Lime Plastering (external)

Lime plastering is one of the most rewarding and hardest jobs we’ve undertaken so far on our build. The reward is the smooth organic finish which can be achieved by weatherproofing the exterior of the walls. However, this is only achieved with a lot of effort which arises from the very tough physical demands of plastering.

Our schedule for 2020 had already been affected by the time lost during the lockdown, imposed in the early part of the year. Unfortunately, it was further impacted by Maria sustaining a serious injury in early July; a broken and dislocated ankle. This meant that our regular workforce was reduced to one for plastering the entire house. Maria was unable to take part in building works for at least three months! Needless to say, this was one of the things we feared most when we started to build, and, unfortunately, it happened. This meant that our potential to be completed by the end of 2020 had vanished. As always with self building, you have to remain positive and embrace the challenges.

Sadly, our wonderful Springer Spaniel companion, Jal, passed away in September. She was with us on every day of our build, but sadly her part in the story has ended.

Early summer was all about preparation for plastering. During this time, we met fellow straw bale builders Pat and Heidi. Luckily they had arranged for Miki, a plasterer, who was trained by Straw Works, to work on their house. I spent a day plastering their house and Miki spent a week on our site, getting us started. I would recommend to any straw bale builder starting plastering to get some experience beforehand. The job is quite daunting and not one you want to repeat.

Lime Plastering

Lime plaster is the proven protector of straw bale walls. Straw has a natural ability to allow moisture and air through it and lime is a breathable material. If cement was used, it would cause the straw to rot, as it is not breathable, which would lead to a build-up of moisture in the straw walls. Lime plaster also has greater flexibility and is more suitable for natural building methods. In its lifetime lime plaster will continually absorb C02 from the atmosphere as it returns to its original chemical composition (CaCO3/limestone) and is an excellent, sustainable building material.

Mixing the plaster

Due to the moderate exposure of our site, especially to prevailing south-westerly winds and rain, I used NHL3.5 with a 5mm down coarse aggregate for the exterior walls.

The quantity of silt in the aggregate is an important factor to consider. Too high a content and it will cause cracking in the plaster. Our aggregates came from Shiel Sand and Gravel and have a silt content of around 2%. For a very detailed understanding of plastering with natural materials, I found Weismann and Bryce’s book, Using Natural Finishes, a really useful reference. Our lime was supplied by the Traditional Lime Company who also offer advice and training.

a) First Coat (Scratch Coat)

The plaster was mixed 2:1 (aggregate to lime) by volume. The aim of the first coat is to get the edges of the bales well covered and provide a suitable substrate for the second coat. The plaster is worked deeply into the bales by hand. The straw on the edge of a bale is alternately chopped or folded. The chopped edge is much easier to work the plaster into (photo below shows the first coat).

Plastering is a very physical task, involving a considerable amount of heavy lifting. Each tonne is lifted three times; firstly into the mixer, then into buckets and finally onto the wall. Plastering by hand is quite tough, as it uses different muscles than usual. It takes a while for the strength to build up in your hands and fingers. It also takes a while for your hands to get used to the feel of the plaster.

For plaster to dry (cure) properly, it is important to control the atmospheric conditions of the wall. I protected the walls from the elements (mainly wind and sun) by hanging tarpaulin from behind the fascia. In addition, I hung hessian between the wall and the tarpaulin, which was dampened periodically to aid the curing process.  Luckily, the very humid, calm summer of 2020 provided the ideal weather conditions for plastering.

The plaster changes to an off-white colour as it cures (see photo above). When it becomes solid to the touch, it’s time to add a second coat.

b) Second Coat (Straightening Coat)

The mix is also a 2:1 ratio, but chopped straw is added to give additional strength. The purpose of this coat is to fill in the grooves and any other holes in the first coat. This coat is then ‘keyed’ using fingertips to provide a suitable substrate for the top or finish coat (see photo below).

As NHL3.5 cures quite quickly, I aimed to apply the first coat for about a week and then add a second coat. The second coat is easier to apply as the more difficult task of getting the plaster to stick to the straw isn’t a factor, as it is in the first coat. The plaster sticks better with this coat but still has to be worked into the bales, albeit with slightly less force.

c) Top Coat (Finish Coat)

Due to Maria’s injury, it wasn’t possible to complete all three coats in the time available. I was lucky to have help on several days, but as I was mainly working on my own, it was only realistic to complete the first and second coat by mid-September. I set this as the cut-off date as the colder, frosty winter weather from mid-November onwards can arrest the curing process. We will complete the exterior top coat in late April/early May next year.

By mid-September, practically all of the first and second coat had been completed. It was a considerable task as the total exterior wall space is around 200 square metres and each week I added between 1 and 1.5 tonnes of plaster.

