earth & hempcrete garden snug
2017 Hertfordshire
designer | contractor
This was a lovely little project with some some very interesting features.
I had developed the structural earth blocks, earth mortar and earth plasters whilst working at HGMatthews and this was the perfect project to use them on.
I had some of the earth blocks fired in a kiln to make giant bricks for the plinth which worked really well and looks great.
The floor looked so good in the earth blocks that I linseed oiled them before the client sanded them then re-oiled and waxed them, they are rock solid and far more resilient than a trowel applied clay floor.
This project is, as far as I know, the first ever to use a structural hempcrete roof deck. I designed this for ease of building as it would have been impossible to use a plywood roof deck with the ash pole roof joists.
It was also a pleasure to work with Jody and Alice on the block walls, they both made top class masons.
Total project cost: £15,000.00
The plinth blocks were the same earth blocks as the walls but I had them fired in a kiln so they were like giant bricks.
The buckets contain pre-mixed clay/straw mortar.
We built this in the winter but tarpaulins were all that were required to keep the blocks dry.
The mortar is used very wet and the block is knocked down firmly to achieve a tight joint.
Once we had a few courses up we could screw timber to the lower blocks at the corners making sure it was plumb, then we could use our string lines attached to these or just span a long level between the two.
Glass blocks were built into the rear wall to catch the morning sun.
Wooden lintels going on, bedded on mortar and screwed through to the blocks below.
We used a railway sleeper for the main lintel over the entrance doors which is exposed internally and externally.
The rafters were whole Ash poles from a neighbours plantation.
We were aiming for thin joints.
Over the ash poles I laid hessian and stapled it to the ash poles. I then cast hempcrete over this with the hessian acting as permanent shuttering.
I only used the feather edge boards over the roof over hang to give a nice finish from underneath.
The hempcrete, once set, acts as a roof deck and will support foot traffic on the green roof. With this simple low tech solution there is no need for plywood or OSB boards.
Absolutely no cold bridges through the roof.
The floor insulation was compacted glass foam aggregate made from recycled car windscreens.
Onto the glass foam aggregate I laid earth blocks on a lime mortar with earth pointing between them. The blocks are the finish and are linseed oiled and waxed for protection.
Blocks before they were oiled.
The finished structural hempcrete roof deck.
Over the hempcrete I first laid pond liner felt to protect the pond liner.
Over the felt I laid the pond liner then another layer of felt, then the green roof substrate and planting.
I plastered the walls with clay/straw plaster.
The windows were re-used from the clients house.
Note the Ash poles with the permanent hessian shuttering in-between. The hessian pillows down and after the hempcrete has set its a hard finish.
We hired a portable saw mill and miller to mill the dead oak tree that stood at the site, this was used for the cladding and skirting.
Preparing for the wood burner flue.
The roof membrane is sandwiched between this ply and the flue flashing to water tight the join.