Rebuilding a Deck: How to Make it Structurally Sound
LESLIE: Steve in Iowa is on the line with a decking question. What can we do for you today?
STEVE: I’ve had my deck on my house for – it’s been probably at least 15 years. It’s a floating deck, so it’s not attached to the house. And the only problem with that is that part of the deck has a cistern underneath of it.
TOM: Oh, so it’s covering this old cistern. OK.
STEVE: Yes. But the cistern is still – I don’t use it often but it is nice to have, so I don’t want to take it out.
STEVE: Because my deck is settling at different levels and the cistern – above the cistern, obviously, I can’t put any (inaudible at 0:13:32) in to stop the heaving.
TOM: Yeah. So how do you actually get to that cistern when you want to get to it? You have to pop deck boards up or is there a hatch?
STEVE: No, there’s a pipe that runs outside the deck and you just dump the water into there.
TOM: Well, if the deck is heaving, if it’s structurally moving, then there’s nothing that you’re going to do, short of basically replacing that with a better foundation, that’s going to stop that from happening.
How big is this deck?
STEVE: Twenty by twelve.
TOM: Yeah. Is your concern that the deck is moving and that the floor is getting uneven? Or is your concern that the lumber is cracking and checking? What’s your big concern with it?
STEVE: The deck is very uneven. By the house, it has settled probably, maybe, 8 inches. And then where the cistern’s at, it hasn’t settled at all.
TOM: And this cistern, this is not like an open well, is it, where somebody could fall into it? This is a pipe that comes out?
STEVE: No, there’s – yeah, there’s – it feeds directly into my basement and there’s a concrete lid over the top.
TOM: So you really do need to have some sort of a structural cover for this. So, I guess what I would do, in this case, is I would probably take the old deck apart and rebuild it. I would reframe it and basically do it all from scratch. And put in some better footings for this.
Now, you can use columns in the ground but they have to be on their own footings. So what you might want to do is dig down and sink posts – like 6×6 posts – into the ground and kind of do this almost like it’s a pole barn. But you’re really only doing this to support the girders and the beams for the deck. And then you string your new rafter – I’m sorry, new joist – across from that.
And then I would think about using composite decking on top of this. And I would definitely build in an access panel, which could be sort of like a hatch that lifts up or just the panel that lifts out to give you access to that cistern space, in case you want to use it.
STEVE: Would you ever consider pouring concrete first and then put – building the deck over top of that?
TOM: No. I mean if you were going to do concrete, then you would just do a concrete patio. But isn’t that going to make it hard to get to the cistern and access the space?
STEVE: Yeah, I would have just thought – I didn’t know if pouring concrete all the way around the cistern first would work and then put the deck on top of that or …
TOM: No. No, no. No, no. You don’t need the concrete to make this deck structurally strong and to stop it from wobbling. If it’s designed properly from the get-go, you’re not going to have this issue. I suspect it was not when it was built and that’s why it looks like it does now.
STEVE: OK. Thank you much.
TOM: Good luck with that project. Thanks so much for calling us at 888-MONEY-PIT.