The Centre for Alternative Technology AKA CAT

I’ve wanted to visit CAT for circa 8 years, but it had always being to far out the way to justify. However being just over an hour away from the build, I finally got a chance to visit and it was fantastic! Far better than I had expected and I would encourage anyone to visit if you get the opportunity.

Founded in 1974, CAT has been going for over 40years. Over this period of time they and learn a lot in the five main area’s (energy, building, gardens, wildlife and woodlands), and are passing there knowledge on to the wider public. More information can be found at the CAT website http://www.cat.org.uk

They have many great activities for kids, and information is fun and accessible to people of all ages. CAT has one of the best gift shops with a fantastic selection of book for the sustainable nerd! Only problem is choosing which ones to buy! But whilst you’re choosing your books you can marvel at a beautiful rammed earth wall.

There really is too much great stuff for me to list here. However some my highlights where; seeing the Ecococon modular prefabricated straw bale panels and how they work. I believe this system could help make straw bale building more accessible to the commercial sector. Producing great results, in a relatively short period of time. For more information please visit the Ecococon website http://www.ecococon.lt/english/.

After finishing my visit at CAT I decided to make the most of the Welsh countryside and do some wild camping and to visit a few places. I hadn't spent much time in Wales before, maybe a couple of weeks on holiday. But I have to say I am falling in love with the Welsh countryside a bit...

Plastering Part 1, Reveal Coat and Dubbing Out

We are gong to do 4 coats of plaster on our build the first being the reveal coat / slip coat / key coat.

The reveal coat is a very wet thin slip coat, who’s job is to give a good key for the following coats and reveal any gaps etc that need more straw.

The reveal coat is put on by hand (mainly the finger tips). It’s very important to get your fingers into the straw as deep as possible. Working the slip (clay and water mix) into the bales. If your just brushing the surfaces, your not building a good key, the deeper it is the better key it will be. Imagine fingers interlocking, if its just the tips you don’t have much grip and they can come apart easily if pulled. If your fingers interlock further and you try to pull apart your notice it’s harder.

Massaging the slip into the bales, any holes / gap that are discovered ‘reveal’ them and make them obvious, this will help in a moment. Work a lot of slip into these holes and crevasses. 

One thing I learn it it’s a lot quicker overall to work slower and better at the reveal coat, than it is to rush the reveal coat and have to patch it later on!

Once the reveal coat is on you can see the contours of the bales, and most likely the joins between bales. Where you have deep holes / gaps, these should be ’stuffed’ with dry straw (better insulation). See below picture, after reveal coat, dry straw stuffing, and 'stuffer' as mentioned in previous post.

After the reveal coat but before the matrix coat comes the dubbing out.

Dubbing is made from clay straw, it’s more like dirty straw than it is a plastering wet mix (see picture below). It’s hard to give quantities as its more a feel / knowing. If you’re unsure, its best to book onto a short clay-plastering course, or have an expert leading the build if self building. 

The Dubbing is then pressed into the shallow gaps between bales to get a uniform-ish surface. The dubbing need to be arranged into a birds nest with all the straws criss-crossing to help add strength. If you’ve ever had tangled hair your understand the principle. If your hair / straw is nice and smooth and all lines up. It’s easy to get a comb through and comes apart easily, if your hair / straw is all miss matched like a birds nest, its harder to comb and wants to stick together… Great for plastering, not as desirable in hair… With your bird nest dubbing mix, make sure your really poking it in with your fingertips and twisting it, this is going to make it into a beautiful interwoven strong straw clay plaster.

Once the dubbing out is done the whole surface should be uniform. Please see below before and after pictures. 

Notice the slip / key coat on the wood-fibre board at the bottom.

Don’t worry if you haven’t got your dubbing in deep enough or twisted enough… Your soon find out when the dubbing mix starts dropping of your wall!

This is a great example of when it’s faster overall to work slower and melodically through each stage.

