«The Cob Builders Handbook You Can Hand-Sculpt Your Own Home Table Of Contents: Acknowledgements and Warning INTRODUCTION What is cob? Why build ...»
Light-clay straw One way to prevent straw from burning so well is to coat it in a clay slip. Put water, and the purest clay you have, into a big bucket or drum. Stir until the clay is suspended in the water - about the consistency of thin cream. Sand and stones will fall to the bottom. Push the goo through a screen to clean the mix and break down all the clay. This is called clay slip. Throw loose straw on a tarp and pour the clay slip on it. Use about the same proportions as salad dressing to salad. Two people can grab the corners of the tarp and toss the straw 'salad' and clay slip 'dressing' until each piece of straw is coated with the slip. Let it dry a little, then put it loosely into the insulation space. Use at least ten inches of this kind of insulation. It will provide you with about 2 or 3 R of insulation per inch. Remember to leave a gap (at least 2 inches, more is better) over the straw-clay for ventilation.
Wool Combed wool has about the same 'R-value' as fiberglass. I imagine, in the nottoo-distant-future, it will be easy to buy wool insulation commercially, as people become less willing to live with toxic fiberglass and chemically treated cellulose.
Wool insulation batts are made in New Zealand but the U.S. requires toxic treatments before importation. Is it fumigated? If so, are you willing to live with it? Consider doing it yourself. Sheep farms often have dirty or scrap wool they're happy to get rid of. Cleaning the wool is important, to discourage critters. You'll need to brush (or card) the wool to fluff it up and make the airspaces that give it its ability to insulate.
Cleaning and brushing the amount of wool you'll need is a big job. You can put the wool in loose in your insulation space, or you may choose to first stuff the wool into agricultural/burlap bags or tubes.
Cork Cork is bark that can be harvested without killing the cork trees. Cork comes in granular form or pressed into sheets. Untreated cork seems to be a very non-toxic insulation material. It may be hard to find and will be expensive.
Pumice Pumice is a volcanic rock that is so full of air pockets it floats on water. I have never tried it but if you live near a pumice deposit, you might want to try using it to insulate your roof.
Wood Sawdust or wood-chips have been used for centuries for insulation. You can imagine some of the problems: fire, rot, insects, etc. Recently, some low-toxic treatments for wood chip have been developed in Europe to minimize these problems and may soon become available elsewhere.
Seaweed When I was in Australia I heard that seaweeds that have flotation bubbles were used in a lot of the old homes for ceiling insulation.
Cotton Cotton is a possible insulation material, although the production of cotton is very hard on the environment. Let us know if you figure out a good way to use recycled clothes.
Ground up newspapers (chemically treated, blown in cellulose) In Southern Oregon, most of the roofs in new subdivisions are insulated with shredded newspapers that have been treated with something (probably toxic) to reduce their flammability. This is blown into the insulation space or attic with a big machine. If you decide to use untreated shredded newspaper, be aware that it is a great fire starter.
Soy milk containers Some friends in New Mexico insulated the roof of their earth home with soy milk containers. They cut them in half, washed them, and stapled them together. These were set into the insulation space face down, towards the heated house. They report that this works as well as the fiberglass insulation (about a foot thick) in an identical house next door. You could try using whole cartons.
Cardboard My grandmother's house was built in the 1920s. It wasn't super wellinsulated, but it was reasonably warm in the winter with one woodstove. In 1995, the house was smashed by a big tree in a wind storm. Luckily my grandma was OK! I watched as the bulldozers tore down what was left of the house and I noticed that a lot of the house was made out of layers and layers of cardboard glued together. I didn't see any mouse tunnels in it, even after 60 or 70 years!! Some of the glues used in cardboard might be toxic.
Fiber glass Fiber glass insulation is made out of yucky, itchy, sharp fibers that may be stuck in your precious lungs forever! They make your skin itch and they get stuck in your eyes and nose. Some brilliant company now sells fiber glass insulation in 'poly bags' which contain the fibers, and help protect people using the stuff.