When I worked with Miki, we completed a small portion of top coat. Some of this coat was worked in using a float and, where this was not possible, we used our hands. The mix was slightly weaker 2.5:1 with fibres added (see photo below).

Other jobs:

a) Underfloor Heating System

In early July, our plumber, Pauric, completed the installation of the pipes for the underfloor heating system. We will be installing an air-to-water heat pump for hot water and heating. This type of heat pump is practically standard on new builds and will satisfy some of the requirements of Part L of the Building Regulations.

Prior to the pipes being laid (see photos above) we covered the OSB floor with polythene and also added an expansion gap around the exterior walls, and the posts to accommodate any expansion in the floor.

b) Floor Screed

The floor screed is a vital part of our heating system as it forms our main thermal mass. It needs to cover the pipes and set properly without cracking (which would obviously damage the pipes). We were recommended Cemfloor and got in touch with a local contractor – Bracken and Mulligan – who poured the floor in about half a day. It has a relatively quick set, however as we didn’t need to work indoors, the screed was left for over a week before we walked on it.

Building a raised wooden floor

At the conceptual part of our design process, we decided that we would aim to build with as little cement as possible. This was an environmental choice. Cement is an extraordinarily useful substance in construction but it also carries a heavy environmental price. We decided our floor would not be a monolithic slab of concrete but would be a raised wooden floor.

Putting this idea in practise meant that we had to build and insulate our floor. Our plan was to get as much interior work done until the weather was suitable to plaster the outside walls.

However, Covid19 has resulted in all supply lines to non-essential building ceasing. Currently, we are awaiting a change in the rules so that we can continue with our build. Until then, like everyone else, we wait in hope and observe the constraints that have been put in place for the good of public health.

We did manage to complete our floor and some other work before the lock-down was instigated. Below is the story of building our floor.

Stage 1: Setting out

We worked with our engineer, David, to check the levels on our wooden ring beam (which is the wooden plinth that supports the straw bale walls) in order to mark the correct positioning for the wooden flooring joists. The flooring joists have to span  about 10m (north to south) which means that additional supports were required. This span is too great for a single length of wooden joist. We put the supports in place when we were building the car-tyre foundation by placing two sleeper rows of car tyres (running east to west) inside the outer ring of car tyres.

Stage 2: Installing the joists

Our floor used 110 joists which were 3.6m (12ft) long and 225mm x 44mm (9″ x 2″) at 400mm (16″) centres. The joists were secured to the timber ring beam by timber-to-timber joist hangers. Rather than using timber noggins between joists, we used metal herringbone straps, all fastened with twisted shank nails. The advantages of the straps include; they are ready-made; will help to reduce thermal bridging and allow for more insulation in the floor. The main disadvantage is that the insulation will have to be cut around them and that they have to be nailed to the top and the underside of the joists.

There was a considerable amount of nailing in this stage. Before fastening the joists we used folding wedges to help us achieve level and plumb joists. This is an ancient woodworking technique and still really useful when you are trying to achieve good work. We dedicated a lot of time to ensure that we achieved a high level of accuracy with the joists – lots of measuring, levelling and checking.

 

Joists in place. Note support at mid point where joists are joined together and battens to support insulation at the bottom of the joists

 

Folding wedges used to keep joists level and plumb

 

 

 

 

 

 

 

On each joist we nailed short lengths of 44mm (2″) by 19mm (1″) at a 200mm (8″) chalk line to support the two layers of rigid insulation. We worked out the spacing of these in advance to accommodate the herringbone straps and insulation, as this would reduce wastage.

 

Stage 3: Insulating the floor

We used PIR insulation from Xtratherm for the floor. Their product – PIR XT/UF – is specifically for raised floors with under floor heating systems. The sheets of insulation are 2.4m (8ft) by 1.2m (4ft) and 100mm (4″) in thickness. We cut each sheet in three to make smaller 800mm (32″) x 1.2 (m) 4 (ft) sheets. This then gave us a spacing for the herringbone straps at 800mm (32″) centres. This simple calculation minimised the wastage on each sheet.

Floor insulation arrives!

Installing the layers of insulation. Note metal straps rather than wooden noggins

 

 

 

 

 

 

 

 

 

This job was quite time-consuming as we had to install two layers of 100mm (4″) insulation, so as to avoid any thermal bridging. We installed the herringbone straps with the insulation so there was a lot of cutting around the straps, nailing to the underside of joists and dust…lots of dust.

