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I have a customer in Michigan who I completed a roof for several years ago and now we have a problem. The attic has lots of moisture in it which is seeping through the drywall into the living space. I installed a ridge vent and a previous contractor installed soffit vents but the insulation may be stopping the airflow somewhat. He also have gable vents and I am not really sure how this is affecting the airflow performance. This house is a 2 story chalet so there is not much insulation room and not a good way to ventilate it seing as it have 2x6 rafters and 6" of insulation. Can anybody give me some advise? The underside of the roof sheeting has moist mildew and has had it for a very long time and the customer wants to get it fixed???
 

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frostbitten1 said:
I have a customer in Michigan who I completed a roof for several years ago and now we have a problem. The attic has lots of moisture in it which is seeping through the drywall into the living space. I installed a ridge vent and a previous contractor installed soffit vents but the insulation may be stopping the airflow somewhat. He also have gable vents and I am not really sure how this is affecting the airflow performance. This house is a 2 story chalet so there is not much insulation room and not a good way to ventilate it seing as it have 2x6 rafters and 6" of insulation. Can anybody give me some advise? The underside of the roof sheeting has moist mildew and has had it for a very long time and the customer wants to get it fixed???
Combining ridge vents with gable vents ends up short-circuiting the ventilation. In the ideal case, the warm air rising in the attic will exit at the outlet vents, and create a suction that will force cool, dry air from the soffit vents to enter the attic area. When you have ridge vents combined with gable vents, the air ends up entering via the gable vents, and exiting at the ridge vents, leaving the lower areas of the attic stagnant.

Your note that this is a chalet probably means that the vapor barrier is non-existent, and the fact that the space between the rafters is filled with insulation means that you in effect have a cathedral ceiling situation, which by definition is almost impossible to vent. When faced with this situation, we have had to build a second deck on top of the first roof deck (2x4 on end spacers supporting a 5/8" plywood deck) which allows about 3 1/2 inch of ventilation space. Of course, for this to work, you also have to finish the lower end with proper amount of soffit ventilation, and the upper section with ridge vents. It's not a cheap solution, but sometimes this is the only way to retrofit a home where the ventilation was not properly designed in.

I believe that Grumpy, who frequents this forum has also done a number of such retrofits.
 

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Without getting into all the details this morning, I'll just say roof isn't venting at all. The simplest solution will be easiest.
After you get all the sheet-rock and insulation down, inspect underside of roof deck for damage. If it's also bad, most likely, you'll also have to remove roof and decking to replace everything there.
Then, put vent baffles on underside of roof deck, ensuring soffit vents aren't blocked. Then put 4" insulation in also insuring no vents get blocked. You can now put a silkscreen? or plastic vapor barrier on underside of joists before re-installing sheet-rock, taping and painting.
PS: Somebody else may decide to add to the thread with more details about what went wrong. I don't know as much about the details of moisture as some of the other posters. Frank
 

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cover the gable vents and remove the iunsulation from the soffits.

Personally I think it is YOUR responsibility to cover the gable vents and the customer's to remove the insulation.

Also look for bathroom or kitchen fans which vent directly into the attic.
 

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What's the ceiling? Wood, drywall, etc? If wood, it is easy to check for vapor retarder (and to install one if needed). Turn off any furnace humidifier. As mentioned, check first for duct ends or leaks. Bathrooms, kitchen & furnace. The rest as Grumpy says.
Jim
 

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Discussion Starter · #7 ·
pgriz said:
Combining ridge vents with gable vents ends up short-circuiting the ventilation. In the ideal case, the warm air rising in the attic will exit at the outlet vents, and create a suction that will force cool, dry air from the soffit vents to enter the attic area. When you have ridge vents combined with gable vents, the air ends up entering via the gable vents, and exiting at the ridge vents, leaving the lower areas of the attic stagnant.

Your note that this is a chalet probably means that the vapor barrier is non-existent, and the fact that the space between the rafters is filled with insulation means that you in effect have a cathedral ceiling situation, which by definition is almost impossible to vent. When faced with this situation, we have had to build a second deck on top of the first roof deck (2x4 on end spacers supporting a 5/8" plywood deck) which allows about 3 1/2 inch of ventilation space. Of course, for this to work, you also have to finish the lower end with proper amount of soffit ventilation, and the upper section with ridge vents. It's not a cheap solution, but sometimes this is the only way to retrofit a home where the ventilation was not properly designed in.

I believe that Grumpy, who frequents this forum has also done a number of such retrofits.
Thanks for the help I really appreciate it. I am new to this board and will check out advise here from now on. All will be taken with a grain of salt but it is refreshing to see gentlmen who freely offer their advise on such topics.
 

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Ventilation?

It sound like you have gotten some good advice. I've have done many built-up roofs in my neck of the woods! Often run across is type of thing. Lack of insulation and venting, leading to the dewpoint forming under the roof. If its just from heat loss here's what I've done. Oh, Mold is another issue. But as for insulation and venting. I'll strip the roof and cut eave line off. Then with 1.5 in. ridgid foam and 2x4 on flat, do a perlin type layout up the roof, this allows you to nail or screw to the trusses or rafters. Then over this I'll install another layer of 1.5" or 2" ridgid foam between 2x4 on edge, leaving you with a 1.5" or 2" airway. New sheeting on top of that, also sub-fascia, fascia, soffit and venting. One other thing is when the roof is stripped, closely inspect the decking. I once removed the lower part of the roof as to allow for additional insulation or replacement of. This does require a fair amount of time, but your able to leave the inside undisturbed. Word of caution, tread and work as softly as possible as not to damage the ceiling. Clients I've had could not believe the difference, from ice dams to barely an icicle. I hope this maybe of some help!
 
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