Preparing for plastering

As with most things in life, the secret lies in good preparation!

As we where building our bale walls, we made sure there where as plumb as possible. Now it’s time for the final adjustment. This involves going around with a sprit level and the persuader (big hammer!), and hitting the bales into place from either side. It most important to get the outside looking stright at this is needed for good weather protection. Also on the inside the walls are going to be broken up with furniture etc, where as the outside you just have a line of the wall to focus on.  It takes longer than you might think, but means we will have lovely straight walls once the plaster is on. Therefore it’s going look more like a ‘normal’ house and less like a ‘hobbit’ house. I use the term ‘hobbit’ loosely, as it seems to be a popular Daily Mail term when it comes to straw bale…. Though I know many people are keen to point out that the hobbit house in the films where actually Victorian in design. 

See!

But if hobbit houses are actually Victorian, does this mean that the Daily mail prints things that aren’t true…. I will leave to your discretion, and get back to the topic in hand.

To make our bales less ‘hairy’, we gave them a hair cut. Because the surfaces are now flatter, it means it has less surface area and will take less plaster to make it into a nice smooth finish. It also gives the plaster a better key, as well as making sure the wall is flat and smooth. This was done using a garden strimmer and a hedge trimmer. At the corners, where we wanted to create nice curved reveals, we used the alligator saw to do this. The curve makes the plaster stronger, as in gypsum plaster you need metal corner stops and all sorts to give it strength.

Before and after pictures, and our hair cut equipment AKA ‘Joe Strimmer’, and ‘Dick Van Dyke’ (Strim Strim-in-ey, Strim Strim-in-ey, Strim Strim Strim-ee)

Where we had openings, it was important to tie the bales together, to iron out any gaps and give ourselves a good key for plaster. I will try to explain but please see diagram & pictures below. Start at the top bale, loop around the bale below (second bale), and then back up to the top bale, loop around, then down to the third bale, loop around, then up to the second, loop around, and continue down until all bales are tied together, tie off at the end. Repeat either side of window/door post.

Diagram in elevation, applogies for my drawing!

Where we have our box beams we need to give them a good key for the plaster, we do this by attaching (with nails) 20mm woodfiber board either side of the box beam (inside and outside). The wood fiber board also acts as an insulation, and helps reduce any thermal bridging through the box beams.

Notice the wooden plaster stops at the bottom of the wood-fiber board or on top of the window frame, with drip edge to help shead water.

Where we have any deep gaps/holes in between bales this need to be ‘stuffed’. This is for many reasons: to improve insulation values, to improve airtightness, to avoid weak patches at plastering stage, to give a uniform wall to plaster onto. Remember though, SNUG NOT TIGHT, or the wall may start to snake!

To stuff grab a handful of straw, and pull apart to make it 1.5 times the length it was (this way straw are intertwined and stronger), twist the straw and fold in half, twist again (like we did last summer….). Insert the skinny end in first; you can use a stuffier (stick, preferable with a notch in the end to grip the straw). The twisted straw will expand slightly and act like a wall plug holding the straw in place. 

At opening where the bales didn’t quite meet the window post in a nice rounded fashion, we needed to infill with sausages (bundles of straw tied together). These where then stitched to the bales, using bailing needles going through the whole bale. Or held into place using ash staples. Please see pictures below.

And now to prep our clay for the plastering mix! Dig dry clay from site, sift through 5mm mesh, use stones as hard standing, put clay into bathtub and soak over night, whish thoroughly until thick custard consistency, we can always add more water, but we can’t take it away! Please see pictures below. 

Dropping the roof!

The roof plate was held up with folding wedges, to hold it higher than the finished height of the wall. This was to allow room to manoeuvre the bales into position and to allow for compression. Once the walls where built and the roof was ready to be dropped, the wedges could be knocked out, allowing the roof plate to drop down steadily.

