I am a remodeler and have been asked to do my first 2nd story addition. I am looking for advice from more experienced pros on how to minimize the "open time" between taking off the existing roof and getting the new one up, and on how to minimize damage to the 1st floor and structure during the process. I was reading through a thread here from about a year ago that involved the following exchange (slightly condensed) between Richard Hetzel and JayinMinnesota, so I am kind of hoping one or both of you might see this and reply - especially Richard since our project mirrors your procedure exactly - but any solid advice from builders who have tackled this scenario before would be appreciated:


Richard Hetzel:
I've designed several of them (2nd story additions). The two main problems are the ability of the center girder in the basement (if any) to carry another story (which it seldom can do) and the placement of the stairs. Many houses are 24 feet deep, and a stair plus a landing will require at least 13 feet of length, thus requiring modification of the center bearing wall or girder.

The center girder issue can be dealt with by clear-spanning the entire house using composite joists. Even if the girder can be strengthened easily, one never knows what the capacity of the footings are below it.


JayinMinnesota:
Well our company has did a few of them, in fact we are finishing one right now but one thing is for sure - not one of them has been quick or economical. There are so many variables in doing this type of project and I wish I had more time to get into them. In short here are some things to consider;
- Electrical runs, vent pipes, exhaust fans in the roof you are about to tear off
- how will you heat the new space, is the current system enough, usually not. Is there room in the current mechanical space for the upgrades?
- How do you get all the weight of a second story safely transferred to the ground (as Richard mentioned)
- does the current stucture, inluding foundation, have the ability to carry the new loads
- protecting the existing structure from weather once the roof is torn off.
- is the existing house old enough that asbestos may be an issue?

If this addition is over the entire house, then you won't be able to live there during construction. I've put second stories on before where we were able to keep the ceiling of the first floor and add a floor system over the top of that, and the homeowners still wouldn't have been able to live there, trust me - find somewhere else to live in the meantime, you won't regret it.

As for the AC unit in the attic, I'm not aware of any type of ac unit that would reside in an attic but if you mean the air handler itself, then it will have to be relocated somewhere. Usually you alot a room in the new 2nd floor for additional mechanicals, we do this so we don't have to tear apart the first floor gaining access for mechanical & electrical tie-ins.


Richard Hetzel:
I have done several second-story additions, and in every one of them, the owner has been able to live in the house while the work is being done.


JayinMinnesota:
How do you live in a house with no roof or ceiling?


Richard Hetzel:
What I usualy design is to drop pieces of 2x4 or 2x6 (depending on wall thickness) on top of the top plate between the ceiling joists. This raises the bottom of the new floor joists 1 1/2 inches and allows the ceiling and its framing to remain. It has a side benefit that floor and ceiling framing are independent, so sound is not transmitted through the framing from the floor above.

Sure, somebody always slips and puts a foot through the ceiling, but other than that, the families have all been able to live in the house while the second floor is constructed. I've done probably seven or eight of them, all the same way. Thank goodness for those big blue tarps!



Our scenario is a 1 1/2 story being converted to 2 story. Footprint is 24x30 w/ existing rafters and joists spanning the 24' way. 2nd story floor will be 18" trusses cantilevered 2' on each side. Existing 1st floor ceiling joists are 2x6 @ 16", and we intend to remove existing upper subfloor and place trusses beside these, spaced off the top plate w/ 2x blocking, as specd by Richard above. Existing mechanicals, elec, plumbing will suffice and the plan is to convert a 1st floor closet into a chase. Mechanicals will then be run through truss webs.
In my head then, the process will essentially go as follows (but since I haven't ever done this before I am happy to hear advice and/or corrections):
Clear out inside of upper 1/2 story (Drywall, carpet, kneewalls, etc)
Take off roof and rafters
Remove existing subfloor
Add blocking and set floor trusses
HVAC, Plumbing, and Electric runs through truss webs
New subfloor
Exterior walls framed and sheathed
Roof Trusses
Roof sheathing

Thoughts? Problems to look out for? Omissions in the process?
Any way to get subfloor down sooner to protect 1st floor ceiling but still allow access for web runs without cutting it all apart?
If tarping is only possible protection, any advice on how to do so in a way that will survive Midwest spring/summer storms?

Thanks in advance.
Chris

I only draw the pictures, so I don't know the nuts and bolts details of doing such a job. I do know that the contractors look for a good five-day stretch of weather in the long-term forecasts, and schedule their work so the house is open mostly during that time, and they rush to get it framed and get the sheathing and roof on. I know we've had tarps blow off, and I've heard of some midnight repair stories, but generally, by scheduling the work according to the weather, the majority of my second-story additons have gone really well in that respect.

Any experience or opinion regarding SIPs? I have been looking into them to speed the process but only know one family that has used them before.

I don't think they would save much time, and probably would cost more. The framers I have seen doing second-story additions got the thing framed really quickly, like in two days. I don't have any direct experience with structural insulated panels, but I can't imagine they would save that much time.