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1. What is 30# and 60# roofing felt?

Thank you everyone who answered this for us: It's basically bitumen sheets which come in different thicknesses. We'll try and work out what 30 and 60# equate to here and let you know.

2. How can we achieve the right R-value?

Between the ceiling and final roofing there needs to be a layer of insulation. It's recommended that this is to specific an R-value. We can't find rigid polyurethane insulation here, all we've found so far is expanded polystyrene which has a very differenet R-value. We've seen sprayed on polyurethane. To get the recommended R-value using polystyrene we need 30cm of it. This increases the depth of the roof by 10cm, but we can't see that being a problem....yet.

4. How do we join the roof beams?

Because we've increased the width of the U we have to give extra support for the roof beams. We're doing this by adding in two centre columns that hold a main beam stretching from front to back. This beam will then take the weight of the cross beams which will join on top of it. Because all the beams are round there is a very small area of contact. We didn't want to flatten them off too much because we didn't want to take the strength out of them.

Dave has been talking to Joseph who is building an earthship in Northern Spain. He's a carpenter and has given us some great advice. I'll put up diagrams soon of what we are doing based on his advice. Thanks Joseph.

3. What is roof under-layment?

Building the tyre walls for an earthship is a very straightforward process. The Earthship books detail how to do it properly and after learning that it's just a matter of muscle and stamina. The books also show all the other stages in great detail, for instance the roof and greenhouse construction. Because of local conditions, regulations, new knowledge and materials these areas sometimes need input from local specialists. We're at the roofing stage at present and have tried to find out from local roofers what materials are easily available. It seems that roof construction here in Almeria, Spain is very different from British or American construction. The language change is also something we have to take into account. Luckily Dave is fluent in Spanish but we're still finding it hard to get the recommended materials and knowledge locally.

So, we thought we'd set up this area to list all the questions we have ourselves and that others have asked. If anyone has answers we'll be forever grateful and will put them up here for everyone to have access to. After all, the more people who build Earthships the better for the planet.