Deck Design - Multiple Questions.

Old 08-18-16, 12:24 PM
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Question Deck Design - Multiple Questions.


I recently bought this house, which could really benefit from a deck in the back yard:
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There's a concrete slab (mostly level, but not exactly - close enough to shim, I'm sure) directly out the back door. 11" below the threshold of the door, and 22'x7'.

This is a draft of the plans I had in mind:
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Two rows of posts screwed directly onto the concrete (one row closest to the house, one row closest to the french drain - distance between the rows: 6'4") and a third row of posts dug into the grass past the french drain by a short distance. Three posts per row (distance between the columns of posts: 10'). Total deck size: 22'x14'.

A 2"x8"x14' pressure-treated pine beam on either side of each post. 10 joist hangers attached to the beams, evenly spaced ~15" apart. This allows the joists to sit on the concrete as well. Joists will be 2"x8"x10' pressure-treated pine.

Decking on top of all this, 2"x8"x14' cedar. So the total height of the deck would be 10", fitting just under the 11" threshold clearance without having to sacrifice for thinner beams, thinner decking, or removing the concrete prior. This 1" margin should be safe since it's on concrete, which won't swell/shrink with the weather.

- If I want to place a hot tub on this (assuming ~6000lb. max), would the joists on the concrete provide enough additional vertical stability to allow for this, or should I alter the plans to include more posts and beams?
- Would a better plan be to place the hot tub directly on the concrete (since 7'x7' is a relatively standard hot tub size, it would just barely fit, if snug against the wall of the house), and build the deck around it? This may be difficult due to the placement of the french drain, which I don't want to remove for a variety of reasons.
- Are post bases even needed for the section above the concrete, or could shimmed beams sit directly on the concrete?
- Building a deck on top of concrete is typically discouraged due to moisture. If the portion of my deck that sits on concrete is also covered by the roof, is this still a concern?

Let me know if you have any questions or comments. I would greatly appreciate feedback! Thanks for your time!
Old 08-18-16, 12:27 PM
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Welcome to the forums Paul!

Moisture is still a concern because the deck isn't protected from blowing rain.
It would be better to set the hot tub directly on the concrete slab. IMO if I wanted to extend the size of the patio I would do so with concrete .... or maybe pavers depending on the design.
Old 08-18-16, 12:30 PM
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I think you would benefit most from a new patio, I don't think you have the height to allow the necessary airflow under a deck to keep the wood from rotting quickly.
Old 08-18-16, 12:42 PM
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I'm another one voting for a patio. You just don't have the elevation to get a wood deck off the ground to prevent rot. Luckily you have many options for a patio from concrete, stamped concrete or paver. Any of which could hold a hot tub without any special treatment.

Where are you located? What's your climate like?

How is the house oriented? Does the back yard patio area face north, south....?
Old 08-18-16, 01:04 PM
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I think your concerns about the moisture are valid. Without removing the concrete, it would be very difficult to create enough separation between the ground and the deck, and with the joists being horizontal and sitting on the concrete, they would definitely trap moisture. A patio is probably a more affordable and durable solution to achieve a larger back-yard recreation area.

Would pavers or other patio material require removal of the french drain and/or the concrete slab, or could the structure and surface material be placed on top, as my deck plans previously specified? Once removal/relocation of one or both of those portions becomes necessary, this is most likely no longer a DIY project for me. A few days with a jackhammer sounds miserable.

The goal of the deck was to increase room to allow for a hot tub, patio dining set, and standing room. At the current 22'x7', this would be very tight. 22'x14' was the deck goal. Would a patio of the same size be able to cross over the french drain, or would the french drain need to be relocated?

Thanks for the feedback so far, everyone!

@Pilot Dane:
I am in Bozeman, Montana. It's a ski town, so moisture and below-zero temperatures are very common in the winter. The back yard faces almost directly south, which is good for the sun exposure. Sunlight reaches all the way to the house, despite the roof extending >7' past the base of the house.

Last edited by Paul Sanderson; 08-18-16 at 01:22 PM.
Old 08-18-16, 01:04 PM
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Add another vote for extending the patio. A deck is nothing but a maintenance nightmare. Concrete is one of the most maintenance free materials out there.

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