4 Season Room on Deck

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  #1  
Old 09-13-18, 03:02 PM
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4 Season Room on Deck

I have a 14x46 deck that I want to turn the one end (14x16) into a 4 season room. I have friends / family who have similar rooms, and there never is anything different about the deck structure under the room. I have had 2 people tell me now that when there's a room on the deck, regular "deck numbers" are no good. But from every picture I can see of these multi-season rooms on the internet, the deck framing is the same as the side with no room on top. Is this right?

My deck has 2x10 joists, 12' to the beam (3-2x12), and 2' overhang. Beam spam is 10'. Posts are 6x6 on 12" tubes going 3-4' down.

I don't see how a deck with furniture and 20 people on it is any different from some lumber making a small room.

Thanks.
 
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Old 09-13-18, 03:21 PM
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The wall and roof add dead load, plus you may have snow load calculations to figure in now that you have a roof. You should be getting a permit and your inspector may require an engineer's stamp of approval on your plans.
 
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Old 09-13-18, 03:28 PM
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The footer requirements for a room are often stricter than for just a deck.
 
  #4  
Old 09-13-18, 05:01 PM
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You guys can't just say what you have done / seen?

I could just do my joists 12" and do 7' post spacing and remove any questions about strength, but I'd rather not if there's really no need.

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Old 09-13-18, 05:46 PM
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No. What you propose is not just a deck anymore.

I might also add that the purpose of this site is to help guide you... not just to diy, but also how to avoid diy mistakes. We can't always tell you exactly what you need to do as if we are your designer, builder, engineer and inspector all rolled into one. (Who are all paid, btw.) This becomes a issue because of the extent of your proposed addition. Codes are there for a reason. Minimum energy standards for living space are there for a reason. Inspections and permits are done for a reason. And structural engineers are paid for the work they do. Our site is a good source for general information but we don't take the place of designers or architects... advice we give is not meant to skirt the legal permitting and inspecting process, (which is definitely needed for any new living space attached to the home) and doing so can result in a structure that is substandard and/or that is not safe. Not saying it will be, but it could be.

Pointing at someone else's room, saying they did it, doesn't prove anything and doesn't make it right.

We cannot see your deck or inspect your footings. That can only be done in person. A 12" sonotube is probably not sufficient if it does not sit on a footing. Google "DCA6 deck guide", download it, and look at figure 12 on page 13. It is based on R403. For footing sizes, see table 4 on page 12. I would just assume you have no footings under your sonotubes, so that aspect may already be substandard.

Also, if this room has a shed style roof, all the weight of the roof and potential maximum snow load will be on the front wall... and if the room is 14' long, that wall will bear on the end of the 2' cantilever... not directly over the beam. Only a structural engineer will be able to tell you if that is okay or if it should only be done with some modification to the existing structure. That is why they get paid the big bucks.

No one that is responsible would want to give you bad advice, or have your project fail. Some armchair quarterback might give you the go ahead, but it might not be smart to listen to his advice. That's why I suggest you would be wise to get a permit, have your plan approved by an engineer and get it inspected. You won't regret it when the day comes to sell your house and questions start being asked about that addition.
 
  #6  
Old 09-13-18, 07:32 PM
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I hear you, and agree with you for most of it. However, I don't believe that codes are there for a reason. There are thousands of municipalities in the country, and the codes vary to very extreme to very lax, yet somehow all the buildings are safe and not falling down all over the place, the only thing they have in common is they are "to code". I believe that codes and permits (at least where I live) are put in place to squeeze money out of taxpayers and / or force them into hiring a contractor they don't need.

I always ask here because usually answers are like "yeah I did it this way and it's fine" or "well you should really add this and this...".

All the snow / roof weight isn't on the wall. On a 2/12 roof, it's slightly more than 50% on the wall, the rest of the load gets taken on by the ledger holding the rafters. Your point about the wall not sitting over the beam is a good one and I need to think about that.

Every single picture I can find of these things looks just like a plain deck frame. No elaborate foundation, no extra beams, nothing.

That DCA6 guide you referred to is what I built several decks by. I like that guide because it's very straightforward. But that table you mentioned... what is "footing thickness" (last column)? This can't mean depth, correct?

