How much insulation is enough?

Willie Corbett_2

Can you provide me with some basic info regarding how much insulation to use for a new home being constructed in coastal Maine? The basics are 2X6" walls, 2 1/2 story house sitting on a basement, Tyvek housewrap for moisture barrier, vinyl siding, vinyl windows with Low E by Paradigm, oil-fired boiler feeding radiant on 1st floor and HW baseboard on 2nd floor.

Example: If I go with R-19 in the walls, do I need to put styrofoam on the external walls under the vinyl siding? If "yes" what would be a crude estimate of payback timing? [I realize you would need more data for a true estimate.]

What is considered best practice for insulation at the 2nd floor ceilings? R value? Fiberglass batts?

Any other recommendations?

Thanks for any advice you can provide

John@Reliable_9

Heres a great link for all you need

Check out R-value recommendations bottom left.
Hope this helps John@Reliable
http://www.ornl.gov/sci/roofs+walls/insulation/ins_01.html

Uni R

How much insulation is enough?

Those 2x6s walls will cause major thermal bridging. If you can use rockwool instead of fibreglass do so. I'm pretty sure that when they lab test for R values, it is done at 70°F. The rockwool is denser and stops airflow within the batts when the temperature is low. It is also more fireproof and can hold its R value better if it gets wet. The styrofoam under the siding would help with the bridging problem of the 2x6 walls. Just remember that there are diminishing returns with insulation. The first R saves you more money the second, and the third even less than the second. Sill insulation is critical as are basement walls and under the floor. Pay careful attention to the bridging points. Also on the top floor, make sure that the tops of all the inside framing is tight. I read an interesting piece once about special housing for people living in the Canadian arctic and they actually went as far as putting up the full ceiling vapour barrier before erecting any of the internal walls. That way there were no "holes" for moist warm air to end up in the attic. Styrofoam on the outside of your basement walls is probably the best place for it. The styrofoam near the surface needs to be protected from the elements. If you can take it right up to the layer under your siding that would be great. As for your 2x6s, can you use 2x4s instead and stagger them fore and aft? That would help. If you do 2x6s and don't do a styrofoam layer (two thin glued staggered layers would be better), you'll be able to see the studs with an infared camera on a cold day! For your ceilings you are looking at R40 minimum. I would try for R60 celings (rockwool) and R25 walls (rockwool and stryofoam) including basement. Remember with this house being so tight, an HRV is a must.

GMcD

Don't forget the windows

Great wall and roof insulation may help, but a significant percentage of the heat loss from most buildings is through the windows and glass. Poor windows in winter are like big radiant cooling panels that a lot of warm air or radiant floor (or ceiling) will have to work hard to create some amount of comfort. Try to use double glazed argon filled windows at a minimum, and I strongly recommend triple glazed or Heat Mirror suspended mylar film windows to get reasonable performance. Same comment on the thermal bridging as mentioned above. We've recently completed a building envelope study for a large building in a cold northern climate, and the thermal bridging of the 2x6 studs through the exterior wall reduced the overall R value of the wall insulation by about 35%, with the net result that condensation, and then ice formed inside the walls in winter, even though the drawings and specs required R-20 wall insulation. By the time the insulation got wet and never dried out, the effective R value was probably around R-3 or 4, and when it gets to -35F outside, it's not a good thing.....

Uni R

Windows

Actually, windows are bad compared to walls no matter what you do, but they are a necessary evil. They are bridging nightmares and I don't believe any of the data for the ultra high performance ones. I think the key advantage of the better windows is how well they seal. The rest is questionable. Argon slowly leaves through osmosis, triple pain windows often have the centre lite drilled for equalization allowing an air break. BTW, I just got rid of some very crappy 30 year old aluminium sliders with some low E, argon double pame windows. I didn't drop the money for the R, I did it for the tightness and the looks (the old ones looked like crap). One night when half the new windows were in and it was nice and cold I took my temp gun and found very little difference in surface temps inside and out between the two. I think storm windows with a 6" airspace is probably as good as any technical trick. I'd love to see some research data done on this. So far I haven't and so far I'm not convinced that you can get too far from R3 or R4 in windows, especially when the framing gets factored in.

hr

I've never paid

that much attention to the thermal bridging, until I witnesses some steel stud construction in cold climates. Wow! After 1 winter every stud could be seen with dark shadows on the interior painted walls. Not a pretty sight. Homeowners could actually feel where every stud was in cold weather.

