ceiling insulation - is Durovent necessary

[turbo6justin]

As the project moves along the roof area is next. I have a standard 2.5 car garage, 2x4 trusses on 24" centers. I want to insulate the roof behind the roof sheething to leave the 'attic' area open. I have no problem locating the insulation (which is cheap this time of year of course) but I am wondering do I really need to install Durovent or similar sytrofoam type baffels between the insulation and the plywood sheething? I do not have soffit vents or a ridge vent (roof is fairly new so I will not be adding one anytime soon) to allow air in and out to circulate. The baffle would seam a little unnecessary given this plus I would like to save on the cost of course. The insulation will be kraft backed fiberglass like I put in the walls and may eventually get covered with drywall or something.

Let me know.

 

[nehog]

Yes, the baffles are necessary. Without them, the roof surface temperature gets way too high, and the shingles will fail early in their life. The Styrofoam leaves an air gap that allows ventilation. Note: You must also use a ridge vent and vents at the bottom to allow air flow! They are part of a system, and all parts need to be there. Without ridge vents, they have no effect.

Of course, if your roof is not subjected to direct sunlight (or limited sunlight) the need is much less than if it is in the sun all day long...

 

[eagleknight]

I agree with nehog they are needed and will add it will help keep your garage cooler too because the attic won't become as hot.

 

[turbo6justin]

But the situation remains I do not have a ridge vent or soffit vents. I could install a few soffit vents easy enough but the roof is relatively new and I am not going to start ripping things up for a ridge vent. I agree the baffles would make an air pocket but with it 'capped' on each end how much air-flow would there be? It would seem to me that any moisture would just stay in this pocket of air behind the styrofoam similar to how it would stay in the pocket of air the fiberglass creates. Either way the air is relatively stagnant.

So with this being the case how do the baffels really do much?

 

[csp]

You don't have any kind of venting?

 

[D.J.]

IMO, you need soffit vents and ridge vents to prefom as the system Nehog is talking about, you will not be satisfied with the buildings preformance ( shingle life, etc.) if you do otherwise. +1 on needing this system, plus the durovents in the cavity where the walls meet the roof.
________
The Cigar Boss

 

[VHF]

There are several alternatives to a ridge vent for letting the hot air out of the attic, including gable end vents, square roof vents, and wind turbine roof vents (which really **** a lot of hot air out if there is any breeze at all.)

 

[turbo6justin]

I'm glad to see this is getting some attention, I really appreciate it. I like the soffit vent idea except it would do nothing for the insulation in the roof. The turbine or square vents would help but only for the 'cavity' they are installed in. There are 13 or 14 spaces between the trusses and that would be a lot of vents haha.

I am not as worried about summer heat as I am keeping winter warmth in.

So without ventalation either at the soffit or the ridge would the durovent do anything other than take up space and cost money?

 

[Busted_Knuckles]

The lack of the durovent or baffle, is the how and where "ice dams" are built or caused. By keeping cold air running through there, the heat escaping your interior lid, does not melt the snow on the roof and then turn it into ice, backing up and out of the gutter.

Just one of the reasons. Ive added a cobra snow country ridge vent to the 4 car garage I actually park cars in, and its easily 20 degrees cooler in there on a hot sunny day, and the garage has a lid at 8', makes a massive difference. Food for thought....

 

[csp]

If you have composition shingles the excess heat buildup in the attic space will shortenthe life of the shingles. It won't be long and you'll see blisters forming on them, leading to premature failure.

There are lots of reasons to install adequate ventilation. Installing a ridge vent doesn't require re-roofing since you mentioned it being pretty much new. Pull the ridge cap, cut the gap at the top of the sheathing, install the ridge vent, then new ridge cap.

Anyone that lives in snow country needs to be sure that the ridge vent they use will not allow snow to blow into the attic.

 

[timgr]

If you are going to build a cold roof, it has to be vented.

You can take a different approach, and keep the roof cold with insulation. You can put rigid insulation on top of the roof sheathing, and your roof material on top of that, leaving the sheathing exposed to the interior. This is known as a hot roof. You can also apply the insulation on the interior side of the sheathing, with a 100% vapor barrier between the occupied space and the insulation. This is a warm roof. The perfect vapor barrier is essential, because any water vapor that gets out of the living space and into the insulation will condense or freeze on the underside of the sheathing, and the roof sheathing will rot.

You may not be able to get your local building inspector to sign off on a hot or warm roof if they are not familiar with the construction methods. The cold roof is the standard approach in most areas.

 

[bchee]

Where do you live, and how old is this house?

Seems strange they would install a roof without any kind of ventilation whatsoever.

 

[kb2tha]

When I see a post like this, it makes me wonder why the question is asked to begin with. It seems that you are looking for technical advice. If you already knew the answer, you wouldn't be asking the question. So....

Why not take the advice that you have been given. Many here have pointed you in the right direction, yet you still are looking for the easy way out. There is no easy way. If there was, it would be the standard way of doing it.

