roof ventilation and Insulation
We recently purchased a summer cabin in the San Bernardino Mountains in the Running springs area. We are going to do a bit of interior and exterior renovation to make it a (hopefully) four season cabin. We have found it extremely difficult to find an adequate number of local contractors to provide info/bids on projects we will be performing over the next few years. Our first project will be to remove the existing heavy cedar shake roofing and replace it with an architectual type composition shingle to increase fire safety and maintain curb appeal. Our current roof is a 4-12 pitch and is constructed of tongue and groove 2X4s running vertically to the peak rafter without an attic space (Cathedral Ceilings). The interior is finished and stained and the exterior looks to have 1/2 inch OSB with roofing paper cover and then the cedar shingles. We want to remove the existing shake shingleroofing and frame the roof with 2X6 or 2X8 with some type of hard insulation between the framing and then deck it with 5/8 or 3/4 exterior grade plywood, roofing paper and a quality 3D shingle to somewhat replicate the existing heavy cedar shake. We have been getting mixed signals from our bidders as to whether or not to ventilate this construction by adding soffits and a peak roof vent. So our questions are as follows:
1.) Is it really necessary to vent the added framing and insulation or to leave it sealed?
2.) Would it be more cost effective to utilize SIP Panels rather than frame the roof?
3.) What are some of the higher grade 30-35 year 3D shingle manf that can provide composition shingle to replicate heavy cedar shake on a 4-12 pitch roof?
4.) How can we determine if this construction will result in a significant difference in heating cost (forced air natual gas) savings to justify the added costs to add this insulation (we don’t have past winter heating bills for comparision) or should we just replace the decking and shingles and leave well enough alone?
Thanks
Jim Banzet
P. S. Our contractors are estimating our roof will require approximately 11 squares of shingles.
Edited 6/29/2002 2:35:05 PM ET by Jim
Edited 6/29/2002 4:15:22 PM ET by Jim
Replies
I do not know much about this. I just know we had an aluminum ridge vent installed on our Lake house when we had it framed in 1989. We have been doing everything ourselves since. Our next roof on this Lake house will hopefully be aluminum shingle(like our regular house is) our metal standing seam.
I stapled up those baffles myself and stapled up fiberglass batts over those. Then last winter Hubby and I used 1/2 thick 4 by 8 sheets of combo stryo/fiberglass over that. Will hopefully get paneling or suspended nice ceiling this winter. Pay as we go.
Jim,
This sounds like a perfect application for a product called Nail Base. It's sort of like an SIP only cheaper. IT's foam of whatever thickness you want to use...4" is typical...that has OSB on one side of it for naling shingles to. You just screw it down with long screws, foam between the boards as you put them down, build up your fascia to cover the edges, and shingle over. no venting needed.
If you really want to vent, do plain old foam layers to desired depth, screw 2x battens running soffit to ridge, and shesheath over that. You will get the best thermal performace if you create an unbroken sheet of foam.
Steve
Many different opinions on venting roof spaces from the pros. In my DIY opinion I would vent with a ridge vent in your climate and the shingles will resist curling up and last longer. Here in Canada the snow in winter requires us to use ugly "forgetmenot's" for vents. These are vents that stick up from the roof and you can't forget them, 'cause you can always see them.
When in doubt..... Over do it!
1.) Is it really necessary to vent the added framing and insulation or to leave it sealed?
You'll get plenty of varied answers here too. Cathedral ceiling are a great headache from that point of view.
2.) Would it be more cost effective to utilize SIP Panels rather than frame the roof?
I don't know from the cost point of view but the solid foam is the only way to go on this roof, IMO.
3.) What are some of the higher grade 30-35 year 3D shingle manf...
Elk, GAF, Celotex- up here we get IKOs from Canada
4.) How can we determine...cost...
As a general rule of thumb (as scientific as asking how heavy is mud since their are so many variables) insulation will pay for itself in three years but you are not just doing an insulation job, you are totally improving the property so do it right and let the chips fall...
Asking us for cost analysis won't do you any good because you and only you know the answers to all the variables about local climate, your heating and cooling preferences, quality of windows, cost of fuel two years from now, ten years from now, whether you will do some of your own work or spend top dollar in an overdrawn labor market...
Now if we can lay cost issues aside for awhile and say, "We want to own this house for a long time and be able to enjoy it with minimal maintainence budget"...
I would use the thick foam panel sip or the other described above. Then dry in with thirty pound felt. Now you run two bys on the flat over it and install a second plywood sheathing. Notice that you've got an air space an inch and a half deep. You'll design your facia and metal edge to allow a smal space for the airspace to breathe. You've just created a "cold roof" which is very common in mountain and arctic climates, a ventilated thermal buffer that helps prevent ice dams and condensation problems.
Choose your shingles and apply them 'till your knees and back squeel with delight at the thought of a hot tub!
Excellence is its own reward!