We bought a 1904 farm house, with a finished attic. The roof needs replacement, but is only 9 years old. The roofer we like the best had an estimate more than double the others — he’s recommending a “cold roof”, adding a new layer of sheathing with furring strips on all the rafters, to improve ventilation. He said the problem is that the finished space has insulation right against the roof planks, causing the roof to cook and fail prematurely.
It all sounds plausible and this roofer comes highly recommended by good friends who work in construction. Any comments? Does this seem like reasonable advice, worth the extra money?
Replies
2 thoughts:
Some shingle manufacturers will not warrantee their product on unvented roofs installations...
Are you sure the finished attic has the insulation shoved right up against the bottom of the roof sheathing? Are there knee walls in the finished attic, behind which you could view the insulation from?
Do you know what brand the old shingles are? Certainteed had some bad batches about ten years ago, and you may be able to recover some money from them.
Here's a list of old threads dealing with some of the issues you mentioned:
27861.6 23651.14 6019.17 2674.4 10171.18 5389.7 39891.2 35678.5 31123.24 38756.4 14232.1 5756.1 33146.4 21700.1 14435.1 40569.3 21650.1
That all you could find?
I reroofed a house that was about 7 or 8 years old(the roof not the house), tore off the shingles and all the sheeting was rotted underneath, isulation right up to the sheeting.
Dont know if thats your case but it could very well be.
Doug
I've seen that way too many times. It would be interesting to know what sort of VB this house has.
IMO, premature shingle failure in asphalt shingles has more to do with poor manufacturing than with overheating. Overheating has been shown to advance the aging of asphalt shingles by about 2-3% per year. That means that if we take the agressive 3% advanced aging and apply it over ten years, a 20 year roof would still have a 7.452092 year life expectancy instead of the normal ten year life left.
Nor enough to account for a roof that has failed after only nine years as in this thread.
That is not meant to take away from the intent or quality of the job proposed by the roofer mentioned in the first post here, I might do the same and the cost might be appropriate. I simply question whether it adresses all the possible problems this roof haaas. I ain't there and cannot inspect the whole roof system to know.
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7.452092 years? Dang, that means the roof is going to fail a week from Thursday at 03:14:26 AM, Greenwich mean time. It would be good to schedule the tearoff crew for a little later that day, or at least bring some tarps to the job to cover it.
Did you remember to adjust for your latitude?
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I think you should set the schedule for a little earlier that day, for just before it starts to fail and leak, and start on the southern exposure. {G}
I'm with Piffin, my experience is that presence of insulation shoved into the rafter bays doesn't seem to affect roof life significantly, at least in my area.
For example, I have looked at hundreds of cape cods with kneewalls and the finished sloped part of the roof stuffed with insulation and none in the roof structure in the kneewall sections or at the peak, with no visible difference between those sections of roof.
Drive around any modest income neighborhood from the 50's and look at the roofs of the capes. I doubt if you'll see any with unequal aging which reflects that sort of insulation patterns in the roofs.
FWIW, In my area, we typically get the full 20 years on 3 tabs, so most of the capes are on their third roof, with a few still sporting their second, a few well into the third.
On the east/west streets, you can often see a difference between north and south exposures (especially noticeable as roofs are nearing term), but not between insulated and non-insulated areas.
Let me see if I can describe myhouse so that it makes sense.
It is basically T shaped and would have 3 gables. However one of the small arms of the T the room under it has a clearstory wall and "vaulted" ceiling. So the roof on that part is a shed roof, but it is a continuation of one side of the gable roof from the other arm of the T.
That ceiling is well sealed with poly and not breaks in it (no electrical boxes). There are soffit vents, but nothing at the top so no air flow. Filled with FG bats, but I don't know if they put in any chutes, but without top vents there is no air movement.
The remainding roof is well vented with sofit vents, gable end vents on the 2 remaining gable ends and a turbin at the T intersection.
That gives me one roof plane where about 1/2 of it is vented and the other have not.
The roof is 25 years old (Timbeline) and does need replacing because of old hail damage.
But you can not tell any difference between that part that is vented and that part that is not vented.
Your's is a perfect test case and example confirming my own opinion.
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Bill,
That does seem to validate the idea of hot, or unvented roofs.
In old houses with little moisture control and open, unfinished attics, I certainly see the need to allow air movement through an attic so moisture doesn't build up and condense on the sheathing or other parts of the attic framing.
Crappy construction or design with a finished cathedral ceiling? Sure, put in baffles or some other form of air channel in the rafter bays so when vapor gets into the bays it doesn't rot them out.