All 8 sets of wedges where knocked out simultaneously, to lower the roof in a controlled and even fashion. Our bales compressed circa 10-15mm per bale, which accounts to 60-90mm for the whole wall. 

The weight of the roof alone will do a lot of the compression of the walls, but we wanted to speed this process up and make sure the whole roof plate was level. This was done with a number of ratchet straps and our trusty water level. With the ratchets wrapped around our roof plate and our box beam, we where able to make adjustment to ensure the roof plate was level around the whole building. The roof plate was then fixed into position with screws into the window / door posts.

Half bales, notching, stakes and fiddly bits!

To get a good brick style course of bales your going to have to have make ‘half’ bales. This means splitting a bale into two parts. Not necessary equal, but to fit the space you need it to. Splitting is done with a giant needle and thread. It’s hard to describe, and to be honest the best way of explaining it would be in the diagram in the ‘Building with bales’ by Barbara Jones book. I will give a brief explanation for the purpose of this blog. 

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Measure the space that you want your bale to fit. Thread your baling needle (this is essentially a metal rod with two eyes at the point end, and a handle at the other) with two pieces of baling twine. If you do one going left to right, and the other right to left, it helps to distinguish the twine in a second. Measure your bale to the size of your gap using a tape measure. Insert your baling needle at the desired length, and at the same height as the existing string. If your happy that the needle has come out at the right height (i.e the same as the existing twine) and has gone straight through and not at an angle. Then you can remove the twine from the eyes and withdraw the needle. Make sure needle points are stuck into bales when not in use, to help prevent accidents! With your two pieces of twine, do two truckers hitches, one on each half. Repeat process for the lower twine. Once your happy you should be able to cut the existing twine and split the bale into two…… Hopefully your twine hasn’t become tangled during the process! A little tip is to cut the existing twine at the knots, this way you can re-use the twine for more half bales. 

Pictures from earlier straw works course, it seems I got so excited with the walls going up I forgot to take many photos!

At your window / door frames your going need to notch the bales around the posts. At doorframes or where there aren’t bales the other side this will me a full notch. Where you have a bale either side of the post do two half notches. Two half notches is better than one full notch and a square bale. As the corners slow down air movement by creating vortices, meaning a better air tightness and therefore fewer drafts. 

Use a template (bit of wood same size as your post) to help you notch to the right size. Measure to make sure your template in central to the bale. Using the Alligator saw (Ours was nicknamed Ali), or you can use a hand-saw (though slower, and in my opinion not as cleaner cut). Cut either side of the template to the required depth. Being carful not to cut the twine. Clean out notch and check depth of your notch. A terrible explanation I know, however fortunately Jeffery made a handy video!

http://jeffreythenaturalbuilder.com/straw-bale-building

From the third course onwards we staked through our bales. Two stakes per bale, to pin the whole wall together. On the third course ash stakes where 90cm long (penetrating three courses of bales), thereafter stakes where 70cm long (penetrating two courses). As I have said before hazel is the preferred choice for stakes, however we could coppice the ash from next to the site. 

If you have some bales that are tough to get into place. A little tip is to use a plastic sheet that you can slip in between the bales to reduce the friction. Once the bale is in place you can whip the sheet out….. Kinda like the old whipping the table cloth out from under the plate trick….. Remember though, SNUG NOT TIGHT!

The First Straw.....Bales

From this point in it is very important to have fire extinguishers onsite, (if there isn’t one in place already). Whilst straw when compressed or covered with lime/clay gives a very good fire protection (2hr+), lose straw is just tinder! Therefore lose straw should be swept up regularly. Lose straw is also very slippery, and you can lose tools in it, so a regular sweeping is most important.

Before we can do anything with the bales we first need to ‘dress’ them. We do this because bales aren’t actually 100% rectangular, they tend to bulge a bit at the ends. So by ‘dressing’ what we really mean is flattening off the ends of the bales. So when in course we can have a flat end against a flat end. Therefore improving our air tightness, and insulation values.