Fitting the insulation

Installing floor joists

 

 

 

 

 

 

 

 

The temperature over the winter inside the house (without the floor being insulated) was usually around  8 to 10°C, even on the frostiest morning with sub-floor natural air vents circulating cool air. After we finished the insulation we noted temperature of 14 to 16°C, which is partially the result of the onset of Spring, but also shows the impact of insulation. We also noted that on really cold mornings, the house feels warmer than outside and on sunny, warmer days it is slightly cooler inside, which is exactly what a well insulated house should be. Obviously when the house is fully finished we will know much more about its thermal capacities.

 

Stage 4: Sheeting with OSB

The floor was completely covered with a layer of 18mm (3/4″)  OSB. This was a fairly simple task. As we had maintained 400mm centres with our joists there was relatively little cutting and waste.

The important thing here is to make sure the first sheet of OSB is affixed perfectly square and plan the sheets so that they are laid like bricks. This gives additional strength and solidity to the flooring joists.

Beginning to look like a house inside.

What we noticed was that different manufacturers produce OSB to slightly different measurements. It’s worth checking the measurements of OSB sheets before beginning to lay them as they may not fit exactly if they’re from different manufacturers.

All boards were glued and nailed on to the joist.

The end result was really transformative…at last we had a proper, level floor to work on. Unfortunately soon after this the Covid19 pandemic interrupted our building work as all supply lines were closed.

The next stage for the floor will be to put in the underfloor heating system and screed.

Other Jobs:

a) Studded partition:

We began work on the internal walls in the house after we completed the floor. The timber used was 100mm x 44 (4″ x 2″). We used a simple Fukuda laser level to set out our walls. There were some challenges here as we were marrying round to square wood in some  places. The stud work was more complicated toward the ceiling where we had to accommodate the roundwood rafters and the slight slope of the roof. The laser level was very useful in this situation.

Partially finished internal studded partitions

Even with this job being only partially complete, the stud work really changes the house internally. It had been completely open-plan until this point. Now, not only is there a clear indication where the rooms will be but there is a greater sense of how circulation and light will work inside the house.

b) Fascia:

We took advantage of some of the early Spring weather to clad our fascia with some 18mm (3/4″) larch boards. The underlying fascia boards were horizontal and in a slightly zig-zag arrangement due to the shape of the roof. Affixing vertical fascia boards has ‘softened’ the appearance of the roof and given it extra protection.

Waney-edged larch fascia boards

Fixing the fascia boards

 

 

 

 

 

c) Plumbing

Our plumber, Pauric, installed some of the under-floor pipe work before we started to insulate. This included the kitchen and bathroom supplies and some of the pipes for the underfloor heating system.

d) Spring Planting

We planted around 30 native broad leaved trees and some shrubs on the large pile of top soil which was removed at the beginning of our build. Initially we considered using this soil in our garden but we’ve decided to plant trees as a shelter belt protecting us from south-westerly winds (our prevailing wind direction).

 

Building the Roof (111)

During late August and September, we finally managed to insulate and waterproof our roof. We worked with our roofing contractor, Ed Sullivan, to complete the job. He reckoned that it was probably one of the most awkward roofs he’s worked on! Due to the roof’s myriad planes and slopes, both insulating and waterproofing were time consuming, difficult tasks.

Our roofing system is a warm deck (i.e. the insulation is above the OSB deck) and this brings it inside the building’s insulation envelope. This should eliminate condensation as there should not be any cold surface on which condensation could form. It also eliminates the problem of thermal bridging which would occur on a cold deck, as the insulation would be between the joists (see video for comparison between warm and cold decks).

The roofing system we used was Resitrix Full Bond, an EPDM covering which was supplied by Laydex. This layer was bonded to the polyisocyanurate rigid foam insulation (PIR) which was mechanically fixed to the deck. PIR is normally used for living roof structures as  it provides much greater thermal efficiency than wool-based insulation, and its rigidity allows the EPDM layer to be bonded to it fully. We were unable to find a suitable ‘natural’ alternative to PIR and had to observe the specifications of the roofing system we opted for.

For our roof, we were required to achieve a U-value of 0.16 W/m²K – to do this we needed a minimum of 150mm insulation. We decided to install 160mm, as retro-fitting insulation to the roof would be almost impossible and the extra depth will help to achieve our overall A3 rating.

The roof insulation arrives!

Insulating the Roof:

Working with Ed Sullivan and his crew, we decided that we would insulate and cover the flatter, more gently sloping parts of the roof first. Then Maria and I would insulate the reciprocal roofs before Ed and his crew returned to complete the bonding of the EPDM covering.

