I am planning on building a house in the Seattle area. It will be stick framed using 2×6’s on 16″ center. I want to achieve a more comfortable living space by adding extra insulation. Besides using Tyvex over the ext. sheating, sealing the window & door openings with 4″ rubberized tape, and adding R-19, would it make sense to add 1″ rigid foam inside and against the exterior sheating before installing the R-19?
Would this trap moisture in the wall cavity? Is there a better option such as increasing the R value of the insulation or using encaspulated batts?
Replies
Well, there's R21, which is a higher density fiberglass. On this forum you're going to hear from a lot of proponents of Cellulose.
Pete
In preparing for my construction this is also in Coastal Washington, What are basic price differences and pros/cons of cellulose?
I'm not advocating cel, just pointing out that a lot of folks on this board favor it. I'm a homeowner and DIYer and FG seems easier to me, but the best opinions come from the folks who do this for a living.
Pete
I have lived and built in the South Puget Sound area since the late 70's and for my money you can't beat 2x6 walls with blown in fiberglass, "BIBS". Call Carrig & Dancer Insulation company in Olympia and talk to them about it. I've been using it for a few years now and I'm convinced. It costs about 20% more than fiberglass batts, but is way, way, way better.
As far as adding more layers of insulation, I guess some of that stuff makes sense in harsher climates, but remember our climate is different than in other parts on this continent. It matters. I see a lot of people build houses here that are better designed for other climates.
Thank you for your response. Have you encountered much settling from this type of insulation? I would be concerned about developing cold spots from settling. I will inquire further but appreciate the feedback.
Brian
Where I live there are specialty insulation contractors that will spray urethane foam in the wall cavities. With a 5-1/2" cavity, you can easily get a 4" average thickness and about R28. Urethane seals everything tight, so you will be air-infiltration free.
i would build a 2x4 wall 24" oc, strap the interior horizontal with 2x3 flat. and then blow dens-pak cellulose.. we call it a "mooney wall".. lots of bennies.. including almost no thermal bridging...
Mike Smith Rhode Island : Design / Build / Repair / Restore
"would build a 2x4 wall 24" oc, strap the interior horizontal with 2x3 flat. and then blow dens-pak cellulose.. we call it a "mooney wall".. lots of bennies.. including almost no thermal bridging..."
Mike
How does this compare with what I think is your normal construction of 2x4 walls, 3/4" sheet foam and 1" strapping and dense pack in the walls.
In one case you have 5" of densepac vs 3 1/2" plus 3/4 foam and 3/4 air space. Without cranking the numbers I would expect that they are similar. And both systems minizing the bridging, butt the foam would be better.
And while the foam sheets, sealed would be a much better air barrier I can see that much getting through 5" of dense pack either.
Seems to me that this would give very similar results and be cheaper to use. But that is only off the top of my head.
bill.. the [2x4/1" foam/3/4 strapping] is our old energy wall..(R13+R7= R20)
the new one , developed here in a discussion... and tim mooney asked me why i didn't just change the strapping to 2x ... duh..
so [2x4/2x strapping] is our new energy wall ( R13 + R5.5 = R18.5..) at half the cost.. so, the "mooney wall" is the way i'll go whenever we need a better wall than 2x4.Mike Smith Rhode Island : Design / Build / Repair / Restore
Thanks
I saw that discussion, but got lost in all of the details. So I did not realize that the "money wall" was a replacement design.
yeah, Tim "show me the money" Mooney.....but no patent, so feel free...ah doan think tim will mind
Mike Smith Rhode Island : Design / Build / Repair / Restore
Edited 6/13/2003 3:20:02 PM ET by Mike Smith
Brian,
We strapped our 2x6 wall with 2x's running horizontally, for a wall cavity of seven inches. Then blew in loose fiberglass (used the BIBS system, "blow-in-blanket"). Ended up with R-28, I believe.
Only one winter so far, but it was severely cold (far colder than Seattle ever gets) here in Maine last year, including quite a few subzero stretches. Very easy to keep the place comfortable--basically I just ran a Vermont Castings Encore (moderate sized wood stove, 37,000 BTU tops) while doing the finishing inside, and the place retained heat amazingly well. Of course we also sealed around doors and windows meticulously. If I left and came back a day or two later, the place would still be 50 degrees or so--pretty remarkable.
Strapping will also make your sheetrockers very happy, and from what I've been told makes the sheetrock less prone to moving and cracking at joints (time will tell here--so far, so good).