The way to ‘dress’ a bale goes something like this; Stand bale up on its end, move the excess straw under the string from the bulge to the low point (this is normally a bulge in the middle, to the edge), this is generally best done by hand. Once you have done this for both strings and both sides pull out any excess straw from any remaining high points, but not so much that the strings become lose! A little check at this point is the strings should now look flat against the bale. Now flip your bale on its other end and look how it is standing, if its leaning forward / backward or side to side, its not flat and will need further dressing…. Repeat this process until its flat & then repeat for the other end. Now you should have one dressed bale. Please note that dressing the bales reduces the length by circa 30mm, so make sure this is taken into account for your measurements etc.

The first bales go in quite easily onto the base plate ladder, held into position with the wooden stubs. When laying the bales, make sure you start in the corners, so they are nice and tight in the corner. Using your boards as a guide. With a hand either side of the bale (one on the outside of what will be the house, one on the inside) check the bale is sitting centrally on the base plate. Once you happy with the position move on to the next bale. This process reminds me of playing with Lego as a kid. I'm probably still a big kid TBH....

When putting the next bale in try to get it snug up against the first bale. This will mean better insulation / air tightness values, and save on the stuffing that comes about later. This is very important, SNUG NOT TIGHT! If it’s tight, it may cause the whole wall to snake, and takes a hell of a lot longer to sort out, than if you did it properly in the first place! Don’t be tempted to cram bales in where they’re tight. The only reward for being a strong macho person in straw bales is the fact you get to practice correcting your mistakes!

Pictures from earlier straw works course, it seems I got so excited with the walls going up I forgot to take many photos!

At the corners of the building, it’s important to tie are bales together to give them added strength. First tie the string to the inside bale, then loop under and over the first string, then loop under and over the second string and tie up. Remember snug not tight!

This is my crude plan showing the tying of corners.

Stuff vertically in between bales where the strings meet, as there is normally a slight gap here. There shouldn’t be gaps anywhere else, as the bales have been dressed! Remember snug not tight, or the whole wall may begin to snake! There is no need to stuff horizontally as this will compress. If there is any horizontal stuffing, the compression could become uneven!

Depending on the machine used, most bales have a cut and folded side. The cut side is better for plaster adhesion, so this is the side we have on the outside for the first course. As it could be a potential weak spot for plaster. But we need to alternate the cut and folded side per course, as the folded side compresses more. So if we did it all cut side out our walls would bow! 

Cob house visit

Hey, so this was a little cob studio we went to visit in the next valley. Was a really cute little place, which some great features.

The only thing I would say though is because it was a studio / yoga place, and therefore not heated full time, the thermal mass of the cob didn’t really come into play. So it felt quite cold in there. Cob as I’m sure you know is not an insulation, but it does act as a thermal store. Meaning if it is heated constantly, it will retain the warmth. It can therefore help regulate temperature fluctuations.

A couple in there 60’s with the help of a friendly builder, built this over a period of a year. I don’t think that’s too bad going, especially since I know they struggled with health problems during the build.

Preparing for the bales

We're all very excited, nearly at the straw bale stage! First though we need to prepare...

So we've braced our window/door posts, this is to stop them bowing when the straw walls are built.

Our bales will sit on a base plate this is a timber ladder fixed directly onto the box beam. Its job is to raise the straw bales above finished floor level. Meaning that if there is a leak/spill the straw won’t get damaged. It also can provide a fixing for skirting boards.

The base plate will also provide fixings for our stubs. The stubs hold the straw bales in place. Now normally in England there are 2 quite chunky hazel stubs per bale, and these stubs are held into position in the middle of the bale with noggins. 

   
  
 
  
    
  
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    This is a picture I have from an earlier Straw Works course.

This is a picture I have from an earlier Straw Works course.

However the noggins aren’t insulative, and therefore could potential act as a cold bridge, and will definitely reduce the amount on insulation that can go between the base plate.

