Curved timber windows

It has been a while since the last post, but we have been pretty busy and slowly getting things done on the house. We finished the first window months ago and are pretty happy with how it came out. Well it's almost finished, we still have to get the window latch and then coat it in something (most likely some natural oil finish).

So as you can see from the pictures the glass follows the outside curve, this has two advantages. The first is that the curved wall does not look odd the glass is only slightly offset in from the wall so we don't end up getting what would look like a chunk of wall missing from certain angles. The other advantage is that we end up with a really nice ledge on the inside to put things like ornaments and dust.

When we decided that we were going to make the windows and doors ourselves I decided that we needed a new tool to make the job easier. I was initially thinking of a biscuit cutter (good for edge joining) or a dowel joiner. This was when I came across the Festool Domino XL, it is basically a dowel joiner but on steroids. It is a reasonably expensive tool(the most expensive that I own now) but it is so well made and is so easy to use that it is worth every dollar. The XL is the larger of two models offered by Festool, and is able to make a domino hole 14mm x ~30mm x 70mm deep. Which is big enough to use in the construction of solid timber doors. Here are some photos of it in action:

This is cutting holes in the top and bottom of the window. The Domino XL makes it really easy to line up the holes which are also cut into the side pieces. In the picture below you can see one of the guides that is used to align the holes.

I also made a special jig so that I can align the tool correctly to cut the holes for the middle two columns that holds the center glass piece.It is setup to align the posts with the curved edge.

I used long pieces of all thread to clamp the window together while the glue dried. I bought some nice solid stainless steel hinges to hang the window panes from, I was a bit surprised at how bad most of the hinges I found were though.

The only issue we have had is the company we bought the glass from has gone out of business so now we have to find a new local supplier. We have also made frames for two doors which just need glazing and fitted two door frames.

Render Update

Well, we finally finished the first coat of render on the outside of the strawbale walls on new years eve and we are pretty happy with the result. Our technique in mixing the mud and applying changed as we went along.

We actually ended up taking longer in putting the mud on the walls by about halfway around and taking time in making sure the render penetrated the bales for good adhesion. This was done by pushing the mud into the bale wall with thumbs and fingers, I would estimate that we got around 50mm penetration and you can tell the difference between the earlier walls and the later walls. The other advantage of working the render into the straw was that the render mix changes as it is worked, it is actually hard to explain but it is certainly noticeable when doing.

In mixing the mud we ended adding the sand and then clay and then water to a wetish mix (not too wet) and then mixing the sand, clay and water with a shovel. Once mixed only then add the straw which dries the mixture slightly. We also often left a wheel borrow load of mixed sand, clay and water without straw overnight.

The next step is to build and install the window and door frames. For this we are using 140x35 hardwood planks for the window frame and 140x45 for the door jam sourced from a local sawmill. We are using 4 edge joined to make a single ~560mm plank. The planks are joined with floating tenons at about 200mm spacing and glue, the boards are clamped using homemade threaded rod clamps. I did initially use some Irwin Quick Grip clamps but while being quick were not able to apply the required pressure, while the cheap homemade threaded rod clamps apply more than enough.

Because the walls are curved the upper and lower planks have to be curved, to do this we make the plank as above. Once the glue is dried (left overnight) the outer curve is marked through the center of the board and a jigsaw is used to cut it, the two pieces are then swapped and joined. Once the join is dried the inner curve is then marked and cut. You just have to make sure that the initial plank width is the desired width plus the difference between the inner and outer curve. You can see one of the curved pieces in the picture below.

I have currently joined enough timber to make two door jams and one window and hopefully in the next week I will put together the first window frame.

As we put the window frames and door jams we will also be able to apply the next coat (may end up being final if good enough finish) of outer render which should come upto the frames with a ~10mm overhang. We are hoping this coat is easier to apply, at least there wwill nt need to be any working the mud into the bales.

Clay, Sand, Straw and Water...

