“I would like to build my daughter a small treehouse. Are redwoods suitable trees for building treehouses in? As you know they are quite fast growing. would a single tree or multiple trees be preferable? not too many branches all trunk. What fasteners would you recommend? I am a contractor and am going to build the treehouse myself. Thank you for any insight you may have.”
It sounds like you have done your research on your redwood trees and are asking the right questions to build your treehouse. I know of a lot of treehouses build in Coastal Redwood Trees (Sequoia sempervirens). The two issues to keep in mind with redwood trees are that they grow fast and the wood is soft. These are two reasons to use larger treehouse attachment bolts when building in redwood trees. The larger bolts give you 1) more bearing surface on the tree’s wood, and 2) they space your beams out away from the trunk so that the tree has more room to grow.
The bark of a coastal redwood tree can be several inches thick and it is non-bearing. This means that your load from the treehouse beam is going to be perched out some distance from the bearing surface, and there is significant leverage the further away you place the load. So, unless the treehouse is tiny, I would back up the treehouse attachment bolt with a suspension cable , and then you’re all set. Here is an example of a treehouse bolt that would do the job, and a suspension plate that fits on the end to cable up to reduce leverage. You can connect the suspension plate to a large lag bolt with some cable. This type of a system costs something to buy all the parts, but it will allow your redwood trees the greatest future growth opportunities and still provide more than adequate support for most normal sized treehouses.
Best wishes with your treehouse,