# Vaulted ceiling venting



## mark sr (Jun 13, 2017)

The ventilation needs access all the way to the exit vent, the ridge if it's a ridge vent. A lot depends on the size of your rafters and how thick the insulation is but if the intake air can't make it to the exit vent then it doesn't do any good.


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## Richard Pryor (Jun 25, 2016)

Rafters are 2x12 and insulation will be r38. Yes I thought so. Thanks.


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## Bud9051 (Nov 11, 2015)

Just to clarify, the rafter vents should only be above the insulation where they protect the bottom of the roof from contact with the insulation. vents should not extend above or below insulated areas. If vents were run from soffits to ridge there would be little temperature induced air flow. The warm air we want to exhaust out is actually the reason the ventilation works.

Bud


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## Richard Pryor (Jun 25, 2016)

Hi @Bud9051 . I don’t quite understand your answer. If I’m using r38 batts, they would be packed tight against the bottom of the roof correct? So I need vents from soffit to ridge or not? Like this?


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## Nealtw (Jun 22, 2017)

Yes you need that on the slope and at the soffit but not in the space behind the nee wall.


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## Richard Pryor (Jun 25, 2016)

I guess I chose a bad picture. This is a vaulted ceiling with rafters. No trusses so there’s really no knee wall. I need to use bats all the way from soffit to ridge.


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## Richard Pryor (Jun 25, 2016)

This is a better picture. Is this the way to do it?


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## Nealtw (Jun 22, 2017)

Yes, and you will be doing above the light too?


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## Richard Pryor (Jun 25, 2016)

That was the plan @Nealtw unless you tell me otherwise. It’s just a picture I found on google.


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## Nealtw (Jun 22, 2017)

Richard Pryor said:


> That was the plan @*Nealtw* unless you tell me otherwise. It’s just a picture I found on google.


 That is about what you want. :wink2:


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## Bud9051 (Nov 11, 2015)

*Here's* a good article on insulating a cathedral ceiling.

I realize those were just sample pictures but one concern I have with the narrow baffles is they only address the middle portion of the rafter cavity, especially if 24" on center and just one baffle is used.

Bottom to top is correct however, if you are adding recessed lights, especially if more than one per rafter bay, the amount of ventilation for those bays will be far short of what is needed. Example:
Guidance on ventilation for a regular attic is intended to remove excess heat from the entire attic so a few can lights share their heat across a large volume. But a cathedral ceiling limits the volume of air to just the gap above the insulation in one bay, each bay being separate. A better approach is full width baffles, often made on site, and a larger gap, 2" is recommended. But the limited space doesn't allow for added insulation above the lights so difficult to make it right. LED lights would help or surface mounted would be better.

Bud


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## Richard Pryor (Jun 25, 2016)

Thanks for that article @Bud9051. After reading it, I’m a little concerned about my situation. We have a valley on one side of the vaulted ceiling. The framer’s idea of venting is as follows.










I realize this is a recipe for disaster so I’m hoping you and @Nealtw can tell me what to do.

I would be inclined to do spray foam on that side of the ceiling only, but that corner will have a wood stove chimney coming out. And in my current shop we have spray foam and the amount of leakage due to condensation where the chimney exits the building is insane during winter. So I would rather avoid spray foam altogether.

Here’s a look at the house from outside.










PS every bay was vented prior to framing the valley. So there is venting there.


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## Richard Pryor (Jun 25, 2016)

Maybe I can do spray foam on every bay except the one where the stove pipe will be installed to avoid condensation problems? Here’s what my shop looks like. You can see drops of water if you look closely.


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## Bud9051 (Nov 11, 2015)

I'm not totally understanding the intended air flow and valley situation, but do know that valleys create a block preventing low to high ventilation. for your next house the solution is to strap the top of the rafters before the sheathing goes on. That provides a gap so all rafter bays can communicate with all others and complete the air flow.

let's see what neal says.

Bud


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## Nealtw (Jun 22, 2017)

Did the rafter tails get cut off at the wall outside? 
We have done that with a gable truss just outside the wall so the bottom space would get a vented soffit. It was 12 or 16" out from the wall.


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## Richard Pryor (Jun 25, 2016)

This is what it looks like on the outside. Second picture is what it looks like on the other side of the house and how the valley side looked before doing the valley.


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## Richard Pryor (Jun 25, 2016)

Any pictures of what you mean @Nealtw? By rafter tails cut off I mean.


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## Nealtw (Jun 22, 2017)

Richard Pryor said:


> Any pictures of what you mean @*Nealtw*? By rafter tails cut off I mean.


 Yeah yours are cut off. 
What kind of siding are you planning for that area?


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## Richard Pryor (Jun 25, 2016)

Nealtw said:


> Yeah yours are cut off.
> What kind of siding are you planning for that area?


Plan is to have horizontal lap all throughout. 6” reveal.


