Is it possible to OVER-insulate?

[bams50]

Didn't quite know if this should be here or in 'Heating and A/C'...

Suppose my new shop has minimal windows, and those are the most efficient; the walls are all spray-foam insulation; ceiling well insulated and sheetrocked; the doors are the best, most insulated they make; and the slab is well-insulated with in-floor heat.

Could this be TOO air-tight? If I'm building new I want to go all-out on saving heating/cooling costs (mostly heat). I've never heard anyone talk about this. Would there need to be some sort of air exchanger or something?

 

[Tim The Tool Man]

No. Don't worry about that. An overhead door, no matter the quality, will always be a weak link in your thermal efficiency. They just cannot really be made air tight. Perhaps there are a few commercial doors out there that are but I am unfamiliar with any.

Just build and insulate your garage at or slightly better than your local building code suggests for a home. Of course you need to remember to ventilate your soffits and install a ridge vent on the roof...

Now, if you were building a home, then absolutely yes over sealing and insulating can and is a real problem. To tight a home can lead to all sorts of moisture and mold issues. Building and insulating practices differ regionally for this reason. If you built a home in Atlanta, Georgia using the same building codes and insulation practices as you would with one built in say Toronto, Canada, The house would bet a smelly, musty, mold pit within one or two months...

 

[Beaumont67]

My 24 x 30ft graage is over insulated some, with two 20 gauge steel sectional 10'widex8'high doors (factory insulated), one man door and zero windows:
- 3 year old natural gas furnace came out of a town house, 85% med efficient...(unit $200)
- furnace vented outside, for fresh air intake supply to combustion chamber...pillot light is 5 ft. off the floor
- furnace has house duct work, 3 cold air floor returns on the North wall and 3 hot air ceiling grills over the garage doors (spread out every eight feet)
- concrete floating slab was poured on 1" thick of foam (no infloor heating), floor does not sweat and floor moisture is zero
- 6" stud walls are insulated with R23 Ruxol http://www.roxul.com/home
- 14" wood-I structural ceiling (supporting 2nd floor) is R46 (doubled up Ruxol bats to 11", joints staggered)

- 6mil poly vabour barrier, on all walls & ceiling plus fully drywalled
- 12,300 sleeve air conditioner (another used purchase, $200 unit...like new)

12 years ago, garage was heated 24/7 the entire S/W Ontario Canada winter.
- our gas bill went up $250 for the entire season
- temperature maintained at 72-74^F around the clock
AC worked great to, garage was easy to keep cool in the summer months...with no windows.

bams50
Anything over 2" thick of closed cell spray foam, is not cost justified....I would not use cheaper open cell spray.
- suggest doing 2" thick spray, followed by Ruxol bats.
Is it possible to OVER-insulate?
- yes, and you will waste good $$ going to far, but nothing wrong with over building standard guidelines

 

[bdamico]

Yes.

 

[BeachBoy]

The only issue being too air tight is moisture and air circulation.

many houses that are insanely insulated require an air exchanger.. if your garage doesn't have one, you are prone to a ton of moisture (because of melting snow for example, or just breathing). also stale air is not very good (mold and stuff).

I would say you can never over insulate, but if you put an airtight envelope you need to have something to change the air.

 

[BrianC636]

The only issue being too air tight is moisture and air circulation.

many houses that are insanely insulated require an air exchanger.. if your garage doesn't have one, you are prone to a ton of moisture (because of melting snow for example, or just breathing). also stale air is not very good (mold and stuff).

I would say you can never over insulate, but if you put an airtight envelope you need to have something to change the air.

This is exactly what we did. We foamed the house walls, roof deck, shop walls, shop roof deck and also insulated some interior walls for sound.

A simple call to our HVAC guy during this process took care of everything. He piped and installed a Honeywell ERV and as of right now, we have no issue.

Summer will be the true test. I have a feeling since we have an air exchanger we're going to be just fine.

 

[darkk]

We added a 900 sq ft garage with 13 ft ceilings no windows two insulated overheads and one man door to outside and one to inside and a 900 sq ft a second story, a 2 story connector all to our existing home. about 2400 sq ft total. We insulated the whole thing to the max.Our original home was only 980 sq ft to start with. we insulated that as well. The heating bill for the last two years is not that much more. It only added around a 35% more fuel to the bill. Good insulation works...I'm glad considering fuel yesterday just cost me $4.03 gallon for #2 heating oil. Man that hurts!