Silver bubble wrap This is what it says it is. It's expensive and would require more than one layer to really insulate a roof enough. The reason I mention it here is that it is very flexible, so it works well for an organic shaped roof. It takes up very little space for the amount of insulating value it gives. It is also reflective. It could add an insulating and reflective layer to augment some other kind of insulation. It can be stapled onto the bottom of the sheathing and/ or laid just above the ceiling. Pieces of this stuff lining the backs of window shades or against skylights really helps keep the heat in on cold nights. Bubble wrap is often used to wrap water pipes to keep them from freezing.
Rigid foam This is a commercially available product made out of urethane foam. It's sheets of styrofoam-like stuff. It is extremely toxic when burning and probably not that good for you to live near even when it's not burning. This stuff is expensive. One of the good things about rigid foam insulation is that you get a lot of insulation value in a small amount of space.
Anything that has trapped air spaces in it Use your imagination! What about old film canisters with their lids on? If you discover a natural or nontoxic recycled material that can be used for practical insulation, your name will go down in natural building history! Please let me know!
A reflective layer reduces the amount of insulation you'll need
Shiny stuff reflects some of the heat back. Put the shiny side towards the heat that you want to reflect. This means shiny-side down toward your room to keep heat in where it's cold, shiny-side up to reflect the sun's heat away in hot climates, or both. Put the reflective layer between the heat source and the insulation. The heat will be reflected regardless of what is on top of the reflective layer. Silver bubble wrap and silver paper, both available at supply places, can be used for a reflective layer. One free source of reflective material is soy and rice milk containers, opened, flattened, washed, and stapled in place. In some countries, milk that doesn't need to be refrigerated comes in those kind of containers. This is a useful thing to do with a hardto-recycle product. Another way to reflect the summer sun is to paint the roof surface with a reflective white paint.
CeilingSee the illustrations on pages 123 and 132. Purposes of a ceiling
The ceiling's job is to look good and to cover the (usually) ugly insulation or reflective layer. Ceilings can also be used to hold the insulation up. In a house with an attic, the ceiling serves to separate the attic from the rooms below. If you are using something toxic for the insulation, it is important to choose a ceiling that will separate you from the toxin as much as possible.
149Getting the insulation and ceiling up there
If you are building the kind of roof where the insulation sits in the roof structure, put the insulation in place and the ceiling up (or whatever will support the insulation) before you do the sheathing. Ideally, you will have enough time before wet weather to get this done. This way you can stand on the rafters and work with gravity, setting the insulation down into place on the ceiling, instead of standing on a ladder and trying to get the insulation to stay up. Doing things in this order will postpone the day your home is protected from rain, but will save you time, effort, and a sore neck. Use your judgement and weather forecasting skills.
If you put the roof sheathing and surfacing up first, you will get a lot of neck and arm exercise when you put the insulation in from underneath. Getting everything to stay up there requires ingenuity and patience. If you are using sheets of something for the ceiling, you can put them up one at a time, starting at the lowest side of the roof's slope. Then stuff the insulation into the space that you've created. You can use strips of wood, lath, sticks, burlap, strands of wire or chicken wire to hold the insulation up.
These can be sturdy enough to provide permanent support for the insulation, or just strong enough to hold the insulation up there until you get your supporting ceiling attached.
If the ceiling is holding up the insulation, it will have to be a strong enough material to do so, and it will have to be attached securely to the bottoms of the rafters. Use your common sense.
Ceilings can be attached to the bottom of the rafters with nails or screws. Working over your head like this is challenging for your body. Do any part of the job you can on the ground, (like painting, drilling holes, and starting the screws), before putting the ceiling up - this will save your neck, arm muscles, and eyes.
You may want to cover your insulation-support with something pretty, like fabric, reeds, woven sticks, and/or plaster. If you want to plaster the ceiling, make sure that whatever you use to hold up the insulation will also support the plaster. Ceilings do get dirty, so you may want to repaint or refabric occasionally.