Seems to make sense to provide some sort of break at this detail, deeper studs or a foam layer would make sense.

Super performing windows get real expensive, not sure they are worth the extra bucks from a good grade low e. The seal around the window, and type of window opening style are considerations.

Check the link below for some #'s.

http://www.pmmag.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2379,120140,00.html

hot rod

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Mark Hunt

Dense pack


cellulose gives you R-3 per inch AND it is an air barrier.

Foam on the outside is useless, put it on the inside as a thermal break.

Build it tight and vent it right.

HRV will be needed.

Mark H

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Dale

Windy?

Assuming you are going with the energy saving roof trusses that allow the insulation to go over the top plates and that you will have plenty of summer venting ( the winter takes care of itself if the summer amount is there) then if you are in a windy area I would go with crossed fiberglass batts in the attic. one layer of 3 1/2 and 2 layers of 6" gives an R50.That way the insulation can't be blown arround like loose fill sometimes is. And, you can be sure you are really getting the r value you are paying for, which sometimes is a problem with blown in. Also, the usual problems with a new house is holes to the attic, just before the insulation is put in. Go up and caulk all drilled holes, plumbing stacks ect. yourself unless you REALLY trust the builder. With the mold issues now I wouldn't put anything in a basement wall insulation that could hold moisture, styrofoam on the outside wall below grade and spray in foam on the inside would be my choice.

Constantin

Paging Dr. Hunt to the OR!

Allow me to disagree with you slightly. If you have a look over at the Building Science Corporation web site, they make some pretty convincing claims that insulating the exterior of the foundation is to your advantage. Insulating the foundation wall on the outside allows you to increase the termal mass of the house and hence its resistance to temperature changes.

It's the same reason we insulate below and not above the basement slab. Some folks go as far as only insulating the slab around the edges of their foundation, leaving the center bare, so that they can turn the ground into heat storage as well (particularly with radiant systems). Furthermore, exterior foundation insulation will not lead to condensation, mold, etc. problems the way that improperly applied interior insulation can.

Since I am not allowed to insulate on the exterior above ground (where most of the heat loss occurs in winter) due to historic district restrictions, I'm insulating inside (full wall) and out (below ground only). However, I am going to have to be careful with the interior insulation because the water in the curing concrete foundation walls has to go somewhere. Since the exterior is sealed with Rub-R-Wall and 2 inches of XPS, that only leaves the inside of the house!

Above ground, we're going to use a mixture of Icenyne and closed-cell polyurethane foam, depending on the location. For example, the third floor walls, the roof deck, and all bay windows, etc. will use closed-cell PU (R6.5 to 5 per inch) simply because there isn't a lot of depth to play with...and full-size 2x4 studs make excellent thermal bridges. More importantly, the PU will act as a vapor barrier as well. Elsewhere, new 2x6 walls will allow an acceptable R value via Icenyne and the vapor barrier is done the conventional way.

Interestingly, I found that infiltration is one of the biggest heat losses that HVAC-Calc computes for our home. However, the program makes no adjustments for high-quality vs. discount storms nor does it allow the installation of HRV's - you can merely approximate them. So I have no idea whether the calc is right or not. I'll simply assume the worst case scenario and size accordingly ~110kBTU for a 5000 sq ft house at -15F.

Oh, and to minimize the ductwork, etc. we're going with 3x 2 ton AC units and 3 Lifebreath DCS 195 HRV's. The current plan is for 2x HSX15 for the upper floors (very similar exposure) and a HSX19 for the basement, and first floor leftovers. Almost like a mini-split system! One large Nortec in the basement will then keep the whole house humidified.

Boilerpro_3

My nickel

Back in my college days, I was a research assistant for developing affordable housing in Chicago and one of the things we looked very closely at is energy usage.