If, in the end result, you opt for a short cut don't be surprised when you start seeing failures with shingles, moisture, etc. as mentioned above, but what do I know?
Just my .02

 

[bczygan]

Justin,
Do you want to be stupid or smart? Stupid is asking for, and getting, good advice and then trying to discount it and finally ignoring it. Smart is asking for good advice, listening to it, understanding it, appreciating it and deciding you want to take advantage of it by incorporating it into your course of action. You are part way there. I want your next post to be one where you see and understand and have decided to benefit from the work people have done to help you. Otherwise we all (Including you) will have wasted our time. Continuous or spot eave or soffit vents and continuous ridge vent or numerous cans and even powered vents and of course, the continuous durovent in every cavity. Is it more money and effort? Yes. Do it right or don't do it at all. You will be glad you did.


Think of this as if you were advising someone you really care about. You wouldn't want them to shortchange themselves by doing a botched job, would you? Well, think of yourself as that person, and take better care of yourself.
Yours,

Bill

 

[redsky49]

Justin,
Do you want to be stupid or smart? Stupid is asking for, and getting, good advice and then trying to discount it and finally ignoring it. Smart is asking for good advice, listening to it, understanding it, appreciating it and deciding you want to take advantage of it by incorporating it into your course of action. You are part way there....
Bill

Perhaps this might help (or maybe it's just casting pearls before swines):

Attic ventilation is required under all United States and Canadian model building codes.

Attic ventilation is required for four primary reasons:
1. Preventing moisture damage
2. Extending the life expectancy of temperature sensitive roofing materials
3. Preventing ice dams
4. Reducing the heating/cooling loads

You do not state your location. This may or may not make a difference regarding insulation requirements/installation method.

Use of a vapor retarder (and the kraft paper backing of fiberglass batts is a vapor retarder) should be examined for your particular application.

There are various methods by which your attic space may be ventilated. In each case, there will be a requirement for both an inlet and exhaust. A sometimes used rule of thumb calls for 1 sq. ft. of ventilation area for each 300 sq. ft. of roof. This likely is on the low side for best performance, and your application may vary.

The installation of (future) drywall will impact the roof assembly and should be examined not only for the proper performance of the insulation and venting, but also for the possible impact on the truss assemblies, running of wiring for electrical requirements, recessed lighting fixtures, etc.

As for advice, you are certainly free to disregard any and all comments offered on this forum. However, you should remember that someone spent time, effort and hopefully, thought in providing you some help with your issue - in which case you should acknowledge your gratitude and quietly proceed as you wish.

As my mother always said, "You can lead a horse to water, but you can't make it drink".

as always, offered only as opinion

 

[bczygan]

Perhaps this might help (or maybe it's just casting pearls before swines):

Attic ventilation is required under all United States and Canadian model building codes.

Attic ventilation is required for four primary reasons:
1. Preventing moisture damage
2. Extending the life expectancy of temperature sensitive roofing materials
3. Preventing ice dams
4. Reducing the heating/cooling loads

You do not state your location. This may or may not make a difference regarding insulation requirements/installation method.

Use of a vapor retarder (and the kraft paper backing of fiberglass batts is a vapor retarder) should be examined for your particular application.

There are various methods by which your attic space may be ventilated. In each case, there will be a requirement for both an inlet and exhaust. A sometimes used rule of thumb calls for 1 sq. ft. of ventilation area for each 300 sq. ft. of roof. This likely is on the low side for best performance, and your application may vary.

The installation of (future) drywall will impact the roof assembly and should be examined not only for the proper performance of the insulation and venting, but also for the possible impact on the truss assemblies, running of wiring for electrical requirements, recessed lighting fixtures, etc.

As for advice, you are certainly free to disregard any and all comments offered on this forum. However, you should remember that someone spent time, effort and hopefully, thought in providing you some help with your issue - in which case you should acknowledge your gratitude and quietly proceed as you wish.

As my mother always said, "You can lead a horse to water, but you can't make it drink".

as always, offered only as opinion

Wow redsky49,
You write and lay it out so well. Are you an Architect or Building Official or Code writer?

My mother always said, "You can push a horse into the water and he'll probably drink some just trying to get out".............no, I just made that up.

Bill

 

[turbo6justin]

wow, I was just sitting here and reading like I often do and here is my post from a few months back. As an update, I looked at what I use the attic space for and how often I would use it if I moved a few things around vs. the cost of heating the extra air space up there and decided on a conventional ceiling at the 9 foot level of the botom of the rafters. It is insulated with fiiberglass above the drywall which I just finished up last week. Durovent vents at the soffit of course. I have the soffit vents installed and am waiting for a little warm weather for the snow to melt on the roof to get the ridge vent installed. ( I have done some crazy things but working on a snow covered roof is not going to be one of them). If I had gone the other direction and left the attic open I would have followed the advice I was given here of course. That is why I ask when I am unsure or just looking for justification for something.

To clear up one thing when I moved in and the garage was just stud walls and open rafters there was no ventilation to speak of, no cans on the roof, the soffits were solid, etc. I live in Milwaukee, WI and as far as I can tell this is normal construction here. It is once it gets closed in that venting seems to be a requirement.

With that said I was just out in the toasty 55-60 deg garage and loving it. 10-12 deg outside today and I am working in a flece jacket without gloves. Nothing like it.

Thanks for all the help both for me and anyone else who might have the same questions I did.