Q: This summer we had siding installed around our house and we painted over the ventilation vents (husband’s idea). My husband decided to cover the attic vent on top of the roof with a plastic bag because he said it would help seal the house better. I had a weird feeling about this, but I don’t know anything about home repairs. Well, now we have a problem with condensation in our attic (that’s what I think). He went up there last night and found that there were icicles on the frame. Somehow, I think we cut off all ventilation and now we have this condensation problem that is freezing because of the cold weather. He thinks we have a leak and that we need to replace the shingles. Do I make sense? Is there any advice you can give us?

A: You’re actually making perfect sense, and while I hate to step into the middle of a marital disagreement, what you are thinking is probably correct.

High and low ventilation in an attic is essential for a passive airflow. Cooler air enters the attic through the low vents and moves through and out of the attic through the upper vents. As that air moves it captures moisture in the attic and flushes it to the outside. Ideally, you should have approximately one square foot of ventilation for every 300 square feet of attic, and that should be divided equally between high and low vents (for example, a 1,200-square-foot attic would need 4 total square feet of ventilation, with 2 square feet high and 2 square feet low).

By cutting off all the ventilation in the attic, you have now allowed the moisture to accumulate up there. Since it has no where to go, it can now condense on the cold surfaces of the underside of the roof sheathing, and the resulting frost and ice is what you are seeing. The more moisture you put into the attic — for example, if your bathroom and kitchen fans duct into the attic but not all the way to the outside — the worse your moisture and condensation problems will become.

If the moisture is allowed to remain up there, as the temperatures begin to come up again that frost and ice will turn into liquid water, which will wet the insulation, damage the wood framing, and potentially introduce mold.

You need to reintroduce ventilation into the attic as soon as possible. I would clean off the paint on the vents, or simply remove and replace them, then I would definitely remove anything you have put over the vents to seal them off. I would also strongly recommend that you talk with an insurance restoration contractor who has power fans and dehumidification equipment. If you have trapped enough moisture up there that you are seeing icicles, it is probably something that needs to be dried out with more aggressive methods than just the normal passive ventilation. Finally, make sure all of your exhaust fans are vented all the way out of the attic.

All that is not to say that you don’t have a roof leak as well. But you need to deal with the ventilation and moisture issues first — once all that is dried out, you can assess if you have a roof leak as well.

Q: Are there any general rules of thumb with regard to the partial demolition when adding onto a house? For example, removing an external wall typically costs $X/foot, or removal of a partial roof is $X/square?

A: There are different estimating books and software available for general and specialty contractors that attempt to put prices to demolition, but to be quite honest I have always found them to be inaccurate enough when it comes to remodeling that I never was able to utilize them. From wiring to plumbing to the tremendous variety of loads and framing variables present in a home that has to be partially dismantled, there is simply no way to predict and estimate partial demolition costs with any kind of accuracy without seeing the home.

About the only thing I can suggest is to talk with a general contractor in your area who specializes in remodeling. If he or she is familiar with your type and age of house and the regional framing methods involved in its original construction, they may be able to give you a rough idea of demolition costs that would at least be in the ballpark. You might also be able to pay the contractor a flat fee or an hourly rate to come out and inspect the actual work you want to have to have done, and provide you with a more accurate cost estimate for the demolition phase of the work.

Remodeling and repair questions? E-mail Paul at paulbianchina@inman.com.

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