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New Construction Attic Woes


mgbinspect
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New home construction find: A home approaching the termination of the one year builder's warranty.

The home had soffit and continuous ridge vent. This is probably the fifth time I've found ridge vent that did not appear to be cut through the felt paper (and probably the shingles). It's typically rather hard to tell without real scrutiny.

The outside temperature was 100 degrees. The wood trusses were measuring between 129 to 134 degrees. The surface temperature of the cooling system evaporator coil cabinet was 115 degrees and the surface temperature of the roof sheathing on the sunny slope was a blistering 149 degrees.

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The link below shows ignition temperatures of materials. It's pretty sobering that decayed wood can ignite at 150 degrees. Paper yellows at 120 and ignites at 218. Wood slowly chars at 120 - 150.

http://www.tcforensic.com.au/docs/article10.html

The home had a large front gable attic area with a false gable vent. That attic was hardly open to the main attic and not all the way up to the peak.

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All of this was all too typical for new home construction. Nothing seems to be well thought out. And how in the world does someone install a ridge vent without cutting it through?

On top of that, the second floor cooling system, which struggled to muster a nine degree differential, suffered from the typical symptoms of a careless HVAC installer - bare suction line in that blistering hot attic and a poor seal around that suction line where it entered the evap coil cabinet.

I suppose if I managed an HVAC company, I'd probably follow behind my guys occasionally and when they left gaping holes like the one below I'd tell them they if walk away from such a condition a second time, they'll be unemployed. The number of times I see gaping holes in new HVAC installs is unbelievable.

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The most outrageous find on a new home happened about nine months ago. The folks had lived in the home they had built for three years and were preparing to put it on the market. The attic was difficult to access and they had never been in it. When I entered it, I discovered they had been trying to heat and cool a 4000 square foot home with merely a half inch of drywall between them and the outside. There was no ceiling insulation anywhere throughout the attic. It was pretty stupefying and the home owners were justifiably pretty ticked off.

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I don't think those ignition figures are correct. I was always told that wood ignites at 500-600 degrees, depending upon the moisture content. Think about how many flue pipes you've seen that were touching roof decks, but the wood was pristine.

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Those are celsius temperatures in those models and you were measuring farenheit temps.

How closely did you look at the "paper" under the ridge vent. Some vents have a dark filter fabric that from below looks something like paper, depending on how far away from the slot one is.

OT - OF!!!

M.

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My bad on the link to the temps, but that makes sense. Now that you mention it, the link is to Australia I guess.

Mike, I wasn't fully convinced that the ridge vents weren't cut through, but could not even see any appreciable change in the look of the material where I knew the ridge vent overhead terminated and the ridge cap continued. That teamed up with those rediculous temperatures just had me assuming it may not be cut through.

I suppose the bottom line for me is that an attic shouldn't be that hot even if it is 100 degrees outside. It wasn't a shallow attic. I imagine it was about thirteen feet or so to the peak.

Any insights are welcome.

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I suppose if I managed an HVAC company, I'd probably follow behind my guys occasionally and when they left gaping holes like the one below I'd tell them they if walk away from such a condition a second time, they'll be unemployed. The number of times I see gaping holes in new HVAC installs is unbelievable.

It's all driven by the dollar now. If a crew is bringing in the sales and only a few if any callbacks, that's all that matters to the boss. I lost my last job in HVAC resid/light commercial because I fixed too many systems and didn't change enough condenser units or entire systems. Condenser/system changeouts bring in the most money. A certain 'HVAC tech' that I had to work with actually changed a condenser unit on a job when I knew that the condenser wasn't even related to the problem. He was a good talker and could sell. When the callback came, I got sent out alone to fix it, with the understood warning not to reveal the problem to the customer. The other tech got the credit for the overall account because he brought in a good quick sale. I brought in nothing because it was a callback and I couldn't charge for it. I had been with the company long enough for the boss to get to know me and my work. He knew what was going on but eventually laid me off because performance was measured in dollars only and I didn't do so well.

Marc

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I suppose if I managed an HVAC company, I'd probably follow behind my guys occasionally and when they left gaping holes like the one below I'd tell them they if walk away from such a condition a second time, they'll be unemployed. The number of times I see gaping holes in new HVAC installs is unbelievable.

It's all driven by the dollar now. If a crew is bringing in the sales and only a few if any callbacks, that's all that matters to the boss. I lost my last job in HVAC resid/light commercial because I fixed too many systems and didn't change enough condenser units or entire systems. Condenser/system changeouts bring in the most money. A certain 'HVAC tech' that I had to work with actually changed a condenser unit on a job when I knew that the condenser wasn't even related to the problem. He was a good talker and could sell. When the callback came, I got sent out alone to fix it, with the understood warning not to reveal the problem to the customer. The other tech got the credit for the overall account because he brought in a good quick sale. I brought in nothing because it was a callback and I couldn't charge for it. I had been with the company long enough for the boss to get to know me and my work. He knew what was going on but eventually laid me off because performance was measured in dollars only and I didn't do so well.