For modern, well-built houses? My first choice is to bring the attic space inside the structure's conditioned envelope and to have hot, unvented rafter bays. And to have just what you have in the4 attic of cathedral ceiling...ZERO penetrations through the ceiling plane.
For what it's worth, I still don't understand the logic of putting HVAC in an attic space that's outside ot the house's thermal envelope.
Now, I am in New England, that may be a factor.
Still, with a hot rof I'll sacrifice a theoretical 5-10 years off a 40 year roof to get the thermal and air infiltration performance that I want. If I live in a house for 60 years and I have to re-shingle at the 30 year point? Oh well. Works in my favor, as it'll be easier for me to reshingle the roof when using a walker at age 60 than when in my wheelchair at age 70.
Thanks everyone for all the info...
The insulation IS installed right against the roof planks (100 yr old farmhouse) Interestingly, only one of the roofers even asked to look.
The roof pitch is maybe 9/12 or 10/12. The house is in Northern Virginia
If the consensus is that there might be some value to doing the cold roof, we'll do it, even for double the money (which is about what it works out to) . Even if it won't make the shingles last longer, it might help make the ROOF last longer, and might give us some insulation benefit.
Marvin
Good enough. It may be that the greatest value in this is the peace of mind you have not only in knowing that you bought the better choice, but in knowing that the roofer is probably the most knowledgeable of the bunch and that he is therefore likely to be doing the better job in a myriad of small ways that you will never be aware of.
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Marvin,
That seems to be the best choice.
You have an old house. The attic is finished. Plaster, I thought.
So it's doubtful that you have a super-tight envelope, and in that case, it's best to maintain an escape path of some sort. Moisture through the plaster, through the FG, past the planks, and into the air channel.
Best of luck with your project, I hope it turns out well for you.
In the early days of FHB, if I recall correctly, cold roofs were discussed. I seem to recall that the opinion given was that the cold roof air gap at to be 3-4"
But I might well be remembering wrong.
Where are you located?
Do you have the pseudo laminated shingles, 3 tabs with patches of lamination to give the effect of an architectural shingle?
They don't seem to last as long.
Can you post a few pics of ypour roof? Say from 2-4 feet away, south exposure?
The pseudo-lams is what we have. Supposedly 25-year shingles, failed in 9. The roof is well-ventillated -- ridge vent and soffit vents at least every other bay. And the old shingles (before ridge vent and added soffit vents) lasted over 15 years.
Clearly bad shingles.
If they are the ones I'm thinking of, there is some warranty coverage - you take pics and send a sample to the manufacturer, they take a couple of months to decide if there's coverage, and then send you a pro-rated amount which, after this period of time, won't even cover the tear-off.
In the extreme weather of mountain Colorado, cold roof systems are common. They are often only 1-1/2" spacing
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Thanks for the info. I've never seen one in my area.
A few factors can come into play.
Your climate.
The color of the shingles.
Vented vs non-vented.
The quality of the original shingles.
Worst-case, in a hot climate with direct solar exposure, dark asphalt shingles can reach 190-200 degrees on unvented roofs. Venting can drop that by 10-20 degrees.
On a hot roof, low-quality shingles, as piffin mentioned, can lose a good portion of their expected life, up to a third. Better quality shingles last much longer, losing only 10-20% of their advertised life.
If you have 15 year low-end shingles with nine years exposure on an unvented roof? They could actually be expected to last for only ten years, losing five years of expected life. You could be at the anticipated life expectancy for those shingles.
Take a good quality shingle today. Today's 25-yr shingle could be expected to lose 10-20% of its expected life...or 2.5 to 5 years.
With the cost of shingles being, for the most part, a small portion of the total cost of reroof, it makes sense to put on the best shingle you can afford.
A manufacturer's warranty? I consider them to be virtually worthless when you figure what you MIGHT get form the manufacturer vs the total cost of a reroof.
So...find out what type of shingle you have. See what's under them. Is the finished attic excessively warm/hot in the summer? Radiant gain through the roof, etc?
If all is currently well, the tear off shows no suprises, your climate allows, and your not suffering heat build-up in your attic space, you could get away with a simple reroof with a high end product.
If it looks like problems are uncovered, or currently exist, with the existing roof, then the "fix" your roofer is proposing is indeed plausible. Realize that furring needs to be more than simple 3/4" furring strips. You need a 2" or so air channel to make things effective, with continuous soffit-to-ridge venting. When going that route, it might help to add some sort of foam insulation, or a radiant barrier, but that depends on your location, etc.
On the face of it, it sounds like your roofer is trying to do the right thing.
Still, I'd first try to answer the question of "what was the life expectancy of the original roof?"