Now in America they tend to hold the bales in place using nails that are only part driven in to the base plate. This is quicker, reduces the amount of noggins and therefore potential of cold bridging. But it introduced other problems, such a condensation on the nails, which can lead to decay (both of the nails and the straw).

So looking at these two methods we chose to use a hybrid method. Smaller ash (hazel is best to use, but we could coppice the ash from 5m from site!) stubs running along the ladder. Thus reducing noggin and the potential for thermal bridging, but not introducing the problems of metal within a straw wall.

In-between the base plate is ‘Leca’ insulation. This is a lightweight expanded clay insulation. It’s a good option because; its natural (it’s made by firing the clay, meaning no chemicals are added), it doesn’t degrade over time, and most importantly clay naturally wants to absorb moister. This means that if there is too much moisture within your walls, the ‘Leca’ is going to pull moisture down and out of the bales, where it can naturally leave the building due to the permeability of the materials used. As you can probably tell all the materials have been heavily though over, and where chosen as they compliment each other. Therefore in theory making a building that works in harmony and is greater than the sum of their parts….. Not unlike the interns ;)

Roofing

With our rafters in place we can move on to making the building weather tight.  First job is fit the out riggers that are going to act as our roof overhang, and give our straw bales a ‘good hat’. They also mean that the gutter is outside the building shell, meaning they if there where a leak in the gutter, it shouldn’t leak into the building.

The outrigger on the east & west side where then simply fixed to the rafters, and lined up to get them all level.

As part of our roof build up we are having a breather membrane above our rafters with a 50mm ventilation gap to move any water vapour out of the building. To install the breather membrane we first rolled out our ‘paper’ over the rafter at the lowest point before being stapled into place. Before we could lay the next stage of paper we nailed some temporary batters to give our selves something to work off (we are not all nimble mountain goats, like our pet roofer and all round good guy Joe Duirwyn! (part of Hartwyn.co.uk, along with Jeffery).

Side note, batterns go at 90° to the rafters, counter batters run in the same direction as the rafters. But are called counter batters because they are counter to the normal plane of batterns.

We next installed outriggers to the north & south side on our roof. These can then be used as a ladder to help us move up and down the roof.

I have to say it’s a shame we can’t incorporate a roof deck up here because the views are amazing!

For our main roofing deck we have chosen to use waney edge larch boards for the following reasons;

  • Larch is a very hardwearing board due to the high sap content and should need no further protection.
  • It has only been rough sawn, so therefore has minimal embodied energy compared to sheet materials.
  • It is half the price of the equivalent sheet material.
  • It gives us a beautiful soffit detail when looking at the soffit of the overhang and just generally looks better in my opinion.

We installed our waney edge board at a 45°, both for strength and to give us a nice soffit detail when viewed from below.

As is a very old tradition with roofing, we had a topping out ceremony. This involved a branch of a mighty oak tree, and a wee bit of bubbly. 

Extra Curricular Activities

The place we’re at is amazing, lots of nice places to take the dog for walks. There is just so much abundance to be found in nature. It’s been really nice getting back to being in harmony with the environment around us, both on and off the build.

This harmonising has included, foraging for wild mushrooms, jam & syrup making from the wild berries and plants around the property, and making spoons from the ash on property. 

What a wonderful experience!

Rafters Part 2

With our roof pate in position we could then install the ridge beam, this was held into place by supporting posts fixed to the roof plate.

With our roof plate in place and held in position we are able to add our wall plate (two 2x4 that sit in the middle of the roof plate). The rafter’s birds mouth then sits snugly around the wall plate, preventing the rafter from slumping over time.

Using a scaffold tower on the temporary floor and a ladder at the roof plate we where able to lift our pre-made & pre-cut rafter into position. They did need a bit of tweaking, however most of the work had already been done at a safer level.

First we installed the gabel end rafters on either side, and then we filled in-between working our way across.  This allowed the second half of the floor to go in simitaiously. 