Not trying to be a jerk, but I thought for sure someone here has built one of these. Just looking to hear what they did.
 
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Old 09-13-18, 07:56 PM
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The footing thickness is just that. How thick the footing is.

if you look at 10' beam span, joist span < 14', it specifies a 27" round (or 24"x24" square) footing that is 11" thick. That is what your 12" sonotube (12" vertical stem) would sit on, as shown in figure 12.

this assumes certain things, such as your soil bearing capacity, which unless you test it, is an unknown.
 
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Old 09-13-18, 08:44 PM
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Also important to note that just because I am a contractor doesn't mean I can build whatever I want. My license designation is a class "C" home improvement contractor and commercial improvement contractor. I can build decks all day long, can remodel kitchens, bathrooms, flooring etc. But as soon as you add putting a roof on it, I am not allowed to take the job. It requires passage of an exam based on code and building techniques and the designation of a class "A" license.

Codes exist so your house doesn't burn down (electrical), doesn't blow away in a hurricane (building), doesn't flood and destroy your flooring and structure (plumbing) or sink into the earth (structural). They are all there for a good reason and to protect your safety. To think otherwise is silly. Yes, some areas are more strict than others, as long as they are guided by local authorities there will be variances.

100% of the load of the roof and structure will be on the outer walls which you propose to set on a deck. Everything overhead rests on the outer walls. Relying on 5/4 board and some deck joists with a 12' span is not how you support a load bearing wall. Not even going to comment on your cantilever.

I know you are looking for an easy answer that justifies your plan. But when you have been in as many houses as I have, you would begin to understand why some things are as they are. Particularly in 100+ year old houses, yes they are still standing, but for some, I don't know why they haven't fallen down. Have walked away from many "flip" jobs that someone wanted me to do as there was just no way of safely salvaging what the starting point was.

Also, last deck I built the inspector had me place the supports for the main beam on 5' centers. Your 10' foot centers on your beam would not make it in my neck of the woods.
 
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Old 09-13-18, 08:56 PM
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Your 10' foot centers on your beam would not make it in my neck of the woods.
Actually according to the span table, if the beam is SYP, his triple 2x12 beam is fine at 10'. That's about the maximum it should span with his joist span. If it is anything other than SYP, it is slightly over spanned (by just a few inches).
 
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Old 09-13-18, 09:29 PM
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Actually according to the span table, if the beam is SYP, his triple 2x12 beam is fine at 10'. That's about the maximum it should span with his joist span. If it is anything other than SYP, it is slightly over spanned (by just a few inches).
LOL, I didn't question him as the head person at the permit office. I just said "yes sir" and added the extra supports. He made the notations on the plans and then stamped them for approval. Sometimes, you do as you are told, not necessarily what you think is OK. Required 4 extra holes for footers and the project moved forward.
 
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Old 09-13-18, 09:45 PM
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Yep, that's how you do it.
 
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Old 09-14-18, 03:20 AM
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There are thousands of municipalities in the country, and the codes vary to very extreme to very lax, yet somehow all the buildings are safe and not falling down all over the place, the only thing they have in common is they are "to code".
I live in an area where the code [mainly code enforcement] used to be very lax. Not so anymore and I suspect the main reason for the increase in code enforcement is due to all the substandard building practices that were common place, both by diyers and the hayseeds that thought they could build. It's fairly easy to spot the structures that were built correctly 10-20 yrs ago and those that were not.
 
  #13  
Old 09-14-18, 08:57 PM
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[100% of the load of the roof and structure will be on the outer walls which you propose to set on a deck. Everything overhead rests on the outer walls. Relying on 5/4 board and some deck joists with a 12' span is not how you support a load bearing wall.
There are no outer walls supporting anything really. Just 1 wall at the end. The sides don't do much if anything. This wouldn't be a gable roof, just a slant from the house.

And I'm not just building the thing on top of decking. Where the room would be would be 5/8 plywood on the joists.
 
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Old 09-15-18, 03:35 AM
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It's not the decking or joists that is the issue - it's foundation underneath. Additions are held to a higher standard than a deck. Your front wall would be a load bearing wall.
 
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