These are the basic ingredients to the base coat of render that we are using to protect the straw bales.

All the straw bale walls are all up (with only a few minor parts to fix) and we are rendering. We have started with the outside first to help protect the bales from the elements. The roof overhang does do a pretty good job of keeping the water off the walls but no amount of overhang will stop the almost horizontal rain we sometimes get throughout the year.

First coat of render on the bathroom wall, the top part is cob which fills the gap between the top of the wall and ceiling

The amount of work to render the house:

• we have about 50m of straw wall that is on average 2.4m high
• which is 120m² (subtract 20m² for windows and doors, leaves us with 100m²)
• 100m² x 2 sides (inside and out) is 200m² of 50mm render
• or 10m³ of mud to mix and apply

This is not an insignificant amount. We are mixing and applying the render manually.

We have decided to go with a natural mud render rather than a cement render for a variety of reasons. The recipe we have chosen at least for the base coat is as above. So far we have been mixing up the render in a wheel barrow using a shovel, the wheel barrow makes it easy to get the render to the part of the wall we are working on. It is a lot of work mixing the render in the barrow though. The steps to mixing are:

1. Put four shovels of sand in the barrow
2. Add four shovels of clay (generally we get more clay in each shovel over the sand, I would estimate the ratio to be 3 part clay to 2 parts sand)
3. Mix the dry clay and sand so they are basically combined, chopping up the clumps of clay
4. Add a few hand fulls of straw (so far we have been using up the stuff that has fluffed out of the bails in the wall whilst putting them up)
5. Mix straw in
6. Add water and mix in
7. Keep mixing until the render changes colour slightly and is very sticky.

Preparing a load of mud render

The recipe does not have to be overly precise and during the render process we have tweaked it slightly, for instance we have lowered the sand content and added the straw. We did get hail on one wall which has made us realise we will need to add lime or some other weather proofing agent to the final coat. I have been using a short spade to "chop" the straw into the mud mix. The water content also plays a part in the ease of which the mixing is, a wetter mix for instance is much easier to mix and apply but it may also make it more susceptible to cracking during drying.

Wetting down the bales about to be rendered

Applying the render is pretty simple. First the bales that are going to be rendered are wet down slightly, this stops the straw from drying out the render too quickly and is supposed to help with adhesion. We used a garden spray pack and also wet the surrounding timer that the render was going to attach to. We then make balls about 15-20cm in diameter and squish them onto the straw. The mud is then worked in so that the mud penetrates the bail. We have noticed that the fluffy side of the bail it the hardest to work in but we get a much better mud penetration. We are leaving the first coat rough to hopefully help the second coat stick better

Working in the render

We have also been using the mud render mix to make cobs to fill in the gap between the top of the wall and the roof. We have been really happy with the result. The mud mix does have to be on the dryer side otherwise we have found that we get some slump which leaves a gap at the top (it is pretty easy to fix with a little bit of extra mud however). We also added a strip of wood (1/3 of a bit of 4x2) to the ceiling to key the mud to. A key was also added to above the doors and windows.

It is really exciting now seeing how the walls are going to look. We have been really happy with the colour and how it is all coming out. The rendered curved walls look fantastic. Before the final render coat is applied we need to finish off around the window and doors jams (we are thinking of using several planks of cypress glued and biscuit joined to fill the 550mm width).

Left side un-rendered straw wall, the right wall has the first coat applied

The rendering process is pretty slow and involves a lot of manual labour (mixing is a complete upper body workout) and there is soooo much to do, so a word of warning to any friends and family coming to visit over the next few months, wear old clothes ;)

And they huffed and they puffed...

We had the strawbales for our house delivered in mid December last year and there was a bit of huffing and puffing getting them unloaded from the truck and stored under cover. Would you believe that we had rain while we were unloading the bales from the truck, thankfully it was only light. On the morning there were 5 of us to unload the ~250 bales so it didn't take too long.

