Roof venting, ridge vent or power fan?

[trader4]

I'm getting a new roof which of course has lead into the age old discussion of how best to vent it. I've got 2 contractors saying ridge only is best, the other insisting that power fans are superior. Personally, I can see advantages and disadvantages to both. I'm interested in other experiences and opinions.

So, here's the deal. The roof consists of 3 seperate sections. One of those is a cathedral ceiling, so using a ridge vent there is a given. The other two sections which are the area of interest are:

Section 1 - Currently has a gable vent in one end and a power fan near the other end.

Section 2 - Currently has a gable vent in each end, with a power fan blowing air out behind one of those gables. This section is over the 2nd floor bedrooms where keeping it cool is very important.

All sections have continous soffit venting, about 2" wide. All 3 roofers say that is sufficient and doesn't need to be improved.

Two of the roofers say to go with ridge vent on both of these roofs, get rid of the existing power fan.

One roofer insists that I should stay with using fans on the two roofs as it is now. His argument is that a power fan moves a lot more air than a ridge vent system can. Climate is NJ.

Thoughts?

[Existential Angst]

Like this?

How about both, putting pancake/muffin fans along the peak, to force air out of the ridge, on a thermo/humidistat? And controllable dampers at the soffit (point 6 in the pic). Intuitively, I think on very hot days, some power assist would greatly help.

Also, how bout a double-wall roof, about a 4" gap. This would radically reduce the heating load in the summer, as well, and could also be controlled with louvres, dampers. The attic would be more usable, climate-wise. This may elim the need for fans altogether.

[Tim Watts]

On Thursday 21 February 2013 13:25 [e-mail] wrote in alt.home.repair:

Passive venting beats active.

Reason?

Power venting might be "better". Until it goes wrong and stops working.

How many houses have you been into where the bathroom/showerroom fan has died? Even less people are going to care to mend a building structure fan. Until something goes rotten...

[trader4]

If you have a ridge vent, then THAT is the vent at the peak. You don't want other vents in the roof too, certainly not power vents and especially not anywhere near the ridge, because then air flows from the other vent that is nearby, over to the ridge and out. That doens't do anything to cool the rest of the attic. With a ridge vent the idea is that air enters the soffits and exists via the ridge, uniformly moving air.

Also humidity is not an issue with either the existing approach of going with a ridge vent.

By getting a new roof, I meant tearing down and re-shingling, not building a whole new roof.

[trader4]

That's a valid point, but not an issue here, because I'm only dealing with what I do. And if a fan craps out, I'll fix it.

[Frank]

I agree with passive. My fan stopped working and I replaced it with a passive vent when I got new shingles. My neighbor was not so lucky. His caught fire. He might have died had other neighbor coming home late at night had not noticed it and alerted him.

[Existential Angst]

If you have a ridge vent, then THAT is the vent at the peak. You don't want other vents in the roof too, certainly not power vents and especially not anywhere near the ridge, because then air flows from the other vent that is nearby, over to the ridge and out. That doens't do anything to cool the rest of the attic. With a ridge vent the idea is that air enters the soffits and exists via the ridge, uniformly moving air.

Also humidity is not an issue with either the existing approach of going with a ridge vent.

By getting a new roof, I meant tearing down and re-shingling, not building a whole new roof. ========================================================

Well, when the shingles are off, they could just put some 2x4s on edge, and tack on the plywood sheathing. Then you'd have yer air gap. I've always wanted to do this for myself, but I got slate, which has about another 100 years left on it....

I thnk it's worthwhile looking into, and might not add that much to the whole roofing job. Course, you don't want your roof to be a 1,000 sq ft squirrel's nest, either.... lol

[Doug]

As my brother in law told me once... why pay to move the air? Having lived in Long Island, I think ridge vent is better. And more important, if 2 outa 3 roofers like ridge vents where you are, I'd give that serious consideration.

And FWIW, I once had one in Texas and it stopped working... problem is, I don't know for how long before I discovered it.

[(PeteCresswell)]

Per [e-mail]:

I am about 23 miles west of Philly.

We had two installs of power fans: one was in the roof facing upward and the other was in a "window" in one end of the attic.

Never again. The noise/vibration was not worth any increase in effectiveness.

With the roof mount, I mitigated it somewhat by detaching it from the roof and hanging it on bungees... but it was not enough of an improvement for me.

[John Grabowski]

The ridge vent and other passive venting will only provide a minimal amount of air movement. If you want to be able to cool down the attic space in order to lessen your air conditioning load, then you need a powered fan. I have a ridge vent and also a mushroom type attic ventilator fan on the roof which definitely lowers the temperature of the attic in the summer.

