Cold roof in Kalamazoo

If the air is blowing "IN" the vents, that is the path of least resistance. Air is lazy and it will do that. The path of least resistance MUST be from soffit to peak. The only time you might want air to be moving out of the soffits is if you have a whole house fan and it is turned on sucking the air from the house and into the attic. The attic will be presurized and the wir will flow out any way it can. This is a good thing.>>>

Roof vents O/S. 12/12 w/ a knee wall>>>

Vents, as in roof vents? We used to use coravent and we had troubles with piles of snow building up beneath the ridges because just that thing was happening; no external baffle. I aggree that the best way is to just raise the roof to get the total ventilation thing going, but the proper vents properly installed work quite well. When we install them on a retwo fit soffit installation, we will push the insulation back away from the soffit before we insert them. I don't like the insulation touching the bottom of the roof as it does transfer the heat to the deck.>>>

You may have missed my point O/S. With things being equal at the ridge and soffit, I do not have the confidence that simply installing vent chutes, when the insulation is fairly tight, will prevent condensation, or provide adequate airflow.

At most the chutes are what, 1" depth ? And then part of their surface may press against the deck too.

I was up in attic a few weeks ago w/ the chute system and the air was blowing IN the vents. I don't know where to place the blame--intake, exhuast, chutes-- but it did not leave me feeling confident that simply installing SV 2 will solve any shortcomings in the system.

You & Pauls way of doing it is indeed complete. And as you said, there are no irrelevant details>>>

If the proper vents are not working to expectations, I would suspect that the intake is not equal to the outlet. When we do the cold roof, we always cut out the soffit and clear out the insulation. We will always install a fully vented aluminum soffit system. The aluminum perforated has twice the net free area as the vinyl soffit system. 5% for the vinyl and a bit over 9% for the aluminum. If it an't "breath" in, then it can't "exhale" out. We always use the Air Vent II also. It has the external baffles that draw the air out when the wind blows. The Cora Vents and the Cobra Vents will stop venting when the wind starts to blow because they don't have a baffle. It creates a negative pressure at the ridge and it will cause the air to be drawn out of both sides of the ridge.l Very important.

There are no irelavent details! When everything is installed properly and the system is balanced, it is a thing of beauty.

Woody, If you look at one of the first pictures, you will see that we installed a 2 x 6 up the rake. We bent a special piece of fascia for it so that it "stepped" out beyond the old fascia. With that detail, instead of looking like it is a really wide fascia it gives it some depth and another horizontal line. It looks very nice. I will try and go by and take another picture or two of it for you. We finished it about 2 months ago.>>>

Length of the run does not matter?

I have come to the conclusion, simply thru observation, that vent chutes don't cut it. Better than nothing, is about it.>>>

Twil, what Pgriz said! We could have made it 2 " if we had laid a 2 x 4 on the flat and added a piece of OSB over the top for the 2" but this was simplier. It is also easier to fasten the 2x lumber to the old structure this way. We nail the 2 x cleats to the roof after extablishing a square line up and down. We strike lines to mark one side of the rafters on either 16 inch or 24 inch centers and then nail the cleats on on alternating sides; that way we can keep the new rafters dead straight and nail them from the side every 3 or 4 feet. We pull a string along the bottom and top to make them all level and then we pull a string from top to bottom to make sure there is no bow to the new rafters. This roof was 2 inches out of square and we were able to straighten everything out. It is easier to pull all the lines and straighten when the boards are vertical instead of lying flat.