We purchased enough insulation for two layers of 80mm (160mm of insulation) to cover the whole roof. As the insulation is rigid, we needed two layers of 80mm sheets as we were able to ‘bend’ them into the contours of the roof. This would not be possible with 160mm sheets. This did entail a lot of repetitive work as each layer was quite similar but we had to ensure that we bridged the joints in the insulation, where possible, to make the insulation effective. The insulation was affixed to the deck with metal fasteners and was then coated with a primer which was fully bonded to the EPDM cover.

 

Bonding the EPDM to the insulation

PIR insulation affixed to the deck

 

Once the flatter lean-to roof was insulated and covered we began to work on the reciprocal roof. This was towards the end of July and luckily the weather remained mainly dry. It took about two weeks to complete the insulation of the reciprocal roofs as there was a lot of cutting, fixing and offering-up. The day after we finished insulating the roof the summer rains began falling!

Lots and lots of cutting…

Completing the insulation jig-saw puzzle

 

When the insulation was completed, we had a delay due to weather and contractor commitments. However, by mid-September the weather had improved and we were able to complete the EPDM layer…at last.

 

Welding the EPDM layers

Detail of roof light upstand

 

After the roof was waterproofed we were really exhausted and decided to take a short break – our first holiday in several years. A welcome rest.

 

Other jobs:

a) Insulating the Void: The void between the top of our straw bale walls and the underside of the roof was insulated and covered with wood fibre board.

For the insulation we used both hemp lime and wood insulation. We purchased the hemp lime from Marcus at Hempire Ltd. We were aiming to fully insulate with hemp lime, but as it needs to be shuttered into place, it was really difficult and impractical to try to insulate right up to the underside of the roof with it. We decided to insulate the lower part of the void with hemp and complete the rest with wood insulation.

This was quite laborious, about 4 tonnes bucket-by-bucket, working under the roof overhang. Ideally this could be sprayed into the shutters if there is equipment or a contractor available to do it.  

 

A ton bag of hemp lime insulation

Hemp lime insulation in the void

 

b) Installing Wood Fibre Boards

When we finished adding hemp to the void we bought some external and internal Pavatex wood fibre boards (40mm) from Acara Concepts. This product is a very ecologically sound one, as it is made without any bonding chemicals or deleterious practises. It also performs very well as an insulating material, and it allows for breath-ability and acts as a thermal mass.

The external boards are slightly smaller but much more densely packed than the internal ones. The were affixed to the wooden framework we built on top of the bales at 400mm centres. This job involved a lot of cutting as the fibre boards had to be shaped around the roundwood rafters. It was also slow moving as it involved working from a  scaffolding deck.

 

Fixing wood fibre boards internally

Wood fibre boards in place

 

 

 

 

 

 

c) Windows and Doors

Openings in walls are very obvious places where water can ingress, and where heat can escape. For straw bale walls, dampness can lead to rotting straw which has to be replaced if it cannot be dried out, and it is a very difficult problem to correct. This is one of the most important details in our walls.

We began looking at windows and doors after we started building our walls. We visited several showrooms and searched for ideas. In order to satisfy building regulations, our windows need to achieve a U Value of  1.2, and our doors a U Value of 1.4 (or better) – these values could be achieved with double glazing.

Luckily my cousin Joe at Finlay Build is an agent for Camden Windows. As Finlay Build is a local firm Joe was able to spend a good bit of time discussing our requirements and providing us with excellent on-site advice. We decided on triple-glazed UPVC windows and doors which were installed in September, increasing from double to triple glaze added approximately 10% to the total cost, which we decided was worthwhile. This enabled us to achieved an improved U Values of 0.9 for the windows, and 1.2 for the door.

Finlay Build installing windows and board

As well as installing windows we had to decide on our window sills. Wooden sills, whilst appealing, are rarely installed locally. Concrete sills weren’t desirable and would have been too heavy to work into the straw, so this left aluminium sills. We worked out some of the detailing with Joe who installed the windows and then we contacted David Gorry at Gorry Stainless Steel who manufactured our sills.

We found it very useful to use locally based suppliers and manufacturers. One of the lessons we’ve learned on this build is if there is something that you require to be made bespoke, it is vital to be able to speak directly to the person who is making it, particularly when the tolerances are only a few millimetres. This relationship with the suppliers or manufacturers is more easily achieved when dealing with local, small-scale firms.

The windows and sills were installed in a day and a half. The roof was waterproof and we now began preparing for plastering!

d) Preparation for Plastering

The Lime arrives…but…

We thought that we’d have time for plastering before the weather got colder. However some early frosty weather in October meant that we had to cancel plans for plastering this year and complete it in late Spring 2020 (lime plaster needs to avoid temperature below 6ºC or it may crack before drying).

