Natural floor insulation

Thermofloc is a natural floor insulation. Made from cellulose that has added minerals to make it fire retardant. It is simple to install and is much more affordable than any other natural insulation we found.


double whisk mixer

To break apart the insulation blocks we used a double whisk mortar mixer. By using an online calculator to work out how much we needed for our floor dimensions, we could be sure to achieve the correct density and therefore U-value.


NaturePlus – Thermofloc is the first cellulose insulation to be awarded the coveted NaturePlus mark of quality and sustainability.

  • Laid density of 40kg/m3
  • Thermal conductivity 0.039W/mK
  • Fire classification as per EN13501-1
  • Free of hazardous substances as defined by ETA-05-0186

Assessments show Thermofloc does not provide a suitable habitat for rodents and as such rodents will avoid nesting within the insulation.

Locally sourced materials

It is important to us to build with locally sourced materials. We have lots of clay, so are utilising that as much as possible. If this build were elsewhere in the country we would be choosing a different approach. We can’t just have a template for a ‘sustainable home’ that doesn’t factor in what local materials are available as transportation accounts for a huge amount of energy usage.

our straw crop is locally sourced
Our straw crop – a few days before it was baled (Photo Jake Chadwick)

Our locally sourced materials

  • Our straw comes from a farm less than 5 miles from the site. We were able to go to the farmer, check the size and density of the bales… and even request that they be made as tight as possible… which they did! (The even cranked it so hard the baler broke – once the part was replaced, fantastic dense bales were the result – The best I have ever used!).
  • Most of the timber is from a local saw mill, using locally sourced timber.
  • Our gravel and sand is from a local pit.
  • The sheep wool insulation is all from Welsh sheep.
  • We are making clay plasters from clay dug on site.
  • All of our lime comes from Ty Mawr Lime, 60 miles away.

These are our obvious success stories….

Not so local

We have not been able to source everything locally, our smartply for example, came from the Czech Republic. Not great!

Other considerations

There have been other more subtle design choices that have allowed us to use more local materials. An example of this is how we have sheeted the roof. The conventional way is to use 18mm ply sheets, usually shipped across the country, if not Europe. We have opted to use larch planks from our local saw mill – It takes longer to build, but the environmental impact is far better.

More reading

Car tyre foundations – Video

Car tyre foundations team

This week we have been laying our car tyre foundations for our #BalesInWales cabin.

We have chosen to use gabion basket foundations. Though our Gabion baskets are reclaimed car tyres.

Car tyre foundations are the perfect choice for this build as:

  1. They are cheap – actually the tyres are free, local garages have given all the tires we need as they have to pay to have them disposed of. We are only paying for the pea gravel to fill them.
  2. They make a capillary break – Rising damp occurs when a porous material is used as a foundation. To combat this, conventionally a damp proof membrane (plastic sheet), is used to stop moisture coming up in the wall… but what if any moisture gets into the wall from above? It creates a paddling pool which our bales would sit in. Because neither pea gravel or rubber is porous, moisture can only travel downwards with gravity.
  3. They find a use for an otherwise problem material. Tyres are said to have a life span of 30,000 years, so disposal is a big issue.
  4. They are low embodied energy. To turn a tyre into a foundation, just takes the pea gravel and some porridge to power our workforce!

This last week we have been happily filling our car tyres in neat stacks, here is intern, Jamie showing us how it’s done!

Foundations Video from JeffreyTheNaturalBuilder on Vimeo.

Things what I did make.

In between clay plastering and Earth floors, I found some time to create a few items for a customer.

A couple more items to finish, which are spectacular, so far happy customer. Happy Jeffrey.


Straw Bale, Lime and clay on this stunning roundhouse

I recently helped Straw Works teach the natural building elements on this beautiful roundhouse built by Ben @ It was a fantastic 10 days that transformed the structure into an all encompassing structure. Massive thanks to Straw Works and all the wonderful course participants!

(And will be returning in July to run an earthen floor workshop)

round wood round house

The week began with the straw:

We then moved onto to preparing the bales for lime render on the outside and clay plaster on the inside: