Insulation Question

[mix123]

So I have just finished insulating my double attached garage. Roof walls etc. The previous owners built the garage. They built a little addition on the back of the garage for tools and a workbench. It is 2x4 construction walls and roof. It has 2 exterior walls and other wall is the house. Singled with soffit and facia etc. The walls were easy just regular R14 2x4 Batts and then vapour barrier.

The roof however needed a bit more planning. Since we're working with 2x4's and then vented at the end of the roof just stuffing insulation against the roof and sealing it up with vapour barrier was a no go. There would be no ventilation and the insulation would be against the cold roof and the warm garage causing condensation. So we took some 2x2's and added them to the studs and lowered down where the insulation would sit leaving a 2" gap for airflow between the roof and the batts, and making sure that the soffits are not blocked by insulation. Now the insulation is 2" down from the roof and air can flow in and out the soffit allowing good ventilation.

Just wondering if this seems like the right plan. I am no expert in any of this stuff. I havent gotten all of the vapour barrier on the roof completely sealed yet (its pretty close just some minor things to seal...staple holes etc), but today it was -6C in the garage and I heated it up to about 2C with and noticed that at where the roof meets the walls in 2 spots there was some frost on the outside of the vapour barrier of the roof (side inside the garage not on the insulation side).

Is this a problem or something I should worry about? Any input would be awesome.

 

[Teken]

Picture > > ?

 

[mix123]

I'll get one up here later....

 

[IDASHO]

In places that get really cold, it is commonplace to use insulation baffles to keep insulation away from the underside of the roof sheeting, allowing for proper soffit to ridge venting.

The baffle staple in place to the top cord of the trusses or the underside of the sheeting. They come in cardboard and poly.

Like so...

 

[mix123]

If I already have a 2" gap in there...is there really a need for these baffles?

 

[IDASHO]

Thats common if you have a steep roof pitch. Normally if you have a 6-12 pitch or steeper, there is enough room even with 2x4 trusses.

If you can overlap the top plate of the wall with insulation, and you still have a gap, you are good to go. I was able to do just that on my garage. No need for baffles.

 

[mix123]

Currently the insulation stops at the extrerior walls. Should it go over the top plate?

 

[IDASHO]

It really should go further.

 

[mix123]

With the baffle in place I can put insulation over the wall plate and into the soffit...as ventilation would still come into the roof through the baffle end at the soffit?

 

[IDASHO]

Correct, though you dont want insulation IN the soffit. Just insulation on top of the top plate.

 

[mix123]

Ok. I will buy some baffles and change this around. I can probably get away with one baffle at the end of the roof as long as that 2" gap is still unobstructed all the way up. Thanks!

 

[mix123]

Here's some pics of what I'm talking about. They're from my phone so they're not that great...but should give you an idea.

The area in the garage:

Here's where the frost is forming. The stops are just there to help hold the insulation up when putting up the vapour barrier, the back part of them is cut off and they are butted right up to the top plate. So currently there is no insulation on the top plate. I purchased some baffles today, so I will be cutting up the vapour barrier putting them up adding insulation to top plates then sealing it all back up. Should that get rid of the frost?

 

[IDASHO]

Looks to me like the lack of insulation on the top plate is allowing enough cold to penetrate into the corner, and the temp difference between the corner and the interior of the structure causes condensation, and frost.

 

[mix123]

Thanks for your help! I'll have to get this fixed up.

 

[Teken]

Looks like Roxul insulation in there . . .

 

[mix123]

I fixed it all up...Removed all those stupid stops, added baffles, insulated above top plate, It seems much warmer in there now as well. Thanks for the input.