If you are using poles or pieces of wood (like a small beam system) to hold the ceiling up, you could leave them exposed so you can look at them, and then put the ceiling on top of them. You will need to build your rafter system to create the insulation space and to hold up the roof. This is a very sturdy way to build and it's easier to attach the ceiling down to the tops of the ceiling supports than up to the bottoms of them. If you have an abundant ecological wood source, you might want to build your roof system this way.
You can leave a ledge in the cob to help you hold the ceiling up there while you attach it to the rafters. Put the ceiling up and cob your walls up to it.
Ceiling materials that are used mostly for looks, to cover whatever is holding up the insulation
Use your imagination! Here are some ideas:
Plaster Plaster covers the insulation and helps isolate the insulation 'dust' from the room.
If you plaster the ceiling, the plaster will need something rough enough to stick to and strong enough to support it. There are various things to attach to the rafters to hold the plaster up there, for example: wire lath, sticks nailed on top of the rafters, woven sticks, thin wood sheathing with holes drilled in it, and pegboard. (See the picture on page 101.) These can be nailed, tied, or stapled to the rafters.
Homemade sheetrock This is a concept that is still in the experimental stages. The idea is basically plaster with a fabric core. You could play around with cloth (old sheets work great) dipped in clay slip or wet gypsum plaster. Depending on what you've used for insulation, this lightweight 'sheet-rock' may be able to stick right to it. Adding a little glue to the plaster or slip will help. Or you could attach it with wood strips nailed through the fabric into the rafters. You can also put the fabric up first and paint it with the clay slip or homemade paint. Experiment until you find something that you like that works.
Another homemade sheet-rock idea is to use layers of magazine pages or newspaper, instead of using fabric. These could be dipped in clay slip and stuck onto each other.
I've only seen this in an experiment, but I think it might be worth trying for a ceiling or an interior wall.
Thin plywood or veneers These could be left exposed, plastered, painted, or covered with wallpaper. You could play around with making your own homemade wallpaper or papier mache.
Fabric You could use fabric stapled up to the rafters to cover the insulation. This provides a very lightweight, beautiful, organic shaped ceiling. It may need to be replaced, washed, or painted over in a few years when it gets grubby.
You might want to keep an eye on the roof system to make sure it's functioning properly. (No leaks, is there enough insulation, are those mice having fun?) So it may be a good idea to use a ceiling that is easy to take down and look under, at least temporarily.
Woven mats or reeds You can buy long rolls of reeds or bamboo woven with metal wire. These are ordinarily used as window shades or fences. These make a very pretty, naturallooking ceiling and can be attached with strips of wood or staples.
Bamboo, twigs, or reeds These can be nailed or tied to the rafters, or woven together first and then attached to the rafters. These can be plastered over.
The pieces of wood for a ceiling only need to span from one rafter to another, so they can be short. This is a wonderful way to use up the little scrap pieces of wood from mills or construction sites. You can run a long strip of wood where all the little pieces of wood meet if you want to cover the seam.
PLASTER (RENDER) Purposes of Plaster
1) On the exterior walls, plaster protects the cob from erosion by wind, rain, sun, and snow. Exterior plastering on cob is only necessary if you live where there is winddriven rain, or snow buildup beside the house.
2) Plaster gives the walls a smooth finish.
3) Plastering reduces dust.
4) Plastering is a great excuse to have a party! I wonder if that's where the saying "getting plastered" comes from? When you plaster, you caress every inch of your lovely new home or re-caress every inch of your lovely old home.
153 The line between cob, plaster, alis, paint, and washes is nonexistent. One graduates into the other as the amounts of water and particle sizes vary. When you see the word alis, it refers to a fine plaster or a thick paint. With natural buildings it is vital to use a plaster that breathes and moves. These plasters will absorb and release moisture, allowing the walls to dry out quickly. Vapor must be allowed to escape from interior spaces and the building materials themselves, where they could cause damage.