Ceiling insulation for cupola/gable vent detached garage

[Pattycakes]

Hello- I am wondering if there is anything I need to be aware of with insulation a detached garage with working cupola vent and gable vents in each side. As far as I can tell, there is no soffit venting.
with regards to fiberglass insulation, is the job any more involved than laying the insulation along the bottom chord on top of the strapping and then Sheetrock? Do I need to use baffles even though there do not seem to be any soffit vents?

 

[Pattycakes]

After thinking about this more… I think my bigger simpler question at this point would be it it is acceptable to insulate and condition a building with the cupola & gable vent system and no soffit vents. Will the attic space be able to ventilate properly after installing flat ceiling and conditioning the space? Do I neee to look into installing soffit vents and removing the gable vents?

 

[billconner]

I'd say you're fine to leave as is without soffit vents. With flat ceiling, you should be able to achieve a very good vapor barrier. The cupoula with gable vents should keep and humidity below acceptable levels.

Why not blow loose cellulose? should be less expensive, easier, and do a better job of filling all gaps.

 

[duneslider]

If you don't have soffit vents you basically don't have any venting going on at all. There is no place for air to come in down lower where it is cooler and move up higher to create air flow. There might be a minor bit of turbulence up high in the attic space but not much air change is happening. Right now if I understand correct you don't have a ceiling in the garage so air flow is coming from gaps at the garage door, windows, etc. If you close off the ceiling there is no longer anyplace for the air to travel from to go out those vents.

If you are going to put a ceiling in then either completely seal the attic area and create a sealed environment, or add soffit venting to create air flow. Or seal it and condition it, that is an option too.

 

[Pattycakes]

The plan is to condition the building as a workshop & golf sim- so not necessarily as “conditioned” as a house but I would like it to be comfortable in the winter and summer if I am in there (Massachusetts).

if I were to add soffit vents, would the cupola be enough ventilation at the ridge or would I need to add some other vents along the ridge line (like a ridge vent but not continuous I am thinking?)

thanks for the responses

 

[billconner]

It sounds perverse but is there a vapor barrier under the slab? Just trying to assess potential for humidity.

 

[Pattycakes]

Highly unlikely, the building is built into the side of a hill and there is a lower level with now unused horse stables and a garage door that opens to the back. It is defiantly damp down there but the upper level which I want to insulate seems to be sealed off pretty well with subfloor and plywood flooring. That flooring does act as a vapor barrier correct?
I would likely have close cell foam sprayed down there between the joists if more temp control is needed after doing ceiling and walls with fiberglass

 

[billconner]

Without seeing it, I'd be surprised if the lowest level of floor wasn't a source of moisture in the house. The lower in portion of a building is generally under negative pressure and upper portion positive, at least in heating season.

Usually better to include basement/crawlspace with interior conditioned space, but again, without seeing hard to know.

I would not count on flooring to be a vapor barrier. I would expect a lot of gaps and cracks and seams in it.

 

[kj_mustang]

How big a building? My building was built as a unvented attic space, no soffit or ridge or gable vents. My cupola only had about a 18"- 24" long section of open ridge to the inside of the cupola. That length by about 5" wide is not much venting space.

 

[Pattycakes]

Unfortunately it wouldn’t be possible in this case. Lower level is very interesting, like time stopped. No horses for many years but all the harnesses still hanging and a 1940s wheelbarrow full of hay with a pitchfork.
if moisture is an issue coming up from that level best solution I can think of is the closed cell foam to seal it off

 

[KJ in VT]

The purpose of the soffit vents is not just moisture management, but to maintain cold roof as well. Without the cold roof, ice will accumulate, at best creating an ice-fall hazard and at worst an ice dam that can create leaks. I'd say soffit vent required, baffles depending on how the rafter/ceiling joists interact. If insulating the joist bays with your planned depth reduces the passage between the top of the insulation and the roof sheathing to less than 2", baffles are needed.

As far as the adequacy of the cupola vents, though probably not ideal, if there is enough vent area (typically a 1/300 ratio of enclosed area to vent area), I think you'll be OK. But you know what they say about opinions...