Durisol is a type of insulating concrete formwork (ICF). With ICF, you start with hollow insulation moulds (formwork) and pour ready-mix concrete into the moulds, rather than adding insulation to the structure afterwards. The resulting wall is incredibly energy-efficient.
Few professional developers use ICF, because it is rarely cheaper than conventional methods. However, self builders like ICF because it’s easy to use and it delivers a very high quality home.
There are many different types of ICF. What the ICF businesses have in common is that they use pre-formed moulds and casings, designed for easy assembly on site, and they are used solely for building walls.
Most ICF suppliers use polystyrene insulation to make the formwork. However, one type of ICF uses wood cement, also known as woodcrete. Woodcrete was first developed and patented in Switzerland in the 1930s by the company Durisol, the name still predominately associated with this building system across the world.
Using Wood Cement for the Formwork
- The wood goes through a process called mineralisation that makes the product inert and fireproof.
- The mineralised wood is then mixed with cement to make a rigid and sturdy hollow block, ready to be stacked up into a wall on site.
What are the Advantages of Durisol?
There are three main advantages of using woodcrete blocks rather than polystyrene insulation:
Durisol blocks are heavier and more robust than plastic ones. This makes building with them a little easier, as the structure requires less bracing before the concrete pour. The structure is also easier to work with.
Durisol is similar to polystyrene block ICF. However, the inner face is thinner, which makes it better at releasing usable heat from the thermal mass of the concrete.
Woodcrete itself is not as good an insulator as polystyrene, but the Durisol blocks come with an added layer of mineral wool insulation pre-fixed. The U value of the Durisol block compares favourably with polystyrene ICFs.
ICFs have been criticised for using a lot of ready-mix concrete, but Durisol is starting to use low-carbon Cenin cement to make the blocks. The system still requires ready-mix concrete to be poured into the moulds on site, but less is needed.
Durisol is also working with Cenin to offer a low-carbon concrete version.
Other Advantages of Durisol
The system also scores highly in terms of building performance:
- Woodcrete is inherently fireproof, once the wood chips have been mineralised.
- It’s also effectively waterproof but remains breathable to allow any moisture build up to evaporate harmlessly.
- It is suitable for basement builds and can readily be used below ground.
What are the Disadvantages of Durisol
There are certain features like curved work and cantilevers that are not suitable for this type of building system. However, the system can usually be adapted to most self build designs.
Generally, the sooner the decision is made to use a system like Durisol, the better.
Training for Self Builders
Almost all ICF businesses put great emphasis on training days to help give prospective customers confidence. Durisol uses the National Self Build and Renovation Centre at Swindon to deliver free full day seminars on how to use its product.
The company now joint markets with a Yorkshire-based company, CRS Future Build, which sells an insulated floor system called IsoLohr. The two products make a great fit for anyone wanting a low-energy house and customers can now do training days for Durisol in Barnsley via CRS.
Although Durisol is the best-known name in this field, other businesses have developed similar products. One such active in the UK is Velox, which originated in Austria and now operates six factories across Europe.
How Much Does Durisol Cost?
Costs appear to be almost interchangeable with expanded polystyrene (EPS) ICFs.
The materials costs are slightly higher than blockwork, but this can be clawed back by lots of DIY input, which is why it appeals to DIY builders.
Final costs also depend on the choice of cladding. Durisol works well with renders applied directly but there is a price penalty for external masonry claddings. Generally, the system makes more sense with renders or lightweight claddings.
Find out more on insulated concrete formwork.