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    boards.hgtvremodels.com    HGTVRemodels Message Boards  Hop To Forum Categories  Trades and Specialties  Hop To Forums  Remodeling    Feasability of Adding a Second Story over a 2 Garage... Help!
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Feasability of Adding a Second Story over a 2 Garage... Help!
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I'm thinking about adding a second story over the 2 car garage on my house. The house has 2 single vehicle doors, and is approximately 28' wide by 32' long. The current trussing on the garage is across the short span; the roofline in line with the vehicle parking. It is on a slab pour with no stem walls under the exterior walls. In addition, the walls are constructed of 2X4 studs on 16" centers.
Electrical and plumbing will be very accessible, as well as HVAC.
In addition; a staircase will be easy to install as well based on the current floorplan.

Just a few questions about the project feasability.
1. can I build a second story on 2X4 walls?
2. Can I build a second story on walls which have no stem walls?( garage being constructed with walls simply set on the slab)
3. Can I get a joist which will provide enough strength to span 28' with no center post? (possibly a 12" TGI?; don't have span tables in front of me; wondering if anybody knows off the top of their heads)

What other ramifications am I not thinking of?

Any information you can throw at me would be greatly appreciated.
 
Posts: 5 | Location: Washington State | Registered: 10 February 2008Reply With QuoteReport This Post
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Two things I would be concerned about -

1) If your local building codes allow a second floor on top of a 2x4 structure. Call your local building department and ask.

2) If you have an adequate foundation to carry the new load. And is if frost protected. The fact that it is an attached garage as opposed to a detached probably means that it is frost protected. But you will need to verify the foundation nevertheless.

I would also recommend open web floor joists as opposed to TGI's. They can span a lot further and you can tuck all your utilities in there without hacking them apart. Nothing hangs below. 28 ft clear span can be attained using this type of floor system. Although it will probably be 18 or 20" thick.


General Contractor/Home Builder
 
Posts: 497 | Location: Minnesota | Registered: 15 January 2007Reply With QuoteReport This Post
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The 2x4 walls are not a problem, but the absence of a foundation extending below forst level definitely is, unless your climate is one in which frost does not occur. Still, you would be bringing huge loads to the egde of the slab, and it may crack and fail at the edges. If the garage doors are in the long wall, the headers over the doors must be deisgned to carry the floor load and roof load from above.

You're probably looking at a 16 or 18-inch deep composite´joist to span that distance, and Jay's suggestion of open-web trusses is a good one for the reasons he gave. You will want someone to design the joists properly so that you will experience a minimum of "bounce" in the second floor. Bounce can be an annoying problem with long-span joists. I would guess that trusses would perform better.

If you can solve the foundation problem, it's not a difficult project.


Architect (NY) and Home Designer (PA)
 
Posts: 2870 | Location: Tobyhanna, PA | Registered: 24 October 2005Reply With QuoteReport This Post
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Thanks for the help guys! That's good information. I'll get in touch with our building and planning dept and let you know what I find out. We have heavy frost in this area; Eastern Washington State; so my hope is that there are some footings in place. I'll dig down and see how deep I get
QUESTION:
The shared wall with the living space obviously is on a foundation footing. What is the feasability of putting a center post and beam 1/2 way across the span and a SECOND post and beam at the end of the span near the 2X4 wall in the event the 2X4 wall cannot bear the entire load due to the lack of a footing? I'm thinking this would decrease the load on the very outer portion of that pour. If the slab wouldn't support the weight 6" or so in from the edge, I could also cut out squares in the concrere and pour deep peers out at that wall.
I know I need to get with an engineer; I just don't want to spend the money to plan the project if it's going to be impossible due to the foundation.
 
Posts: 5 | Location: Washington State | Registered: 10 February 2008Reply With QuoteReport This Post
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Update: Building and planning says the big challenge with a 2X4 wall on 16" centers is lateral sheer. He thinks I should be able to accomidate this with the use of plywood sheathing on the inside of the wall. He's also going to need an engineer of record on the project as well as some fire egress requirements met; looks seemingly feasable to me. I'll keep you posted!
 
Posts: 5 | Location: Washington State | Registered: 10 February 2008Reply With QuoteReport This Post
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Oh, you have seismic issues there. We don't have such issues here in the northeast. I can't imagine that you don't have a proper foundation if you have heavy frost in your region.

A center girder would relieve some of the weight on the walls, but 2x4 walls can easily carry a second story. IF you put in a center girder, you would need large footings at each end, and that's relatively difficult to do.

The clear-span joists and bearing walls is the best solution. I can't advise you about seismic considerations though...a local architect or engineer surely can.


Architect (NY) and Home Designer (PA)
 
Posts: 2870 | Location: Tobyhanna, PA | Registered: 24 October 2005Reply With QuoteReport This Post
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If you plan on leaving the garage as a garage, then I would take the planning dept advice and put structural shealthing on the inside. I've seen this done and painted, it doesn't look bad. Seems a lot easier than trying to pour 2 massive foundation for a post and girder system. Any time I've put a second floor on an existing building, the engineer has yet to say it couldn't be done but the general consensus here is that it's all going to depend on your foundation.


General Contractor/Home Builder
 
Posts: 497 | Location: Minnesota | Registered: 15 January 2007Reply With QuoteReport This Post
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Well, if it's a garage, the entire garage has to be clad in 5/9 Type X gypsum board when it supports another story, so don't sweat the paint job. The plywood will have to be covered.


Architect (NY) and Home Designer (PA)
 
Posts: 2870 | Location: Tobyhanna, PA | Registered: 24 October 2005Reply With QuoteReport This Post
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The exterior is rock/stucco stuff, can I put the gypsum on the inside of the wall? If so, can I just hang it over the current drywall? and do I need to hang it on all walls of the garage or just on each side?
 
Posts: 5 | Location: Washington State | Registered: 10 February 2008Reply With QuoteReport This Post
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Yes, you would install plywood, if that's what's needed for a shear wall, inside your garage, and then cover that and all walls and ceiling with the 5/8 Type X gypsum board. It must also be taped and spackled, but doen't have to be finished. Any headers or beams must also be covered. If there is a door between the room above and the garage (if you install stairs), it must be a fire-resistance rated door. Your architect should advise you of all code requirements.


Architect (NY) and Home Designer (PA)
 
Posts: 2870 | Location: Tobyhanna, PA | Registered: 24 October 2005Reply With QuoteReport This Post
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Now that Richard brings up the stair issue: opening into the garage from the living space sounds like a recipe for carbon monoxide poisoning. The whole stair should be encased in a fire rated enclosure with a gasketed (FR) door (no, not the stuff you buy at home depot that is sticky backed). But, ask YOUR architect.


NYS Registered Architect
 
Posts: 6 | Location: Elmont NY | Registered: 18 December 2007Reply With QuoteReport This Post
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The staircase is going to be to and from the living space only. The garage door does have a gasketed door currently in place. A fire rated wall means I'm going to need to tear off the current drywall in the garage and sheath it with plywood, right?
 
Posts: 5 | Location: Washington State | Registered: 10 February 2008Reply With QuoteReport This Post
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the plywood is fine, but still need to fire rock the exposed surfaces that face the garage. Also perhaps because its a egress to the 2nd level you may need additional protection, depending on the local code requirements.
 
Posts: 1933 | Location: New Jersey | Registered: 31 January 2006Reply With QuoteReport This Post
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