Whether it’s a roof truss or a floor truss, either is engineered specific for its intended use. Most roof trusses are engineered for the obvious purpose of providing a roof system over a building capable of withstanding the snow loads that may be imposed.
At the truss manufacturing facility they are engineered based on the specifications provided by the architect, engineer or sometimes just the contractor.
What basic information does the truss manufacturer need?
Snow load zone, wind zone, if there any roofs above that dump snow down to this roof, overhang detail, raised heel requirements, cantilever requirements, pitch, special load bearing needs, whether or not it is a regular or attic style truss and what is the “attic” used for.
Whoever orders the truss needs to understand how to order them and why.
If a building is intended to meet the prescriptive requirements of the NYS Energy Code, was the truss designed accordingly?
A ‘regular’ truss may not allow for compliance to the prescriptive method of compliance to the energy code, at least in the northern zones of New York.
The raised heel truss provides more space for insulation where the top and bottom cord meet at the wall.
It is a simple design for the truss, not very expensive when ordering, but if not done properly can cost a lot of money in other areas, like insulation requirements.
The idea of an ‘attic’ truss is quite popular, and a very handy design idea.
Who doesn’t want to try to maximize space for storage?
However did the design consider access like space for a stairway?
This may require special consideration of truss location and layout.
Not a big deal if thought out properly and the truss manufacturer is told up front.
The most common problem when using the ‘attic’ truss idea is not considering the actual use of the additional space. An ‘attic’ truss is used for just that… an attic.
It is intended for storage only. Not habitable space for a game room, bedroom or living area.
These types of uses have different floor load and structural requirements, of which storage is the lowest.
Without getting into the merits of the differences in the structural design requirements of storage, bedroom space or living space, the NYS codes clearly have distinctions.
We all know someone who has an attic that is so full of stuff is has to exceed what the code envisions, but the codes (which are recognized by the NYS code and the International Code) clearly have different loading requirements for different uses.
If you are in the process of designing your house, addition, garage or whatever, with an attic truss concept, you may consider using the highest minimum bottom cord structural load.
For the typical residential situation storage only requires 20 lb/sq ft, bedrooms 30 # lb/sq ft and living space 40 # lb/sq ft.
This will offer several benefits.
Usually the bottom cord will be a larger dimensional board, such as a 2X10 instead of a 2X6, thus providing more floor cavity space for plumbing, heating, wiring and especially insulation.
A regular ‘attic’ truss, for storage only, will create quite a challenge later on if a future remodeling project includes turning that attic into any kind of habitable space.
Typically garages may have the attic truss, thus requiring the appropriate fire rated separation between potential habitable space above and the garage area.
If this was not done the first time, it just creates another challenge when wanting to remodel that attic to habitable space.
The state building and fire codes are here for a reason. Residential codes are the simplest of all.
However, improper planning, not knowing how one thing can impact another, may lead to unnecessary complications later on that involve a host of different issues and cost money.
Where does that code guy come up with that stuff anyway?
Ask questions, knowledge and understanding.