attic roof fan and insulation for flat-roofed rowhouse

melissastarJune 14, 2011

Earlier I posted a question about my CAC being unable to cool the third floor of my row house, and it was suggested that I may need to better insulate the attic. So, I've been looking into that. I've learned more about the situation in my house now and it has been further suggested that I consider an attic roof fan. I'd really appreciate some feedback/advice from you folks on this site, as I'm a novice on this.

Here's the situation: Largish, old rowhouse, with a flat (actually just very slightly pitched) roof, that seems to be some sort of shingles/tar. LIttle or no access to what attic there is...the only opening to the attic, in the ceiling of a closet, is blocked by the CAC unit for the third floor (it's an all-inside, high velocity type system).

One insulation guy who says he's worked on these old rowhouses for 20 years, says insulation may help somewhat, but that it will be fairly costly and involve creating two access points in the ceilings. And, he says, the real problem is that there's no way for the hot air in the attic to get out.

Can anyone give me an idea about whether putting a fan on an old flat roof is a good idea, and if so, what kind? A turbine fan? I also found one called an aura fan, which is like a turbine, but no moving parts. And is this likely to be worth the expense and risk of roof leaks? And should I still go ahead with the insulation?

Any other advice?


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A flat roof needs to be waterproof. If you penerate the deck with a turbine fan it has to be sealed properly in order not to leak.

If you add an exhaust, then you have to add intakes of the equivalent size otherwise you have little air flow. The problem would be where to put these. I suppose they could go on the roof deck, but again it has to be a waterproof stack of some sort. Another option might be to put intakes through the back wall.

The attic probably has little or no insulation right now. I would investigate adding the insulation. Perhaps you can create another access point through a closet and have insulation blown in.

    Bookmark   June 14, 2011 at 1:45PM
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thanks Mike. I am still pursuing the insulation question and will probably get stuff blown in in any case. I understand that given the length of my house, I'm likely to have to have two new access points cut...and one company says each needs to be large enough for a man to crawl through or I won't get good coverage even with blown in.

As for the fan idea, is it so terribly iffy/hard to make sure that a fan or intake penetrating the roof is waterproof? I have seen ads for some fans that are meant for flat roofs, but I gather from some things I read that many people think of cutting a whole in one's roof as akin to back it only if you absolutely have to.

It does seem as if there needs to be some way to exhaust the hot air at the top of the house to have any hope of keeping it cooler. So I wondered about maybe installing a whole-house type fan (or at least a largish exhausting fan) simply in a third floor window and regularly opening another window or two on the second or third floor. My concern with this is what it might mean to the CAC systems. Could I simply leave them on, but set high enough in the evening to not turn on? What would happen if the fan on the third floor was on and the downstairs CAC system were as well? Would I wind up air conditioning the whole neighborhood? IS there some way to make these work together without running up and down the stairs three times in an evening, opening and closing windows and turning the AC on and off?

    Bookmark   June 14, 2011 at 4:18PM
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Does the ceiling of the third floor feel warm when you touch it? If so then I think you will be the most benefit from adding the insulation.

    Bookmark   June 14, 2011 at 8:28PM
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Good question! I'll wait till tomorrow afternoon and touch it!

    Bookmark   June 14, 2011 at 8:51PM
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In much of the country, opening windows like you are considering is a bad idea since the humidity load that enters the house is harder to remove than the heat loss you experience.

It has to be a really dry and cool morning here before I'll open the windows.

Don't forget to seal first before insulating - the infiltration out the ceiling is usually the worst place in the house. In my model house of 1000 sq ft per floor - an uninsulated ceiling gains 11000 btu/hr. Just getting the r value to 7 (2 inches) gets it down to 4000 btu/hr. Code is r-30 or better and that gets it down to 1000 btu/hr.

I bet everyone is working to get to code levels of insulation - which is great. But if you could just get a couple of inches up there, you would be worlds ahead.

I'm surprised it hasn't come up but attic fans are rarely a good idea. Unless designed well, they depressurize the attic and pull conditioned air out of the house. I built new and didn't consider one. A radiant barrier is a far better idea. More insulation is the best idea. How were you supposed to get a fan up there without access? So you need access for the fan install - better to insulate (IMO - admittedly from a distance).

    Bookmark   June 15, 2011 at 5:54AM
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Thanks, DAvid. Seal first? (I'm a definite novice on this stuff.) Seal what...all the rest of the leaks in the house? Seal between the attic and house? How?

I'm wondering about moisture build up in the attic...could that be a problem if there is no ventilation in the attic?

As for access to install a fan, I have found a couple of options designed specifically for flat roofs with no attics. Here's one Another would be to install a turbine type fan on the roof, or this one:, (the aura) which is a passive system, operating on wind and pressure only or with a solar panel as well.

Oy. I'm no engineer.

    Bookmark   June 15, 2011 at 8:57AM
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One insulation guy just here asked about something I hadn't considered. IN this old house, much of the electrical is still knob and tube. That's almost certainly the case with what's in the attic...not the stuff servicing the AC units, but the overhead light fixtures, for sure.

He says "You're not supposed to blow insulation over K&T, but I've never seen anything happen to it or ever heard of anything happening. Electricians I know say they've seen blackened insulation, but never anything that caught fire."

