Building with straw bales is a relatively recent concept in Ireland. Most buildings were constructed within the last two decades, representing a tiny proportion of all homes, but, in many ways, ideally suited to the novice self-builder.
There are many reasons to build with straw; low environmental impact, cheap and locally available, excellent insulation and breathable properties, providing a very healthy living environment (see a summary by Andrew Morrison at Strawbale.com). As beginners we found Barbara Jones’ book indispensable. We also attended some courses run by Straw Works in the UK before returning to Ireland.
Construction of our non-load bearing walls was reasonably straightforward requiring a minimum of tools. However, there was preparation work to be completed before we began to build our wall. Similarly, when we had built our walls, we needed to work on the space between the top of the walls and the underside of the roof – the void – we called it!
1) Wooden ring beam/plinth: we built the ring beam in May 2017 after we finished debarking our roundwood. The beams consist of 300mm x 50mm (12″ x 2″) C24 timber with OSB (18mm) on the top and bottom. It’s important to use long lengths – as the ring beam will bear the weight of the bales, doors, windows and floors – so it needs to be very strong. The completed ring beam sits on top of the filled car tyres, we also placed damp proof course (DPC) and marine ply to meet regulations and to reduce the possibility of any water ingress.
The other main function of the ring beam is to provide a raised plinth to protect the straw bales from water splashing upwards during periods of rainfall. Externally, the ring beam will be covered with lime plaster.
The ring beams were stored until we began to install them in January ’19. We insulated the beams and covered them with OSB. We also added lengths of 100mm x 44mm (4″ x 2″) timber on top of the OSB to further strengthen the beam and to support the door and window openings and house the hazel stubs. The spaces between the timber were filled with Leca which acts as a moisture soak in the event of any water getting into the straw.
Fixing posts for windows and doors were added at this time. These posts consisted of 2 x (2 x 100mm x 44mm) (4″ x 2″) nailed together and fixed to the ring beam at the bottom and the wooden frame fixed to the roof rafters at the top. We needed to change some of our original window locations and sizes to accommodate the wooden braces in our main structure.
2) The First Bale
We began building our walls in mid-February. Our bale plan is based on an average bale size of 1m (40″). However, it is impossible to produce bales to a single length, so bales have to be re-sized and cut for window and door frames. It’s important in the early stages of building with straw to take things slowly and carefully.
The first course was secured in place by hazel stubs and as our walls rose to the fourth course we pinned them with longer (1m / 40″ hazel sticks at two per bale). Before pinning we checked the walls for straightness.
3) Compressing the walls
By mid April we were up to the sixth course of bales. As our walls are not load-bearing we had to come up with a solution to filling the space between the top of the wall and the ceiling. We did this by building a wallplate panel using 100mm x 44mm (4″ x 2″) timber and OSB. We suspended this from the roof rafters to allow for the seventh course to be put in place. We then compressed the walls with ratchet straps and sealed the compression with polystyrene straps (purchased from BM Packaging). The ratchet straps were placed under the ring beam and over the wallplate panel which meant that we were able to spread the compressive forces equally along the wall.
Compression has a transformative effect on the walls, giving them much greater solidity and stability. We gained an average compression of 100mm (in seven bales). For windows and doors we did some test compression so that we could place lintels correctly. If they were too high or low they would affect the compression. When satisfied with the walls we gave them a hair cut to remove all the loose straw.
Before we completed the work on the walls we had to build our porch, as it wasn’t part of the main roundwood structure and would be load-bearing. We had to wait for some dry weather as we reckoned it would take two weeks or so to build the porch and its roof.
Unfortunately, during the building of the porch we suffered a leak and had to rebuild part of the wall – one of the disadvantages of building without a roof overhead.
We completed the porch and roof in mid-June and were now in a position to begin the focus on insulating and water-proofing the roof.
Additional jobs: Earth Anchors
We installed earth anchors so that our structure is correctly anchored into the ground. Despite our structures strength it could be susceptible to uplift in stormy weather, with wind acting on the 500 mm roof overhang which extends around the perimeter.
The anchors are driven about 2m (6ft) into the ground and the stainless steel lanyard is then jacked up with a tractor jack to apply the correct force and ensure that the anchor is properly employed. The lanyard will be eventually connected to the posts to prevent uplift. We were grateful to Osian for helping us install these and to Bobby Bazelgette from Solarwheel who advised and supplied the earth anchors.
The next task is to insulate and waterproof the roof and then begin preparing for plastering the exterior walls. We hope to be able to move inside in the winter months to begin work on the interior.