On windows. They are not a "necessary evil" when it comes to heating. Proper orientation and design of a structure with large amounts of glass will significantly reduce energy usage by generating sustancial heat gains due to solar energy. Any window construction, other than single pane, can generate more energy than it uses, when properly placed in a structure. I can't locate the data for your area at the moment, but for the Chicago area, if memory serves, typical savings in heating fuel when just using south facing standard double pane windows range from 15% for windows that are have no night time insulation to 40% with nightime insulation (ie, heavy insulated curtains). The larger your glass area the better, so long as the structure has enough mass to absorb the heat during the day and then release it at night. These numbers vary widely on how much solar insolation you have in your area. In areas like Colorado (pre heavy air pollution) these number were much greater. I would do some research into inexpensive passive solar design, before completing the design and siting of your home. The possible small additional investment in larger windows is likely going to be much more cost effective than superinsulated walls or super high efficiency heating equipment.

On wall insulation. Many building technology resources have very serious concerns with the use of foam insulation on the exterior of conventionally framed walls in colder climates due to the great potential for moisture becoming trapped in the wall. Large amounts of moisture are generated inside homes an this creates a vapor pressure on the walls as that moisture tries to move its way to the outside, dry winter air. Vapor barriers, and many say high density blown in fiberglass, rockwool, or cellulose insulation, slow this momeemtn considerably, but do not stop it. As this moisture moves through the insulation the temperature steadily drops as you get closer to the exterior. At some point the dew point temperature will be reached and the moisture will condense. If you are lucky this dewpoint temperature will be in the foam board, so the moisture won't necessarily condense in the between stud insulation, even though it may on the studs. Now how is this moisture to get out of the wall? The wall is now wrapped with thick moisture resistant foam on the outside. It has no place to go, so its just stays put, and rot damage starts. Moving the foam board to the inside, and using a vapor permeable, but water and air blocking wrap on the exterior, allows this moisture to escape to the outdoors. Be careful what you use for sheathing, since nearly all typical wood products can greatly slow water movement due to all the nonpermeable glues they contain. Tyvex, as far as I know, is the only common housewrap with these characteristics. All the others are perforated plastic that allow moisture and air flows, but stop, fairly well, water. From some personal experience, I favor high density blown in rockwool or fiberglass installed before the interior surfaces are installed. It provides a high R-value, reduces air leakage (the largest source of heat loss in insulated structure), and does not support combustion, which,as has been reported, many cellulose products due after they age.

The comments about metal studs on exterior walls are right on! I believe the the Forest Products Laboratory did some testing on this type of wall consturction and found that 6 inch studs with 6 inch fiberglass batts in a typical wall system gave an average R-value of about 4 or 5. With wood 5 1/2 inch studs with 6 1/4 inch fiberglass batts, the average R-value is more like 15.5 to 16.

My overall suggestion: layout your home with the long axis facing south with your larger living areas along this wall, use large amounts of double pane glass on this wall,(and some on the east, if dsired)with some sort of effective night insulation. Insulate 2x6 @ 24 inches oc walls with blow in rockwool and a foam layer on the interior with the most vapor permeable materials on the outside. Use metal studs only on interior walls. Pay speical attention to air tighting the interior surfaceof the esterior walls and ceiling (check out Canadian standards for some input on this). When done, don't just calculate the heat laod for your home, but check solar resources for methods on calculating average heat load to dtermine your fuel usage and cost. It is likely that the average usage will be so low that supe high efficiency equipment cannot be justified.

Boilerpro

hr

It's probably

a cost driven decision also, but 90% of new construction here is using TuffR type of foam for the exterior sheathing. Plywood or OSB on the corners only.

A think climate plays into the decision also, as to where the foam should be. Humid cooling climates seem to present a different challange.

A company in JLC recently suggested an ideal exterior wall insulation would be a couple inches if Isoneyne foam sprayed (excellent for infiltration seal)against the sheathing, then a blown in product, maybe cellous, over the top. This makes some sense as Isoneyne in 6" thickness gets real expensive.

hot rod

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Boilerpro_3

Yep, you hit the nail on the head

The problem I see is that foam on the outside belongs in humid cooling climates, not up north in heavy heating climates. I suspect that 20 or 30 years done the road, alot of those homes with foam on the outside are going to have extensive structural damage due to moisture buildup in the walls, unless they get that insulation really thick to keep the stud wall warm.

One other thing on foam, I wouldn't bother using the souped up polyisocyanate board, as it also off gasses and the r-value drops from 7.5 per inch back to 5 per inch. Certianly don't calculate heat loads based on 7.5, someone may get cold 20 years down the road in that house.