Currently we are working on installing our raised wooden floor and ideally would like to have the floor completed (including the underfloor heating system) before we begin plastering next year.

We do hope to complete our house in 2020. It is impossible, at this stage, to suggest an approximate date as delays and difficulties will always play a part in any building timescale.

We do think it’s realistic to be finished some time next year…

The swallows have kept us company during the summer with their beautiful singing and amazing flying. They nested inside in the roof and have had two clutches. These young chicks are learning to fly. They were untroubled with us working close by and regularly serenaded us singing from the scaffolding. We look forward to their return next summer.

 

This is my favourite photo from 2019. I think it really encapsulates the essence of being a self-builder.

Building Straw Bale Walls

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.

 

Wooden ring beams laid on top of the car-tyre foundation

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.

Jal testing the warmth of our insulation

Working on the ring beam

 

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). We’re really grateful to our friend Nerina, who spent part of her summer holidays preparing countless hazel sticks. Before pinning we checked the walls for straightness.

Pinning the first four courses beside a fixing post for a  windows.

Hazel stubs in place for the first course of bales. LECA added as protection against moisture.

 

 

 

 

 

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.

Wallplate panel suspended above the walls before compression.

Walls compressed using ratchet straps

Trimming the loose straw before compressing the walls

 

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.

 

Building the porch roof

Straw bale walls can be built with simple tools

 

 

 

 

 

 

 

 

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.

Using a tractor jack to apply 2.5 tonnes of pressure on the anchor to ensure it opens and is correctly installed

Installing earth anchors with a jack hammer (with a special applicator tool)

 

 

 

 

 

 

 

 

 

 

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.

Living roof in bloom

The wildflower roof on our workshop in Summer

 

 

 

 

Building the Roof (II)

Summer 2018 was a record-breaking season with the warmest and sunniest weather in over 40 years. Such exceptional weather was ideal for building a 200 sq m roof as we were working under the sky for the entire summer. The overhang (500 mm) adds a lot of extra area to the roof – the overhang being necessary to protect the walls from driving rain. We had already covered a lot of the roof with cladding and now needed to build the roof deck to support the insulation and the living roof.

Part 1: Roof deck

The roof deck involved fixing square timber to round timber, which added a level of complexity and difficulty to the task. The first layer of the deck consisted of 150 mm x 50 mm (6″x 2″) timber laid over, and in opposition to, the roundwood rafters at 400 mm centres, where possible (for greater span we used some 220 mm x 50 mm).

Building the deck on the L-shaped part of the roof (north and east side) was reasonably straightforward as the surfaces were quite even and only slightly sloping. However for the reciprocal roofs, it was a very difficult and time consuming task, as the roof surface is made up of many different planes which needed be connected and covered. The complexity of this task considerably lengthened the time budget for the roof. We once again engaged Osian to help us with the carpentry on the roof and to speed up the process. The roof deck took 16 weeks to complete.

The north-east corner of the roof

Larch cladding on the roof. This is also the internal finish on the ceiling.

 

Each reciprocal roof required over 100 separate and different pieces of OSB to cover it – like solving a big wooden jigsaw puzzle. Each piece had to be individually measured, cut, offered up, altered, glued and nailed.

 

Detail of completed OSB deck on the south side of the roof.

Detail of the 150 mm x 50 mm deck

 

Timber size and strength dictates the span it can be used for (see span tables). An alternative approach for our roof could have been to use larger timber e.g. 225 mm x 50 mm (9″ x 2″) to enable greater spans to be achieved, and would have used slightly less timber. However, the complexity of covering the reciprocal parts of the roof would remain. Another alternative would have been to make up grillages on the ground to cover this part of the roof and use a crane to lift them into place (a more expensive option).

 

Lots and lots of measuring, cutting, nailing, gluing, offering up…at least it was sunny 🙂

View of the east side of the house

 

 

Part 2: Fascia

The purpose of the fascia is to cover and protect the roof’s supporting timbers and insulation. Due to the size of our roof rafters and the deck we built, the height of the fascia in places is almost 1,000 mm. It also follows the contours of the roof, so that it is wavy in appearance.

For most of the roof, the fascia consists of 3 lengths of 225 mm x 20 mm fascia board which is biscuit-jointed, glued, and screwed together. It was then nailed on to the roof. The fascia was built in various sections, which were then fitted together onto the roof. This work took place at the beginning of September. The weather was still good for roofing and we were hoping to complete our roof covering before the weather changed.

 

Fascia following the roofs shape

Osian helping us out to build the fascia

 

Part 3: Vapour Barrier

The purpose of the vapour barrier is to prevent the build up of moisture in the roof’s structure when cold and warm air meet. We contacted Laydex who supply systems for green roofs. The Vapour Barrier we used was Alutrix 600, which is a high performance barrier. Applying this was straightforward, a primer was painted on and then the Alutrix was applied (there are excellent videos to help do this).

