Friday, April 12, 2013

Constructing Raised Bed Frame

I want to make the raised beds as close to 1'/30cm deep as possible. Mel Bartholomew, author of The Square Foot Garden claims a 6"/15cm depth of soil is OK. I think 1'/30cm is required. Therefore, my choice of lumber was 2" x 12"/ 50mm x 30cm boards.

The finished dimensions of the beds will be 4' x 4'/ 1.2m x 1.2m. There were only two lengths of 2x12s available at my home improvement store, 12' long and 16' long. I didn't want to have any waste but that wasn't possible with only those two lengths available. I calculated the most efficient purchase to be two 2" x 12" x 16'/ 50mm x 30cm x 4.9m and one 2" x 12" x 12'/ 50mm x 30cm x 3.6m for the sides. Adding one 2" x 4" x 8'/ 50mm x 101 x 1.4m board to connect the corners.

I had the boards cut at the home improvement store in order that they fit into the car. The 16' 2x12s were cut into four 4'6"/1.37m, two 4'/1.2m and two 3'/.9m lengths. The 12' 2x12 was cut into four 4'/1.2m lengths. The 8' 2x4 was cut into eight 1'/30cm lengths. The 3'/.9m lengths of 2x12s will not be used and are therefore, waste.

When you are buying the lumber choose the straightest boards with as few knots, checks and cracks as you can find. This is not absolutely imperative but will get you the best product and keep the splitting on the ends to a minimum.

The first task is to check the ends of the boards for squareness. To do that use a framing square. The one in the photograph is a 2'/ 31cm square. The reason to check is that the saw may not have been set up correctly. If it was not, the ends will be out of square. Out of square ends will make construction more difficult. You can see in the above photograph the end is square. 

Next task was to screw one 1' length of 2x4 to each end of the same side of the 4' 2x12s. I used three 2-1/2" exterior deck screws to attach each 2x4 length.

To keep the end splitting to a minimum place the screws in the above pattern. The top and bottom screws are spaced about 1-1/2"-2" from the top and bottom of the 2x12. If the screws are placed closer to the edges they will probably split the 2x12 reducing the holding power and stability of the joint. Place the middle screw to the inside of the 2x4, as you can see in the above photograph. If the three screws were placed inline with each other, the 2x4 may split from end to end if you kept the screws inline. If the 2x4 split in half, it would need to be replaced.

Attach all the 2x4s to all the 4' 2x12s completing that part of the construction.

Next task was to screw the 4'6" lengths to the 4' lengths. So why are there 4' and 4'6" lengths when the frames are 4' square, you ask? Well, I will explain. If all the lengths were 4' long, only the inside edges of the ends would touch. There would be no overlap so the two boards can be fastened. 

Then you may ask, if the boards are a nominal 2" thick, actually 1-1/2" thick, why didn't I cut the other sides at 4' 3"? Well, here is the answer. End grain does not hold nails or screws well. The fasteners would just pull out of the ends. So, increase the lengths of the sides by 6" or 4x the 1-1/2" thickness of the boards and you can fasten the sides into the 1' lengths of 2x4s I fastened to the ends of the 4' lengths. Get the idea?

Next step is to fasten the corners. Stack several of the 4' lengths atop each other and then stand one of the 4' lengths up right next to the stack. This will help keep the upright 4' length standing upright. Then bring one of the 4'6" lengths to meet at one of the corners.

This is what the corner will look like. You can see that if the surface on which you are working is level and flat the corner will come together squarely. If not you will need to shim one of the sides to the corner meets squarely. You can see the end of the 4'6" length is already cracked. A screw placed near that crack will weaken the joint. Be careful of the screw placement.

So now is the time to screw the two boards together. If the screws are placed too close to the end of the board they will split it. Start the screws in from the end more than the thickness of the 2x4 on the 4' length and place the screws at a shallow angle. An angle that will go into the 2x4 but not exit the 2x4.

Get the picture?

Originally I wasn't going to paint the frames. But, after speaking with a few friends and my wife, I decided to paint them. Start with an exterior undercoat. Make sure to get paint on every bit of board that can be reached with the roller and then use a brush to get in even tighter crevices. 

Still there were places that had gaps. Gaps that needed caulking. Fill the gaps with paintable caulk before applying the finish coat. Two finish coats, if necessary.

To be continued ...

©Damyon T. Verbo - all rights reserved

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