insulation

D107

I live in a 1924 neo-colonial with no envelope insulation and 20 yr old thermal windows. We will soon be installing vinyl siding over the wood clapboards and may blow in insulation into the walls in addition to rigid insulation over the clapboards. Insulation questions aside for now, my concern is what kind of vent is recommended for the uninsulated attic?

Rolled ridge vents are very popular now--they would seem to take the hottest air out since they're at the highest point. Then there's the Nutone mushroom vent --with thermostatic fan--. Currently there are no soffit vents (2" holes will be drilled into the existing soffit board and then covered with the vinyl grill.) and no other venting except two partially opened attic windows. In summer the attic is stifling. Seems to me if you have either ridge or mushroom vent, gable vents would be redundant. I want to make sure to allow moisture out of the attic.

Seems to me if I put in soffit vents --letting in cold air--without some kind of vent at the top-- i run the risk in winter of the cold outside air condensing the moisture in the heated air entering the attic from below, the water from which could cause mold, rafter rot, etc. Or are the open windows enough? (Bottoms of both window sills are about 3 feet above the height of the attic floor. 2-inch window opening has been recommended to me. one or both windows?)

Any thoughts?

Bob_36

Insulation

I want to have some insulation installed in my walls. I have a few questions although this is not the general topic discussed. First, which type is the best to have blown in? I have read that the foam type is the highest "R" value, but I am having a hard time finding an installer in my area(Long Island). If I go with another type, which do I choose and where do I look to get a good job done? Any help would be much appreciated and thanks in advance.

Uni R

Insulation

Don't go by just the R value. An R10 wall that is airtight will hold the heat in far better than an R25 wall that is has large infiltration rates.

Bob_36

I realize airtight is desirable, but I can't start ripping my walls apart. So I can't put plastic vapor barrier up to prevent air infitration. That's one of the reasons I was looking into foam. Other than foam, which insulation do you suggest and where do I look for an installer?

Constantin

Foam is great...

... I used it throughout our house.

However, I would also consider dense-pack cellulose. As the prices for the source materials for foam continue to skyrocket, the plentiful, cheap supply of cellulose is pretty attractive. Dense-Pack will also stop infiltration and shares many qualities with Icynene, except that it's harder to ignite, more insect resistant, and generally less expensive.

Installer-wise, I would go around the community and ask around. Yellow-pages ads are too unreliable, word-of-mouth and referalls work better. If any of your friends work in construction, they might know a crew or two as well. There is an industry association, but I cannot recall its name at the moment (sorry!).

Constantin

I'd consider a gander over to...

... buildingscience.com. Have a look at their homeowner resources. Based on their roof-deck testing in Las Vegas, I came to the conclusion that an unvented attic was the superior choice due to all the objections your thoughtful post raised. Make the attic a part of the conditioned space and the only thing that might potentially suffer (besides your wallet) is the roof shingle life.

jerry scharf_3

infiltration resistance vs air tight

The only things I know that comes close to air-tight are closed cell foam or SIPs. Neither is appropriate for retrofit work, since you need to pull the the interior face or the wall to install it. Even this is limited by the detailing on things like plates and trimmer studs.

Vapor barriers are not really infiltration resistant because of all of the penetrations. Also, if the air can move inside the insulation (can you say fiberglass?), you lose insulation value anyway.

So the next best thing to do is to get something that is resistant to both wind driven infiltration and interal convection. Both open cell foam and dense pack cellulose fit this bill. The cellulose is a much cheaper option, on par with blown in fiberglass but much better. Open cell foam is more expensive for material and installation, and it does seal up better. Both are a mess to install and should be done by a pro (mandatory with foam.)

When looking for a contractor, always get references. Try to go to a site they are working at. Are they curteous, do they treat the house, contents and owners with respect? Are they neet (within the limits of the materials.) Do they show up when they promise. If something comes up, do they call ahead of time? How well do they clean up? Are the people adequately trained? How do they measure how well they are getting the fill?

Also, when they show up, offer them coffee or water to drink. Treat them with the respect you want them to treat your house. Maybe buy them lunch or some other gesture. Pay on time for a job well done.

good luck,
jerry

jerry scharf_3

I'm not a fan of the exterior isulation

David,

I'd read Joe Lstebureck's (sp?) site (buildingscience.com.) He's fairly opinionated and brutal, but has the evidence to back it up. The problem with the exterior foam is where it puts the condensation point. You have warm moist air inside, and cold air on the outside. The moisture moves through the wall that is void and then loses it's heat right on the outside edge. This surface is the condensing surface and it can't dry out. Rot, rot, rot. There are some fairly bad pictures around from this style of insulation.

If you have the vinyl ventilated and the insulation in the cavity, the moisture doesn't get concentrated and the sheathing/clapboard can dry out. So I would go with an infiltration resistant fill (open cell foam or dense pack cellulose) blown in through the outside wall. Since you will cover the clapboard, repairs don't have to be cosmetic quality.