Applying primer

Vapour Barrier on roof lean-to

 

The completed roof…

 

Part 4: Roof Lights

During the building of the deck, Osian made four wooden dodecagons (12-sided shaped) which were affixed to the roof openings, once the rafters were cut back and levelled. We recycled some of the Larch we had kept from our framing bed for this.

 

One of the four larch dodecagons for the roof opening

Larch dodecagon in place

 

We purchased two roof lights online and they were relatively easy to install, although this depended on the weather. As it was now November, we had to wait for a calm, dry day to complete the installation.

 

Roof light installed

Roof kerb in place

 

Unfortunately, time and the weather were against completing the roof in 2018. It still needs to be insulated and covered with the waterproof barrier. We were a bit disappointed because ideally the roof should have been water-proof by the end of the year. It may well be that our time scales were over-ambitious as there is a high level of unforeseen complexity to the work, which, as amateurs, we found difficult to factor in.

Towards the end of 2018, we covered the entire roof with 1000-gauge polythene to protect the vapour barrier. We will be aiming to complete the roof in 2019, with perhaps a more realisable timescale.

Building the Roof (I)

Building in Winter was a real test of stamina and strength. Building in late Spring and early Summer has been, in contrast, joyful. The site has been transformed by the rush of new growth. Birds building nests or searching for food, the cows basking in the glorious May sunshine with bellies full of grass. New wildflowers appear on a weekly basis, adding additional colours to the landscape. The season has also seen a prolonged period of fine, sunny, warm weather, a welcome break from the epic Winter we’ve endured, and ideal weather for roofing.

Following on from our roof-raising, we have been working on completing the rest of the roof structure. It consists of several main layers: 1) principle and common rafters; 2) waney-edged cladding/sarking boards; 3) decking, made from 6″ x 2″s and OSB; 4) insulation; 5) waterproof layer; and, lastly; soil.

The first layer was completed towards the end of April. This involved ensuring that everything was fixed properly and soundly, as the roof structure needs to be able to support its load. It has to be fixed so that any shear forces are directed downwards, or contained. The majority of the fixings were M20 high-tensile threaded bar and M20/M15 galvanised coach screws (300mm).

The roof valley with the Slieve Bloom Mountains in the distance (May 2018)

Fixing the secondary rafters onto the hip rafter (April 2018)

 

When we completed this layer, we said goodbye to Osian, our carpenter and friend, who helped us to realise our dream.

He has been superb in the quality of his work and also in his dedication to completing the structure through one of the longest and coldest winters in recent memory.

 

 

We began our second layer, which was to cover the entire roof with waney-edged cladding/sarking boards, in late April. We started on the easier part – the lean-to – rather than the reciprocal parts. We purchased a cordless drill and a circular saw to speed up the process. Holes needed to be pre-bored for the nails, as the timber is quite green and is likely to shrink over time, possibly resulting in splitting. The circular saw was essential as there are several thousand cuts to be made during the construction of this layer!

Luckily, the weather has really picked up and we have rarely been interrupted by adverse conditions. Ideal conditions for roofing.

 

Cladding completed May 2018

Ideal weather for roofing May 2018

 

Cladding the reciprocal roofs was quite challenging, as all boards have to be placed in a certain way so that from the inside, it should be appealing to the eye. Each board has to be individually measured and cut, drilled and nailed. Each reciprocal roof needed about 700 boards. A further issue with cladding the reciprocal roofs is that, because we have round wood rafters, it is not always possible for each rafter to be on the same plane so that some corners of the boards will stick up. However, this may only be a problem on the top of the roof; from the inside it will look fine.

Reciprocal roof – view from inside

Our next phase will be to complete the additional layers of the roof and the circular openings. When this is completed, we will have a waterproof roof and we can begin building our straw-bale walls.

Our timeline to achieve all of this is quite challenging as, ideally, we would like to complete our walls by early to mid-September – they need to be plastered before the Autumnal frosts begin.

Raising the Roof

We are now one year into the build. We’ve reached a significant milestone in that we  have now finished the bulk of the work on the main roundwood structure. This has taken the best part of six months. We are delighted with the outcome and are very thankful to Osian, our carpenter, for his skills and attention to detail, and to David and Chris for their engineering advice and opinions. We have a beautiful, unique and incredibly strong structure for our house.

…to this! (Feb ’18)

From this (Feb ’17) ….