Now we have the bales it was time to start putting them up. There are a few ways to make a strawbale house each with advantages and disadvantages. We chose the framed house with infill walls type of building. One reason was because our outer straw walls are reasonably complex and we didn't want the stress of having to get all the walls up and roof on before rain (this usually involves getting help in to get it done quickly). The downside with infill walls is that you end up with a gap at the top of the wall and roof that needs to be filled (but i'll talk more about this once we work out what we are going to do with our gap).

The strawbale wall is basically made up of a bottom plate, strawbales and then top plate with straps from the top to bottom plate to compress the walls. All our outer straw walls are curved, which adds some extra complexity.

The bottom plate does two things, it raises the bales off the floor to give you a moisture gap and it gives you a solid base to compress the bales against. For the bottom plate we ended up using 90mm x 45mm pine framing timber made up into frames that are 450mm width (the width of the strawbale) and trapizoidal in shape with the long edge 1000mm long (just over the length of  bale). These were dynabolted to the concrete with 4 bolts each so that the frame followed just inside the edge of the concrete slab. Short pieces of strapping were then slid under the frame through notches made before bolting the frame down and the space in the frame filled with 25mm blue metal (bluestone gravel) so that the bales don't sink into the frame.

The door frames were dynabolted to the floor, nailed to the bottom plate and attached to the ceiling with a block that was glued and screwed. The door frames were made up of 2 bits of 90mm x 45mm with noggings (like a ladder) and then a piece of 12mm structural ply glued and nailed to brace it and to give the strawbales a solid end to press against.

The window frames are made like the bottom plates and the door frames, they are designed to sit inside the bales. We will probably attach the windows to the ceiling to add stability to the walls. The windows are curved with the walls. We also designed to windows to fit within a bale width. Later on the door and window frames will be lined (most likely with floor boards).

We have half a wall to finish as of writing this post then we start on filling the gap between the top of the straw wall and the ceiling.

Lining the ceiling

Its a few weeks now (time really does get away from you sometimes) since we finished lining the ceiling.  We decided to use ordinary pine lining boards (V-groove), as a reasonably eco-friendly material (Radiata Pine is plantation grown - and although there is some potential that the plantation was planted on what was previously old growth forest, most of the pine plantations I know are on what was previously degraded farmland, and it is renewable).

nailing the first board!

The lining boards were hand nailed to the bottom of the purlins, which allowed us enough space to put in some serious insulation (R5 batts), which  added to the wool blanket on the sisalation that was put in when the roof went on gives us (we think) a total of R7 insulation in the ceiling.  Not too bad, and will complement the high insulation qualities of the strawbale walls.

putting in the insulation batts as the boards go up.

It took us about one day to line each 'wedge' of the ceiling, working between our main beams that form the post and beam frame.  So sadly now much of that heavy timber is not visible, but a good insulated roof is more important that showing off big timber.  We got quicker in our methods, pre-cutting the angles on the boards (since each wedge is the exactly the same there were only two angles to cut, the centre angle and the outer facia angle).  The full ceiling is lined completely, including what will be eaves.

So about ten days in weekends, and its another big job done.  Its nice to start seeing 'finished' parts come together instead of digging away at trenches that will be filled in with concrete!

All done!

Now onto the most exciting part of building a strawbale house, the walls!

The great concrete pour

It was a very foggy and gloomy day (one of the few we have had all winter) that we finally poured the concrete slab for the house.  That was about a month ago now, time flies when you are having fun.

We had a crew of about five volunteers, and a paid concreter who was happy to work with us (harder to find than you would think!), and two guys who operated the concrete pump.  We had to hire a concrete pump (a line pump) as the slab site was just too far from the driveway to be able to shoot the concrete straight out of the truck, and while we contemplated it for a (very short) moment, we decided against wheelbarrowing 40 cubic meters of concrete!

the pump truck with concrete truck

pumping the concrete, first into the trenches, and then over the whole slab

it was a fairly relaxed affair!!

