Insulating a garage remodel

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  #1  
Old 06-17-02, 11:05 AM
markmardon
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Insulating a garage remodel

Is there a way to vent between rafters? I am remodeling a garage and want to open the ceiling all the way to the roof. Because of the way the roof steeply angles upward, I have very little room for roof vents (see attached image). However, I want to keep air moving under the roof. Is there some way to baffle/vent across rafters to a single roof vent near the peak?
 
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  #2  
Old 06-20-02, 07:03 PM
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The correct way to insulate between the rafters is to install styrofoam baffles from the top plate of the walls which your rafters sit on to your ridge at the peak of your roof. Then install the insulation properly. There should be vents on your ridge and at your eaves or soffits (adjacent to top plate). If you have the ridge vents and not the eave or soffit vents, you don't have free venting and your roof will not ventilate. Which will eventually destoy the roof in your application. The easiest way to illustrate free venting is a straw that you dip in water and put your finger at the top of the straw. Take the straw out of the water and the water remains in the straw. Release your finger from the top of the straw and the water falls out of the straw. That's free venting. If either vents are missing or obstructed ( the purpose for strofoam baffles is to allow for clear passage of air from the eaves or soffit vents to the ridge vents), it has the same effect as your finger on the top of the straw.
 
  #3  
Old 06-20-02, 08:04 PM
markmardon
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resercon,

Yes, I understand the importance of proper ventilation under the roof and correct way of doing it. That's why I posted this message. I want to do it and I want to do it right. The problem is that I don't think it's possible to put vents along the ridge because the roof on the garage has 3 planes (one above each exterior wall) which form TWO ridges that are steeply angled and come together in a single point, forming a peak which is attached to the house.

So, it seems like I have a couple of options... 1) install two ridge vents along the ridges, 2) install a roof vent near the peak and somehow channel air from between all the rafters to the one vent. Option 1 doesn't seem desirable since the ridges angle up steeply to a single meeting point. Option 2 just seems like the more logical answer, but I'm not really sure. Is there another option that I'm missing? Does option one make more sense?

Thanks for your feedback.
 
  #4  
Old 06-20-02, 09:46 PM
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Ridge boards are at the very peak of the roof and are level. What you have is known as a hip roof. This board should run diagonally from a cornor of the garage up to your house. The rafters run from the top plate to this board and meets it at an angle. The problem here is how to ventilate the entire roof because of its design?

The easiest way to insulate is to installed it in the ceiling joists. If this is an area where there is a floor and you want to insualte it, then create a room smaller than the area and insulate that. The spaces where the rafters meet the top plate and the house in this case are so small, they are usually unusable. Unfortunately, there was no image attached for me to see.
 
  #5  
Old 06-21-02, 06:49 AM
markmardon
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Sorry about the image but by your description, I think you see the problem. However, I'm planning an open/vaulted ceiling and really don't want to lower it just to be able to get some ventilation up there.

I'm planning on replacing the roof as well. Is there an opportunity there to somehow channel the air across the entire roof to a single vent near the peak by furring out the sheathing slightly? What about furring it out between the sheetrock and the rafters on the inside? Kinda defeats the purpose, I think, to ventilate UNDER the insulation. Just grasping at straws, I guess.

My problem can't be unique. Any other ideas?

Thanks.
 
  #6  
Old 06-21-02, 10:02 AM
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If you really want the ceiling height and are willing to go through the time and expense, then the only way I would recommend to accomplish what you want is to install a cold roof and a vaulted ceiling.

The roof area that is above the vaulted ceiling is where you put your roof vent(s).

To install a cold roof, you have to remove the existing roof and even the sheathing or underlayment. Some contractors recommend perforating the sheathing. I recommend removing it and exposing the rafters. Then install those styrofoam baffles between your rafters. On all your rafters and the board that the rafters meet at an angle install 1 x 2 inch furring strips. Where the top of the rafters meet that board, keep the furring strip 4 to 6 inches away from the board, thereby creating a gap between the furring strips. This gap depends upon local building codes pertaining to the distance nails have to be apart. So if your code says 4 inches, then make the gap 4 inches. Any roofing contractor knows the code. Then install the substrate and the rest of the roof. Then you can insulate the ceiling to your hearts content and you'll have adequate ventilation.

DO NOT ACCEPT NOTCHING OUT THE TOP OF THE RAFTERS AS A SOLUTION. The purpose of the substrate is to distribute the load, this applies torsion stress to the rafters. YOU CANNOT NOTCH THEM!!!
 
  #7  
Old 06-21-02, 01:40 PM
markmardon
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I didn't know what to call it, but the "cold roof" idea is exactly what I was thinking of. Thanks for the information.
 
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