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Attics
Attic Ventilation Q's and A's

Ventilation Ratio | Poor Ventilation | Adding Ventilation | Insulation & Ventilation | Whole House Fans | Vents & Ventilators | Frost Problems
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Attic Ventilation Requirements

What is the proper ratio of ventilation per square foot of roof?


1.5 in per sq. ft. Just make sure that the ventilation is installed so an airway is formed to remove heat through the highest part from the lowest part. Ridge vents and soffit vents work best for this. Also, it is better to have ventilation the entire roof length rather than the 8x12 square vents occasionally in the soffit.

I can't say if it's cost efficient or not, but my attic fan cools the attic a lot. When it's in the 70s outside and the attic fan has not run at all, the attic is too hot to go in. On hot days (80+) it comes on in the early afternoon and runs until about 6:00pm. When it's running I can go into the attic without any problem and it's much cooler.

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Another Answer:

The ventilation ratios go according to attic floor size not roof size. You can go as low as 1/300 of the attic floor area (for attics which have a continuous vapor barrier below) to a high of 1.5 in inches x the floor area in feet. So a 1000 sq. feet of attic floor area would require between 480 sq. inches to 1500 sq. inches. That is a huge difference in allowance. I would go with the higher number.
One other thing.. the best system uses ridge vents and soffit vents skipping gable end vents entirely. The number would be split about 50-50 between soffits and ridge.







Attic Ventilation Poor

I have a 2500sqft ranch in Tampa, FL that has 42 soffit vents and a full length ridge vent (new), along with two 2x3 ft gable end vents at the roofline. The attic is 15ft tall at the peak and has 12 inches of blown insulation it - but it is still very, very HOT and has almost zero airflow through it. When I open the pull-down attic door in my garage, it feels as if I turned on a BIG fan because of the air being sucked up there. I haven't found any soffit vents that are plugged. My local electric company told me that an attic fan would not be cost efficient (go figure),but I am looking for a solution! Is there something wrong here, or is this somewhat normal? What can I do?

A whole house fan, sucks from your house pushes into the attic (then out the attic vents..ridge, gable ends, and soffits... where ever)
The gable end fan, mounts over your gable end vent and sucks off the attic discharging outside.
This may very well be your solution....
Having said THAT, let me say that over the last month I have been doing some research and now I am not so sure. There are loads of theories out there (and loads of theorists)... each with his/her own.
Here is some of the comments.. the gable end fan doesn't lower the temp much.. especially with a ridge vent nearby.. (it may just suck from there) or.. it will inevitably suck from your house, bringing your air-conditioned air to the attic and outside air into your house...
My take is still the gable end fan. you can try it. They only cost around $50 (I believe) and one or two, may do the trick. Mine runs the whole time the sun is on the roof, and shuts off after the sun goes down. (they run on a thermostat). I do believe they help. I think my house is much cooler since it was installed.


Poor Ventilation Makes Room Hot

Ventilating an upstairs I have a 1 1/2 story bungalow with a bedroom upstairs. The square footage of the house is 1000 sq. ft. The roof has a 12/12 pitch with 4 rectangular vents (2 on front, 2 on back).
The room (25 ft x 10 ft) is heated and cooled with one register and no return air duct. The temperature during the day in this room is quite extreme. I am having the roof replaced with 6 roof vents along the back of the roof only. Will this be sufficient to cool the room down?
Should I add a return air duct from the upstairs to the furnace air return? If so, how should I go about that? I am remodeling the bathroom which is below this room and is most accessible for doing repairs.
I am really trying to get the temperature down in that room so I can sleep.
Any suggestions or advice, please.

A couple of suggestions. Try using an attic fan to cool the upstairs. Also, I believe the best place for an air return for A/C is on the upper level so you might want to try a return up here also.



Adding Attic Ventilation

I recently bought a colonial style home that has a floored attic. Blown in insulation exists below the attic floor. During the house inspection, the inspector noted black stains on the plywood roof around the roofing nails that protrude into the attic. He said these stains were caused by moisture condensing on the roofing nails, and suggested I add more ventilation.

The attic already has soffit vents and a ridge vent. I'd like to know whether it would be better to add gable vents or through the roof type vents. I'm thinking the gable vents would allow better airflow through the attic and might help it cool down better during the summer. Could you please share your thoughts on the method you believe will work best?

I would look at putting in more soffits vents first, then the roof vents and leave the gable end vents as the last resort. I have been reading recently, that they work the least best (least best?? )


I would also have you consider one more item before proceeding.
That is: do you have an unvented gas heater, unvented gas fireplace or gas logs anywhere in your house? If so, this may actually be the cause of the problem and not lack of ventilation.
Unvented gas appliances such as those I mentioned give off lots of CO2 and H2O.
This dramatically increases the moisture content of air in your house and is most noticeable as condensation in your cold attic as frost on nail heads, wet insulation, mold buildup, etc...
Since this would not be apparent now in the summer, the stains you see could be the result of cold weather condensation. In which case the answer is not more ventilation, but rather less humidity by either eliminating the unvented heaters or adding a dehumidifier to your attic.



