Insulating Pole Barn Scissor Trusses Reader

ROB in OAK HARBOR writes:

“What is the best way to insulate the ceiling/attic of a pole barn with scissor trusses? There is a approximate 4 to 6 foot gap between the underneath side of the roof deck and the peak of the scissor truss. On the wall ends there is hardly any space at all. They are not raised scissor trusses. Thank you!”

Here is where lack of planning by your building provider has left you in an uncomfortable situation. Raised heel trusses would have made for such an easy design solution.

For extended reading on raised heel trusses, please see: https://www.hansenpolebuildings.com/2012/07/raised-heel-trusses/

Architect Terry Smith of TDSA Architecture in Washington state recently contacted NAIMA with a question about how to properly insulate scissor roof trusses. Terry rightly pointed out insulation is intended to be most effective when uniformly applied or layered to cover full extent of space being insulated. But there are instances, such as narrow areas near top plate of scissor trusses and sloped ceilings, where this is not possible.

Terry could not find any guidance in his state’s building energy code to address how to properly insulate narrow areas near top plate of scissor trusses where this area is very narrow. Similarly, fully insulating sloped ceilings to meet code requirements can be tricky. There is no code specific guidance to specifically how to do either properly.

General Guidance on Insulating Narrow Areas

Generally, R-60 is code requirement for Ottawa county, you can install full height R-60 for areas where there are no height constraints, and then fill areas having constrained heights (but making sure to install eave baffles). Alternatively, you could have a raised heel truss and install a minimum of R-49 across entire attic floor per 2021 IECC R402.2.1 (similar provisions exist in other IECC versions).

Guidance for Sloped Ceilings

Insulation Institute spoke with Johns Manville Research Manager and Engineer Francis (JR) Babineau regarding whether state codes provide specific guidance on insulating sloped ceilings. After conducting his own search for answers from state building energy code guidelines, J.R. noted only written information he found relative to insulating sloped ceilings was from California:

“If the ceiling is sloped (for instance, with scissor trusses), loose fill insulation can be used as long as the slope of the ceiling is no more than 4:12. If the ceiling slope is greater than 4:12, loose fill should be used only if the insulation manufacturer will certify the installation for the slope of the ceiling.”

See reference link here: https://energycodeace.com/site/custom/public/reference-ace-2019/index.html#!Documents/35insulationproducts.htm

Bottom line: insulation manufacturer must certify installation for ceiling slope. But is this happening or do code officials simply sign off on insulation presence – regardless of whether it is or can be installed at required thickness given slope?

When Codes Do Not Specify

While state building energy codes can provide prescriptive guidance, properly insulating sloped ceilings and scissor trusses – appear to be areas where additional guidance would help clarify intended code requirement is met. Prescriptive guideline absences could leave much to individual interpretation and put onus on manufacturers to address a problem avoided with proper guidance from state building energy codes.

For your building, I will assume you have properly vented soffits and ridge. In area closest to sidewalls, where trusses have minimal height, I would install rigid insulation boards at exterior roof slope pitch, allowing one inch of clear air flow above. Rigid insulation should be extended towards peak until reaching a region where full blown in insulation depth can be achieved.