 

Our work on the large roundwood poles has involved a huge effort. We’ve been working outdoors throughout the winter and have a new-found respect for builders, farmers and other workers who have to brave the elements in their daily endeavours! Working in sub-zero temperatures is tough and can be physically draining. Stamina, as well as creativity is a vital quality for a self builder, you just have to keep at it until you are satisfied (see video of the frame being erected here)

 

Using chain-blocks to position each brace into place

Misty, damp, cold morning

 

 

 

 

 

 

 

 

Raising the roof involved placing the two reciprocal roofs we built last year onto their resting place along the wall plate (beams). Great skill was needed, not only in building the reciprocal roofs, but also in constructing the posts and beams to accommodate them accurately. Ill-fitting beams and rafters would  compromise the strength of the structure. Osian’s attention to detail, and his carpentry skills, meant that we were very confident that everything would be fine. Ultimately each roof fit snugly and correctly into place.  It’s important in this type of construction to avoid tension in the joints and connections, as too much tension would eventually cause problems.

 

Timber Engineering: Three beams meet at this junction. They are connected with M20 threaded bars and the trough is then filled with Rotafix TG6 Grout.

Detail of one of the corner posts with beams and braces.

 

 

 

 

We contacted O’Grady Crane Hire to assist us with this lift, as each roof weighs about 2 tonnes and mechanical lifting was the only way to do this safely. We also needed to lift into place our largest rafter (600 kgs) which rests on the north-east corner of the lean-to and supports the joining of the north and east roofs. Some of our friends and family attended our Crane Day, and it was great to share this exciting day with all of them. The topping-out ceremony was completed by fixing some sprigs of Douglas Fir and Larch to the roof and adding some Holly (to symbolise longevity), completed by sprinkling some whiskey and a song in Welsh by Osian!

 

…lands perfectly in place

Reciprocal Roof lift, and it…

 

The completed structure

 

Luckily, we were able to complete the work with the crane on that day because by the following week Storm Emma had caused the countryside to grind to a halt for several days.

Our next stage is to complete some of the remaining work on the frame, organise our scaffolding and begin work on adding the various layers to the roof. With straw bale building in a temperate climate, it’s vital to have a covering before you begin building the walls so as to protect the straw bales from absorbing excess moisture.

 

 

Assembling the Frame

Over the last month, we have begun to assemble the frame, which will support our roof. This process involves three distinct phases, 1) Initial working on roundwood, 2) Laying-up – checking the individual members (posts, braces, beams) fit together. This takes place on the ground, ideally on a level surface, and, 3) Erection of the frame – this usually involves erecting individual bents (post and beams joined together and braced) and joining them to each other with connecting beams or rafters. These processes take time and need  great skill and accuracy to achieve a strong structure. We have completed most of the first and second phases, although each phase will run until the end of the entire process.

Assembling the frame brings with it a great sense of achievement and, having spent the last four months working on the ground, it allows the structure to express its three-dimensional shape. It also allows us to begin to understand how our home will relate to its site and its environment.

 

Erecting sections of the frame using a tripod and scaffolding

We were able to erect parts of the frame with our tripod and winch system (see video). However, for the large reciprocal roofs and beams, we decided that hiring a crane would be the most efficient and cost effective method of erecting the frame. Mechanical handling of the wood means is unavoidable given its size and the demands of safety.

Another important factor was the time it would take to dismantle and re-assemble the reciprocal roofs at height.

 

A section or bent of the east frame being lifted into place

We contacted O’Gradys, a local crane hire firm to advise us on raising some of the structure. Our plans were interrupted by Hurricane Ophelia and Storm Brian (as cranes are not tolerant of wind speeds over 40-50km/hr) but eventually the weather settled and on a bright sunny morning our crane arrived! (see video)

Erecting the frame was an exciting experience for all involved. Working with a crane enables large heavy structures to be moved quickly and smoothly around the site. It is very satisfying to witness the bents we’ve been working on being lifted and slotted into place producing a really strong structure.

 

We envisage working with a crane on two subsequent days to fully complete the structure.

Charring the bottom of the post to improve its resistance to moisture

Pumping Rotafix Structural Adhesive (RSA), a strong resin which bonds the threaded bar to the wood.

The east and north sides of the frame

Drilling through the brace and the post to accommodate the M20 threaded bar which secures the structure

Building a Reciprocal Roof

A reciprocal roof is type of roof where the individual rafters mutually support each other. They originated in medieval Japan but probably date back further and aspects of reciprocity can be found in the roofs of many early human settlements. Reciprocal roofs are generally found on round, elliptical or polygonal buildings as the weight of the roof can be easily directed downwards via the post and beam henge on which it sits.