Adding Ventilation

I recently bought a house that has the attic renovated I need to add some type of ventilation. I was told something about "baffles" or "gable vents". What are these and can we do this job ourselves. The problem is there is no air circulating through the insulation and this is causing some condensation. My roof also has two layers of shingles. This combined with the insulation is making it unbearably hot up there. Any suggestions?

This is a huge topic....
First off. Is there any attic space left above the ceiling.. or does the ceiling follow the roof line sort of cathedral style? What part of the country do you live in? Where have you notice the condensation?

Here are some things.. I believe you are saying there is NO attic between the ceiling and the roof.. except the space between the rafters... so I will proceed in that belief.
First, the double layer of shingles is no problem. It is not adding to your troubles.
Second, any insulation you have above the ceiling is only helping keep the heat out.

What there SHOULD be is some ventilation path above the insulation.. between the insulation and the plywood of the roof. And there should be vents at the soffits (under the eaves) and at the peak. That would be idea. That vent path would help carry away the heat from the sun on your roof.

If you have nothing but living space up there, then gable end vents are not the way to go. They are used in the area of an attic above the insulation... But better than those are ridge vents, which is a continuous vent from one end of the house to the other along the peak.

O.K.. if you have some attic space, then the best route IS to install one of those ridge vents. You want to find one with external baffles, which just means where the part is that keeps the rain and snow from coming in. Then you need a path from the lowest part of your roof, the soffits to the peak. If there is insulation in the way, you slide styrofoam (I can't remember the name) vent channels to keep a path open under the roof.
You are looking for about 1 square foot of vent area for every 150 square feet of attic floor space.


Is No Ventilation A Problem?

I contracted my house for soffits and to put a new roof on. I got to thinking there was no ventilation if I had done it would have had some perforated soffit and some ridge vents. Well, they didn't, will this be alright?

Without any ventilation, you're bound to develop moisture problems. Putting in ridge venting after the fact is not difficult. I assume you used vinyl soffit material. Pop out every other section and, using a 3" diameter hole saw, drill an opening. Replace these sections with vinyl PERFORATED soffit.

Ventilation Expenses

Is it a real expensive job to have my attic ventilated properly? I have no soffets vents or gable vents no roof vents whatsoever. Is this a 500.00$ job, 1000.00$ job, or more? The roof is just a straight-line roof 60 feet long.

, Well, to be certain you should call for an estimate in your area. Labor charges vary widely. The materials themselves are relatively inexpensive. The vents will be in the neighborhood of $250. (total) If you have, soffits (without vents) adding them isn't too hard, so I believe the total will be certainly less than $1000 for the whole job. It will add years to your roof's life and lower your cooling bills.

Improving Attic Ventilation

How can I improve the ventilation in my attic if there are no soffits? The roof has a ridge vent, and gable vents are on each end of the house. However, condensation is still a problem. Many years ago, I added 6" bats of insulation in the attic over the top of the old insulation. I'm now wondering if there was some kind of vapor barrier I should have laid down first.

Your problem may be from inside the house, not from the attic itself. Condensation is caused from warm air ENTERING the attic from the inside of the house itself.

You should start in the basement if you have one and work your way up, blocking any areas that may be causing warm air to go up to the attic and condensing.

The first place to start is your vent stack. This is about the most common area of moist air going up from inside the house. Get some low expanding foam insulation in a spray can and seal any basement air gaps, especially those one that can be direct flowing like you vent stack form your plumbing.

Then move onto the next floor where if you have paneling, for instance, and crown molding or some molding. Remove the molding and caulk along the top of the wall and ceiling and put the molding back up. This is a common warm air gap escaping into the attic area.

Bathroom fans are also a common area, so again remove the fan cover, and use the spray insulation to close off any moist air escaping.

Go to every floor and just using a common lit candle can sometimes direct you to where a pull of air is going up to the attic area. Watch the flame. Look for cob webs or spider webs. They are created where you have a draft.

Then once in the attic area use some foam insulation again around your stack vent and any light fixture openings, of course, being careful not to foam in any electrical wire. You may even want to put in some cellulose blown-in insulation instead, which will settle and stop any warm air from entering the attic since it settles nicely into these areas. You can lift up some of your insulation and see if it is damp or discolored. This is where air is coming in from the others floors of the house.

