Do I really need the attic fan?


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Old 02-06-16, 02:12 PM
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Do I really need the attic fan?

Hi,

I am facing a reroffing project due to unforeseen circumstances.
Going with the metal roof Gerard Shake, most likely. If it matters, I have my network routing equipment and hot water pipes going through my attic.
Currently have a small (not sure what is the CFM) solar power attic fan.
In the new roof proposal I don't see install or reinstall of the fan, just the ridge vent, that I don't have now.
For as long as I am doing the roof I was going to take some fire preventative measures i.e. install fire proof vent "plugs" - something like these - Fire Safe Eave Vent
I suspect it's not the best solution, but it's much better than what I have now - just a mesh with bunch of holes as well.
At one point I had an idea of pressurizing the attic from the inside of the house if I open the attic access door by reversing polarity of the said fan with a switch. Needless to say, it did not work, I am guessing it's the design of the fan that did not allow me to do it.
So, is it better to just nix the fan and make all the attic entry points as fireproof as possible or should I look into getting another fan where I could do the switcheroo?
Thanks in advance.
 
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Old 02-06-16, 02:19 PM
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I think that an attic fan is an asset. I wouldn't eliminate it.
 
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Old 02-06-16, 02:39 PM
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Thank you Pulpo,

Is there any data proving it's benefits compare to unforced ventilation?
If yes, what kind of fan can I get so I'd be able to reverse polarity if I wanted to?
I really don't want to be sucking the burning embers inside the attic when things start flying.

thanks gain,
 
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Old 02-06-16, 03:15 PM
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Dealing with hot embers is not something I have ever had to deal with (knock on wood). But in general, attic fans are a double edge sword. Where they can exhaust a lot of attic heat, if the attic floor/ceiling below has not been well air sealed, that same depressurization will pull lots of the expensive cold air out of the house. Now, if you do not use ac, then not so bad. But ait sealing involves the tops of all walls plus all penetrations. Lots of help here if you need to address that.

As for natural ventilation, it requires lots of vent area and that sounds counter to keeping hot embers out. Just guessing, but I would suspect some good guidance from organizations in your area, fire inspector is where I would start. I'm certain they have attended many presentations and or training on this very topic.

Now, not sure if you want to consider this at this point, but a sealed attic with an insulated roof deck would definitely be an advantage. Just watched a large nursing home replace their shingles and at the same time they added about 6" of rigid foam, new sheathing and then the new roof.

As for the rigid foam, there are non-flammable alternatives (I believe) like Roxul batts. I know they are used on the exterior of buildings but not sure how they would be installed under a metal roof.

Food for thought.

Bud
 
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Old 02-06-16, 03:22 PM
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Proper soffit ventilation coupled with a good ridge vent is passive and most effective. Quite often I find forced air fans on roofs don't live that long, so replacing it may be in the near future. Since you have a ridge vent, but didn't mention soffit venting, let us know about the latter. If you have both, then I would forego the active ventilation as it may be marginal at best.

I don't think a solar powered fan will help if you have a forest fire. You don't want to pressurize the attic (which would be almost an impossibility) anyway.
 
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Old 02-06-16, 04:02 PM
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Thank you both for a quick reply!

a. I do have soffit vents, at least that's what I think they are - just 1 1/2" holes drilled through the end-boards.
b. My little solar fan is pretty slow but lasted 13 years, I am not planing on pushing my luck.
c. maybe pressurizing is an incorrect term. Maybe more balancing out the incoming air pressure(with ambers) with air from inside the house?
If it's not obvious, I don't know what I am talking about here.

If you can please point me to where I can find the information on sealing the top of the walls and the rest of the interior envelope.

Thank you,
 
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Old 02-06-16, 04:19 PM
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Below is a link for air sealing, rather extensive.
https://www.energystar.gov/ia/partne...ide_062507.pdf
I agree with Chandler that the small solar fan would do little to pressurize the attic and it isn't the natural pressure you would need to counter, it would be the wind driven pressure.

A 20 mph wind creates a pressure of about 20 pascals against a house. Typical attic pressures during the summer would be 1 pascal. The natural pressures are created by the temperature difference between inside and outside along with the difference in height between the high and low vents. If you really want to pressurize the attic, review whole house fans which pull air from the house and blow it into the attic. They are used to draw in that nice cool evening air in place of ac. But, drawing air in anywhere might be a concern.

As for soffit vents, what you described sounds like vent holes in the front of the fascia board. Although that may work, typically the round vents with a screen and louvers do not provide a lot of ventilation. Count and measure those vents, calculate their area and derate that by 50%. Some are derated as much as 80%, but I'm not sure what you have.

Bud
 
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Old 02-06-16, 06:54 PM
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Thank you for the link Bud!

