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lsak 05-01-2011 01:30 PM

Suggestions regarding "cold roof"
I'm about to have my house re-shingled. There's 2 layers now, so having them torn off and starting new. I don't know yet the condition of the sheathing. The house is in Central NJ (Monmouth County). (See images at end of post).

The problem is that there is insufficient attic ventilation. It's a small house (approx. 1000 SF) built in the 1930's, with very little attic space. There are 3 small gable vents (maybe 12" x 8") and not much space to add larger ones. There is one vent on each side of the house, and a smaller one on the front dormer. There's is a non-working attic fan that I'm guessing burned out due to insufficient in-take ventilation. There are no soffits on the house, as the eaves are open with exposed rafters.

I can see inside the attic through the access hatch for the fan (attic is maybe 2 ft high at highest point) and there is very little insulation. Also, the available attic space does not appear to be connected. By that I mean when looking into the attic fan hatch, I can see the gable vent on the chimney side of the roof (see attached photos), but not the vent on the opposite side. That section of the "attic" is blocked off. I also cannot see to the front gable vent, so that too may be blocked.

I'm considering having a cold roof installed as it seems I can then be sure the entire underside of the roof is properly ventilated. Does this make sense in my situation? I've also seen what appears to be 2 schools of thought:

- Attach rigid foam insulation to the old sheathing, then frame on top with 2x4's to which the new roof sheathing (and shingles) are attached.

- Add a 2nd layer of roof sheathing using 1 x 2's installing new shingles to it. No rigid insulation used.

Does anyone have experience with this? Any suggestions or information would really be appreciated!!

Grumpy 05-01-2011 04:51 PM

You have a cold roof now, meaning it is vented. It's not vented well, but it's still a cold roof.

Your house was designed to be ventilated. it's just an old house and they didn't vent much back then. What you can do is install a product such as Air Vent Edge Vent or DCA Smart Vent. This will create an intake. Then install a ridge vent, and close the gables.

An intake is always preferred but you could install a bunch (1 vent for every 150 square feet of attic floor space) of attic vents to meet minimum code and manufacturer shingle warranty requirements. We do this some time when other options are just not economical. While it always works better to have intake, the passive mushroom type breather vents will still work without an intake.

The other option is to install fans on the gables to create a constant pulling from one gable to the other, make sure all gables have vents. Solar fans would work.

You could convert it to a warm deck. Look into the Atlast insulated ventilated nail base. I think it's called Atlast Cross Vent AC. It will provide insulation but also provide ventilation which is essential for most shingle warantys, unless you want to replace your roof again in 15 years. But that's really over complicating things and un-necessary.

Another option, I am sure some would suggest, but I do not like, is spray foam on the bottom side of the roof sheathing within the attic and then negate all ventilation. I'm not a fan of this, but it's becoming more and more common.

Your lower roof is a whole different animal and needs a low slope membrane not shingles.

lsak 05-01-2011 05:21 PM

Grumpy, thanks for responding.

I realize what I have now is considered a "cold roof", but I was referring to an air gap being created above the current sheathing by framing and adding sheathing on top. I know it's expensive, but am having trouble finding other workable options. Any thoughts on this approach?

I have looked into the vent products you mentioned and discussed them with my roofer. His concern is that if there's any insulation compressed against the underside of the sheathing, the air supplied by the vents would be restricted. And I'm not sure if there is a continuous, uninterrupted air passage from the from eave of the house to the ridge (can't see from my access hatch). Do you think these are valid concerns?

I've also considered both replacing the attic fan as well as installing a single gable fan to pull air from the other 2 gable vents. It seems as though any attic fan would be over-powered for the amount of ventilation I currently have (the small gable vents). I realize that would be solved using one of the vent product you've mentioned IF there's at least a 1" gap for airflow. And the fact that I can see (from inside the attic) at least one gable vent is not part of the main attic space (it appears that there is a divider on top of the bathroom wall in the attic, so I can't see the attic space above the bathroom or the gable vent on that side of the house), I'm not sure how effective a gable fan would be.

The lower roof is being handled separately as you suggested with a low slope membrane.

I've been in this house for 17 years and this is the first time I'm replacing the roof. I recently found an area that's leaking and I don't know how long it's been going on. Since I have to go through this now, I'm trying to do my homework to get it done right, so thanks for any additional advice you can give!

Grumpy 05-02-2011 02:05 PM

I've done what you want to do (building up a false roof deck) when the attic rafters have already been improperly insulated and now redoing everything wasn't an option. I think it's alot of work when there are more reasonable alternatives. It will work, but it's kinda overkill in your situation IMO.

Has anyone actually looked in the attic? Alot of questions would be answered by looking inside the attic. I don't see why the sheathing would have insulation up against it, your ceiling was most likely insulated, not your roof... and if your roof was insulated those gable vents are a waste. If the ceiling insulation does come in contact with the roof sheathing, as it probably does directly next to the wall, it's easily moved at the time you cut the opening for the edge vent/smart vent.

The roofer's concerns are valid but again just seems like overkill in my opinion. I wouldn't approach it the same, but that doesn't make him wrong. He's seen the job, I've only seen pictures.

lsak 05-02-2011 03:14 PM


Since my last post I've looked into the attic and agree with you...the ceiling was insulated (although not well), not the roof. So using an eave vent product to provide intake looks to be the best way to go about this - definitely better than the expense of building up a false roof deck.

Can you provide any feedback on the product "In-Vent" made by Cor-A-Vent? I only ask because my roofer mentioned he had used their ridge vent in the past and thought it was well designed. Are the 3 brands (Cor-A-Vent, Air Vent and DCI) all comparable, or is it worth considering one over the others?

Again, thanks for all the information, you've really helped me to make my decision!

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