Hmmmm.....sounds like this could be a much bigger project. It will also involve cutting at least one access hole in the hallway near the stairs. Into an original plaster ceiling. That probably means the whole ceiling will start to come down (it's not in good shape anyway) and will involve laminating over the entire thing with drywall.

Maybe I'm reconsidering this because it's cool and pleasant today. The next miserably hot day and I'll be willing to spend anything!

    Bookmark   June 15, 2011 at 9:49AM
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What is the climate where you live?

    Bookmark   June 15, 2011 at 10:04AM
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I live in Baltimore, Md. Summers can be hot and sticky (frequent 90 plus degree days), winters fairly cold, but not frigid (average low around 35). I'm more concerned about summer time energy use and comfort than winter, because although I've got an old, expensive-oil burning furnace and steam radiators, I have installed a pellet stove in the living room and a gas stove in the kitchen. Between them, I heat the space where I am most of the time and keep the central heating at a very low temperature. Enough of the heat rises to keep my son's room on the top floor fairly comfortable as well. But it's a misery for him to try to sleep up there in the summer.

    Bookmark   June 15, 2011 at 11:33AM
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Any further thoughts, anyone?

    Bookmark   June 17, 2011 at 10:12AM
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I wouldn't install insulation over k&T wireing.
investing time in the air barrier between living space and attic would be a diy and have a good payback. plus increase comfort.
do you have recessed lights?
what type walls and ceilings?
Paneling & ceilitex, sheetrock?
ceiling moldings?
answer a few more questions and we can walk you
thru some air sealing techniques. gotta run, but
will check back later.

best of luck

    Bookmark   June 17, 2011 at 11:38AM
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A metal roof would be cooler than an asphalt roof since it will not retain as much heat and will dissipate heat far quicker.

Even so, you would still need proper venting and insulation underneath. Not a DIY project or something to consider if you intend to move in the near future.

Eventually someone will have to replace the knob and tube wiring.

Radiant heat barrier paint would probably not be a solution.

    Bookmark   June 17, 2011 at 12:54PM
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Thanks guys. Let me see if I can provide a clearer picture of what I'm working with. The house is over 100 years old--a brick row house in the center of a block. Most walls and all the ceilings on the third floor are plaster, with lots of lumps and bumps and a few small cracks, but mostly solid. There are no ceiling moldings.

To call what is above this floor an attic is a an exaggeration. It is a space that ranges from about 3 foot tall at the front of the house to about half that at the back of the house (roughly 40-feet on that floor...first and second floors have a bigger footprint and do not need insulating between living space and roof.)

There is a central air (newish high-velocity, narrow tube) system that snakes around the "attic". The blower is installed at the one access point there had been. This system serves ONLY the third floor and has two outlets in each of three small bedrooms and one in the tiny bathroom. The system serving the first and second floors is in a second floor closet.

The insulation guys tell me that they can blow insulation in but will need to cut at least one new mansized hole in the ceiling to get in--possibly two, one toward either end.

There are no recessed lights on the floor, and only three overhead lights at all. All other lights are wall brackets, wired from the floor up, rather than from the ceiling down. Of the three was put in new by me, so isn't K&T. One the previous owner says was moved by them, so isn't K&T (But may connect in to K&T at the meeting of wall and ceiling. And one is the bathroom overhead, which can easily be checked. My electrician replaced the fixture there, so he should know what's above it.

The roof is asphalt and fairly new (say 5 years old?) so, I'm not inclined to want to replace it anytime soon. I've gotten a quote for $950 to cut an access whole and blow in insulation. I'd have to pay someone else separately to fix up the access panel afterwards, probably adding another few hundred.

Most neighbors don't even try to do much of anything with ventilation in their "attics", as they are all scared witless of cutting holes in their roofs. But I have found info on the Brooklyn Brownstoner blog about successful attic and whole house fan installations and one neighbor loves the whole house fan he has which sits in a sort of plastic cove on the roof. Unfortunately, he bought it with the house and has no idea who installed it.

I don't intend to move in the near future, or even the more distant future. But I would like to make the third floor more habitable in the summer, especially since at some point in the next two years or so, I'd like to turn it into a separate apartment and rent it.

Honestly, I seem to be finding such conflicting information and I'm so dubious about how knowledgeable folks you hire to do this stuff are about old and "out of the norm" houses that I really, really, do appreciate any and all help I can get here on this forum.


    Bookmark   June 17, 2011 at 3:19PM
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I'd really appreciate any further advice I can get. Not sure where to go with this....

    Bookmark   June 20, 2011 at 12:23PM
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I think your best option would be to add the insulation and not add any ventalation. But you have two problems to solve. First you have figure out if you really K&T issue. I would not feel comfortable leaving it in the attic and having insulation blown around. The second is the access point to the attic. You have to cut a hole in the plaster and lathe and hope the ceiling doesn't fall down! I can't advise how risky this may be.

Another thought is to add insulation below the ceiling. I assume you have ceiling higher than 8 feet. You may be able to frame a drop ceiling, add insulation, and cover it with sheet rock. You would have to relocate your three ceiling fixtures to the new ceiling. It may be easier to abandon the old ceiling wiring and run new wiring and wall switches.

    Bookmark   June 20, 2011 at 1:49PM
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