Lean-To Addition on Gable End - Ventilation & Insulation

[HarbourCustoms]

Hey folks,

First off, want to say it's a great forum you've got here. I've referenced it many times in the past, but now I'm coming looking for some advice as well.

I've got a 25x30 garage (9' wall, 6 on 12 pitch roof) that I'm looking to add a 10x20 lean-to style shed onto the rear gable wall to create a studio space. I'll be heating with a mini-split so it'll have to be insulated. Also planning on pouring an additional concreate slab and building out with 2x6 and batt insulation in the walls to match the existing garage and make it a bit more efficient in winter (I'm in Newfoundland - cold, damp climate) No windows planned in the space, just a singular man door to enter from the existing garage.

I've seen a few threads on something similar, both on gable ends of on the side wall of taller buildings, but I haven't stumbled across much on venting it the ceiling space. The lower portion could be easy enough with soffit, but with a planned short 7' wall to accommodate enough roof pitch/slope in the 10' of run I have, I'd like to just sheet the interior roof as is, rather than box it all in with a flat ceiling and having to make a truss up to hang the ceiling. To me a straight rafter seems like the easiest solution.

With the high end of the roof being stitched onto the gable end of the existing garage, I have no way to install a common ridge vent. It would seem to me that each rather space would effectively be "closed in" at the high point, not able to ventilate.

I have seen several threads on using spray foam to seal it all in, but I'm unsure if that's a suitable option.

What would you folks recommend in this case? Thanks in advance !

 

[JBranstetter]

Sounds like the spray foam is your only option. What dimension will your rafters be? What will be the height where they connect to the garage? Will a 7 ft ceiling be enough room for you? What type of roofing are you thinking about using? In your area I think your only choice is spray foam if you are only going to have rafters with drywall on the bottom. Or you will need airspace in between your ceiling and roof with ventilation to prevent moisture build up. How to do the latter option will depend on the elevations of the roof and ceiling. You will also need to keep in mind the snow load on a low pitch roof.

 

[HarbourCustoms]

Thanks the reply.

7' should be ample where its just studio space. I could go 8', but I would think I'd have to decrease the overall width of the addition to allow the rafters to fit between the existing gable end, probably 10x16. To that end, I'd rather the floorspace than an extra foot of headroom.

On a 7' wall, I'd place the tie in at 10' to give just over a 3.6:12 pitch to accommodate snow load. Not a huge concern where im at, but we do get some snow thru the season.

Not planning on draywalling it out, but just sheeting in with OSB, or sound absorption board.

I just wasn't sure if there was any other option for insulating, as I dont know how I'd vent the high portion of the roof where the rafter ties directly onto the side of the existing garage.

 

[JBranstetter]

You would have vented soffit at the tails and you could have standard roof vents up towards the existing garage. If it ties in on the gable of the existing garage, then I would think that you could even vent it through there by cutting some of the existing siding out, basically connecting the two attic spaces.