I agree with Jim--BIBS is worth the money. Whatever you do, good luck!
Edited 6/13/2003 4:59:09 PM ET by MONSIEUR_ED
Since the question is, "Whay's best?", the answer is spray urethyene foam. All you need is a 2x4 wall. The corbond company has studies showing that cost return and efficiency drop off after three inches thick. No infiltration on windy days.
Excellence is its own reward!
Would the urethane foam give off continual outgases? And, would it accelerate a fire if one were to happen?
In the last few years, they drastically changed the formulas to reduce the off-gassing. Last time I had it done, I couldn't notice it when walking in in the morning after three days and I have an more then average sensitive nose.
I think that the deal on fires is that it can generate some bad gasses in a fire as the most important thing. Whether it will accelerate a fire - I don't know. You do need to be sure it's all covered. foam in sheets as you are thinking of would still give you the same concerns.
R-values for fibreglass are established at a differential of 68° to 18° in testing, a temp when you don't need to worry much aboput heating or cooling. That might match your location just fine. But at a temp diff of 18° to minus 32° (same fifty degrees) the efficiency of fibreglass drops way off while the sprayed foam remains nearly as efficient. Add wind infiltration and you find that fibreglass is next to worthless. housewrap helps, I suppose.
Fibreglass lets a lot of air exchange through it but sprayed foam is good and tight. I really love it..
Excellence is its own reward!
Edited 6/13/2003 6:11:04 AM ET by piffin
Edited 6/13/2003 6:16:45 AM ET by piffin
Brian716
One of your questions is whether the extra layer of rigid would trap moisture in the wall cavity. - The insulation may not be the factor that traps your moisture in your wall. You mentioned Tyveking the exterior with tape and rubberized gastkets, etc. That, combined with your interior layer of 6 mil poly, would probably contribute more to 'trapping' moisture than an extra layer of rigid insulation.
What is your exterior cladding? Stucco? Around here, the preferred method is to use tar paper behind stucco instead of Tyvek (or equiv) specifically to let the wall breathe a bit. And we don't tape up those joints.
That said, there are definitely two camps on theories.: Either hermetically seal the house or let it breathe. I like to let them breathe.
Do you ever use de-humidifiers in your area? I am curious if there is a humidity differential between indoors and outdoors in Seattle. The air-bourne moisture will tend to migrate from moist to dry.
Your insulation may not be a factor - It hardly gets too cold there.
I think you ought to consider your wall system for moisture.
Fez
Nobody here (Quebec) builds new construction in anything less than 2x6, but I gather you don't have the temp range we do. In summer here it can get to 30 or 35C; in winter it hits -40C at least once a year for a few days.
My preference for a variety of reasons--not the least of which is ease of installation--is naked fibreglas batts in the walls. I use Tyvek housewrap on the outside, which is not moisture-proof, by the way; it's a wind barrier. On the inside, there are three basic choices: polyethylene film, aluminumized paper, or 'bubble-wrap' mylar insulating vapour barrier film. I think from your question this last choice is what you're looking for.
The stuff I put in my own place about 8 years ago was sold under the brand name Reflectix. It's supposedly rated at R-10 (which is pretty good considering it's about ½" thick; I'd check the rating if I were you when you buy your film.) I do find it does a good job; I put it underneath 8" fibreglas batts in the second storey ceiling and inside the 4" batts over Rafter Vents in the lower roof of my gambrel. It takes 8-12 hours for the temperature in the second floor to rise to the ambient air temp outside in summer, and that's with black asphalt shingles on the roof. In winter, it takes 10-12 hours for the temperature inside to drop 8 to 10 degrees Celcius when the wood stove goes out and it's -20 or so outside.
You staple this stuff on the studs just like an ordinary vapour barrier, but if you're going to lay gyprock over it, you'll have to put strapping on top of the Reflectix first; the bubbles are too thick and bouncy. You should use aluminum duct tape to seal the joints unless you deliberately want to let some air permeate through the walls, in which case don't bother to tape them at all.
Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
Dinosaur,
Its the taping of the joints of tyvek that I think may prevent the moisture from leaving the wall.
If the joints are lapped like siding, and the dewpoint occurs on the surface of the exterior sheathing, I believe lapping contruction paper gives the moisture a better chance to escape outwards, away from the wood wall.
In fact, re-reading the original post, an extra layer of rigid insulation under stucco would help move the dewpoint further to the outside of the wall, away from the wooden strucure.
