Building a Deck Low to the Ground
Deck Design Considerations for a Wooden Deck Built Low to the Ground
One thing that was a bit unusual about our original redwood backyard deck is that some of its supporting pieces are bolted to the foundation. It you look at some of the books and magazines about how to build a deck, you will see a lot of free standing decks that are supported on post and pier systems. You will also find deck designs that fasten the deck to the side of the wooden structure of the home. Sometimes this is an attachment to the framing wood of the house on the first floor, and sometimes the deck plans discuss how to build a deck that attaches at the second floor of a house.
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With our single level ranch style home that we bought in Santa Cruz that we bought when the house was about twenty years old, the foundation was poured cement that rose about a foot and one half above ground level. This deck off the back of the house was probably added very soon after the initial home buyer had bought the property and had moved in. The house has a U shape, and the part of the backyard that was inside the surrounding U of the house was idea for either a cement patio, paving stone patio, or a deck.
However, it also made a lot of sense to have the outside be at the same level as the interior floors, so that you could just step through the doors from the house onto the patio or deck. However, building a patio was not as practical as building a deck. In order to build a patio made out of cement, paving stones, or flagstones, it would have been necessary to haul in a huge amount of dirt fill, which might have settled and undermined the patio. Gravel would have worked better, but about 20 to 25 cubic yards of gravel, which would have been expensive and very labor intensive. Then, all the cement or paving stone would have had to have been brought in, as well. Furthermore, if you did not get the patio design right on the level with your interior floors, you could have some nasty rainwater drainage problems.
However, there is another kind of aesthetic consideration with an elevated patio. Whether or not your elevated deck is a low deck plan or a higher deck design, a deck should always “look right” – of course, unless the deck design and construction was done poorly. In a sense, you always know that a deck must be built over the ground level, and therefore it feels right. However, if you were to fill in the U shaped part of a back yard that a ranch house surrounds, things might not “look right” when viewed from the remainder of the yard.
You would have a built up mass of cement, that might look very hulking. This is probably a good way to trash your property value, since an elevated patio would probably look out of place. Also, pity the poor schmoo who bought your house in the future (presumably at a discount) and then decided to get rid of the patio. To get rid of an elevated patio would take jack hammers and a lot of sweaty guys days and days. However, I digress and it is time to go back to some observations about the deck that was on my house and how to build a deck that is low to the ground.
When you build a deck, it can be a challenge to build your deck, when it is very low to the ground. Depending on your support frame, it can be difficult to use a cement block and post system, because the length of the posts is so short that any post would splinter with nails or screws. Longer lengths of post wood tend to hold together better. The shorter they are the easier they are to split. This is in part why it many times easier to split the trunk of a tree that has been cut off with a chainsaw in 12 inch to 15 inch chunks rather than 24 inch or even longer lengths.
You could design a deck foundation for a low level deck and still use a longer 4×4 inch treated wood post, but that building method is different. You can do this yourself by digging large diameter post holes, putting longer posts into the holes, and filling the rest of the holes with concrete. If you do this make sure that you mound up the cement around the poles somewhat and smooth it. This does not have to be pretty, since it will be covered by the deck and nobody will see it. You should do this so that you can have as much rainwater run off as possible, rather than seep into the post hole and more quickly rot out the post. Even pressure treated lumber can have its lifespan shortened significantly, if it is exposed to excessive water and a lot of wetting and drying over the years.
You should also note that it is possible to find pre-cast cement piers that have a dual design. In the center, they have the normal indentation for a vertical post deck design. In addition, they are cast with horizontal slots at right angles across the top of them. This allows you to lay a cross work pattern of joists horizontally that would support the decking surface boards. These piers can be pretty useful in designing a low free standing deck with a single or double step up from ground level, and this design can allow for rapid deck construction. However, this pre-cast deck cement pier design is not commonly available, and you have to search around to buy them. (Use Google, before you use your car to save money on gas.)
The second shortcoming of this cross hatched concrete pier design is that it assumes you base is very level, otherwise the joists will not be supported evenly. Finally, this approach is not very useful in building a deck that you want to level with the inside flooring of the first story of a home. Since you are stuck with fixed width horizontal deck frame joists, you can only adjust the height in two inch increments. With a cement pier and post system, you can attach the joists to the piers at whatever level you need them to be. I suppose that you could level the deck by nailing on or screwing on additional leveling joists that attached to the faces of the joists that rest on the cross hatched cement piers, but this approach would waste a lot of expensive wood.
While this is a lot more labor than dropping cement pier bases on the ground and mounting posts on top of them, sometimes this is the best approach for a redwood or other deck that has to be low to the ground. However, this approach is rather unforgiving toward poor planning and measuring. If you do not lay out your holes carefully and set them properly in the holes with concrete, they will not be where you want them to be when you add the joists to provide the support for the surface of the deck. Not only do you need to be sure that the post are all lined up and spaced properly, you need to be careful to stake them properly so that they are properly vertical, after the concrete dries. Try righting a post in cement, when the concrete has set up!
Furthermore, you may have to dig a lot of these holes so that the spans are not too wide. There is nothing more disappointing than a deck that has too wide a gap between the supports. The kids might enjoy the flexing of the boards, but any adult with any sense will worry about the weight of too many people and the safety of the deck. Nobody with any sense wants a deck that is too springy.
Also, if you are sinking posts into the ground, do not get so eager to cut them to the proper heights. It is far better to leave extra length on the posts until you know how tall then need to be for final cutoff. If you are building a deck that is low to the ground, you probably will not have room for a post and beam and joist decking surface support system. You might only have room to attach your treated lumber joists to the faces of the posts that you sunk into the ground. This is why you should mount all your joists and bolt them to the vertical posts, before you do any cutting.
Just leave the posts in place until everything is mounted and leveled out and you are able to confirm that the deck surface will be level and at the correct height, when you screw down the horizontal surface planking of your new wood deck. After the whole joist system is in place, then you can cut off any extra length of posts that may be sticking up. If you have a decent reciprocating electric saw that could do the trick. If you set the depth properly with an ordinary electric circular saw, and are careful how you hold it that might work. Or, you can saw of the posts the old fashioned way with a regular hand saw to rip the wood. Now, back to the deck that was already build on the house we bought in Santa Cruz.
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