It is the kind of question which doesn’t normally get asked until planning permission is out of the way and the client is undertaking the detailed design. But it is important to consider the different insulation options early on in the project, as it could have a big impact upon the wall thicknesses, appearance, as well as the environmental targets for the scheme.

What are the options?

There are a range of products on the market which broadly fit into three categories: Oil based polymers, mineral and natural. Oil based products are normally rigid boards made from polystyrene (EPS or XPS) or polyurethane from suppliers such as Celotex and Kingspan. Mineral products include rock and glass wool. These two catagories have dominated the construction market for many years but are not necessarily the most effective. Recently there has been a resurgence in the use of natural materials available including wood-wool, woodfibre, sheepswool, cork and hemp.

Insulation requirements

In England, the current building regulations give the performance requirements for insulation in buildings. The unit of measurement given is called the U-value (W/m2K) which is the amount of heat lost through a meter squared area of the walls, floors etc, per 1 degree temperature difference between inside and outside. It sounds complicated! But remember the lower the U-value, the better the performance of the building element. Current regulations state that the maximum U-value for a wall should be 0.28 for an extension and 0.16 for new builds.

Clients, especially self-builders may decide to go for insulation levels which are better than the governments minimum targets, so as to improve the energy efficiency of the building. This will provide long term savings in terms of energy costs, bring better comfort to the space. In my Wellington Lane project we adopted a Passivhaus approach and achieved a U-value of 0.10 for the walls, with a build-up of 300mm mineral wool between timber I-joists clad with 100mm woodfibre external wall insulation. This made the walls very thick but the house super toasty! I will look closer at this project and the materials used in a future post.

Which insulation performs best?

Rigid synthetic board products such as Celotex are, as a rule of thumb, twice as good as mineral wool and natural materials such as sheep’s wool and wood-fibre. But remember that is not the full story. The performance can be bumped up with more insulation so it is worth considering the overall costs of the product, installation and other factors which are important to you.

Which is cheapest?

It used to be that rigid board was the most economical option even though it has always been the most expensive, because much less of the material is required to hit the required U-values. But over the last few years the price has gone up considerably, and now there is much more of a level playing field compared with the eco products which are far better for the environment.

Which is most environmentally friendly?

Whilst synthetic rigid-boards are an effective insulator they come with great environmental cost to the planet. They are manufactured from petrochemicals which cause resource depletion and pollution risks from oil and plastics production, and have a high embodied energy. Natural products such as wood-fibre can lock carbon carbon inside the material reducing the impact on global warming and generally have a lower embodied energy.

Other positives for natural insulation

If you are undertaking renovation work to historic buildings it is important to use a breathable material, such as wood-fibre insulation, which will not lock moisture within the structural fabric of the building. Natural products such as sheep’s wool have proven to reduce problems with asthma, and help to create a healthy internal environment.

We are thrilled to announce that our project SOPHA has been shortlisted for South West Building Excellence Awards 2019 in three categories.

- Best Change of Use of an Existing Building or Conversion

- Best Inclusive Building

- Best Small Commercial Project

It is great that the award has recognised the work we put in to convert the former hotel in Somerset, into an open and accessible commercial space. The project required connecting several independent buildings on the site into one continuous level space at ground floor, by significant excavation construction of new floors. The shop has been provided with a platform lift provided by Gartec, for accessible access to the first floor.

Success in the regional awards will automatically shortlist the project for the national grand final. Watch this space!

People often ask “do architects still use a drawings board?” Well I can say yes they do…

I often use computer aided design (CAD) software to prepare a lot of my drawings, especially on projects such as Wellington Lane where the proposed building is square and regular, or in other cases such as SOPHA where a lot of technical information about the construction is required and contained within the digital model. More about this approach, called BIM in the industry, another time.

But sometimes it just feels right to get the drawing board out, not just for the early concept and sketch design stage, but to proceed right through the design process to planning permission and even for the technical/construction drawings.

I quite often work on old buildings, for example thatched cottages in Cornwall and Devon, where the walls are never square, floors are not level and the materials have aged over time to bring natural curves to the internal and external surfaces. Drawing straight lines on CAD, not only doesn’t capture the essence of the building, but can force an inaccuracy to the representation which will be a problem later down the line.

If I am undertaking work to listed buildings, it is important to look closely at the building and understand the qualities of the existing building which makes it special. A conservation officer looking at drawings will want to be assured that the building has been recognised as special and will be dealt with sensitively by the design team, client and the building contractors.