Boilerpro

GMcD

High performance windows

Well, I have data and field measurements that confirm and support the performance of the mylar film window systems in terms of their interior surface temperatures and thermal resistance performance, so I'm a believer. Anyway, if the House intends to be there 20 or 30 years from now when the enrgy prices are going to be a lot higher than they are now, going with high performance windows now is a way of "future-proofing" the building. I agree with the other post below regarding the orientation and passive solar gains in a heating dominated climate- fine tuning the window selections can have much higher bang for the buck compared to how much wall and roof insulation one uses.

jerry scharf

don't like that siding insulation

Willie,

I have always been concerned with the risk of rot with siding insulation. You put that money in tyvek to make the outside of the insulation layer let out moisture. If you put siding insulation on, it then prevents most or all of that and you now have the risk of condensation of moisture.

If you look around the net, I am sure you can find some really ugly pictures of rot produced by exterior insulation. I've seen a few articles on this, and the pictures made me sick thinking about the repair. It's not localized rot like old foundation sills, it's entire sides of houses, sheathing, studs and all. It can also lead to compromising the health of the people living there.

jerry

Uni R

My dream house envelope...

My ideal home would be a concrete sandwhich. Outer concrete shell and basement slab. Then foam insulation in a continuous coverage to the corners and then another layer of concrete on the inside and another concrete floor on top of the insulation. Then a stud layer, where the house is framed within the sandwhich to allow easy electrical etc. This inside layer could have rockwool batts for better sound absortion and fireproofing, but would have no vapour barrier. This would be very expensive, but it has exterior thermal mass, interior thermal mass, the styrofoam is 100% termite, fire and UV proofed, and you can incorporate a very durable external finish for the house. The trusswork would also tie in so that it is above the insulation envelope allowing for a perfect insulated perimeter in all directions that is suitable for any climate region. The only downside outside of cost is that I better be darned sure where I locate the exterior windows and doors!

Larry Weingarten

foam core panels

Hello: You may want to look into foam core panels or SIP's if you've got time. Essentially they are OSB inside and out with foam between. They eliminate most of the problems mentioned here with bridging, moisture and air leakage. It IS essential they be well caulked on the inside to keep moisture out of the panels. Another thing to remember is they make plumbing and wiring harder to do. But, the insulation is very effective and will allow you to downsize your heating system, helping offset the cost.

Uni R

Rot - Siding Insulation

I agree, but the cases I've seen like that were renovation situations where there was minimal insulation and no vapour barrier. They put styrofoam cladding on the outside and that's where all the interior moisture ended up.

Uni R

On the other hand...

If the technology of windows is on the rise, maybe buy low E double panes for now and replace the sealed glass portion in 8 years when the new "Ti-Silica 100% Refracto" or whatever models become the new standard. Maybe I should be buying shares in PPG since this should be a huge area in the future when e costs skyrocket?

Paul_26

Thermal Bridging, Insulation, and Panels

Gentlemen

There is a approach to insulating a stick built house that has proven itself in New England and that is using rigid foam (polyiso) on the outside of the stud wall and that is it, nothing in the stud bays. All insulation types that allow air movement are prone to moisture and condensation problems. If the stud wall cavity isn't insulated from the living space, it will be as warm and dry as your living room. 4" of polyiso on the outside should meet everyones performance targets. You do have to handle windows and doors differently, but it isn't hard, just a little time consuming.

We here at Foard Panel make Sturctural Insulated Panels and have for 10+ years. The owner of the company has been making, installing, and servicing panel houses for nearly 20. 20years isn't that long in the lifetime of a quality building, but it is as long as this technology has been mature and in general use. Moisture is only an issue when you don't properly ventilate the house (HRV's rule) and aren't conscientious about your flashing (window sill rot from lousy flashing details are the single largest cause of problems). Wiring isn't difficult, just different, as long as you plan a little. Your plumbing shouldn't be in exterior walls anyway.

Polyiso does derate over time, but not down to 5/inch. More like 6+. If anyone wants data email me. The new LTTR test method is pretty reasonable.

The Wall members obviously love their heating systems, I just wish more Americans would spend some time keeping that hard won heat in. Total heat losses of 25kBTU/hr or less at a 70 deg dT isn't hard with instulated panels.

Paul

DaveGateway

How much insulation is enough?

Hello Willie,
It's hard to say how much is enough.
How long will you live in it? or is it a "spec" for sale? Will you live in it long enough to see energy costs double? quadruple? or more? THEY WILL!!!
Some real good advice in this thread, it all adds up!