 

[Steevo]

It is possible to build structures that are so tightly sealed and well insulated that makeup air needs to be added periodically to avoid dampness or stagnation in the event the building stays closed up.
Some newer homes, such as the one I have in Idaho - built in 2007, are required by code to have exhaust fans on timers and a fresh air intake source. In the case of mine, they ran the 6" intake as a roof vent, which runs down into a basement utility room. In the upstairs laundry room, there is a standard exhaust fan that has a 24hr timer instead of a wall switch. As-built, this was set to run for an hour in the morning and an hour in the evening.

As for how much insulation would be too much? There is a point of diminishing returns where you will never recover the cost of the additional insulation in any heating/cooling savings. In ceilings, it is probably around R60 where you start to see so little difference with more that it doesn't pay.

 

[Andersonfarms]

i would say not. we just built a 60x96x21 tall shop, sand base, insulation 4ft down all around the building r-20. floor heat, walls are 10in batt insulation with tongue and groove subflooring painted white for walls. 2 feet of the blow in non itch insulation in the roof, forgot what its called but its not the ground up newspaper. the biggest issue we have is the water cant circulate fast enough. we have a 28kw boiler set to 120-125 degrees and its 55 in there and gets up to 60ish when its cranked to 140 no matter how cold it gets in ND. but there are no windows in yet, and one large door, 20x38 is insulated well and a normal garage door thats 20x18 tall, ending up its not as tight as we thought it would be.

 

[dsimatt]

I don't think so, thou using more than really needed is possible. The main thing is having proper ventilation in your attic, or drawing hot air out of the ceiling area.

 

[Highbeam]

If your shop ends up pretty airtight I would say the most important thing to do would be to make sure any sort of wood or gas heaters used to heat the building or to heat water are power vented and ideally also of the type that draw their combustion air from outside instead from inside the shop. That would greatly minimize any airflow issues from the shop being too airtight. .

Sure you got this right? I'm all for outside combustion air but a benefit of using indoor combustion air is that you do exchange the air since every pound of air that goes up the chimney means a pound of fresh air enters the building. Full outside combustion air means that the inside air has no exchange.

 

[Falcon67]

Yes - but you have to manage the makeup air coming into the building. I personally would prefer to have my heat sources using outside combustion air (like a fireplace) and use something else to manage the air exchanges in a tight house. Combustion sources use a LOT of air. I have been tightening up out house - new windows, sealing leaks, door seals, duct sealing, etc - and we're to the point that with the 400 cfm kitchen vent running flat out and the two 90 CFM bath fans going you can feel the depression in your ears. My boss' new house is a full spray foam conditioned envelop job and they spent a lot of time engineering makeup air. And that's with a huge rock fireplace.

 

[bams50]

Wow, good discussion. I think the main thing I'm seeing is that this has to be thought through on an individual basis by somebody who knows what they're doing. Who is that- building contractor, HVAC guy, or somebody else?

This is the building in my sig. line, basically shop with living quarters in the rear. My goal is to be as fuel efficient as possible as I keep the interior comfortable. I'm trying to find the best way to meet that goal.

 

[e-tek]

My shop is only "reasonably" airtight and one drawback I notice almost daily is that any smoke or fumes linger and if I turn the duct fan off I HAVE to open a window, or it'll bow the OH doors in!

 

[darkk]

Hmmmm.....I have a Modine hydronic ceiling unit hanging in my garage at the 10 foot height and about 3 feet open above it. No circulation fans but that's coming this year to circulate the heat. My 30x30 garage has no windows, two R18 9x10 overheads and one insulated steel man door. There is slight air intake where the overheads meet the frame. I keep it a 66 deg all winter. We have 2x6 walls with R20 in the walls and 2x12 R30 ceiling, we do have a full second floor with R38 in the ceiling trusses there. It stays very comfy all year round in the garage and upstairs. My first water heating system....I think I like it. The cost is very minimal and I'm sure it isn't 100 % air tight but definitely no drafts...