Rafters had the middle layer of OSB double or tripled up where they met the plum cut and the birds mouth. And where secured into position using corner brackets and special twisty nails.

Please note when working at height it is rather dangerous, and extra precautions should be taken.

  • No-one should be working directly under you.
  • People on the ground should have hard hats on.
  • Harness should be worn (this was especially helpful on some Welsh windy days!).

This in not an exhaustive list, but more a guide. It is worth doing your own research and taking into account the dangers that are present on site, and can in fact be added.  For example if someone is suspended from a fall arrest harness for an extended period of time, the risk of a hart attach increasing significantly at the point they are rescued from the harness.

Floor Joists

Using our self-made I-beams we installed half of the floor and fixed some temporary flooring. This will allow us to use the scaff tower inside the building when we installed the rafters.

First we fixed our ‘mega-beam’ into position on the box beam, this was held into place with mega joists hangers. This ‘mega-beam’ spans the width of or building in the middle. 

Once our ‘mega-beam’ was in place we where able to mark up our box beam and ‘mega-beam’ at 400mm centres. We could then use conventional joist hangers to fix our I-beams at our predetermined depth.

Cover with a temporary board, and hey pretso a temporary floor! 

Raising the roof....plate

We constructed a similar ring beam / box beam (roof plate) to go above the bales & hold the rafters.

Roof plates perform many different functions; they evenly distribute the load of the roof, they provide a rigid structure to evenly compress the bales, they provide a more uniform structure to attach the roof to, they act as a lintel over windows & doors and you can wrap ratchet straps around them to aid in the compression process. 

We constructed the roof plate at ground level, for ease of access and to avoid working at height for as long as possible. Because this roof plate was going to have to be lifted up, we constructed it in four parts so it was lighter to lift.

The lift was done in 2 parts using a team of six people. The first part of the lift was about 4 foot. This meant that everyone could lift from the ground into props.

We then got on our floor beam to carry out the second part of the lift. Raising the roof plate sections to the marked height on our window posts (6 uncompressed bales high + a bit to allow us to get the final course of bales in). At this point temporary posts where screwed into the window posts to hold the roof plate in position. Temporary bracing was also added to stop racking and any unwanted movement that may have occurred.

After the 4 pieces where up, we where then able to glue and screw them into one box beam / roof plate. We then added the mezzanine beam, infilled the roof plate with sheep’s wool insulation, added the top layer of OSB to the box and glue & screw into position.

Temporary bracing was also needed to stop the whole building shifting, this was done with diagonal bracing, as well as bracing at the corners. This bracing at the corners will come in helpful later when we are going to be straw bales, as it will help keep the building square. 

LAMMAS

Lammas was an extremely educational trip and well worth the £5 suggested donation. For this £5 we where given a background to the project, guided around part of the communal space and taken around one plot / household land to see how they do things. The plot changes on a weekly basis, and tours are only held in the summer months. More information can be found at lammas.org.uk

It was great to see a group of people trying to think about building and indeed living in a more sustainable manor. Though some parts of the site looked a bit messy. I think a good tidy would have helped. As old cars & bits that might be useful for something in the future, unless organised, can look unsightly in some peoples opinion. I certainly know this is something that can put off planner and some of the general public, and they're the people we need to get on board if we are all to have a greener future!

LAMMAS are free to experiment with many different forms of building materials, and methods of construction. Which has lead them to learning a lot in the whole process. They have learnt a lot from their mistakes, I think we all can and should. However from my point of view these mistakes seamed partly unnecessary. If they had more of a technical understanding on detailing and construction methods, then they may have build to a higher quality the first time. But of course I would say that! But at the same time because they are less ridged and willing to experiment with everything. I’m sure they will come up with new ideas and methods that may not have been though of, that could be of great benefit. They are pioneers after all! And I wish them the best of luck in the future.

Rafters

We started preparing the rafters for our roof whilst the roof plate was at ground level. This is so we aren’t spending to long working at height which presents more dangers.

