Radiant Barrier attic insulation?

[Salamok]

Modern roofs -- those with the weird "double peak" at the top, already vent air really effectively. I don't think fans add much to that.

those are ridge vents and even on new construction you don't always see them (always see them on rooms with vaulted cielings).

Salamok:

you all talking about steel frame or rebar reinforced cement?  I have a buddy that is a polysteel distrib stuff is pretty cool R50 insulation for you walls and can withstand insane winds (i think he said 200mph+) of course your roof would probably blow off long before the walls caved.  I'd consider it for a home I planned on living in for the rest of my life but if you are going to sell it within the next 10 years it probably isn't worth it (unless the hurricane insurance is helping pay for it).

That insulation look basically like an ice cooler? :) I think that's what my friend has. It's solid, and cut and fitted for the walls. I don't know exactly what sort of frame he has, but a good portion has to be steel because he mentions the only downside is trying to hang shit on the walls, and he has to remember to warn contractors lest they fuck up a drill.

Ya polystyrine forms bolted together 4 inch gap inside filled with rebar and concrete.  the reason it's hard to hang stuff is that the studs are the metal ferring strips used to bolt the peices together so instead of wood studs you have sheetmetal.

I'm still waiting for aerogel to get cheap. :)

it is relatively cheap as long as you stick with peices about the size of rock salt.

[Morat20]

quote]
I'm still waiting for aerogel to get cheap. :)

it is relatively cheap as long as you stick with peices about the size of rock salt.
[/quote]
I want it an inch thick everywhere. :) Heck, sandwitch a few millimeters in the doors. That stuff blocks practically all heat, and it can be treated to simply ignore water. I'm sure there's more effective insulators somewhere, but in terms of "what you can fit into a wall", I don't think you can beat it.

Of course, to properly insulate a house with it would cost a fortune.....

[Merusk]

OK, so I don't know the terminology for house parts.  Here's a picture instead. <snip>
So you are saying I don't need to add anymore insulation?  Even though I can cook bacon in my attic without a hotplate?

@Morat, If I lived on the Gulf, I'd be far more inclined to get a steel frame.

I'm saying go ahead and add it, (R-38 is the new minimum standard using 2006 IECC) but wasn't sure where you were adding it.  R-38 is about 12" of insulation, so if you've got that much you're already at the "Minimum"  Adding more can't hurt you, though.  Here's a change to your diagram!



Dave covered why the heat in your attic isn't such a big deal.  Heat rises, after all, so it's not adding much to your house to have a really hot attic other than radiant heat that happens to bleed through everything. The thermal barrier would help reduce that though, as others have mentioned.  Attics get hot because they're covered in nice black tar, tar paper and are usually enclosed.  It's like a mini oven, whee.

  You should have a ridge vent and soffit vents both. (The soffit is the overhang of your roof)  This helps air circulate to remove water vapor and some heat from the attic space.   

Only thing is, don't use the foil-faced insulation without talking to someone more familiar with hot & humid construction.  (I'm not.)  The foil also acts as a vapor barrier and I'm embarrassed to admit I forget if it's supposed to go on the "Warm side" or the "cold side" of the insulation to avoid getting water in it.  I have a notion as to which, but I can't recall for certain.

[Yegolev]

Muh.  I have 12" of fiberglass already, so... wonder what the risks and costs of adding a ridge vent would be.  No, I don't have one.

[Merusk]

You sure?  Ridge vent isn't an actual thing you see through, it's a cap piece filled with plastic spongy mesh (to keep bugs out) that just slaps over the ridge and is the same color as your roof, typically.  You're not going to see light through it, since that would let water in as well.

[Sky]

If you have a ridge vent, you also want to have soffit vents and no end vents. And there's a whole thing about how the house is oriented with the prevailing winds so it sweeps up into the soffits and out the top, not in one soffit and out the other, etc.

Note when I post, unlike most people in the thread I'm in the Northeast, so we deal with both hot summers and frigid winters. Challenging to say the least.

