Hi all,
Just found this website a couple of days ago and I am truly amazed at what a wonderful resource this is! I've finally got the sign off from the wife and am looking to incorporate a tiny off grid cabin into a preexisting deck and am really not sure of the best type of foundation. The land is in Northern California and we get a very light dusting of snow, so no need to really worry about snow loads and the like. I'm thinking the cabin would be 12 x 16 with a loft. I know I could get out the sonotubes and pour some piers and what not, but seeing how this is going to be build around a deck, space would be tight and it's just going to be me doing the labor. So I'm wondering if using the cement blocks I've seen people use would be ok? The soil is mostly clay so I'm thinking of pouring a small concrete pad to help prevent settling? I'm thinking of ripping up the deck boards and then trying to level out the blocks with the top of the would be exposed deck joists and then building on top of that. Does this seem appropriate?
And thoughts or suggestions would be much appreciated. Below is a link to a couple of pictures to help visualize the 24 x 36 deck.
http://imgur.com/a/iWiLk
Thanks!
Rob
I've thought about it a little more and I'm thinking I could pour a few footings directly underneath some of the joists, sister two joists to an existing joist and then use a simpson post base and 6x6 post to support the 3 joists. If I did this 3x's, I'd essentially have 3 beams 16 ft long that span the 12 ft for my foundation. Now I don't know how level the existing deck joists are, so that's a concern. But if they were level enough, would this work?
Hi, welcome to the forum.
It is hard for me to imagine any scenario where building a house on top of a deck is a good idea - unless that deck is a slab, and that slab was built with some real guts to it.
Especially with little to no frost line, as long as the earth underneath your deck is undisturbed, it wouldn't be bad at all to put down a continuous footing and then lay a few courses of block on top of it. After taking apart the deck, of course. Frame your house, then add the deck back on.
Ok, thanks, sounds good. Do you think I need a continuous footing? How deep should they be? I was envisioning several 16x6x16 footings. If I have the deck out of the way should I look at different foundations options?
The problem with piers is that they will not support the structure horizontally - so an earthquake or or severe winds, the thing could tip over. Piers in general are very sensitive to the ground they are in. And even 20 feet apart there can be different soils and conditions. It is generally thought at this point that if you need or want a pier foundation it is smart to have an engineer design it (even required in most parts of the country).
A continuous footing would be smart, with some rebar running through it. In California they are more concerned with earthquakes - and it is common to tie the horizontal rebar in the footing in with the block wall vertically.
If you confirm your frost depth to around 1' another great option would be a monolithic slab - potentially even leaving the slab as your exposed floor to save on expense. At 12x16 you are not going to be in it for much concrete, and you could probably even do it yourself if you were so inclined.
The foundation then the roof are the two most important parts of a structure.
Is there a county official that will want to become involved in your project? Many places have a square foot threshold for outbuildings such that if it exceeds that footage you will need a permit. A 12x16 has a footprint of 192 s.f., but depending on the loft design it may be considered living space as well. You'll probably want to check in with the county or city to ensure you won't get whammied for being out of compliance.
One option would be to cut out a 12x16 hole in the deck and build your structure completely independent of the deck. You'll probably need to reinforce the remainder of the deck structure though, so at some point the question arises as to why keep the deck? The decking looks to be untreated dimensional lumber that is getting mold on the underside. I would give some thought to removing all the old decking and using what is salvageable for framing the cabin. Then replace the decking with pressure-treated or other rot-resistant deck boards.
NathanS: Makes sense. I think I'll do the continuous footing with rebar.
ChugiakTinkerer: No county officials. The deck is Redwood. Yeah, I'm thinking of ripping out the deck and starting anew with it after the cabin gets built.
Thanks guys!
Another thing to consider. You mentioned clay. You need to be deep enough to be sure it remains stable. You can sink into clay some each winter with enough moisture, and if it is expansive clay it can present other problems. In expansive clay I have had to put 4' deep footings to get deep enough to prevent foundation heaving and breaking on pre-engineered steel buildings. Best to consider getting rid of uphill water if there is a chance of problems with it.
Can you leave it and build alongside?
glenn kangiser: Had a surveyor tell me it's not expansive clay, for what that's worth.
Don_P: Unfortunately this is by far the best place for it. Not ideal, I know.
Assuming I rip up the deck, what do you guys think about getting a footing form (like a bigfoot) and 12" sonotube and sinking them 3 or 4 feet into the ground? Say 5 per 16ft beam with 3 16ft beams across a the 12ft span?
Put your car on the dining room table, it sits there just fine. Now bump the table.
Will it work, sure. Is it safe, not really.
Haha, I like the analogy. Makes perfect sense.
Don_P: Is there a type of foundation that is DIY friendly that you would recommend doing without the need to consult an engineer?
Quote from: robce05 on March 23, 2017, 10:29:43 AM
Don_P: Is there a type of foundation that is DIY friendly that you would recommend doing without the need to consult an engineer?
Follow this (and whatever California may add to it) and you won't need to consult an engineer.
http://codes.iccsafe.org/app/book/content/2015-I-Codes/2015%20IRC%20HTML/Chapter%204.html
Otherwise you probably would need to consult an engineer.
(of course, I'm saying this as someone who built a 10x10 shed on sonotubes without consulting an engineer, but that was much smaller and meant to be just a shed)
Permanent wood foundations are code approved relatively DIY friendly, I think. I've never built one but it looks to be a heck of a lot easier than pouring concrete. Dunno about cost, probably very much region-specific as to how it compares to poured concrete or CMU (cinder block) construction.
Here's one a forum member recently built, sounds much like what you have in mind.
http://countryplans.com/smf/index.php?topic=14205.0
With a post just about the foundation: http://countryplans.com/smf/index.php?topic=14205.msg189580#msg189580
SouthernTier: Thank you, looks like a great resource.
ChugiakTinkerer: Wow, I never even heard of something like that but you're right, it does look a heck of a lot easier than concrete! I'm going to have to do more research but I think we have a winner! Thanks so much!