of equivalent timber framed walls, and so are lighter again.
Another option is to use solid reinforced concrete to provide a heavyweight building solution that relies on enormous strength to withstand earthquake forces. Concrete is a very difficult material to compress, steel has significant strength in tension. Combined, they can provide an extremely robust building solution and buildings that are classified as critical infrastructure where their survival after an earthquake is essential generally use this method, along with lead/rubber isolation bearings to the foundations.
Concrete masonry and ICF buildings such as Superform or Insulform, which provide permanent insulation to a reinforced concrete structure also survived well.
Concrete can be cast in situ or prefabricated in panels for assembly on site. In residential construction sandwich panels can be made that include an insulation layer internally. This allows the internal part of the panel to provide additional thermal mass to the house, helping to even out temperature variations within the house by collecting and storing the sun’s heat during the winter.
One thing we should definitely not be doing is building a lightweight structure that absorbs earthquake energy by flexing and using this to support a heavyweight cladding that does not have the ability to flex as is the situation with our traditional brick veneer over timber frame houses.
Roofing
Lightweight roofing solutions provide the best answers. Timber trusses are inherently lightweight and rigid along their length and are braced against each other laterally and connected to the tops of walls using steel strapping. Roofing can be long-run metal or pressed metal tiles to provide very light roofs.
Another option which provides superior bracing again is to use membrane roofing systems or asphalt shingles over plywood that is fixed directly to the roof framing. This will provide a remarkably lightweight and rigid yet flexible roof system over any type of wall construction.
Claddings
Claddings which have performed well are plentiful. Weatherboards and light- to medium-weight plaster systems that have control joints that allow for movement have performed particularly well, along with fibre cement sheet systems, especially those that use negative detail junctions. These are generally filled with a sealant which allows for movement without separation. Generally speaking any lightweight cladding system can be used, and there are no limitations on style.
Things to avoid
Fairly obvious really; anything that is not tied adequately into the structure of the building and has the potential to break free. If you must use brick or stone veneers at least lay these over a plywood or MagRoc substrate so that if they are to come off in an earthquake you will still have an air and watertight home to live in while you wait for repairs.
Next, I would like to talk about how, with a few additions, we can make our nice lightweight, strong house much more self-sufficient and autonomous so that we can live comfortably and take care of our families during the period of time it takes for services such as power, water and sewerage systems to be repaired.
Rainwater tanks
Connect one of these to your downpipe off the roof. You can use it to water the garden in the summer even when there are water restrictions, you can pump it back into your toilet cisterns if you want to minimise your water usage, and in an emergency you have perhaps 5,000 litres to get you through those first three or four days.
Emergency generator
I have found 2 kW generators available over the internet for as little as $580. It won’t power your whole house but it will keep your fridge and freezer going which will keep the food that you have safe to eat, it will give you lights, charge your cell phone and boil the jug, and allow you to connect to TV news. Ideally, you would have your electrician set up your switchboard to keep your emergency items on identifiable circuits and give you an input socket to connect the generator into.
Solar water heating
No electricity – no problems, although many use a small circulating pump. Connect this either to a circuit powered by the emergency generator or …
Photovoltaic cells with a battery storage pack
Photovoltaic systems generate electricity from sunlight. These can be sized small to large and are ideal for powering LED and fluorescent lighting systems. A full system will have you off-grid with your own self-sufficient power supply for around the price of a new car, or you can have a system that is connected to the grid.
Sensible Design
Design your home for minimal energy usage. Passive solar design sounds technical but it is really only common sense. The sun rises in the east and sets in the west and the house is designed to get the sun into each room at the time of day that you use it. The sun’s energy is free but too often we don’t value that which we can get for nothing. Effective insulation, natural ventilation, storing heat in thermal mass, these things all flow on from a good passive solar design.
It is the easiest and cheapest design feature to incorporate into a house and it will give you the most benefits in return for the whole of the life of the house.
New technologies
Our traditional form of house building has been based around a lightweight timber frame structure. Back in the day, these were originally designed to be pleasantly cool in summer with the downside that they were bitterly cold in winter, so we filled them with open fires and coal ranges and everybody was supposedly very happy.
