Idea for attic ventilation

[Todd Burch]

Location: Brenham, Texas. 77833.

I'm working on a fixer upper. Just put new hardie siding (trim, eaves, rakes, frieze, unvented soffits) and painted it. Looks great.

I went with unvented soffits for this reason. The house was built in 1960 with simple open overhangs - just the rafter tails and 1X6 T&G decking above them. Between each pair of rafter tails, a 2X4 was fit. It would have been a ton of work to remove all of them, so I left them. (As a side note, I've never been too impressed with the effectiveness of soffit vents. Attics are still convections ovens around here.)

I'm supposed to be getting a new roof this next week, if the weather holds out. Roofer (a good one, and a friend) is asking me about ridge vents, and he's reprimanding me for not knocking out all the 2X4 blocking and putting in vented soffits. Too late now - I'm not tearing the soffits and blocking out. (Side note - the paint is still drying - I finished it today).

So I have an idea for good attic ventilation, and would like y'alls feedback. All I have right now is 3 gable vents (3 @ 16 X 24) and two turbines.

The house is pier and beam, with a crawl space under it. There are 6 foundation vents around it (~5" x ~18"), with just the north side of the house ventless (the garage is sunken to the main floor on the north side).

I'm thinking about boxing in a vertical pipe somewhere inside the house, that will connect the <cool> crawlspace to the attic. Visualize a flue pipe, or large plastic pipe, (or, heck, dust collector pipe!) with a screen on the bottom and top, creating a direct duct from the crawlspace to the attic.

What do you think? Think it would be effective? I'm thinking it would suck up a ping pong ball on a hot day. I would probably forego the ridge vents if this will work (save some $$) and the turbines and gable vents would suffice.

Todd

[Phil Thien]

Wouldn't that possibly introduce quite a bit of moisture into the attic?

[Todd Burch]

Don't know.

We had the floor open during this renovation, and on a hot day, standing over that hole, there was a definite breeze, and it did smell musty. Currently the grade of the lot causes water to drain towards the foundation at the back of the house. I'll be changing the grade over the next month or two.

Taking June as an example, morning relative humidity is 92%, which, has quite a bit of moisture in it. Afternoon RH, on average in June, is 56%.

[Brian W Smith]

All things considered in our part of the country,we'd be better served taking the air from attic and "pressurizing" the crawlspace.Due mainly to the damage the moisture does in crawl.Also here,soffit vents when engineered into a complete attic "system" is the only way to fly.

[Jim Matthews]

We used this system with a ridge vent.
The original soffit "button" vents had been painted over by
the previous owner.

http://www.airvent.com/pdf/literatur...eSellsheet.pdf

[Jamie Buxton]

So you're sacrificing interior floor space to get cooling to the attic. Maybe that's not so good?
Say your cooling pipe has a 10"x10" cross section. Go back to thinking about knocking out 2x4 blocking around the periphery of the roof. Knocking out just two of them would give you more cross section than the 10x10 cooling pipe. I hate re-doing work, but it does seem like the better solution here.

[Todd Burch]

I guess I could hole saw a couple holes in each one from the inside. Sheetrock and insulation aren't up yet. I'll have to get a ladder this evening to take a look. Perhaps holes in the blocking combined with the vented drip edge might work well enough.

[Joe Tilson]

Todd,
If you drill hole in the blocking, think about gluing screen mesh over them to keep out bugs and rodents. I have done it several times and it works very well. Put the screen mesh on the inside of the attic space to keep from painting over it, if applicable. Hope it works out well for you, whatever you come up with.

[Jim Matthews]

You're in a very different climate than mine, so YMMW.

We needed to create a path from the drip edge vent
to the attic space. The previous owner had filled the rafters with fiberglass insulation.

Once a path was established, the roof held snow all Winter and the
bedrooms below were 1 - 5 degrees cooler on average.

I think of an attic space as a hat for a house.

I have found that decoupling the attic space from the interior of the house
has made things a little more comfortable - delaying the start of our brief air conditioning season.

If you want a chimney effect, separate the air source from your living space.
You have described an "Earth tube" system.

If your water table is low enough, it might reduce attic temps appreciably.
I would concentrate on reflective or shading strategies, first.

What color is the roof?

http://www.permies.com/t/18609/homes...deas-Hot-Humid

[Stephen Musial]

Winter would be the problem I see. You're going to draw moist air up into the attic and then it will condense against the cold roof. Not good. I'd go with the ridge vents, gable vents and put one of these in. Won't cost anything to operate and will keep everything ventilated all year long.

[Jim Koepke]

One of the reasons for soffit vents is to help in keeping the roof from getting warm and melting snow in the winter. Melted snow can turn into ice dams along the edges.

Roofs and attics are amazing science. Done properly they can last for decades. If done poorly, you will be doing it over fairly soon.

jtk

[Mark Bolton]

The problem with centralized makeup air for the ridge vent (gable vents for example) is they don't provide for smooth, uniform, laminar flow, of air under the entirety of the sheathing. Simply supplying an adequate quantity of makeup air isn't enough. The goal is a uniform laminar flow of air from the eave to the peak. And it's has nothing to do with cooling then attic regardless of climate.

[Jim Matthews]

OP lives near Houston, Texas.

[Jim Matthews]

Flesh that out, please. Should attic spaces be dynamic, or static features? Is the attic a maintenance system for roofing materials first, insulation for living space second?

I'm genuinely interested and the OPs question parallels many of my own.

[Stephen Musial]

The idea is to keep the roof the same temp as the outside air so it doesn't bake from the inside out or freeze from the outside in. The more stable you can keep your roof temp, the longer it will last. This also alleviates ice dams in cold climates. In a perfect world, the attic is the same temp as the outside and the insulation keeps the warm air from migrating up and the cold air migrating down in the winter (and the opposite in the summer).

How it's done via soffit vents, ridge vents, gable vents, power vents, etc. is up to you, the house, and your checkbook. Be aware though that some shingle companies won't warranty the shingles if there is no ridge vent installed.