Can I Use Redwood Instead of Pressure Treated Lumber For My Mudsills?
I get asked this question a lot, short answer…Yes. But there is a reason that very few contractors use redwood over pressure treated (or p.t.) for mud sills and bottom plates.
Let me first say that I have remodeled homes in areas of San Francisco and Marin that were over 100 years old- built thoroughly out of redwood- and are nevertheless in great shape structurally. That is because redwood is naturally high in acids which prevents decay and keeps bugs from eating it, seeing as those are a homes two worst enemies, redwood makes good sense. Until you look at the price tag. Fact is many redwood areas were over logged and the ones that weren’t are now protected. As a consequence the price of redwood is very high compared to other framing products and they are now using younger growth trees which equals more knots, twists, and wanes.
So to cut cost Pressure treated lumber was introduced as a wood that could mimic the attributes of redwood but for half the cost. Pressure treated lumber is usually Douglas fir or sometimes hem fir and injected with many toxic chemicals (copper or zinc napathane being the most potent). These chemicals are what prevent the decay and pest infestations but have also been known to cause cancer by polluting ground water when disposed in land fills. In California, the fragment pieces of p.t. must be disposed of at a bio-danger waste yard. Recently the levels of toxins have been lowered by approx. 50%.
It is also worth noting that it is never permissible to attach un-treated Douglas fir lumber in direct contact with concrete. There are several ways to treat Douglas fir yourself and make it decay and pest resistant. The #1 way to do this is apply copper napathane in either a spray can or regular liquid to be brushed on. You can find this at just about any neighborhood hardware store but be careful doing this! It will stink bad for a day or two so don’t apply directly in living spaces. Be sure to read any and all factory directions regarding the application of any sealant or decay preventing product.
So to answer the question, yes… absolutely, redwood is a great product for mud sills. But if you are gonna use redwood, save yourself some money and get ‘rough cut’ lumber, this will be slightly larger so you’ll have to cut it down width wise, but the price difference is worth the additional work.