Well, obviously not because we have been continually trying to improve the quality of our timber framed houses because over 50% of them fall below WHO standards for health. Since the 1970s, and particularly since the 1990s, we have been adding layers and layers of complexity and treatment and cost to a fairly primitive form of building, so there has been a lot of development in the last ten years on developing newer, higher technology building techniques.
Cross Laminated Timber
CLT has very high resistance to earthquakes. It is formed using sustainably grown timber laminated together with low formaldehyde resins to form a very strong and stable product that can be used for domestic and commercial buildings. The University of Canterbury featured one of these buildings recently that has received a great deal of favourable comment.
MagRoc Insulated Building System
MagRoc is a brilliant new material based on naturally occurring magnesium oxide that we will be seeing a lot more of very soon, and I have been working with MagRoc (NZ) Ltd, a local company to get the necessary approvals to begin building with this material here in New Zealand. At this point I have to declare that I have accepted a minor shareholding in this company, so if my enthusiasm for the product begins to sound like a sales pitch please excuse me, but I am only involved because of the tremendous benefits I can see for clients who choose this method of construction.
MagRoc is a remarkable product. The finish is like fibrous plaster, the strength tests for nail pull out, shear strength, etc. are remarkable and similar to plywood, but its moisture uptake is similar to fibre cement and as there is no chance of degrading so there is no need for chemical treatment. It is totally inert, won’t support mould growth, and fire resistance is no issue as MgO’s predominant industrial use is to line furnaces. It has a low embodied energy content – it actually releases energy during the manufacturing process and absorbs CO2 during its curing process. It is cut using standard woodworking tools and the dust is not hazardous. It is hard to find a downside to this product at all.
The MagRoc Insulated Building System is technically described as a stressed skin either side of an expanded polystyrene core. It is a system that was pioneered in 1964 by Frank Lloyd Wright and originally used in a building constructed in 1974 still performs well today. Life-cycle costing analysis on early buildings is showing up to a 40% lifetime savings cost by comparison with standard construction techniques.
Panels will be able to be manufactured in virtually any thickness; insulation ratings will be very high, and air tightness is very easy to achieve.
The construction process is very much simplified. Rather than taking all of the materials out to site and assembling them there in the mud and the dust and the dirt and the rain, complete wall and roof sections are built in the factory where we can work to engineering levels of precision, and then assembled on site. You may have seen something similar on television programs such as Grand Designs.
The beauty of the MagRoc system is that the internal and external surfaces are ready to finish, and there is no organic product that can decay over time, so there are no chemical treatments required and all adhesives used are water based.
MagRoc is a premium quality product that will be able to be deliver a much higher standard of home at a similar price to what you would expect to pay for a very average quality timber framed equivalent.
There is an enormous amount of interest in these new systems within the design sector of the building industry at the moment and I am certain that within just a few years this type of building will be mainstream. Our production plant is arriving in New Zealand around Christmas 2011 and we will be in production in early 2012. We already have a significant amount of interest and a number of projects committed already and we are fully expecting that within a few years this type of construction will be the new normal.
How do I Begin?
Talk to me. Good design is simply problem solving. You have your site, you know how you like to live, you know what you need to accommodate within your home, you will know how you want it to feel, you know your budget. Tell me exactly what you want and then my job is to work out how best to deliver it to you.
You may have never imagined yourself in the position of building a new home and so be completely unfamiliar with the process, but it is a process that we can go through step by step so it doesn’t need to be daunting.
For earthquake rebuilds most insurance policies will cover the cost of professional fees to reinstate the house that you had to the current building standards. This will cover the necessary geological testing, site surveys, structural engineering and architectural fees, as well as building consent and inspection fees. What the insurance policies generally don’t cover is where you are rebuilding on your existing site and you wish to change the house from its previous configuration they will not cover the design fees for this or any additional building costs that come as a result, for example should you build a larger or more complex house.
I can understand the insurance companies position on this but it would be a terrible shame not to take the opportunity to redesign your home to make maximum use of the sun and to be as energy efficient, healthy and comfortable as possible.
My offer to those who wish to redesign earthquake affected homes is that I will cap the concept design component of the fees at $3500 inclusive of GST with the balance of fees for documentation and any other work required to be paid by your insurance company for work commissioned up until March 31st 2012 on houses up to a construction value of $700000. Outside of this let’s discuss your situation.