It ended up being a fairly relaxed day, nothing really went wrong, and the pace was calm.  The man who held the hose for the concrete pump certainly earnt his wages, he worked like a machine!  So now months of work is covered up, all those trenches and curved reinforcement....  at least we have photos to show for it all!

the boys 'hard' at work

screeding the concrete

our curvy slab, just finished.

its dry!

So now we have a lovely flat area, that will be our thermal mass in our house.  We designed the house to recieve winter sun (but not the summer sun) and its lovely to see how far into the house the sun reaches at its lowest point (to the halfway mark in the house).  This will be integral in our passive solar climate control, gently warming the house with winter sunlight. 

Now to save up for the next stage which is most likely going to be lining and insulating the ceiling. 

And your not going to see any of it!!!

Was the mantra that was repeated over and over by my labouring wife over several months of preparing the house site for the pouring of the slab. This is the last expensive thing we need to do before getting on with the relatively cheap mudbrick making. I really can't blame her it has been a bit of a slog but we can now see the end of this stage of the house build.

To ready the site for pouring the concrete slab it is simply a matter of digging the trenches, adding a layer of sand (road base?), boxing up, covering it in plastic and setting out the steel reinforcing. We have done these steps but of course we added an extra level of difficulty.

Firstly we put up the frame and roof before the slab, which is not normally the way it is done. The main reason we did it this way was to get the house build started quickly so that we would be able to extend our planning permit (ie. frame stage finished). It has had an advantage in that we don't have to worry so much about the weather when preparing for and when we eventually pour the concrete. But we have had to dig the trenches by hand (or pick, shovel and wheelbarrow), which added up to moving about 16m³ of dirt. This was done over a period of a month on the weekends. Because the outer edge is curved half the trenches ended up being curved. The total length of trench was about 160lm. The dirt we moved was dumped next to the house and will be used for the mudbricks and render later on.

The next step was covering the bits of land with about 8m³ of sand. This was done by wheelbarrow and shovel. We compressed the sand by hitting it with a bit of 4x2. The sand needs to be slightly wet to do this well, too dry and it won't hold it's shape, but too wet and it is too sticky.

The boxing up was also a bit different and I think a bit easier (and cheaper) than if we had a square slab. The entire outer edge of the slab is curved, so I decided to use 3ply because it is easy to bend instead of 6x2's that you would normally use. I used scraps of 4x2 and 3x2's upto about 500mm long to stake the 3ply. The bits of wood were staked to the ground with 250mm galvanized fencing nails (these will be re-used for fencing once the slab is done) and then the 3ply nailed to it. The slab is 150mm above the ground level so the 3ply was cut into 200mm strips. Because the 3ply is curved this adds strength to it and hopefully it will hold up on the day of the pour.

Laying the plastic we thought would be a bit of a nightmare seeing as how half the trenches are curved and at odd angles to each other and the added difficulty of working around posts. But it wasn't all that difficult and only took a day. We used about 400m² of plastic to cover an area of 200m², I guess it was in the up's and down's of the trench walls, the overlap of the plastic and a little extra in the trenches so when the concrete is poured it doesn't pull the edges in too much.

The last bit of the preparation really highlights one of the reasons most people don't make a round house. Trench mesh is straight and is really, really hard to curve. So we had about 80lm of straight trench which was easy to lay standard 3xL11TM in. The outer edge and inner trench which made up 80lm of curved trench needed to have 3xN12 bar, which is 12mm notched steel bar, which needed to be curved. This ended up being not too hard to do, but did add a lot of extra time over installing standard trench mesh. There also ended up being a lot of extra cutting of the slab mesh (SL82) because it has to follow the edge of the slab. We also had to navigate the 10 central posts and cut more than half the 18 6000mm x 2400mm sheets used to fit around the posts. But myself and the wife got the job done in about 4days with a bit of help from the kids.

So now we are ready bury the whole lot in about 40m³ of concrete, we just need to organise the concrete, concrete pump and helpers for the day.