Building Homes or Extensions/addition with TGI joists


Hi Dan,

I have a question regarding building a second floor addition on top of an existing ranch home.  The existing ceiling (attic floor) joists are 2x6 and not thick enough for code (2x10 are needed).  The current proposal is to build a pony wall around the perimeter of the home to get above these 2x6 and then use TGI joists for the second floor.  

I like the idea of extra room to run plumbing and electrical lines, not to mention the ability to leave the existing first floor ceiling intact.  But, I have concerns of the extra added height.  Is this considered "normal" construction practice (as compared with "sistering new joists alonside the existing ones)?  Are there any downfalls or negatives with this plan (such as a fire hazard, etc) with the extra void space between floors?

I would appreciate more insight into this proposed plan before moving forward.  Thank you for your time.

Kevin, I've not seen it done this way which does not mean it is wrong.  There is no problem with the additional height between floors.  I do have some concern about the "hinge" effect of a short pony wall.  This can sure be made solid and secure with plywood on both faces and/or bridge blocking between old and new joists and rafter tails.  This area can be difficult to insulate and seal - make sure there is a definite plan.  Make sure that the exterior finish will accommodate the condition and look original.  The existing ceiling will probably need attention once this work is performed.

If your contractor has experience with this approach, can show you other installations that have stood the test of time, and the code authorities take no exceptions I see no problems other than those stated.  There is always the comfort of paying for a structural engineer's stamp on a detail.

I hope this gives you some talking points with contractor and that the weather cooperates with your project.

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Dan Griffin


I can answer almost all questions related to the total construction process. My expertise is in commercial construction, though I can field most any residential question. I have hands on experience in concrete, heavy equipment, masonry, all phases of carpentry, interior finishes, and I am fairly strong in mechanical and electrical.


I have over 20 years experience as a commercial carpenter and commercial construction superintendent. I have another 20 years experience in facility management for a major school district.

My favorite hobby for he past 12 years has been singing bass in a The OkChorale men's barbershop chorus and the Mature Moments quartet.

I hold a Bachelor's degree in English and Math. I have completed many continuing education hours in the building trades. I hold a Master Carpenter card from the AGC, Associated General Contractors.

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