Fez
Edited 6/13/2003 9:23:33 AM ET by Fez
Three points spring to mind:
1. In ordinary residential construction, I can only see the need for one joint per 100 linear feet in Tyvek, at the beginning/end of the continuous horizontal wrap. That strikes me as minimal compared to the square footage of unjointed material--9' of joint for 900 square feet of coverage.
2. I think I read somewhere (probably in FHB a few years back) an article on using housewrap, in which it was specifically mentioned that the stuff was vapour permeable. Does anybody remember the article, and does my memory serve me well? I think the article was by the Rhode Island Boys--Mike, was that you?
3. Moving the dew point further outwards in the wall system does make sense in a static perspective. I'm not sure without further thought if it would make any difference in the 'real world'. Let me scratch my head some and get back to you on this.
Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
Dinosaur,
The tyvek web-page lays out what it claims tyvek will do for your house. (i think tyvek.com?)
Like most people, I am good at regurgitating what someone else has told or taught me, - and I'll believe it too, if it sounds plausible. I guess this means that I can be persuaded to change my opinions over time. Architecture school taught me that you have to keep the water away from the wood. Now that I'm a builder, experience and talking to experienced stuccoers has confirmed for me that the building paper makes more sense.
In the real world, I would expect that the wall system will be less than perfect in some places and water will find its way inside. So my thinking is that you have to let the wall breathe a bit. In this region, we have to put a 6 mil poly layer just inside the drywall by code. I know for sure that the building paper on the outside will breathe, letting 'trapped' moisture out.
Maybe tyvek claims to breathe, but one other concern is lookalike house wraps. I see lots of them going onto houses with "home hardware" or "totem" printed on them. I don't know if they are made by tyvek or not.
Your point about not a lot of taped joints is good, but I always see lots of tape on that stuff. I can understand it too, when guys are trying to wrap the backside of a two story walkout from ladders or scaffolding and cut the tyvek into manageable size pieces.
Fez
I know about off-brands; Tyvek is a brandname, made by Dupont if I'm not mistaken. You could easily be right in your worries. All three of my local lumberyards have housewrap printed with their chain affiliation and name, but I don't know who the manufacturer is.
It's interesting that you say you are required by code to install poly vapour barrier on the warm side. Here I have the option of installing aluminized paper vapour barrier, and that's what I use--specifically to let the house breathe--unless I've got R-value concerns due to stud- or rafter-bay space restrictions, when I'll use a bubble-foil insulating vapour barrier like Reflectix.
Building felt as a house wrap is good; I've got nothing at all against using it, and on small projects or reno's it makes more sense than billing the client a c-note for a full roll of Tyvek, most of which will wind up in a dumpster or my scrap-stock pile after it's lain around his yard for a few months. The downside is speed of installation--plus the fact that our societal penchant for what's new and trendy tends to make clients wonder if we know our business unless they see on their house what they see on every site they drive by on the way to work....Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
Here in Wisconsin we build "Energy Star" homes, because we care about our customers. We have settled this issue for ourselves. We build with 2x6 walls 16" o.c. 7/16" OSB sheathing with 1/2" R-Board over. The walls are insulated with 2" of "Corbon" spray foam insulation with R-13 fiberglass batts over. This gives you an R-factor of 31. But it also necesitates the use of an air to air exchanger, so that the house can breath.
Sam, I'm interested in what you do there, but I hope you didn't mean to imply what it sounded like with the statement about caring for you customers. seems like you might be saying that anybody who doesn't do it that way is uncaring or a hack...
Fact is that regulatory cpommisions like that are often behind the curve on dictating what it takes to do it wel and keep up with building science.
For instance, Corbond has studies that demonstrate that the fibreglass in your description is a redundant watse of the customer's money.
and in a heating climate such as yours, Joe Lisitubrk shows that the foam belongs on the inside3 of the studs if you want it for preventing thermal bridging. The way you describe will trap moisture between the foam sheets and the corbond and rot the sheathing if any water ever gets in past the exterior foam sheets. Do you run tarpaper over the foam or use a rain screen wall?
It's hard to imagine better than a couple of inches of Corbond. I built one that was 34' x 38' with a wing of 24' x 18', two storey with nine foot ceilings that heated laast winter for just over $900 in fuel bills. This was on a beach facing the northwest wind right out of Canada..