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## Nealtw (Jun 22, 2017)

Richard Pryor said:


> Plan is to have horizontal lap all throughout. 6” reveal.


 Wood or some other solid?


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## Nealtw (Jun 22, 2017)

Richard Pryor said:


> Maybe I can do spray foam on every bay except the one where the stove pipe will be installed to avoid condensation problems? Here’s what my shop looks like. You can see drops of water if you look closely.


 Yeah they want you to stay away from the pipe with the insulation. 
I think it should be inside a big galvanised duct that you could insulate right to. And have a drain to the outside at the bottom. 
But in your shop air with moisture in it can get to that pipe, if you cut all moist air you would not have that problem???


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## Richard Pryor (Jun 25, 2016)

Nealtw said:


> Wood or some other solid?


Hardy plank. But I can do whatever you suggest up there.


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## Nealtw (Jun 22, 2017)

Richard Pryor said:


> Hardy plank. But I can do whatever you suggest up there.


 That should be installed with rainscreen which is vented from the bottom so you could use that to vent those cavities.


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## Richard Pryor (Jun 25, 2016)

Nealtw said:


> That should be installed with rainscreen which is vented from the bottom so you could use that to vent those cavities.
> https://www.youtube.com/watch?v=zuGXgRzWQmM


I meant horizontal lap made of James hardy material. So not wood.


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## Nealtw (Jun 22, 2017)

Richard Pryor said:


> I meant horizontal lap made of James hardy material. So not wood.


 Same for anything but aluminum and vinyl.
A *rainscreen* is an exterior wall detail where the siding (wall cladding) stands off from the moisture-resistant surface of an air barrier applied to the sheathing (sheeting) to create a capillary break and to allow drainage and evaporation.


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## Richard Pryor (Jun 25, 2016)

Hmm that sounds complicated. Just saw the video.


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## Richard Pryor (Jun 25, 2016)

Would I be better off spraying 3” of closed cell on the bays of that side of the vaulted ceiling, except the one with the chimney pipe? Then batts on top of that?

Then batts with vent on other side of vaulted ceiling?


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## Nealtw (Jun 22, 2017)

https://www.greenbuildingadvisor.com/article/all-about-rainscreens


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## Nealtw (Jun 22, 2017)

Richard Pryor said:


> Hmm that sounds complicated. Just saw the video.


 With a trim on both sides you might just do the porch area for the venting.


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## Richard Pryor (Jun 25, 2016)

After speaking with my framer, I don’t think rainshield will do anything to increase venting. Tongue and groove will go against the rafters in the porch area. He drilled 4 holes at the top of the rafters that are against the house and he thinks that will provide sufficient ventilation for the whole area of the vaulted ceiling on that side of the house.

I’m inclined to do spray foam on that side of the vaulted ceiling and venting the other side since it’s a straight roof with no valleys. Unless you think this is not a good idea @Nealtw?

My concern with doing this is the condensation on the bay where the chimney pipe will be located, and also will the ridge be sealed on both sides with spray foam or will they be able to block off that side from the other. Also, how will the house behave with one side sealed and the other side vented. Attic will be vented as well.

Or should I just go with both sides vented and drill more holes on that last rafter that’s against the house, and also make holes on each bay inside the house?


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## Nealtw (Jun 22, 2017)

The biggest concern with venting is about the heat off the top of the wall with will dissipate one way or other up into the valley above or up to the peak so I don't see the need to change to foam.


Condensation off the b vent, I think you are comparing apples and oranges. 
The picture you are showing from the shop, air leaks from the shop to the attic area?
B vent not blocked and sealed with the required metal 
So if the b vent is sealed properly you don't have warm moist air from the house and if with venting the air in that area is outside temperature so any moisture in it will be the same temp as the metal work so you would not get any condensation.
See Item six here to see what needs to be done at the ceiling level


https://ontime59.com/how-to-find-seal-attic-air-leaks/


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## Richard Pryor (Jun 25, 2016)

So what do you suggest I do, @Nealtw? Because the way it’s set up now, and considering the porch will be covered by tongue and groove, there will be 6 rafter vents on the valley (3 on each side) supplying air to 15-18 bays. But not all the bays have an opening. He drilled a few holes on the valley rafter adjacent to the house (picture 1). I’m inclined to think that many more holes are needed. And also holes on every bay on the inside of the house, not just 2 like the picture below (picture 2).


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## Richard Pryor (Jun 25, 2016)

The more reading I do, the more inclined I am to spraying 4” of foam on the vaulted ceiling, fill the rest with bats, and call it a day.


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## Nealtw (Jun 22, 2017)

I would just do a ridge vent on the peak above this. and cut the same hole in the rest of the bays.


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## Nealtw (Jun 22, 2017)

I have only heard the bad news from the ones I have heard of so I don't know the success rate. 
https://www.nachi.org/inspecting-spray-foam-insulation-under-roof-sheathing.htm


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## Nealtw (Jun 22, 2017)




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