Wednesday, January 21, 2015

Straw Bale Cat House - Lessons Learned

As mentioned in my Straw Bale Cat House post we recently completed a temporary straw bale shelter for the cats. As also mentioned in that post I made a lot of mistakes and learned several lessons. So many, in fact, that I thought the topic warranted its own post.

Some of the mistakes were related to the design itself, while others happened during the build. So far it doesn't seem that any of the mistakes were fatal to the structure, but I'd certainly do things differently in the future.

My very first mistake was in not measuring the bales once I acquired them. In fact, I should probably have shopped around for the appropriate sized bales, but options were somewhat limited and I wanted to find something relatively close that was also cheap. If I were building a house or other permanent structure I would certainly take more care in selecting the bales. 

My design was based on "standard" two stringer bales, which one would expect to be 18" wide, 36" long, and 14" tall. The bales I ended up with, though, were more like 18x42x14. That significantly impacted my design as I had expected the bales to be half as wide as long, making alternating the courses work out evenly. I didn't realize the size difference until I was already stacking the bales. I should have stopped at that point and gone back to the drawing board. Instead, though, I continued, and just dealt with the gaps and odd overhangs as I encountered them. 

Another major mistake was building on a slight slope. Since the structure is temporary I didn't want to disturb the soil any more than I had to. Rather than trying to make the spot level I decided that I could use the slope to my advantage. I reoriented the structure so that the roof was running in the direction of the slope, giving me even more roof slope than my original design. I also reasoned that the slope would help carry water from the roof away from the base of the building.

If any mistake turns out to be a fatal flaw I think it will be this one. What I didn't expect, but should have, is that the slope caused the bales on the high side to shift. The wall on that side looks ridiculous  because it is so far from being straight. The problem is so bad that after leaving it for several days we found that when we returned to finish working on it the door was more narrow than we originally left it. I suspect that the shifting may not have been quite as bad if the door had been in a different location.

This leads to me my next mistake, which was not pinning more bales and/or courses. I had prepared a few pins in advance, which I planned to use for the half bales by the door. In hindsight I should have prepared many more and used them generously. I especially should have used more on the high side to help prevent it from leaning. I did put a few in once all courses of bales had been stacked, but it would have been better to thoroughly pin as I went. 

Not levelling each course of bales as I went was also a mistake. I should have taken the time to do this, as well as making sure each wall was plumb. I was in too big of a hurry to get the bales stacked, though, and so skipped an important step. I regretted doing this as soon as I started working on the roof and realized that my roof was going to be uneven. By this point I was unwilling to restack the bales to correct, so just dealt with it. I think it'll be fine for this structure, but not if I was installing a different type of roof covering.

The roof itself was designed to cover a 12' x 12' area, providing 18" of overhang on the ends and 9" of overhang on the sides. I planned for plenty of overhang to protect the bales from rain and snow so they can be reused in the Spring. The finished structure, though, was not the size I had planned because the bales were larger than expected. I should have redesigned the roof, based on the actual dimensions of the building. Instead, though, I went with the original design, which has left some of the bales protruding out past the roof edge. This is, obviously, less than idea. Although the cats like it since it gives them a convenient way to get onto the roof.

Another issue with the roof is the design itself. I feel like the roof is overly complicated for such a simple temporary structure. In hindsight I wish I had simply added another course of bales to the high side and then spanned the opening with 2x4s on which sheets of OSB would rest. This would not have covered the bales completely, and certainly wouldn't have provided any overhang. I think it would have been sufficient to support a tarp, though, which could have extended out over the edge of the bales. It would have been much simpler, less time consuming, and less expensive to construct. In hindsight I wish I had gone with this and used the savings to buy a larger and better quality tarp.

The overly complicated roof design had another major flaw. Even though it was complicated, it was also minimalist. In other words, I used the fewest rafters possible, to save money and effort. The result is a roof that is much too weak to put any real weight on. I actually have some concerns about its ability to handle any snow load. The inability to put weight on the roof made it difficult to adequately secure the OSB to the rafters in some areas. It also was going to complicated the application of plastic sheeting and roofing felt I had planned, which is a major reason I decided to just cover it with a tarp instead.

Not having a good tarp on hand when I started this project was also a big mistake. I have several old tarps, in varying condition, which I used to cover the structure. None were big enough on their own, though, which made it tough to get everything covered. At one point we had several days of rain and when I went back to the building site I found the tarps had separated in the center, allowing water to just pour inside the structure.

This also caused me to leave the OSB on the roof exposed for several days, during which more rain came. I had taken great care to keep the OSB in the dry prior to that, but then made the mistake of letting it get soaked by rain after installation. I had hoped to reuse it for another project in the future, but now I'm not sure it will be suitable for that. This was probably my most costly mistake, especially since I ended up buying a new tarp anyway. In the future I'll be sure to have a tarp capable of covering a structure like this, and if I don't have one I'll buy one before starting.

Since I ended up covering the structure with a tarp I have unused materials on hand. Had I planned to use the tarp from the start I could have saved myself the expense and trouble of buying the roofing felt and plastic cap nails. I'm going to try to return them, if they are in satisfactory condition. I was storing the felt inside the structure, so it may have gotten wet. I know that the box the nails are in got wet because they were in the bed of the RTV while we were working and there was a misting rain. One of the boxes with screws in it literally fell apart, but I'm hoping the nails didn't get so wet. If I'm able to return those two items the refund will cover the cost of the tarp. Otherwise it a sunk cost until/unless I find another use for them in the future.

As you can see I made plenty of mistakes on this building. I am certainly not happy with how it turned out. It looks sloppy and I seriously doubt its longevity. I am glad to have gotten it built, though, so we could relocate the cats. Since it is intended to be temporary I hope that the longevity doesn't become an issue. If nothing else it was a wonderful learning experience. You can bet that I'll never make these same mistakes again, especially not all on one building!

Edit: Having said all of the above, I don't want to make it seem like I'm completely unhappy with the structure. Yes, there were a lot of mistakes and both my planning and execution were lacking. It really was a great learning experience, though, and will be valuable because of that. Also, this is the first time I have ever attempted to build something so large myself and my first time building with straw bales. As many problems as it may have, I'm proud of the building and of the accomplishment it represents.

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