As Constantin said, if you can add the entire attic to the "interior" side of the house, it's a better solution. If you have any ducting up there, it's a double win.

just my $.02

jerry

Constantin

Allow me to disagree...

... which is rare with me and Jerry!

If it's properly done, exterior insulation can be a viable way to insulate. For example, I'm impressed by the PERSIST system that has been used from Alaska to Texas with no ill effects, rot, or other issues. The exterior insulation simply has to be thick enough to ensure that whatever dewpoint can appear will only appear in the insulation.

A properly-sealed insulated exterior wall (EIFS is a favorite exterior covering), will experience little to no migration of moisture as there is no mechanism for the air to transport the moisture to the sheathing. What little condensation could potentially happen is then allowed to re-evaporate into the house by not putting a vapor barrier on the inside. Some form of controlled air exchange will then preserve IAQ, control humidity levels, etc.

However, I agree that it's probably easier with open stud cavities and the like to apply Corbond from within and be sure that all cavities are air-tight. I also recommend the builders series of books that Building Science puts out... lots of good information on how to maximize the R-value of walls (through proper stud placement), corners, etc. for example.

Lurker_2

spray-in foam

Constantin,

I'm interested to know how the spray/pour-behind-walls foaming worked for you. . . or did you actually remove the walls to do all of the foaming?

I was replacing a patch of the plaster on one of my walls (1860s vintage home) recently and took a look behind the lath. It was a mess! It was probably filled 30-50% of the way up with stray pieces of lath and plaster, large pieces of wood, bags, you name it. Apparently, the wall had been replaced over the years, and the workers decided that the stud cavity was a convenient place to throw trash. . . I can't imagine this makes it easy for foaming!

I removed some other patches and peeked behind walls in various other places of the house and found this sort of trash-in-walls approach was taken quite liberally all over!

-Michael

Constantin

We opened them up...

... we had too much infrastructure to repair to make keeping the walls worthwhile. We also found a ton of stuff back there, but not trash. More like birds nests, wasp nests, etc.

Open-cavity filling is much more common and much less expensive than closed-cavity filling, as far as the insulation contractor goes. Open-cavity filling is also easier to verify. I opened up one or two small areas where my insulation contractor attempted closed-cavity sealing, and it was far from perfect.

Advanced companies like Foam-Tech out of NH use thermal cameras to ensure that their closed-cavity fills are perfect.

Bob_36

I think cellulose seems to be the way to go. Foam is probably better, but only one contractor in my area is qualified to use this material and he said I didn't have enough area to be done. It takes too long to set up the machine for the amount of surface I need covered. I do have a contact in the constuction field. I'll ask him if he can point me to a reliable firm. Thanks for all replys.

jerry scharf_3

I spoke too broadly

Constantin,

I also like PERSIST. I built my walls with a rain screen design (not insulated,) so I do believe in the concept.

I was responding to the posting where the person was talking about adding rigid foam over the existing clapboards and under the vinyl siding. I really don't like that kind of insulation.

jerry

D107

insulation

Jerry,

just to be clear re: the 1924 neo-colonial with the impending vinyl job, the 3/4" rigid insulation over the clapboards and under the vinyl would hopefully be in ADDITION to the blown-in cellulose or other insulation discussed. the 3/4" would probably produce no more than an R 4.2 but sounds worth it. (Although it would seem based on a few others' comments that in a very old house, the space being retrofitted with the DOW Styrofoam extruded polystyrene insulation could very well be filled with debris. Therefore it would be essential to write up a contract that ensured use of the special camera to verify full insulation, or if not possible, to reduce the charges accordingly.)


The PERSIST system (thanks Constantin) is very interesting but I think difficult on a retrofit where you'd have to build out over 3" from the clapboards.

Most of the contractors here (in Westchester, NY) are recommending NOT removing the old clapboards. And at least one contractor has said he wouldn't use the TIVEK house wrap over the clapboards and under the rigid insulation. Perhaps he assumes that there is already the old black paper house wrap under the clapboards on top of the sheathing.

I'm not sure how one vents vinyl siding other than making sure the vinyl specs indicate some reliable system of water drainage and air passage. I would be concerned about rot though.

jerry scharf_3

I'd still skip on the insulation under the vinyl

David,

When you have two layers of insulation, you still have a condensing band somewhere. If they seal it up nice and tight, you still set up the situation where the condensing band is in the sheathing some of the time. Anything you would be blowing into the walls will still move moisture. I'd rather lose some energy than risk rot in the walls.

Using the vinyl as a rain screen would still be preferable in my baseless opinion. In this setup, you set up nailer strips and the vinyl gets nailed through the strips and into the wall. You can staple or tack the strips up, the securing happens when the siding goes on.

They are quite right about not covering the clapboard with a water resistant layer (The myth that tyvek produced water tight walls if for another day.)

You are right, going with PERSIST is a major project. Not one I would start mid fall.

jerry