Continuing our look at how Oakenstone Design Planning Build are combining natural materials with modern processes to rescue this important historical building.

In line with our clients values, wherever possible we have sought out the most effective, sustainable solutions for this renovation.  Solutions that truly enhance the building, allow it to ‘breathe’ and to function as a modern family home.

In my last post I described how we insulated below the Lime Ash floors using Geocell foamed glass gravel.  In this post we will look at Oakenstone’s approach to insulating the external walls.

The Facts

Humans in houses spend all day, every day breathing and sweating (if only a little!).  They also talk, cook, bathe, shower, do laundry and dry clothes.  All this activity generates huge amounts of water vapour.  In fact, a family of four generates around 14 litres of water each day (that is over 5 tonnes of water per year!), all of which has to somehow escape the home.  If it cannot escape, trapped moisture leads to mould, damp, possible rot, and worsened health outcomes such as asthma and skin complaints.  

Modern homes can be equipped with mechanical ventilation solutions designed to extract excess moisture.  The more sophisticated systems also recover the heat from the extracted air to be recirculated throughout the home.  In this listed building renovation though, mechanical ventilation and heat recovery is not an option.  This fragile building needs natural insulation which allows moisture to pass through the insulation layer, through the brick and lime pointing, from inside the building to the outside. Which allows the building to ‘breathe’.

Hempcrete is the perfect solution. Hempcrete is a bio-composite material made from hemp ‘shiv’, the inner woody core of the hemp plant, mixed with a lime binder.  It is locally grown and sustainable with excellent thermal properties.

• Hempcrete is ‘breathable’.  It regulates moisture, reducing the risk of damp and mould.  Plus, it provides excellent thermal and acoustic insulation, really enhancing the comfort and ‘feel’ of a building.
• Because the hemp plant is naturally pest-resistant, it requires only small amounts of fertiliser in its growing period and no harmful pesticides or herbicides.  This means that Hempcrete in your home contributes to a safer, cleaner indoor environment.
• Hempcrete is fire-resistant, pest-resistant, mould and rot-resistant.  
• Hempcrete is Carbon Neutral.  As it grows, the hemp plant absorbs huge amounts of CO².  And then in use with lime binders, it stores that CO² for the life of the product. In fact, a leading UK hempcrete supplier states that 165kg net CO² is sequestered per cubic metre of hand-placed hempcrete, and 110kg CO² per cubic metre of sprayed hempcrete.
• Hemp ‘shiv’ is mixed with lime binders to make hempcrete.  Lime is produced at much lower temperatures than traditional Portland cement, so the energy used and CO² emitted in its production is much lower.  Due to its lower density, it also costs less to transport than cement.

The sprayed hempcrete installed here allows gentle sculpting of window reveals, and is a slightly less compacted product than if it were hand laid. It is warm to the eye and to the touch and is a perfect base for lime plastering which will commence as soon as the hempcrete is dry.

Hempcrete really is a quite magical material. One which could soon play a significant role in reducing carbon emissions in the construction industry, in retro-insulating existing housing stock, and in creating superb buildings in the future.

If you have a project in mind and would like more information, you can read more about hempcrete here, or why not contact us to learn more about how we source and employ the best, products and methods and skilled trades for our clients.