My wife & I just bought, in Connecticut, a house (Cape-style, built in 1951) with an asphalt shingle roof that is about halfway through its life and needs some relatively straightforward minor repair and maintenance, which we will of course have done. A semi-finished room had been created out of 3/4 of the attic, and we definitely want to finish the room and have it fully habitable. But, although there's insulation blown in beneath the finished portion of the attic and a forced air duct up to it, there is NO insulation under the roof (behind and above the drywall shell of the room created within the attic). The room can only be habitable if insulation is installed; otherwise heating or cooling would prove incredibly costly and wasteful. However, before we move to install insulation and properly renovate, the issue of the roof's ventilation needs to be resolved.
The roof, which is not steeply pitched, is unventilated, except by very small gable vents at either end of the attic, and windows at either end of the attic below them. (One window — in the smaller, unconditioned portion of the attic that has become a closed-off storage closet — has a large fan). There is no ridge vent and there are no fascia, hence no soffits. The lower edges of the roof [which lies on tongue and groove boards that are in good shape, not plywood] simply end at the vertical walls of the house, where the gutter is located.
After speaking with several roofers, there seem to be 3 options for the roof (which have different costs and very different insulation implications):
One roofer suggests adding a ridge vent and a solar powered fan to keep the roof ventilated. If this is adequate ventilation, presumably then some form of insulation batts could be installed while leaving space for air flow. (My concern is that this option, without any soffit vents, still may not set up needed intake of cooler air from below.)
A different contractor has proposed adding a ridge vent AND extending the lower edge of the roof on all sides to allow the creation of fascia and installation of soffit vents leading to the ridge vent. This would definitely work for ventilation of the roof, and presumably conventional insulation could be installed over the vents, while preserving air flow. But I presume the roofing work would likely be extremely expensive — it means rebuilding the roof at top and bottom. (We're still waiting for the written estimate from this contractor.).
A colleague who had a similar situation out at his last home in Seattle suggests keeping the roof in its current configuration (with suitable repair of shingles & flashing), and then using closed cell spray foam insulation underneath it. (I have been told by a friend who is a carpenter that spray foam insulation right under the roof would eliminate the need for ventilating the roof.) Though I know that the closed cell spray foam is considerably more costly than other insulation, this option might be cost effective in view of the costs of alternative number 2.
I would love to hear any informed opinion about these options, especially from someone who is not trying to sell us something. If we put in a ridge vent, can one solar attic fan (or even two) provide movement of enough air (especially cool air in the winter) to prevent mold or rot beneath the roof and avoid ice dams? IF spray foam insulation under the roof proves a cost-effective alternative to adding a ridge vent + extending the roof and installing fascia and soffit vents (plus, of course, conventional insulation), is it reasonable to leave the roof's current configuration unchanged (except for closing off the small gable-type vent) and apply the spray foam? Beyond cost, is this option likely to cause roofing problems (now or in the future)? Do we really have no option other than creating a ridge vent + fascia+soffit vents?
Option 2 or smart vent and ridge vent.
Foamed unvented roofs are fine and now warranted by shingle manuf. too. I will post more later today as I'm currently doing exactly what you mention with the sprayed roof along with a complete roof tearoff which I have to hop up onto right now.
Ventilation is used to solve
1) Excess heat from interior (can cause ice daming) or exterior (causes asphalt shingles to 'cook' and lose lifespan)
2) Moisture problems due to heat from interior or exterior (rot)
3) Heating/cooling efficiency within the conditioned space (tough to cool a room when the attic space above is boiling hot)
Sprayfoam directly against the roof deck probably takes care of 3, maybe 2. It certainly would keep the heat from the sun and 'cook' the shingles though. If I were in your situation, I would consider option 2.
OK, the BEST solution is a combination of what you have heard.
Baffle with foam baffles the entire underside of the roof deck. Install ridge vent on top.
SmartVent is fine but I worry about Ice back up and have seen it fail. Ideally, drip edge venting or building a soffit.
Then sprayfoam encasing the baffles but leaving the airspace(stop 6" short of ridge). The shingles will stay cool and your room will be insulated.
Foam and an unventilated roof will work. Speak with Paul Warren at Icynene ( a foam manuf.)and give him the specs as to expected depth of foam and winter time humidity levels you will maintain. Your particular heating degree days allow use of the less expensive open cell foam which we have on this job too. You'd like to avoid sales oriented discussions but you have so many options in front of you that you really do need to speak with some professionals about your choices. You might try sprayfoam.com/mnps/boards.cfm?mn ... &startat=1 or some of the other q&A boards onsite. Good luck and keep us updated!
12. Any damage or distortion caused by inadequate ventilation either at the eaves or on the rooftop of the building. This includes failure of ventilation caused by blocked, non operative or defective vents or any other condition that renders the ventilation system ineffective. Roof system ventilation should meet local building code standards for total vent area. Ventilation must also be distributed evenly between the rooftop and the eaves of the building;
(b) the roof and each part of it must be designed and built in accordance with the applicable local and National Building Codes. All roof structures must be provided with thorough ventilation and the deck over which the shingles are installed must meet minimum building code requirements. Where local building codes have specific requirements which differ from National Building Codes, the more stringent requirement must be followed.
This basically says non ventilated roofs which use fiberglass shingles will only have a 10 year warranty.
Goes into less detail than the rest, but says warranty does not apply if there is "inadequate attic ventilation"
I'm starting to see a trend here?
I can not speak on the behalf of roofing manufacturers but I highly recommend installing ventilation on any roof regardless of how you seal the roof deck. Remember that if you make a claim with a roofing product manufacturer that they will send an inspector to verify the claim, and if they find inadequate ventilation then you are basically on your own. Spend the extra time, money and effort to ventilate your roof according to your local building code.
You'll need to read page 4 of the Certainteed particulars regarding insulated decks and radiant barriers w/o ventilation. There you'll see the exception made for unventilated decks.
Ok, I went back and re-read the Certainteed warranty. I incorrectly stated that it only applies for 10 years with fiberglass. Here's the breakdown.
Fiberglass or asphalt shingles + proper ventilation = full warranty
Asphalt shingles + no/poor ventilation = 10 year warranty, no 'SureStart Protection'.
Fiberglass shingles + direct to deck insulation without ventilation = full warranty
Fiberglass shingles + radiant air barrier with or without ventilation = full warranty (it should be noted that most radiant barrier installation instructions indicate that the deck must be vented)
So it looks like fiberglass is the way to go if you want an unvented roof.
I'd like to understand how the foam insulator will resolve the problem with moisture in the attic space. That moisture is condensation and the result of a number of factors, only one of which is heat.
It may very well be that, due to some limitations you have, the spray foam may be your best "compromised" alternative. Don't be confused into thinking it is anywhere close to your best alternative or even a suitable alternative AND if you experience some other problems such as condensation.
My father lives in PA and I live on Long Island. Both of our houses have attics sealed with open cell foam insulation and no ridge vents. I also have cathedral ceilings with closed cell foam insulation. The foam insulation seals the wood from moisture in the attic air. The attic becomes part of the envelope of the house. My fathers insulation was done when the house was built in 2002 and my attic was a conversion from fiberglass insulation done in 2007. Our attics are never more than 5 degrees different than the adjoining space temperature. If you would like I can send you some photos and answer any other questions.