Building Homes or Extensions/Retrofitting Roof Truss
I have a stick-framed residential house in Central Texas that has a shed roof with 2x6 rafters 24" OC that span 26' on a 4/12 pitch. I want to remove all load bearing interior walls to create a large open floor plan with a vaulted ceiling. The problem is how to support the roof structure with all the supporting interior walls gone. Another problem is how to achieve sufficient insulation with only 2x6 rafters. Rather then fur down the existing rafters and install large beams, I was thinking that perhaps I could use a sloped parallel top chord bearing truss to be retrofitted from below the roof and installed next to the existing rafters so that the roof structure can remain intact.
It seems that the truss system would give me much room for insulation as well as a path for HVAC. But I am not sure whether this would be feasible from an installation perspective. So I wanted to pose the question to you.
Is this something that you think might work?
ANSWER: Hi Greg, I think I see what you want to do but it is a catch 22 situation. You almost need to take the sheeting and roofing off the roof in order to sister trusses next to the rafters. At that point you might as well remove the old rafters and just install new trusses built to suit your needs and trash or repurpose the old rafters. If you gut the interior you will need to shore up the old rafters and then try to figure out how to slip a new truss up from the inside. Which may be possible if you use some sort of truss hanger or bucket and attach it to the face of your wall stud..I think you are better off just ripping the whole roof off and coming back with new trusses. If you have your trusses built in advance and have your new sheathing on site and ready to go it's probably only a couple days job to remove the old roof and set your new trusses and dry the building in..providing you have a crew to help with the work. I hope this information helps feel free to write again regarding this or other matters, Sincerely Bruce Johnson
---------- FOLLOW-UP ----------
QUESTION: Thank you so much for your response Bruce. As you can probably guess, I am trying to keep costs low by not having to tear off the roof decking. So, I wanted to see what you thought about my original idea of installing a structural beam and then furring down the 2x6 rafters to get enough space for adequate insulation. Given the size of this space, I can't help but wonder whether the labor involved in this strategy wouldn't cancel out the cost savings from not having to rip the roof off.
Hi again Greg, i have found over the years that truss builders are generally easy to work with and can help with solutions to pretty much any roof problem. Since your roof is a shed type you might be able to get some mono trusses that (as you mentioned in your previous letter) that are top chord bearing on one end of the room and sit on a ledger board at the other end of the room. This way you can sister them along side your rafters without a complete tear off or use a ledger on both ends and put the truss directly underneath the existing rafter and tie the two together with plywood gussets or nail plates. You would have to support each rafter temporarily after removing your bearing wall or remove your bearing wall one section at a time as you add your new truss. It sounds like you are pretty much gutting your interior so that would make this a bit easier since your framing will be exposed.
Or as you mention, install a beam where your bearing wall sits now and hand frame your attic/ceiling space. Again a local truss plant can help you with an engineered composite beam that will be lighter and easier to install than a conventional timber beam which could get big depending on your span. Southernpine.com has a pine span table to help determine your beam size depending on loading, snow requirements etc. if you prefer a timber beam.
In reality, anything is possible with a little forethought and planning. Do as detailed a drawing as you can with specific measurements, what you want as far as attic space, location of your existing bearing wall(s), etc. and go visit your truss plant for ideas as to how you can accomplish what you want. Remember too that you may have electric or plumbing issues to deal with in your bearing wall removal so try to plan out how you will terminate or relocate electrical boxes etc.
Please feel free to write again regarding this or other matters, sincerely, Bruce Johnson ..bejohnsonconsulting.com