COB HOUSES

COB HOUSES

Ian
You have mentioned straw bale housing a few times. Is this the same as cob houses? Thanks G.S. Carn.

Reply
Straw bale houses and “cob built” houses are similar but there are certain differences. The straw bales and stacked around a wooden framework to create the walls of the house. The structure is erected very quickly and the finished walls are pressed together with wire and then a lime plaster is put on the surface the keep the water out. Cob houses use a technique that was perfected centuries ago and some are still standing that are well over 500 years old. A cob house is made of clay, sand and straw. The mixture is “kneaded” like dough before it is put into place by stomping on it with your feet, which injects life into the building, or using a cement mixer for larger scale operations. The clay acts as the glue, while the sand gives strength to the mixture and the straw gives the walls tensile strength once hardened into place. Unlike straw bale houses the cob wall can be load bearing so the house doesn’t have to have a wooden frame. Because cob is very flexible to work with, the builder is free to create just about any shape, so you won't find too many cob homes that look similar to each other. The cob can also be used for all of the shelving and seating in the house as well as the staircases and the cooker.

A cob house provides a large amount of thermal mass. This helps keep the house cool in the summer and warm in the winter. The walls of the home are made entirely of natural resources that are available under your feet. This brings up a good point about natural building in general; use the natural materials that are prevalent in your area. Clay is abundant in most areas of the world and the grass sods that you dig up to put down the foundations can be used on the roof to blend in with the countryside. Although these types of houses have been rigorously tested they have certain disadvantages over the conventional builds we see. The first will be planning. I am very pleased to say that most planning offices around the country now see these types of buildings as a serious alternative to the norm as they are far more energy efficient. Insurance companies also recognise these homes and some will insure the properties in the same manner that they insure thatched cottages. With any other alternative house building types, you might have a problem reselling a house that is “different” from the norm. If you need to sell, it may take longer to find a buyer. Cob homes are quite unique to say the least. Uniqueness is not a word that lending institutions like to hear. But why would you want to finance a cob house in the first place? It's probably the least costly house you could build and the cash outlay is minimal. Cob does need to be protected from the elements though. A large roof overhang will protect the walls from all but driving rains. All in all then the finished products could look and cost the same, but cob houses might be better than straw bale at keeping the damp out. it all boils down to how well they have been made I suppose (like all houses!)




STACKWELL CONSTRUCTION

As I am on the subject of alternative building techniques, have a look at the idea that was pioneered in America called cordwood construction (also known as stackwell construction). This utilises short, round pieces of wood, similar to what would normally be considered firewood. For this reason this method of building can be very resource efficient, since it makes use of wood that might not have much other value. Cordwood building can also create a wall that has both properties of insulation and thermal mass. The mass comes from the masonry mortar that is used to cement the logs together, and the insulation comes from the wood itself and the central cavity between the inside and outside mortars. Like straw bale walls, it will require a post and beam or similar supporting structure and then using cordwood as an infill, even though the cordwood method creates a very strong wall that could support a considerable load. This method produces a look that is both rustic and beautiful. The process of building is similar to laying rocks in mortar, where the logs are aligned with their ends sticking out to create the surface of the wall and mortar is applied adjacent to each end of the log. Typically the logs are not coated with a moisture barrier, but are allowed to breath naturally. It is possible to include other materials into the matrix, such as bottle ends that would provide light to enter the wall, just like in the book, Stig of the Dump.
Recent experiments with the use of cob instead of cement mortar to join the logs have been encouraging and this method may provide a somewhat more ecological approach to cordwood building

Environmental