Garage Attic Conversion

Apparently, nobody wants to encourage you.

Everyone wants a 'bonus room', but once the trusses go on, it's a bit late to do much about it.

Unless, as your potential contractor told you, you rip off the existing roof and put up proper trusses.

I am assuming the garage is freespan. Can you do without that freespan? If you would tolerate a beam and it's columns running down the middle you might be able to avoid the roof removal.

I assume your contractor already suggested that, also?

If you sacrifice a little floor space or ceiling space below, you can probably scab in new floor members, possibly flat trusses or tji's to span that length. For the roof framing you can install a ridge beam with support to somewhere on each end and scab in new rafters. This will reduce some of your ceiling head room. After considering all of this you may realize that it would be easier to just remove the existing roof and trusses and start from scratch.

To check if the truss could be modified, you might have a truss manufacturer size an attic truss for you (square in the middle) with the exact same profile as your existing fink trusses. Compare the members to see what would need to be done to modify the existing trusses. You should research proper connection methods (recommend a structural engineer or representative from a truss manufacturer)to assure the members are properly tied together when and if the truss is modified. Keep in mind that if you have to beef up the top and bottom chords of the existing truss, it may be more difficult than just tearing off the roof and starting from scratch. I believe that it's well worth the effort to look into, though.

Lots of ways to skin a cat. Hire a Structural Engineer and don,t rely on a contractors advice.

Some tips to save you money and frustration:

Before doing anything check existing foundation bearing capacity. Spending money on design of this new room will all be wasted if the foundation is not capable of supporting new live and dead loads.

Set some sort of budget for this new room (either what you can afford or what you are willing to spend), with a contingency of at least 10% (if the cost is $15,000, a total budget of $16,500). Bid the entire job out, get all bids in writing. There is nothing worse than remodeling the home you live in and running short of money.

Hire DULY QUALIFIED PERSONS to make all investigation as to structural design and existing parameters. This is of paramount importance, you alone will have to live with mistakes made early in the process (mistakes are very expensive to correct).

Remeber this, it costs what it costs. If costs exceeds your budget DO NOT START, rather, explore ways to increase your budget or ways to limit the project cost (which may be non-existent). In any case, it is far better to live in a house that is to small, than dealing with the stress of an uncompleted one.

One other, but very important thing is construction plans. Be sure that all structural elements are properly detailed DO NOT leave this up to a contractor, this could spell disaster.

I don't know where you are located so construction costs can vary, but I know from experience in my area (CT), it is usually less expensive for you to remove the roof and reframe the roof rather than trying to reinforce the existing trusses.

Also I agree with ERV, find out what the existing foundations are.

Regarding the floor construction, You might be able to still maintain a clear garage. It depends on your ceiling height in the garage and if you can afford to "loose" some headroom.

Hire a local structural engineer who can evaluate your condition and make recommendations. Don't go with a contractor tells you. In the long run, it will cost you more.