Tying floor of new addition to existing post foundation

[Kevin Stricker]

I have a strange situation I was hoping to get some feedback on. A long time client of mine is wanting me to build a exterior storage room under a large existing addition. Originally the plan was to utilize the foundation piers of an existing 8' wide deck adjacent to the house built as a walkway from the basement back door to nearby garage. This would have been simple. Now they are asking if I could enclose roughly double the space and tie into mid span support posts of the addition above. As the ground drops off rapidly after the existing deck, building a standard foundation would be expensive. Digging new piers is also tricky as they have built up around the area and are on a large slab of bedrock. They will not be getting a permit on the room.

So my question is can I tie into the existing 6x6 posts? The piers are 8", so I could get a treated 2x6 outboard of the post. All the additions I have previously built have been on standard foundations, my post and beam experience is limited to decks.

Any advice would be appreciated. Thanks

[Kevin Stricker]

100 views and no replies...yea I wasn't that psyched about the idea either. I will try to post up some pics later today, to see if that helps. The existing footings are bigger than I remember, two 12's and a 15" sonotube. The spans are all less than 10', with the farthest post being 16' from the house. The existing deck has 4 footings all 6' from the house. Once again, all of this work is under a huge 32x50 addition, client is just looking for some storage.

I think I am going to push for using the existing deck footings, and cantilevering 2 feet past to give 8' of width.

[Dick Hackbarth]

“100 views and no replies...”

It could be that 4 people clicked on the thread by accident, and the other 96 thought the problem description was so poor that it wasn’t worth wasting their time on. Remember, none of us know anything about the existing building or what you are trying to do, we can’t see it from here, and you’ve done a darn poor job of laying things out. Now, reread your description, assuming you know nothing about the existing layout, and imagine the hundreds of sketches which could be drawn to show the structural arrangement, all of them matching your description. And, you would like some discussion on this basis?

Some sketches..., plans, elevations and sections, with dimensions, loads, details of existing foundations, their loads and soil conditions, plus intended new construction, would be most helpful in generating some interest in your problem. I can’t imagine what you are trying to do.

[Kevin Stricker]

Hey Dick,
Thanks for the honest feedback, my ego didn't like it but thats life right. I really wasn't trying to complain about the lack of replies, and should have just dug through the code books to find the answer.

Perhaps a more apt title would be: what are the requirements/concerns with trying a new addition into an existing post and pier foundation. I don't have plans drawn up as I was not even sure if it would be a possibility. Being a one man show, I have not figured out how to make money drawing up plans for "maybe" jobs, I guess it is a weakness I should invest more time in. I have attached a few pictures, with a rough drawing of the proposed addition.

Lawrence Proposed Shed Addition.jpgRed is the rough outline of the perimeter of the floor, yellow lines a rough indication of the interior of the walls. Post with downspout is from adjoining deck, and would not be utilized.

Lawrence Addition #2.jpg

Original plan was to remove decking, lay down subfloor and build walls to enclose current deck as an inexpensive exterior storage closet. Client then asked if we could go bigger, using the existing footings. I thought maybe this forum might be a quick way to get an answer from experts. Next time I will take more time formulating my question and try to be more concise.

Thanks for your time,

Kevin

[Dick Hackbarth]

Kevin:
There are a bunch of people here who have pretty good ideas and give pretty good advice, but you have to define your problem well enough so they can understand what you are trying to do. I wasn’t asking for a 600 page set of 24x36 plans, but you have to be able to sketch to the extent that you can start to study and understand your own details and ideas. What are the loads, are the spans 10' or 30', what are the important elevation differences? Can they be built, how do various parts relate to each other, how are you going to do this or that? Doing most of this on paper, or in your head once you have enough experience, is much easier than cuttin and nailin a bunch of stuff together and then rippin it out because it doesn’t work when you get over there. What does the foundation of the new construction look like? You mentioned bedrock, and existing piers which you must work around. How do you frame and attach the new walls to the existing posts and existing structure above? Any water intrusion problems from above, which you have to contend with? How do you even tell the client it can or can’t be done if you don’t do some of this study on your own before you offer to do the job and price it. I hope you don’t just go get a truck load of wood and nails and start sawin and nailin and hope you build something. It’s not an ego thing, it’s a smart builder thing..., how am I going to build this, and giving these clients good advice, and a good finished product?

