Sierra Greenhouses are made of kiln dried redwood. They are treated with the best oil based stain sold in California. Redwood is historically a strong wood that is more resistant to deterioration than other woods. If you are familiar with our greenhouses, you will know that we previously used a treated Doug Fir but, unfortunately, that wood is no longer available in an appearance quality that we will accept. Therefore we have returned to using redwood, which is an environmentally sustainable forest product. As with any exterior wood product, if you want it to retain it's natural beauty an annual re-staining is recommended - but not necessary.