 

[Architorture]

the level of insulation you put in is all a matter of cost/benefit. at some point each additional inch of insulation you add is going to cost more than the potential savings based on your heating or cooling systems.

i've worked on several large chemistry lab buildings that had once through air supplies. these buildings were insulated but it really only served the purpose of managing condensation. they would have had an almost identical thermal performance if they had just had an air film enclosing them instead of insulated walls. so in this case the insulation levels didn't really matter because we were using 100% outdoor air and there would be an air change in the space before it had a chance to cool down or heat up.

so the efficiency of your HVAC system is going to have an impact on your potential return on investment. a super inefficient system will warrant more insulation as each unit of heat lost costs much more to produce.

now on the concept of being 'air tight' that as stated earlier is an entirely different issue. the fastest way to lose heat is through air infiltration so there is a strong incentive to eliminate it. being air tight is not necessarily a problem but you do need to have a means of managing the air supply in the space. if you create a truly tight building envelope you need some way to get fresh air.

my house has radiant floors throughout so in the winter to get fresh air circulating i have an air to air heat exchanger that runs through my AC air handler to introduce fresh air when all the windows are shut.

 

[theoldwizard1]

i would say not. we just built a 60x96x21 tall shop, sand base, insulation 4ft down all around the building r-20. floor heat, walls are 10in batt insulation with tongue and groove subflooring painted white for walls. 2 feet of the blow in non itch insulation in the roof, forgot what its called but its not the ground up newspaper. the biggest issue we have is the water cant circulate fast enough. we have a 28kw boiler set to 120-125 degrees and its 55 in there and gets up to 60ish when its cranked to 140 no matter how cold it gets in ND. but there are no windows in yet, and one large door, 20x38 is insulated well and a normal garage door thats 20x18 tall, ending up its not as tight as we thought it would be.

I would like to see some pictures of your radiant heat set up, especially if have any taken during the installation process.

 

[theoldwizard1]

I'm glad considering fuel yesterday just cost me $4.03 gallon for #2 heating oil. Man that hurts!

OUCH !

I don't know what your annual heat costs are, but maybe it is time to consider a heat pump ! Geothermal are the most efficient, but do cost more to install.

 

[Weedwaka]

You need to exchange the air in any living space x amount of times a day. I cant remember the exact number, but its actually quite a few times a day. It would be less with just a garage if you keep moisture out. Your garage doors will help slightly but with radiant, you may find you need a small HRV or some kind of fresh air makeup. Or just crack a door and circulate the air.

We have the following as well (but we live upstairs):
spray foam ceilings,
ICF walls,
2" insulated garage doors
radiant heat << this ones very important

With radiant, there is no fresh air makeup. Someone running a furnace with fresh air makeup will not understand what a huge difference this makes.

We have an HRV running 24 - 7 in the suite above the garage until summer when we open windows up. If the HRV was turned off, the space would be un livable in 2 days. You would get condensation on everything and mold. The air just goes nasty.

When we were building it and living in it, we got hit with winter before the HRV was active. It got gross really quick once the windows were shut. We stopped everything and installed our HRV right away just so we could survive in there and continue working. The air was nice again and the condensation on the windows was gone almost right away.

If your only working in there occasionally, you will not be bringing a ton of moisture into the space. You may just need to circulate the air around and let the garage door seals do the rest.

Its way worse with a living space as you have people breathing all the time, plants, sinks and water traps. All this stuff is throwing moisture in the air. Wet cars will kill you though if you have no ventilation.

 

[wssix99]

I'm finishing up design on a new heated garage attached to an ICF house. As mentioned above, it would be best for you to address the weak links vs. invest in wall insulation due to diminishing returns. Here are the ones that I'm spending most of my time attacking:

Windows - No matter what you do, the R factor on these will be low. If you put a thermal camera to a house in winter, the windows look like they are wide open. They are a super-highway for heat and the only thing you can do is minimize their use.

Garage Doors - I've seen some R-18 insulated doors, but these will always be a weak link like the windows. IMO - Building a R-50 wall would be overkill of you have R-5 windows and R-18 doors. Your money is probably better spent on an efficient heating source. One other think you can do here is set your opener to NOT go up all the way. If you have an 8 foot door and only need 6 feet to get your car out, you'll let less air/heat out if you set the door to stop at 6 feet.

Floor - You should insulate the slab. Again, you probably won't go above R1- or R-15 here, so this will remain to be a weak link. Putting a thermal break at the edges of the slab, where they meet the foundation is also key.

On air exchanges, just opening the door every once in a while will be fine. The garage door sealing isn't that great, either - so you will have air moving here, probably way in excess of other parts of the structure. In my application, I'm required to have passive ventilation (by local code) in the garage to reduce CO concentrations. Since I don't want all my heat to go out the vents, I was able to get my city to approve using an HRV (set to run 10 minutes after the garage door closes) to ventilate the garage and exchange the air.