We offer up our first rafters either side of the ridge beam (our pitched roof varies on each side). This allows us to work out the plum cut (where the rafter meets the ridge beam) and the birds mouth cut (where the bottom of our rafter meets the roof plate, this is notched out around a wall plate). The birds mouth stabilises the rafters horizontal load, and prevents the roof from slumping over time. Imagine a house of cards, where they want to collapse in on them selves, this is not desirable in something you want to live in!

Once we have worked out the cuts of our rafters either side we can make a template, and cut all our rafters at ground level ready for them to go in.

Ring beam / Box beam

Our build is going to be a load bearing structure. This means that as well as providing insulation, our straw bales are also going to be structural and what will essentially be holding up the roof!

Load bearing has a reduced amount of carpentry work involved and the carpentry is simpler. This makes it more suitable to the self-builder. It’s also getting the straw to do two jobs, therefore your getting your moneys worth!

The ring beam is made out of durable timber (in our case larch), with 18mm OSB3 (exterior grade OSB, we used ‘Smartply’ as it has no added formaldehyde) top and bottom, glued and screwed together. Infilled with sheep’s wool insulation and with full depth noggins at 1200 centres, and at either side of a window/door post.

When building our ring beam we used a chop saw, this not only speed up the process, it also ensured our cuts where square and it all fitted together nicely.

Of course we had to have joints in our box beam between the timber and OSB3 top & bottom. Where this occurred we made sure our joints where staggered by 600mm. This helped to ensure we weren’t creating weak points within the box beam. We also made sure to stagger our joints at the corners for the same reason.

Where timbers are joined, the joint has a secondary timber spanning 600mm (300mm either side of the joint) on the inside of the box beam This can be seen above.

It’s generally agreed that the straw needs to be 300-450mm higher than the ground. This is due to splash back, moisture etc. On a conventional house the DPC would be at 150mm for the same reason. On our build we achieved this with a combination of the pillar foundations and the box beam. We were actually higher than necessary. This was to give us an easier space to work in when under the building etc.

For our window/door posts we chose to use two 100x50mm (4x2) screwed together. The reason being its cheaper and stronger than 100x100mm posts!

If you are trying to save costs it is possible to use a less durable timber on the inside face of the box beam. However this only really applied to the box beams higher up e.g. wall plate and roof plate. As you want the one sat on your foundations to be very durable!

There's no I in beam

But there is in I-beam!

We were quoted £7,000 for the I-beam for the floor joists pre made. This would have been most of the £10,000 budget! By making them our selves we spent £100 on cascamite wood glue, £200 on 2x2 timber, £500 on 12mm OSB 3, and maybe £20 on nails. That’s roughly £820 + labour to make all the rafters and the floor joists.  Quite a saving I think your agree!  Please note that these figures are rough and based on our 30m2 build. Therefore figures should be used as a guide only.

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We made a template to help us make our I-beams, work out our cut lengths required and got started. A break down of this would be as follows;

o   Insert 2x2 (50x50) timber into jig, spread glue on 2x2, ready for OSB3, lay OSB3 on top in jig.

o   Dove tail nails at 400mm centres (50mm nails). Make sure 2x2 joints & OSB3 joints are staggered.

o   Spread glue on OSB3 ready for top 2x2 timbers

o   Nail 2x2 timbers using bigger nails (75mm)

o   Complete I-beam

Our bales

We are proud to say that our bales have come from within 4 miles of the site, in fact we even saw the field they came from! Due to the client having good local ties, we where able to have a great back and forth with the farmer. This meant we could tell him to make the bales as tight (dense) as possible. This actually lead to the bailer breaking, but once the new part came we had the most dense bales we could have asked for. We know this from feeling them but also weighting them (we got some funny looks from the farmer…)

Dense bales are brilliant for building with and thermal insulation, so try and get them as tight as possible as you can, I believe our bales weigh 22kg (460mm wide, x 365 high x circa 950mm long). With the lowest density bale you could build with going down to 16kg. Please note this is dry weight, a wet bale is going to weigh more, but that’s no good! 

