Greenhouse: Wood Foundation

For connecting the greenhouse to the ground there are 3 options: T-shape metal feet you dig down a foot or so and back fill, or pour a concrete pad and bolt the greenhouse frame to it, or build a wooden base and secure the frame to that. I didn’t trust the metal legs to hold up in our climate, and pouring a concrete pad is like getting a tattoo for your yard. So a wood base it was. Anyway, I wanted to practice some timber frame joinery. Metal straps would work fine. I just like the aesthetics of mortise and tennon joints..

Step 1: Digging out the old raised beds. Hated to do it but they had to go.

Step 2. Leveling the pad with compacting gravel. A wheel barrow at a time. You spread out a layer about 6 inches thick and tamp it down. You can rent a tamping machine but it’s faster and cheaper to use a hand tamper for a project this size.

Step 3. Wood base.

Mortising the frame with 1800’s Miller’s Falls boring machine & chisels. Beautiful yellow cedar cut to order from Tenakee Logging, a small, father and son (Gordon and Sterling Chew) sustainable oriented mill here in Southeast Alaska. Great people to work with.


The plywood thing sitting on the beam is a guide to slip over the tenon to make sure it will fit.
Lumber supply stores sell a waxy coating to paint on the ends of green timbers to minimize twisting and checking as the wood dries. Couldn’t find any in town so melted some chunks of beeswax (about 1/2 cup) in a jar with boiled linseed oil. As you see, the mix is in a pot of water on a camp stove. It’s outside because boiled linseed oil has a low flash point and if it caught fire the thing wouldn’t be in the kitchen. It worked out pretty well. I painted the beams with boiled linseed oil (no beeswax) too. Note: a local timber framer said he uses straight linseed oil to paint beams on the first coat because it soaks in more. Then he uses boiled linseed oil as a finish.
Square up the base by making the diagonals exactly the same length.


Duckbill anchors for insurance so the whole thing doesn’t blow away in a storm. The fat end is a toggle like a harpoon. That’s driven into the ground. If you follow the green twine to the hole between the trowel and the tape measure, you see a round metal thing like the head of a spike. That’s a driving rod. Because the soil is mucky under the gravel pad I dug the holes to get the toggles further down since they tended to pull up a couple inches before the toggle turned and caught. The loops at the other ends of cable will attach to cleats screwed into the base.