We can’t see any of this, we don’t know what actually exists, we don’t know what you actually want to do. You have to spell this out for us and for yourself, so you know it can be done. Then we can comment on the details for improvements or for what we see that might not meet code. But, you are not going to get a permit, so who cares. Is this new space intended to be habitable and/or conditioned, enclosed and weather proof as a regular exterior house wall would be? Or, is it just a visual enclosure, to hide stuff from view, and the critters can come and go under and around it? Does it need a frost cover found. btwn. the existing piers and the house found.? If you have a new floor framing in at that lower level, it probably should not be placed on the existing posts and piers unless someone evaluates their capacity. They probably weren’t designed for these new loads.

Is the existing structure above an enclosed and habitable space so dripping water isn’t a problem? This space is apparently already adequately supported by posts and piers, so your walls don’t have to do that. And, more importantly maybe shouldn’t be framed in a way to do that, since that earlier structure might move and deflect differently than your new walls and foundations. You must design for this or design to avoid any possible problems from this. Your new walls are apparently primarily loaded by wind loads, etc., not building loads from above, but they will transmit these lateral loads to the existing structure and posts. Can they take this loading? The code, more particularly the prescriptive IRC, doesn’t cover this kind of stuff, although given time I’m sure they will have a whole section on the topic so as to cover everything under every possible condition. In big picture terms the code intends that something being build should serve its intended purpose, carry all the loads it might see, keep out the weather, keep in the contents, account for the health, safety and well being of the general public. Most of the rest is so much B.S. to keep code writers and building inspectors employed, and because almost nobody can think through a building detail or problem any longer without a code section telling them how.

In short, you have to define your problem with sufficient detail to make it solvable; only you can see it, dimensions, existing conditions and details, we can’t from here; you have to propose some solutions, then we can offer pros and cons on the various possibilities.

[Kevin Stricker]

Wow Dick,
Thanks for the thoughtful answer, though I am beginning to get the sense that this is more of a well rehearsed rant than an actual attempt to help. After all over half of your questions were answered in my original and follow up post, the other half would become obviously irrelevant considering we are talking about a 300 sqft attached unconditioned storage shed.

I know you will find this hard to believe, as you have already placed me in the box of "Cowboy Carpenter", but if I was the saw'n and nail'n type: A) I most likely would not post here, and B) I would already be done with the job.

For your information I had told the client that "No, we couldn't tie into the foundation" when she first asked. The reason for my post was in hopes of getting a real reason(i.e. code violation etc) to back up my gut instinct that it wasn't a good idea. In essence hoping to gain some knowledge to become a better builder. Thanks for taking the time out of your day to educate me.

Have a good one,

Kevin

[MarkMc]

...considering we are talking about a 300 sqft attached unconditioned storage shed.

The reason for my post was in hopes of getting a real reason(i.e. code violation etc) to back up my gut instinct that it wasn't a good idea.

Every place I've worked in the past decade or so requires a permit for anything of that area, conditioned or not, and attaching to the residence would be a definite trigger even at a much reduced size. What's you local book say?

[Kevin Stricker]

Yes Mark, the County would require a permit if they knew about the addition. Generally I would sub out the foundation work if a permit was to be pulled. Even though the homeowner did not want the county involved and no permit was going to be pulled, I would still build the shed to code.

Do they require engineers reports on unconditioned sheds where you are building?

[MarkMc]

Yes Mark, the County would require a permit if they knew about the addition. Generally I would sub out the foundation work if a permit was to be pulled. Even though the homeowner did not want the county involved and no permit was going to be pulled, I would still build the shed to code.

Do they require engineers reports on unconditioned sheds where you are building?

Haven't tried to build one in the conditions you have, so I don't know. The bigger point attempted was perhaps that the lack of replies may have multiple reasons. As a licensed contractor[?] knowingly doing what you are doing raises a red flag or three. The first part of our [adopted local] codes here spells out what work needs a permit.

Around here most basement refits require egress windows even though folks will swear there won't be a sleeping room. Such window installs do require engineered solutions; though most times that solution is purchased as part of the product, it's not always. That requires additional work and depending on how far from 'normal' it is, maybe even engineers.

Sorry, not much help.