Our bales cost us £3.50 per bale delivered, which is about right for construction grade bales (denser, about a third more straw than ordinary bales). However we have an agreement with the farmer that if the bales are sub-par to our requirements, we can send them back & get our money back….. Not something I have come across before, but should be great for our project and encouraged in the future!

Foundation lessons & Bread slicing

So an important lesson we learnt with the foundations:

1.     Make sure you’re on site when matey boy turns up with his digger to level the site, otherwise it might not quite be level.

2.     Make sure your car tyres are all the same sizes.

If both or either of these things happen, there is a to make sure all the car tyre pillars are level….. packers! Make sure you use a hardy packer that is going to last, and use as few a packers as possible, to insure structural stability. We used a combination of marine ply, slates & sleepers for our packers depending on the size needed. We had a long debate about the ethics of using sleepers, but the fact is it was a material that we already had.

To use as few packers as possible, sometimes it is necessary to cut down a sleeper to the required depth. The way so do this is:

 ‘Bread slice’ the sleeper as shown below. Cuts about 10mm apart using the circular saw set to the depth you wish to subtract. Hammer the slices to get the majority of the wood out. Chisel the rest out to the required depth. Go over with a plain to smooth out any last bits.

Car Tyres Foundation

Car Tyre foundation, a great way to build strong sturdy pillars, reusing a waste material & without concrete.

The technique goes a bit like this;

Items needed: Lump hammer, crowbar, plank of wood (same width as tyre), level, pair of gloves.

Level ground where you’re going to place your 1st tyre, and lay a thin bed of pea gravel. Place the tyre on the gravel and ensure it is level using a spirit level (2 foot level seems to work well). Fill the tyre up to the 1st lip where the tyre would have joined the rim. With your fingers jab the gravel under the lip until all the gaps are filled. Fill the remainder of the tyre up until the second lip, and heap up a bit of excess gravel. With the help of a friend, twist / lift up the lip / edge of the tyre and jab as much pea gravel in as possible, working your way around. The more you can jab in now the easier it will be later. Now rest you wood on top of the tyre, so you have a solid platform on which to rest your crowbar. Wedge your crowbar under the edge of the tyre and stuff gravel until you can fit no more. Now hammer the gravel into the side of the tyre, topping up with gravel as required. Repeat this around the tyre, until when you try to squish down the rubber edge of the tyre with a finger there is no movement (I found it took going around about 2 or 3 times before it was solid). Once solid, check your levels of the tyre working your way around like a clock face. If you find low points, lift up the tyre rim with your crowbar and pack with more gravel using your lump hammer. Until the level is right. Never take gravel out of high points, only fill in low points. We estimated that whilst learning it took between 30mins to 1 hr per tyre.

Place the next tyre on top of your 1st centrally & repeat the steps (If not central, more work needs to me done at the levelling stage).

It is worth noting that each tyre will be approximately 30mm higher when filled, compared to an empty tyre. 

We use 10-20mm pea gravel in the tyres, as it can be compacted enough to give us the structural stability needed. But the gaps in-between the gravel are big enough for an excess water to drain down. But small enough that water can’t ‘wick’ up. By carefully thinking about materials we are using, we can avoid the necessity of a DCP (damp proof course, used in brick work to prevent water ‘wicking’ up), this means fewer polyurethane products are needed. Which is better for the global environment and helps the budget! Generally speaking you try to avoid any materials that would prevent the straw bales / natural materials from ‘breathing’. So if you’re in a situation where you want to use a DPC, it’s probably best to go back to the drawing board!

 

Please note when picking up tyres from your local establishment, lorry rims make rather good fire pits!

Please see below a very handy time lapse courtesy of Jeffery the natural builder