Also, you should not have added a vapor barrier. Unless the barrier is placed right next to the ceiling the barrier can trap the moisture in the insulation, where it can condense. Any moisture that finds its way in, needs a free passage the rest of the way through. You can check, under all that insulation, the bottom layer should have the paper vapor barrier right next to the ceiling. You can and should add some soffit vents. Vents will definitely help. The soffit vents will help in the summer to keep the attic cooler ,which in turn will keep the house cooler. This will also help extend the shingles life.

Adding Attic Insulation and Fan Question

I have 2 questions:
1) I want to add more insulation to my attic, laying it down across the joists. Currently all the recessed fixtures have 6 in. of clear space around them. Do I still need to cut openings for these fixtures, or will there be enough room between them and the new insulation?

2) How useful is an attic fan with a thermostat & Humistat (?)

2) The fan is useful with the thermostat during the summer to keep the attic cool. If yours has a thermostat, that will probably help too, (but I am not certain how well that will work in winter.. if it works well .. then that is a big benefit!)

1) The insulation should continue to be left away from the light fixtures. I know .. this is a sad thing. However, if the heat is not allowed to dissipate from the fixture you have a chance of fire. There are fixtures that do allow them to be covered with insulation, but the typical ones do not. One thing you can do to help though is make sure the fixture is well sealed to the ceiling so air (and moisture) can not flow up that way.

Attic Insulation Prevents Ventilation

I live in an old house, the attic has no ventilation other then opening and closing the windows during certain seasons. Rolled insulation was installed in the rafters, there is no soffet vents, so there is no airflow, because of the insulation and lack of vents. For the most part sheet rock was installed and taped up, I have experienced no problems.

My question is should I tear all this down and start anew, or complete the sheet rocking and seal the insulation? It will be used only for storage.

The ventilation is required by roofing manufacturers or their warrantee is void. If you have much moisture flow.. up that way with no ventilation.. your roof deck.. the plywood may rot as well.

Now.. should you rip out what is there?? and add ventilation? That is not necessarily a yes. For instance.. Let's say you live in an drafty house as older homes usually are. And you heat with wood. All that dry outside air coming in.. may may you never have a moisture problem.. and.. the roof... since it is a light color.. and in shade for much of the day doesn't get too hot... well.. then maybe.. it wouldn't be worth it .. know what I mean?

But.... I would do it.. to be on the safe side in my house.. if I were you. I can't say for sure that it will actually make a difference for your house. I have seen well-ventilated attics.. with roof and moisture problems... and houses with no ventilation without problems.. But for me.. why take the chance with the most expensive investment I own.


Whole House Fan

I want to install a whole house fan. However, I'm wondering if the fact that I have loose insulation in my attic presents a problem? Will the insulation blow around? Any installation tips for this project would also be appreciated!

No, I do not think the loose insulation will blow around. The fan will blow up into the air space and shouldn't move the insulation lying between the joists.

For installation.. do you have a framed opening for it now? Or will you cut a new hole in the ceiling and frame it in. It is a fairly involved job. You will have to move away all the insulation form the area. Cut into the joist(s) (these fans run from 24 to 42 inches) and frame in a box to the adjoining joists to support the fan. Use the same size lumber as the present joists and make a box the size of the rough opening required by the fan.

Since these fans draw quite a bit of power if you can, you should run a new wire up there to have it run on its own circuit.

Cost of Whole House Fan

I am considering purchasing a whole house fan for my house. However, I am not finding many manufacturers of this product over the web. If anyone has any suggestions as to where I can find a list of manufacturers of whole house fans, I would greatly appreciate it.

I see them advertised at Home Depot all the time, both direct drive and belt driven, 24" and 30", starting at $109.

Installing Roof Vents

After major foundation work on my 50 year old vacation home, 8 I-beams (925 sq. ft) and minimal cracking (raised 1") I had a new roof installed along with straightening and cross-ties to correct the sagging roof line. My question is this when do the roof vents go on? This actually is a re-roof (2nd layer) and no vents were put in on the first layer thereby causing excessive and premature wear on the first layer. Doesn't it make more sense to cut through one layer of roof and the roof itself as opposed to two layers of shingles and wood? I have had several opinions and versions and am curious as to what the "standard" is. I have soffit vents, however, roof vents are in order. I wonder whether it would have been more feasible to do a complete tear off and then new roof and vents. Contractor initially proposed this and then did a re-roof citing 'cost'.

Cut the ridge vent's hole.. shingle the new roof up to it, and then install the ridge vent on top of the hole. You are right, it is foolish to shingle all the way up and then cut the hole. For one thing the cap shingles will just need to come off, and the last course of shingles may not stay on depending where the nailing strip is in relation to the cut. So.. shingle up to the opening, the last courses will need to be trimmed, but the ridge vent has to cover that last row of nail heads.

more

About the reroofing.
It is certainly cheaper to shingle on top of the present layer. (removal takes time which equals cost.. and disposal of the old shingles isn't free in most places either) It is also acceptable building practice to go that route ONLY if the old roof shingles are lying flat and in fairly good shape.