At the least I need another 8-12" of insulation in my attic, but I've got a ton of shit on my plate before I can get to that. Wiring in the attic crawlspace not to code, no insulation on exterior walls, stuff like that. The joy of homeownership (I still wouldn't go back to renting!).

I really don't want to fuck with the roof since, you know, it's not leaking now... but I might put in another vent if I determine it's worth it.

Get a good roofing contractor. My general contractor specializes in roofing. I've got a 2004 roof that's in great shape, so I was wary about popping holes in it. He did a great job (it's pretty straightforward) and there've been no leaks in the torrential rains we've had this summer. Now I'm contemplating a new stove, and I want to run a vent out the roof, and I'm fairly confident in my guy's ability to make a clean chop. I'll install everything and just have him come out after work on day to cut the roof and install the outer vent piece.

[Yegolev]

You sure?  Ridge vent isn't an actual thing you see through, it's a cap piece filled with plastic spongy mesh (to keep bugs out) that just slaps over the ridge and is the same color as your roof, typically.  You're not going to see light through it, since that would let water in as well.

I'm sure.  I'd be able to spot it from the outside, even if I didn't already know it wasn't there.  I do not have turbine vents, nor those small cap ones I have seen lately, the ones that look like a dryer vent cap.  I have two, uh, end vents?  In the gables.  That's where I put the fans.  I have soffit vents, meaning that there's a nice big gap between my roof and the outer wall in most places.

[Merusk]

How odd. It works, as that's one of the oldest ways of venting a roof, it's just that you don't see it that much these days because it's easier to just slap on a ridge vent.   So long as there's enough square inches of vent, it's still nothing to worry about.  (And the sq. inches required is something you can't calculate without a plan or knowing the plan sq. foot of the roof and the sq. inches of the soffit vents.)

[Yegolev]

You seem to be saying I'm screwed, assuming the end vents are large enough.  How about tacking a soaker hose to my roof peak?  I can leave that running 24x7 and it won't cost me more than $100 by a shot.

[Sky]

How are the fans hooked up, directionally?

[Yegolev]

[Sky]

Hmm. Seems like there's a lot of area not getting vented. Have you checked air flow in the far end and also along the top of the attic (using a stick of incense or something)? Also, is that the direction of the prevailing winds? Excuse me if these are dumb questions, just thinking out loud. Having both vent out might better pull from the soffits on the far end of the attic. IANAC (I'm not a contractor :))

[Yegolev]

I'm interested in putting in a vent on the far end, but that will require hiring someone.  I'm not really sure about the wind direction.  I might re-reverse the fan that is blowing into the attic and see if the soffits are up to the task of venting; the incense is a good idea.

This mental exercise is why I just take the case off my computer.

[Merusk]

Screwed? Nope.  1) It's not what I was saying.  I was saying it they vented the roof different than standard for a modern building.  Not wrong, just different.   I just wasn't sure if they provided enough venting at the top, and I can't tell you that without a lot of house-specific information.   2) You're never screwed in construction so long as your structure is ok.

Now.. those vents seem oddly placed.  I would go ahead and close one up and open one of the same size on the opposite side, like you want.  With the way they're placed right now you're not going to cross-vent the attic.   While they'll both draw from the soffits, (smokestack effect > wind) the one end of the house is going to draw more air than the other.  I'm betting that far end of the attic gets a lot hotter than the end with the vents, yah?

Since i just noticed; if those arrows are the directions the fans are blowing you're REALLY doing it wrong.  You're blowing the stack effect of the soffits and since those fans are in-line you're just sucking air in to blow it out right at the other end.  You've done nothing more than created an invisible duct that'll shuffle outside air.  Nothing will circulate into the greater portion of the attic and pull that roof-baked air out.  The fans will draw air on their own from the soffit vents of your house so they should both blowing to outside.

[Yegolev]

Since i just noticed; if those arrows are the directions the fans are blowing you're REALLY doing it wrong.

Alright, this would explain some of the increase this summer.  I wasn't aware of the soffit thing but it makes sense now.  I'll just get my ass up in the sweatbox and put it back so they both blow out.  I appreciate the information.