When we are finished, we basicly have a 3 1/2 inch "attic" that is venting continously; all the time. we also leave gaps between the ends of the rafters if they are longer than 16 feet so that the air can flow sideways if it wants to. We don't restrict it in any way. The proof is in the pudding as they say. We have done many like this and NONE of them have any ice buildup. Paint peeling stops and so does any mold accumulation. Most peoples initial thoughts when the price of energy goes up is exactly the opposite of what should be done. Proper ventilation with proper insulation is the key to stopping all of the miriad of problems we are running into.>>>

Tom, fluid flow near the edges is slowed by friction with the edge. The fluid further away from the edge is slowed down proportinately less (but I am not sure if the relation is linear or a power curve). The larger the open space, the less resistance to flow there is for a given fluid. It has been determined through tests, that air flow in a typical roof environment needs at least two inches for the flow by convection to occur to a reasonable degree. Therefore, the code (at least the Canadian one) requires a minimum channel height of two inches. So, the air channels with heights of 3.5 inches will conduct more air with less resistance than a similar channel of 1.5 inches.>>>

Hey! That's my house!

I've never done that before and I am wondering OS, why you laid the 2x4's on edge? Would 3.5" be better for airflow than 1.5"?>>>

pgriz and Mike. You are both right. It works like a charm when done correctly, and it doesn't come cheap. As long as the air is flowing, the house will be in balance and nothing bad will happen to the wood or the structure. Balance is the key. If you restrict the air movement, problems will appear somewhere in the structure. There were a lot of problems in the past 20 years here in the States with homes with the Drivit system exterior finish. Most of them were caused by a lack of flashing details at windows and doors. The "hard" stuff to do.

We do quite a bit of the "cold roofing" in rehab situations when people are tired of just putting on another layer and getting nowhere. It helps a lot to be a good carpenter as well as a skilled roofer. You can see the whole picture.>>>

Mike - point taken. :blush: However, we rarely get much above 90%, and usually the humidity doesn't last long. So I guess one has to really know the environment in which the work gets done. I know (and I think you are reinforcing it) that my knowledge is appropriate for the conditions I'm dealing with, but if I move to a different climate region, a lot of stuff will have to be relearned/refreshed.>>>

Hey!!!

That's OUR patented solution!! :ohmy:

Just kidding. We do this a lot. The usual prescription is... 1) remove whatever crap passes for the roof covering, 2) remove the eave boards and cut out the solid wood that is almost always blocking the vented soffits (You'd think that contractors installing vented soffits would cut out at least a few slots into the old solid wood soffit, but they don't. :angry: ) 3) fix the insulation (add as necessary, remove from places where it blocks the airflow, replace if insulation compressed by moisture or leakage) 4) install 2x3 or 2x4 or 2x6 on end as the spacers (the ones we use depend on the degree of ventilation required, and the amount of visual "bulk" the roof can accomodate) 5) Build new fascia, either even with the old if existing soffits are sufficient, or extending past the existing, if we need more intake) 6) Install new plywood 5/8" CDX. 7) Create a new air chamber at the peak. 8) Install either ridge vents (if slope is 8/12 or better), or Maximum vents (these rise above the roof surface about 1 ft. - much better than mushroom vents in snow country), 9) Install I&W or synthetic underlayment (depends on the situation at hand, and our confidence that we took care of the underlying causes) 10) Install whatever metal covering the customer wanted (steel shingles or panels, or aluminum shingles). 11) Install new fascia covers and soffits if required. 12) Install protection devices (snow stoppers, deflectors, fences) as required.

We size the ventilation to have at least 1:150 ratio, split 50-50, with at least a 2 inch clear air channel. In our climate, the insulating minimum is about R38 and we often get customers asking for R45-R50. After this... No more problems. But it ain't cheap.

We've shown this process as a case study on our web site (http://prsroofing.ca/english/casestudies.html). It's been five years since we did the roof and the customer hasn't had any problems, even with the near-record snowfalls we've had the past two years.

Edit: Mike, if the job is properly done, that wood will be as dry as ambient air will every allow it to be, and there is no need for treated wood.>>>

That's what I have always understood a cold roof to be. I would have liked to see a finished gable view to see how you finished off the barge board to not make it look too big and bulky.>>>

Nice work Old School...looks like they chalked it..then said f#@! it and used there hatchet... :dry:>>>