Ok, so there goes idea of creating internal pressure, thank you

As far as creating an airtight envelope, I think the best I will be able to do is to caulk around most open clevises in the attic, but there is no way I can seal everything. So most is still better than none.
I should probably mention that I want to use this opportunity to replace the old insulation and have new insulation blown in place. The only exception would be the vaulted ceiling where we are going to use R19 battens.
I should also mention that I use to have one huge (20x24) vent in the far end of the attic that was replaced with the access door at the point when new HVAC system was installed. I don't see any way to compensate for that vent short of installing the gable vent, but again that would be at the cost of jeopardizing fireproofing of the whole structure I am trying to achieve.
 
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Old 02-07-16, 09:21 PM
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two more question please

1. I would like to use the Vulcan fireproof vent "plugs" as I mentioned earlier. Unfortunately the smallest they have is 2", the holes I have in the fascia boards are 1.5"
Is there a correct way of enlarging the holes to make them fit? I realize, I could just use the 2" hole saw, but how to keep it centered

2. I am still not sure how to provide more air into the attic without jeopardizing my fireproofing efforts. How do I compensate for the big gable vent they had to close to install the furnace?

Thanks,
 
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Old 02-08-16, 03:28 AM
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There are a couple of ways to enlarge an existing hole. You can either fill the hole with a 1.5" plug or cover the hole with a board that has a 2" hole to act as a guide. The first requires making a plug for each using a 1.5" hole saw and the second usually requires securing the template board with a couple screws. If the holes from the screws will be a problem then the first approach is best.

Without going back and reading, do you have any other high vents.

Bud
 
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Old 02-08-16, 10:13 PM
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Thanks again Bud,

As far as the round vents go, I think I will just use VE3522 Fire Safe Eave Vent
to cover the whole span between rafters instead of plugging each individual hole. Will probably have to caulk around them to make it tight, but a lot easier than re-drilling the holes I think. I don't quite understand the meaning of the high vents, will assume we are talking about the ridge vent or similar.
Yes, I do have one solar powered little attic vent at the top, or almost at the top of the roof.
Roofer is offering to install the ridge vent though.
 
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Old 02-09-16, 12:46 AM
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Newbie you wrote about adding insulation next to the roof unless this is foam insulation that really concerns me. What can happen is that moisture from cooking, showers etc. can find its way into your attic if the insulation is too close to your roof you get mold. Also if you don't have enough ventilation from your soffit and you close that off you can get mold. Some caulking is fine and plugging holes up so animals can't get in is important but too much is not good either so there has to be a happy balance.
 
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Old 02-25-16, 08:36 PM
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Change of plans, again.

Just spoke to my roofer, he was going to use two surface vents on top of the roof close to the ridge, but I don't see any benefit to it, just another two large holes in my roof. If he installs correct flashing and makes the roof vent trough the ridge vent, is it a problem?
I am going to use radiant barrier on top of the membrane so the decking temperature should drop a little. plus going to try adding another layer of radiant barrier inside the attic on top of the insulation.
The only place I will be adding insulation almost next to the decking is my vaulted ceiling.
 
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Old 02-25-16, 09:02 PM
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As far as ridge venting goes on an asphalt shingle roof the best type of vent is a ridge vent that goes from one end of the house to the other. With all due respect I think you may be confusing flashing with venting which are two separate but important things. Flashing mainly goes next to your chimney but specialized pre-made flashing around vent pipes is important too.

When you say you are going to use radiant barrier on top of the membrane do you mean that you are going to use a special roofing insulation? I have seen it installed mainly as a sandwich type product with osb on both sides. Quite expensive and in my opinion overkill but it does work. On a regular roof job all you would need on the roof deck for extra protection would be what they call in the industry is snow and ice shield. Now in California depending on where you live even that may not be necessary and in that case you use tar paper and then your shingles.
 
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Old 02-26-16, 06:39 AM
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Thank you hedgeclipers,

I am getting a metal roof by Gerard, no ice daming here, at least not yet 😀
My previous roof had I think an R4 fiberglass insulation with RB on one side of it. The house was cooler in the summer than prior to that install, that's why I am going with RB again. It will be installed as a single layer "foil", no fibergless, on top of the Titanium membrane.
 

Last edited by Newbie; 02-26-16 at 06:45 AM. Reason: Fat fingers
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Old 02-26-16, 07:15 AM
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Oh o.k. Newbie that makes plenty of sense to me often times on any type of roof sheathing a roofer puts down insulation prior to installing a metal roof. This does a few things it helps to protect the roof, it adds a sound barrier and it adds some insulation to help keep your house warm while protecting the sheathing underneath. However if your roof is odd and not quite normal in pitch watch to make sure the metal pieces come together well and that they are properly welded or you may have a problem.

Now not everyone is going to have a problem like that however a family on the show Today's Homeowner did have just that kind of problem. Here is a link to the episode I was talking about these people had mold in their house and a metal roof leak Solving Home Mold and Moisture Problems | Today's Homeowner . This should help answer some more questions and may have you asking more questions of your roofer. Anyway I hope the video is helpful and you enjoy it it is free to watch online.
 
 

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