[Sky]

Yeah, that's what I was getting at, too. You want to suck air in through the soffit vents and out through the gables. Still going to be a big dead air zone at the upper end of the attic opposite the fans, but it should have more circulation if you fix the one fan.

I wish I could find the article where I learned about roof ventilation techniques, it was very informative with lots of illustrations.

[Merusk]

Doityourself.com, this old house.com and askthebuilder.com are all great resources if you don't have a handy, trustworthy contractor to bug.

IMO none of them use enough pictures, though.  Pictures are a requirement for explaining anything construction related.

[Yegolev]

Because of illiteracy, rite?

[Merusk]

Funny, I just made that EXACT joke about 2 hours ago here at the office when someone was complaining about having to draw-up more details.

"Why does Bill want a detail of everything?! Can't I just put a note on the plans?"
"No, too many illiterates and non-English speakers in the field."

Joke aside, no, illustration and pictures just show things a lot more concicely than 5 paragraphs explaining how to do it.  Plus you can point to exactly what you're talking about.   Kind of why we have prints instead of 120 pages of text for a floor plan. 

[CharlieMopps]

You people are friggen nutz. Stop helping dude burn his house down. He needs to hire a contractor if he doesn't even know what a joist is.

If your house wasn't inspected when you built it... you're going to be in a world of hurt when you go to sell it.

[Yegolev]

I'm not selling shit.  You'll have to blast my ass out of here with dynamite.

[Nerf]

Almost finished with the install, the difference in the areas that have the foil up versus the ones that don't is amazing.  I figured it was all snakeoil, maybe a small difference, but holy shit.  The electric bill will be the real test, and we should have at least of month of just the barrier before we blow in another 12" of insulation.

Looks like we bought way too much as well, house is 1800sqft or so, we picked up 2500sqft of the foil, we've only got a small chunk left and still have maybe 1200sqft of foil.

If I ever build a house, the whole fucking place, floor to ceiling, is getting a layer of this shit.

[Morat20]

Almost finished with the install, the difference in the areas that have the foil up versus the ones that don't is amazing.  I figured it was all snakeoil, maybe a small difference, but holy shit.  The electric bill will be the real test, and we should have at least of month of just the barrier before we blow in another 12" of insulation.

Looks like we bought way too much as well, house is 1800sqft or so, we picked up 2500sqft of the foil, we've only got a small chunk left and still have maybe 1200sqft of foil.

If I ever build a house, the whole fucking place, floor to ceiling, is getting a layer of this shit.

Have someone who knows what they're doing put it in, so you don't get problems with water condensing on it.

You really only need it in the attic. That's where the heat collects. Put down a Cool Roof or a reflective backing to lower attic temperatures and roof-surface temps, and good insulation to keep the warm air up there, and with solid venting you're gold. It won't do shit in your walls or between floors or anything like that.

[Merusk]

It'll block the gub'ment x-ray and listening devices, though.

[Morat20]

It'll block the gub'ment x-ray and listening devices, though.

Might hose your wireless, although I doubt it. :)

[Salamok]

From the exterior all a ridge vent looks like is a raise ridge shingle, so the shingles at the very top (peak line of the roof) will just look like they have about a 1 inch drop to the shingle beneath  as opposed to just laying flat like all the other shigles.




The dryer exhaust looking vents you were tallking about aren't ridge vents (they are roof louvers) and are usually located about 2 feet below the actual ridge (unless they are venting something specific like a bathroom fan you don't need these if you have ridge vents).



so are you sure you don't have ridge vents?

[Yegolev]

What does a ridge vent look like from the bottom?  My roof is really tall, hard to see.  If I do have roof vents, I suppose I'm screwed for real.

[Morat20]

What does a ridge vent look like from the bottom?  My roof is really tall, hard to see.  If I do have roof vents, I suppose I'm screwed for real.

Um, back up a bit so you can see the top of your roof? It looks like the peak of your roof is wearing a hat. It's not subtle. You can tell from 200 yards away.

Your roof comes to a peak, right? Well, right there on the peak is a little upside-down shaped V sitting right on top of it.

Here's a flickr shot and another of someone's ridge vent. It's impossible to miss.