Should I convert to unvented conditioned attic?
Please help! My wife and I just bought our house in January. No basement so our hvac and ductwork is in the attic. We have periodically noticed condensation immediately below the attic and have been having issues all summer. Roof is brand new, we have a ridge vent and 2 gable vents but no soffit ventilation. We have loose cellulose on the attic floor. I have been sifting through conducting research and debating converting the attic to a full unvented, conditioned attic or just fix my current vented situation.
1. unvented conditioned attic: I assume I would remove all old insulation and hire someone to spray closed cell spray foam to the underside of the roof, seal up the gable vents and ridge vent? My one concern here would be moisture in the attic. Condensation issues is what I am dealing with so I don’t want a repeat. Would I have to install a dehumidifier or supply vent if I use closed cell spray foam?
2. My other consideration is to replace my solid soffits with ventilated soffits to work with my ridge vent. This would hopefully improve my ventilation issue but I am unsure if this would adequately resolve the condensation issue.
I really appreciate any advice people have on the subject!
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Replies
Unless you are looking to use the attic space for storage, converting to a full unvented attic with SPF under the roof sheathing is an expensive proposition.
If your main issue is summer time condensation, it means warm outside air is making its way to your ducting and HVAC equipment. Your lowest cost option is to build a small insulated and well sealed doghouse around your HVAC equipment. This could be something as simple as a couple of sheets of very thick rigid insulation taped together with a quality tape and sealed to the ceiling bellow with canned foam.
The best way to seal the rest of the ducting is to spray foam encapsulate them:
https://www.energy.gov/sites/prod/files/2013/11/f5/ba_innovations_1-1-3_high_performance_ducts.pdf
Once the HVAC is isolated from the outdoors and the ducting is sealed, you won't get any summer time condensation.
The best thing you could do is get the equipment and ducts out of the attic. Not cheap or easy. Maybe a few minisplit heads on your walls?
A conditioned attic full of HVAC equipment would be better than the current setup but understand it will only be slightly better. This is because now with the insulation on the roof the roof has twice the surface area of the ceiling to lose heat. Putting the insulation on the roof forces you to use the most expensive insulation per R tempting people to lower their R values to control costs. Let’s say you have R30 fluffy insulation on the attic floor that you remove and replace that with R30 on the roof given the larger surface area more heat will escape the home thru the insulation but you will lose less heat from leaky ducts so you may come out ahead or not depending on how leaky they are.
If the bottom of the roof look to be free of rot and mold that would seem to say the current vents is acquit until something changes.
Be careful not to get sucked on to the encapsulation dream. They spray a pathetically small R value of foam on the roof block the vents and leave the old insulation on the floor turning your attic into a mold factory. A conditioned attic must be almost the same temp and humidity as the rest of the house to avoid mold and rot.
If you are a normal person who will be selling this house in the next 7 years from a dollars and cents point of view the smart move is to do nothing but some air sealing and deal with the dripping water somehow.
Walta