Excellence is its own reward!
sam... many ways to skin the cat... since we built our first energy home in '75 we've kept up with a lot of different things in conserving energy and keep the house liveable...
most of the time we stick to 2x4 wall 16" oc with dens-pak cellulose....but we alos insulate our band joists.. 12" x 12".. and we insulate our basements..
and we spend the max budget on the best windows our customers can afford...
and we put 24" of cellulose in our attics...
if that's still not enough.. then we'll go with the R-18... r-19 wall...
this is in a 6000 DD. climate on the ocean with lots of wind..Mike Smith Rhode Island : Design / Build / Repair / Restore
Ours here runs from 5800 DD to 6800DD depending on which direction the weather comes from that year. Also a long drawn out spring lets us have a lot of cold air off the water - like this year..
Excellence is its own reward!
being an adopted yankee with michigan roots.. we turn the heat off on april fools day no matter what the spring is like... ( might sneak it back on on a cold night though )Mike Smith Rhode Island : Design / Build / Repair / Restore
With us - that depends on who is controlling the thermostat. Wife has these heat flushes that make her get urges to open windows and doors while I am shivering from working out in the rain and adding wool blankets to the bed.
Yer wife is probably too young for you to know about that though, eyah?
;).
Excellence is its own reward!
damn.. did we marry twins seperated at birth ?
the open window as soon as we turn off the heat... then i steal all the blanketsMike Smith Rhode Island : Design / Build / Repair / Restore
You mentioned above 24" oc studding, if you do this, do you follow through with the same spacing on the floor and roof system ? I have always wanted to go 24", but I don't like the idea of floors on 24" or the idea of staggered studs, joists, rafters from varying spacings.
carpenter in transition
tim... most of the time we do 16".. with 24" for the trusses...
our floors are mostly conventional framing.. either 16" or 12" OC
if the studs are 16" and a double plate.. there is no problem with trusses on 24"
if the walls are 24" then naturally the trusses will stack over the the studsMike Smith Rhode Island : Design / Build / Repair / Restore
How do you insultate the rim joist.
That always looked like a problem area to me.
I perked up my "ears" when I saw the post. I live in Vancouver, 150 miles north of Seattle.
My customer decided on a wine room below his new deck, so we framed 2x6, thinking it would give us a nice R20.
Now he looked at the installation book, and it recommends foil-backed Urethane insulation to R30.
Since the forms and cutouts for the sheathing are set and the walls framed, I plan on putting in the R20 and adding the Unrethane - but should it go on the outside under the sheathing, or the inside under the drywall? Any suggestions?Quality repairs for your home.
Aaron the HandymanVancouver, Canada
aaron.. you are trying to keep the wine from freezing.. so the foam goes on the wine room side ( inside ).. this keeps the mositure vapor above the dew point..
if you put the foam on the outside moisture may get trapped against the inside surface of the foam.. 6" away from the heat source.. which MAY be below the dew point.. so it would turn into a condensing surface..
at least that's the way i think it works.. and the way we would do it if we were using foam in our jobsMike Smith Rhode Island : Design / Build / Repair / Restore
Actually, the wine will not freeze.
Our average temperature in winter is about 34 deg. F. and summer hottest is about 83 deg.
He is concerned about overworking the cooling/humidity control unit.
Since the unit asks for foil backed urethane, I assumed it should go on the exterior side to reflect out the heat, and the winter would be taken care of by the R20 bats.
The temp/humidity unit also wants all walls to be insulated & vapour barrier on both sides.Quality repairs for your home.
Aaron the HandymanVancouver, Canada
Aaron,
You definitely want the foam on the inside. It will provide you with the best VB and also your best prevent against thermal bridging. We just fixed a wine cellar that had been concrete block uninsulated. The room had its own chiller keeping temps in the mid 50's F. All was well in the winter months, (southeast PA) but as summer and the humidity came, the room became like a rain forest.
carpenter in transition
How about this for a northern "heating" climate. Building wrap, OSB, 3 1/2" unfaced fiberglass batts, 2" polystyrene foam and then sheetrock. The foam would serve as a vapor barrier (if taped or caulked with urethane to the studs) and the dewpoint would occur within the foam. Seems like this method would eliminate any moisture problem.
nothing to fasten interior trim to.. and hanging rock will be a bearMike Smith Rhode Island : Design / Build / Repair / Restore
FG and foam would be installed within the stud bay. You still have the studs to hang the rock.
we build a box.. plywood, foam, thermoply.. or sheetrock. then blow the cavity thru the subfloor.. so the box is the depth of the joists.. and as wide as the first joist bay.. or 12" across the joistsMike Smith Rhode Island : Design / Build / Repair / Restore