I don't know what the "standard" is, but I don't think it would be much more trouble to cut through the extra layer of shingle. You say you have soffit vents, but don't mention any others, or what type of roof it is. If it is a gable roof, does it have gable end vents? Also, I got this response from an attic ventilation question I asked a while back "An attic should have 1 square foot of ventilation area for each 150 square feet of attic feet. So you need to add up all the ventilation area you have in the gable vents and your soffit vents. I am a big proponent of ridge vents, which you may also consider."

Whirly Bird Ventilator Noisy

About five years ago, I installed a whirly bird type ventilator. Lately it's making noise when it rotates, like a bearing might be gone. Could this noise be rectified with WD-40 or do you have a better idea?

Use some oil instead. Household 3 in 1 oil is fine. WD40, while good for loosening up things actually isn't a lubricant.

Metal roofs/ with cathedral ceilings

What is the best type of insulation to be used in a cathedral ceiling under a metal roof. What kind of ventilation issues need to be addressed, and what kind of ventilation should we add if we have a humid home all ready, to prevent condensation problems?

This is a complicated situation. Typically, the rafter spaces in a cathedral ceiling are ventilated using Styrofoam rafter vents (also called pro-vent or proper vent). These are continuous vents stapled to the under side of the roof plywood and run all the way from open soffit vents to a ridge vent.

Normally Kraft faced fiberglass insulation is then applied over the vents. The theory is that the vents allow air to travel freely from the eaves to the ridge peak in each rafter space preventing moisture buildup. The question is, can your metal roof facilitate a ridge type vent? I assume they can but have limited experience with metal roofs. If they cannot, you could still vent the rafters through gable vents as long as you install a 'flat' peak in the cathedral and use this mini-attic so to speak as a way for the air from the rafter vents to ventilate outward through the gable ends.

Vent and Insects

I just bought my first house and am new to the world of the handyman, so I feel better asking someone who knows what they are doing before tackling these problems around the house. My problem is with a vent atop one of the peaks in my roof. The vent leads into my attic crawl space. I recently noticed a large wasp nest just inside the vent. I was wondering what I should use to cover the vent, I was thinking possibly a type of screen. Is there a certain type I should use? Also, what should I use to seal around the edges? Am I even on the right track?

From the inside, staple on some screen to cover the opening. Staple it around the edges to seal it to keep the bugs out. (A staple gun.. ... if you buy one now, you will use it often) Buy the nylon screen. By the way.. you are on the right track.


Attic Moisture

I had my roof replaced (a complete tear off) and a new furnace (w/humidifier)and AC added. This past winter the rafters would become frosty. The frost would melt and soak my insulation. The ceiling tiles are now stained from all of the moisture. I had the roofer add more vents but this didn't help. Any ideas????? Would an attic fan w/ thermostat and humidistat work???

The frost and rain appeared in the winter, right?
Well, the moisture from your house is passing up into the attic. Some things to check for, you should have no vents from your dryer, bathrooms, kitchen, etc venting directly to the attic air space. That would be a killer.
Also.. you have soffit vents and gable vents?
How about a ridge vent? They are inexpensive and easy to add, and they add a lot of ventilation area.
The other thing is of course.. what sort of vapor barrier do you have in the ceiling. You should have one.. but if not.. that will be your major source of moisture then. I have a house with a similar problem and intend to try to mend it by painting the ceilings (and walls in my case) with a moisture barrier paint. Benjamin Moore, I know carries one.. (I have checked) It seals the surface so tight, moisture wil not pass through. It is a oil based primer I believe.

If your ceilings are not due for a paint job, I am not sure.. trying to add the vapor barrier now will not be easy. I haven't come up with a good way..

The fan/humistat may work.. but try all the normal ventillation methods first.... add all the vent area you can.
The problem of course is your humidifier. You have a tradeoff problem either have the humidifier or have wet rafters.


Frost In Attic

What causes frost on the underside of the roof(attic) Is it lack of ventilation?

You got it. Not enough ventilation.. coupled with too much moisture.. Make sure you run those exhaust fans in the bathrooms.. and while cooking.. Avoid using heaters, which are not vented.. like kerosene or gas heaters with out an external exhaust vent.

You can read more on this topic in our article section. one of the articles.. on moisture is posted below:

Condensation



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Click here for our Vapor Barrier Basics Article
Click here for our Insulation Article
Click here for our Ice Dams Article
Click here for our Dealing With Condensation Problems In The Home Article
Click here for our Attic Tips Article



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