The first rafter is held in supported by the upright charley stick. This is removed when the last rafter is in place allowing the roof to settle into its pitch.

Osian scribing the beam onto the principle rafter to achieve a perfect fit.

 

 

 

 

 

 

 

 

 

 

We came across the idea and fell in love with this form of roof when we worked with Neil at Earthmovesdesign. When we were designing our house design we decided to incorporate a twin reciprocal roof over our open-plan kitchen and living room to divide the space and to draw light into it via the openings in the roof.

Checking the angle of the scallop. With 12 principle rafters the angle at which they cross each other is 30 degrees.

Using the tripod and winch to lower one of the principle rafters into place.

 

Our design did present a number of engineering problems. The first issue was how to build such a roof on a non-circular henge. We were advised by a specialist engineer, Chris Southgate, to add additional braces at each corner of the henge to deal with the weight of the roof.

Beautifully executed seat cuts.

Using a plum line to check that the opening maintains circularity. Each opening is 1 metre in diameter.

The other issue was how to set the roof pitch. Normally the rafters are laid on top of each other in the centre and the pitch is determined by their collective spiral height (= diameter of all rafters at their thinner end). Our spiral height would be between 2.5 and 3 metres which would produce a 45 degree pitch. However as our pitch was set for 30 degrees we had to scribe and scallop out the rafters to achieve this. Having a carpenter on board who was able to deal with the complexity of this design was essential.

View from the top of the roof.

View from the inside.

 

The task was very physically demanding as our rafters have a minimum diameter of 200mm and are up to 6m long. We used Tirfor winch and a 4 metre tripod which a local engineering firm, Coughlan Engineering, fabricated for us to lift the rafters into place. We built both roofs on the beams they will be affixed to on the ground, as assembling this at height would be very expensive. We aim to lift of each completed roof and lower it onto the henge when it is erected using a crane. (see construction video)

We were delighted with the finished result which is sculptural and beautiful.  We really look forward to gazing at the sky and the stars though our roof.

The next task is to lay-up the north and east post, beams and braces. We will then begin the process of erecting and fixing the frame and roof, which will take 4/5 weeks. We are hopeful of covering the structure before Winter so that we can complete some of the internal jobs before next Spring.

Working with Roundwood

In the last month we have been working alongside Osian Denman – a heritage carpenter – who has taken on the task of helping us to construct the roundwood frame and roof. This part of our build requires great expertise and skills to realise our design and to guarantee an excellent finish.

Enjoying the weather and the woodwork

We are learning lots of new skills and are using an array of both traditional and modern tools. We’re enjoying learning about how the structure will all fit together.

We have been taking advantage of the long evenings where possible to pack in as much work as we can.

An essential characteristic of working with roundwood is to see both its roundness and the square inside at the same time. Roundwood carpentry is different from other woodwork in that the wood being used is in its natural state. Despite this it still relies on keeping things square and plum as in ‘normal’ carpentry.

Using a plane to make sure the area around the tenon – the shoulder – is perfectly level.

Checking that the flats (the planed/level part of the beam where braces will be attached) are at right angles to each other. You can see ink lines on the wood which are used for measurements.

 

An interesting aspect of carpentry is the use of inches rather than millimetres for measurements. Inches allow for easy subdivision – half, quarter, eighth, etc – are all useful and easily recognisable measurements to visualise rather than, say, 20 mils.

Some of the beams receiving the finishing touch on the framing bed.

 

The Lay-Up

All parts of the timber frame are assembled beforehand on the framing bed, labelled and put to one side. These are then put together in the form of lay-ups (which is essentially a practice run where if there are any inaccuracies they can be corrected before the large beams are suspended in the air. Correcting at height will be more difficult and potentially dangerous, so time spent making adjustments on the ground is time well spent.

Lay-up of the beams which form the henge for our twin reciprocal roof over the living room/kitchen

 

 

Concrete compromise

At the outset of our build we aimed not to use any concrete in its construction due to its large embodied energy and polluting production. Reducing the embodied energy in what we use is very important and this had led us to choose materials in their raw state so as to reduce our carbon footprint . However, we’ve had to compromise on this as our engineering specification for supporting the posts means we needed to use some concrete in order to achieve compliance and to ensure our house will be structurally sound.

We used 4 tons of concrete. I used an online calculator to calculate the amount we had to mix. Luckily our local hardware – Tullamore Hardware – allows returns of used bags of cement as it can be difficult to store on site.

Reinforced concrete pads (17 altogether) with rebar. The rebar will ensure the posts can’t move from side to side, as they will be drilled to house the reinforcement.

 

We have enjoyed several visitors to our site in the last few months. It’s a great experience to share our ideas and dreams with friends and acquaintances.