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Major remodel of existing manufactured roof truss system
2

Major remodel of existing manufactured roof truss system

Major remodel of existing manufactured roof truss system

(OP)
A client would like to add 10 feet of width to a single story rectangular wood framed building that is currently 34 feet wide.  The existing roof ststem is manufactured trusses. The client (degree in architecture, non-liscensed) would like to modify the roof system as follows.  Add cut framing members above the existing roof to creat a higher paralell ridge and new roof line over the widened building.  He would also like to cut the existing truss bottom chord and web members to achieve some open vaulted space in the new cieling.  I am reluctant to get involved in this since it appears to be calculation intensive and could lead to some significant construction issues.  Am I being too conservative?  Is there a "typical" way to handle this?  I would prefer that the entire old roof system be removed and a new one installed.  The client does not want to do this.  I have suggested that he get a different engineer.



RE: Major remodel of existing manufactured roof truss system

You can refer the work to another engineer with this type of experience, or;
Become the project engineer responsible for the building design (correct loadings, lateral-walls, vertical footings, etc.) AND the review of
-New manufactured trusses added
-Site fabricated trusses
-Site modified trusses
all provided (stamped) by a truss specialty engineer experienced in that area.

RE: Major remodel of existing manufactured roof truss system

Consirder contacting the original truss manufacture.  Cutting the bottom cord and webs would scare me....

RE: Major remodel of existing manufactured roof truss system

I'd take the whole roof off and do it over new.  Unless you have all the original engineering for the trusses you can't really check the forces or capacities, especially for the connections.  Even then you are looking at some intense number crunching.  Maybe you can design a new conventionally framed system sistered to the in-place roof to take all of the load and leave the trusses in place and cut as necessary or have them removed.  Then you aren't using them for support.

RE: Major remodel of existing manufactured roof truss system

go to a truss supplier and design a scissors truss to span over everything. then he can cut up the old truss till he is blue in the face or get rid of it.

RE: Major remodel of existing manufactured roof truss system

As a truss designer I would say consult a truss manufacturing company, we have software that can help recreate current conditions, and apply any adverse condition that the trusses are currently suffering. ie plate seperation, and web or cord cracking. If the vault is not interfering with the bearing condition, they will probably design a top cord bearing truss with scabs to control shear. You will probably be applying quite a few gussets, and scabs, and you will need new bracing and blocking details, this is a headache waiting to happen. I would take the safe road and replace them altogether, or if you have an internal load bearing wall, consider using mono scissors and cut or half the existing trusses. Of course if you do this by yourself consult a engineer that has alot of experience with these kinds of modifications, or better still, pay a truss company, that has an in house engineer to design them for you(prefered).

RE: Major remodel of existing manufactured roof truss system

If it is a single family house, there are some cost effective repairs that you can implement to cut the BC and webs, you would need the original truss drawings to design the repairs. IT is fairly common. The replacement of the entire roof system may not be that cost effective. Examine the old roof system and depending on it's condition make your decision. Repairing existing trusses is not that scary. Please let me know if you need any assistance

RE: Major remodel of existing manufactured roof truss system

My 19 year experience has taught me not to ever be the structural engineer for a wanna be Architects home owners. Messing with the existing trusses is an expenssive way to do a remodel. I have recently finished the design on such a project and found that replacing the old roof was cheaper than cutting the bottom chord of the trusses. also by removing the old roof, we where able to raise the top plate by adding a 4X12 beam over the existing top plates.
I suggest staying away from such a project, because clients who are trying to save money in such a manner, are not good payers. I hope that your client is not trying to save all the attic utilities too. Remember unlicensed Architects have nothing to loose but your license.

RE: Major remodel of existing manufactured roof truss system

(OP)
Yikes!  I totally agree with zackmazraani  - but the reality is pretty harsh eh?  Here is the latest on the project.  After working with the Designer and a compenent builder, we have reached a consensus to utilize a brand new truss system vs inserting cut/stacked roof elements.  This really simplifies (ie less cost) interior framing associated with a stacked roof system(no need for interior beams/columns/footing retrofiting/construction etc).  The primary compromise is to leave some of the existing eaves and gable wall intact to preserve the existing exterior finishing.  A general description of the building process is as follows.  We will build the new footings. stem walls and vertical walls. Temporary lateral shoring will be installed. Then remove the existing roof sheathing to within about 1 foot of the eaves (with any needed shoring).  We will then install the new truss system.  This will involve inserting new trusses into the old roof area.  The new trusses will be connected to the top plates and new roof sheathing will be installed onto the new system.  In this way we will place all the roof loads onto the new truss system.  The old system is then rendered redundant and can be cut to accomodate the new ceiling design.

What do you think???  

   

RE: Major remodel of existing manufactured roof truss system

It sounds doable and shows that a creative solution can be reached when a flexible designer is open to working with a knowledgeable contractor.  It is also a reminder that as engineers we have to work out a buildable design.

RE: Major remodel of existing manufactured roof truss system

Moving and rebuilding sounds easier....

Probably cheaper too

RE: Major remodel of existing manufactured roof truss system

(OP)
They considered that, but the lot is very nice and anything comprable would be very expensive (Caliornia prices).  The remodel will probably cost more than many brand new homes in many parts of the country.

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