I retired, & built my house. I hope to live here a long time, so I did the following: exterior is very low mainteance, brick with heavy gage "style" steel roof & all overhangs are steel wrapped, ceilings R65, walls R35 (7-1/4" foam SIPs), windows tripple pain (yes pain) If I had the windows to do over, I would use 2 sets of double pane low-E with 6" or so in between them. this would cost less & have better R-value & lower wind infiltration.
Your vapor barrier belongs on the inside ONLY, Tyvek which breaths on the outside is good. Pay attention to ventilation above ceiling insulation. Of course, calk & seal around windows & doors. My 2 cents. BP

hr

Uni R

The Dow booth at this years Home Builders Show had a concrete form system (10") wall that suspended a sheet of 2" foam in the middle of the pour. I thought this would be good if you wanted exposed concrete for the exterior finish.

With 8" of concrete and 2" of foam you should get R value close to what a 2X4 stud wall, considering the thermal bridge through the studs, maybe??

Concrete inside and out would be a low maintenance wall surface

hot rod

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Uni R

Exactly...

I would think that 2" would actually be vastly superior to any 2x4 wall, but I would still go thicker. They currently use the sandwiches for tilt up construction and also do prefabbed sections but then the weak spots are the joints. This form sounds ideal. I know that someone in the Ottawa area in Canada built a house along these lines and had incredible results. Unfortunately, I can no longer locate the article. I'll check into DOW and see if they have any articles on the forms. To me it has also made more sense for the insulation to be in the middle, yet everyone at home shows is always pushing the fill-em-up Lego blocks.


What do you think of concrete sandwiches for the basement or slab floor? Pour the floor (probably without a vapour barrier) and wait for it to cure. Then 4" of styrofoam are put down (and on the walls if doing everything), uncoil the PEX and then another concrete layer. This way the edge of the floor insulation seals with the wall insulation. Would having a layer of concrete under the slab insulation help?

hr

I think

4" of foam under a basement slab is a bit of an overkill. Gosh currently 4" of foam runs $1.60- 1.80 a square foot in my area.

I agree with the foam protected in the center of the pour. Sorta along the line of the SIPs Larry mentioned. Seal it out of harms way.

I've done two homes recantly where the concrete was the final inside finsh. One was sandblasted for an exposed aggreate look. I thought it looked great in this particular, contemporary home.

Using ICF and carving away some of the interior foam for plbg and wiring always strikes me as odd. Although ICF's do have a place, and a very easy to stack and pour.

hot rod

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Mark Hunt

Foundation insulation


I agree that insulation on the exterior of a concrete foundation has benefits. I was speaking about foam insulation on the exterior of the shell.

I don't think you are going to be needing humdification in your home. Icynene is air tight and properly installed PU is too.

The two boundries that we concern ourselves with are the thermal and pressure boundries. The pressure boundry is where you stop the air movement. The pressure boundry should be as close to the thermal boundry as possible.

Your pressure boundry is your "vapor barrier", when you stop the air movement, you stop the moisture loss. Tough to get folks to understand that the heating system has nothing to do with how moist or dry a home is.

Windows are a rip-off. The best window in the world will still be the weakest part of the wall. I would recommend a less expensive window PROPERLY installed and sealed, over a "high end" triple decker with the works anyday. You should see the looks on peoples faces when I put a blower door test on after they spent big bucks for glass and the air is screaming in around the frame! Also, stay away from metal frame windows. HUGE conductive loss!

Best wishes!

Mark H

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Constantin

Live in the North, do You?

That's some pretty amazing insulation you have there... Your wallet must be thanking you every cold winter day.

Allow me though to disagree regarding the location of the vapor barrier. While it is certainly true that the vapor barrier ought to be on the inside in cold climates, the opposite is true in the more tropical locales. The more moderate climates in between are a toss-up.

However, I agree with you regarding the usage of large air spaces between several panes/windows as opposed to triple-windows with a single sealing surface. Historic considerations pretty much require me to keep the old single-pane windows (don't dispair they're getting reconditioned by an expert) while adding super-infiltration-resistant Harvey Tru-Channel storm winows.

Storm windows have a lot going for them IMHO. They add a lot of wind/infiltration resistance, preserve the windows behind them, and there is no gas to leak out.