Marc

Gee, maybe we should start offering "after the contractor or service call" inspections. [:-eyebrow

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The temps are that high because that space is far too big for a conventional vent scheme to work, even without that stupid fake gable there to goof up the vent placement. Soffit/ridge vent formulas are far from adequate, and the air flow far too chaotic to function properly on anything but the smallest and simplest of roof shapes. The whole scheme is a 30 year old bandaid for bad building practice.

There is a house very similar to the one you pictured near me, where the ridge vent runs perpendicular to the prevailing wind. In the winter the downspope side of the ridgevent is under such high pressure from the wind passing over it that it sucks feet of snow into the attic. Pretty impressive intake rate for an exhaust vent.

Tom

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The temps are that high because that space is far too big for a conventional vent scheme to work, even without that stupid fake gable there to goof up the vent placement. Soffit/ridge vent formulas are far from adequate, and the air flow far too chaotic to function properly on anything but the smallest and simplest of roof shapes. The whole scheme is a 30 year old bandaid for bad building practice.

There is a house very similar to the one you pictured near me, where the ridge vent runs perpendicular to the prevailing wind. In the winter the downspope side of the ridgevent is under such high pressure from the wind passing over it that it sucks feet of snow into the attic. Pretty impressive intake rate for an exhaust vent.

Tom

That's happening because they used the wrong type of ridge vent; one that catches the wind. Had they used one with a rib-downwind that either deflected the air up over the of the ridge or closed the downwind side of the vent in high winds that probably wouldn't have happened.

ONE TEAM - ONE FIGHT!!!

Mike

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The temps are that high because that space is far too big for a conventional vent scheme to work, even without that stupid fake gable there to goof up the vent placement. Soffit/ridge vent formulas are far from adequate, and the air flow far too chaotic to function properly on anything but the smallest and simplest of roof shapes. The whole scheme is a 30 year old band-aid for bad building practice.

Golly, I've always experienced, in general terms of course, that tall spacious attics seem to fare pretty well, in regards to extreme temperatures, and that little cramped attics tend to be like little ovens, no matter how much ventilation they have. (That general observation certainly doesn't take into account what types of ventilation were in place and even functional ridge vents may still not be enough) I do agree, though, that the more complex the roof lines are the more out of balance soffit to ridge ratios can get, which certainly becomes one of the monkey wrenches in the works. I've recommended an independent local interior environment specialist and it will be interesting to see what he finds and recommends. No doubt the builder and his roofer will be doing band-aid remedies when major surgery may be the answer.

[There is a house very similar to the one you pictured near me, where the ridge vent runs perpendicular to the prevailing wind. In the winter the downslope side of the ridge vent is under such high pressure from the wind passing over it that it sucks feet of snow into the attic. Pretty impressive intake rate for an exhaust vent.

Tom

I couldn't help but bust out laughing with your last sentence. Thanks for that.

I'll post that specialist's findings and recommendations here, when they become available.

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Nope. It was ShingleVent II, with external deflectors, internal inverted J water diverters and a woven baffle. The fix was to close the roof deck opening on the downwind slope and replace the vent with a MidAmerica ridge vent that has slightly more agressive internal diverters. There's still snow in the attic, but it measures in inches rather than feet. If it were mine I'd have closed the ridge vent entirely and put in gable vents, none would face to weather. Short of that a snow fence on the windward slope is the only way to keep the snow out of this place. The town has 3 enormous snow blowers to keep a 3/4 mile stretch of road clear, the snow banks in front of this place reach 12 to 15' high at the curb. It's a combination of elevation, poor siting, and a downslope wind off of lake Erie.

Tom

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That's happening because they used the wrong type of ridge vent; one that catches the wind. Had they used one with a rib-downwind that either deflected the air up over the of the ridge or closed the downwind side of the vent in high winds that probably wouldn't have happened.

ONE TEAM - ONE FIGHT!!!

Mike

Do you mean a ridge vent with moving parts, that open and close depending on wind conditions?

Marc

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  • 3 weeks later...

Good info above - I have found similar situations when the soffit vents were blocked and no vent baffles installed or installed incorrectly. And yes the ridge vents were not cut through the felt and shingles at the ridge as far back as recommended by the manufacturer.

Of course I have also seen them cut so far they leak and on one occassion their saw blade depth was too deep and they cut 2" into the roof rafters. oops....

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It turned out that the soffit vents were functional, as was Mike O's suspicion, but clearly this attic was way too hot, which I believe is due to two factors: 1. The front and rear accent gables are not cut through to the main attic and only have about a foot of soffit ventilation and maybe six feet of ridge - an oven. 2. Hip roof attics are especially difficult to ventilate. Of course, the builder has passed it off as typical attic temps for a very hot day, and done his best to wiggle out of any responsibility to improve the condition. I believe replacing the false gable vents and cutting some of the roof sheathing out to merge all the attic spaces would help a lot.

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