[Stormin Mormon]

Years ago, I was helping install AC in second floor of a house. Air handler in the attic. We had a power vent put in by a roofing company. The day they put it in, I wired it to a temporary source of power. Turned it on, and the attic temp dropped many degrees, nearly instantly. I was really impressed how much good it did.

Christopher A. Young Learn more about Jesus

.

The ridge vent and other passive venting will only provide a minimal amount of air movement. If you want to be able to cool down the attic space in order to lessen your air conditioning load, then you need a powered fan. I have a ridge vent and also a mushroom type attic ventilator fan on the roof which definitely lowers the temperature of the attic in the summer.

[clare]

Just don't make the stupid mistake of installing ridge vents AND conventional mushroom vents on the same roof. The mushrooms become inlets, and you get "short circuit ventilation" that does not properly ventilate the lower poertion of the roof/attic.

[clare]

Properly sized and installed passive vents will move as much air as required - and often as much as a powered vent. Hot air ALWAYS rizes. Good eave venta and good ridge or mushroom vents WILL ventilate an attic.

[Tim Watts]

On Thursday 21 February 2013 17:07 Stormin Mormon wrote in alt.home.repair:

Occurs to me:

Was the OP talking about a method of *cooling the attic space* (and thereby the house) or *venting the structure of the roof to prevent condensation and rot*?

Over here (UK) we concern ourselves a lot with the latter. But as people are mentioning aircon and stuff, I did wonder...

[trader4]

Both. Reducing the temp helps with roof life and cooling bills, at least a little. Venting for moisture prevents moisture damage to the wood components, etc. OF those, the latter is the more important.

Hide quoted text -

[Chomper]

I would assume, being in NJ, you do have cold (freezing) weather.

Here's some thoughts before you decide.

- If you decide on ridge vent (which I would suggest), you do not want the existing gable vents to act like the intakes even though you have soffit. I have seen where ridge vent was installed leaving the existing gable vents. During rain storms in hot weather, the natural flow of air actually pulled in the elements of water through the gable vents.

- Power vents are the absolute worst solution to use, where freezing climates occur. They don't work in the winter. A structure must be able to exhaust any hot air of the building envelope, which rises through the ceiling insulation in the winter. I believe I may have told the story in this forum of actually observing water dripping through ceilings in the winter, because the only type of ventilation installed was power vents.

If you do go with ridge vents, you must close off the gable end vents. You must make sure the soffit vents are cut through and unobstructed by insulation. In most cases, baffles are used in the initial 4 ft from top plate of the wall. This helps provide a continuous unobstructed ( think insulation) passage from the soffit intakes.

I guess you must decide what is the most economical, but it won't necessarily will be the best functional system. By this I mean if you must close off the gables, without ruining the appearance of the structure, and making sure you have clear intake passage from the soffits, makes enough sense for the money involved in doing it right. Otherwise, you may want to use another method of choice.

If it were me, I'd have to give some serious thought on just using the existing gable vents _without_ power vents (which block the vent in the winter), and putting ridge vent on the cathedral room. I would also give some serious thought to additional insulation where you can add it. Attic blankets are pretty economical.

[HeyBub]

Without a bit more info, I can't say for sure, but I'm betting your soffit vents are woefully too small.

The "standard" * is 1 sq ft of soffit vent for every 150 sq ft of attic space. If your house, for example, is 50 x 50 feet (2500 sq ft), you need about 20 sq ft of soffit, or At your 2" wide existing soffits, and ignoring dimunition for screening, you'd need (mumble, mumble, carry the three...)

2880 sq inches of soffit. At 2" wide, that works out to be 1400 linear feet.

Now since this example house's perimeter is only 200 feet, well, yep, you're under-soffited!

There IS a fall-back rule and it's this: You can't have too much soffit venting.

--------

• I think this "standard" is for passive ventilation. If you have fans that are putting the big suck on the attic, you can probably get by with much less.

[Tim Watts]

On Thursday 21 February 2013 20:52 HeyBub wrote in alt.home.repair:

The UK guideline for building regs is 1" continuous equivalent.

That means a 1" wide slot all the way around - or the equivalent area. As this is obviously bad for letting mice in, it's usually implement as a 2" wide series of slots (50/50) or a 1" wide slot with mesh.

That's the soffits - obviously it needs to be balanced with vents up top.

[Doug]

Funny you mention this... I recall one of my homes has this continuous venting in the soffits, my own residence does not.

[HeyBub]

I strongly disagree, for reasons I worked out above using real math.

Further, the notion of "balance" is foolish. If you have too little soffit vents, you're not getting maximum ventilation. If you have too much, they're not doing any good.

Remember, you can't have too many or too much soffit vents.