BTW - If anyone is interested - the equations to size a HRV, or other ventilator for a garage space to control CO are given in the 2011 ASHRAE Handbook - HVAC Applications (SI); Chapter 15 - Enclosed Vehicular Facilities; Parking Garages.

 

[Kevin54]

Better more insulation than not enough. I've watched a few specials over the years of homes in Sweden and how well they are insulated. They have to have an air exchanger that kicks on every so often to bring fresh air into the house. Along with that, a lot of prefab homes today are way better insulated than a similar size home that is stick built. A lot of the prefabs are built the same as a conventional house as far as floor joist, studs, etc. but they are built in jigs, more sealant and construction adhesive used, and the insulation is more tightly controlled.

It used to be that a prefab, meant that you had a double-wide trailer. Todays prefabs are way better than that now. I be interested to hear from someone that has a newer prefab in a cold climate and what their utilities run per year.

When I built our family room on maybe 15-18 years ago, I tried to seal everything I could. The floor was built with a sill plate seal all around, the bottom plate when set had caulking under it, the walls were 2x6 construction with R19 insulation and the ceiling had R30 in it. Both walls and ceiling were batt insulation. That room is the coldest room in the house. I've had an energy audit done and all is good. I don't know whether it's because we are out in the country and are getting winds in the winter and all three sides of the house are exposed to the elements or not. New furnace was put in a few years back and 85% efficiency. All brand new replacement windows put in 4 years ago. I can't figure it out.

I'm fairly certain that we are going to put a woodburner in this year. Something to cut back on using propane. If I could find a good layout for the kitchen, I'd like to take out the wall between the kitchen and family room and have a totally open concept. I may have to hire an architect to come up with an idea though.

 

[bams50]

Well thought – out responses here, lots of good information.

I currently live in a "Doublewide", About 1300 ft.², new in 2005. I heat with forced air LP. As you say, it is built rather well, with 2 x 6 studs, et cetera. It was weird moving into it, because there are no drafts, even around the windows. It also amazes me that if you put your hand in front of a heat register, the air does not feel very warm, yet the house warms up and stays warm pretty easily. Still, if I was to keep it at say 68° around-the-clock during winter, I use about 900 gallons of propane. I cut that in half by going with a high of 62 when we're home, and turned off when were not. At 0°, we can shut the heat completely off for the day, say 12 hours, and the house will still be high 40s in temperature. (We usually don't let it go that low, but we have tried it).

So overall for what it is, I don't think that's too bad. On the new place I want it to be as warm as we want; If I do my best to think through all aspects of efficiency, then whatever it costs I won't mind. I just don't want to end up like so many who get that first heat bill and think, "damn I wish I had done thus – and - so when I could have, it might have saved me a lot of money on heating"...

 

[Daedalus]

Oddly, it is possible to insulate too much. On cylindrical pipes, there is a point where more insulation increases the heat loss from the pipe. This is due to the increased surface area of the insulation as the diameter grows.

 

[Architorture]

Oddly, it is possible to insulate too much. On cylindrical pipes, there is a point where more insulation increases the heat loss from the pipe. This is due to the increased surface area of the insulation as the diameter grows.

i don't believe that could possibly be true...unless you are "insulating" with something pretty conductive.

 

[Andersonfarms]

I would like to see some pictures of your radiant heat set up, especially if have any taken during the installation process.

unfortunately i dont have any pictures of this, we ran a quality pex style pipe that was quite a bit better then what you would get at your home improvement store, i want to say we had them 12-16 inches on center, we ran all the lines underneath the cement right on the sand, then a second run on the rebar in the cement from the outside wall to15ft in all away around the perimeter if you get what i mean. plan was to run two 28kw boilers and then a 10kw during offpeak

 

[Kevin C]

i don't believe that could possibly be true...unless you are "insulating" with something pretty conductive.

http://eng-shady-mohsen.blogspot.com/2012/07/critcal-economic-radius-thickness-of.html

Fun read.... The first link has a decent explanation.

http://www.tandfonline.com/doi/abs/10.1080/01457639708939897

People spend a lot of time on this subject.

the theory of critical thickness of insulation for cylindrical and spherical geometries is discussed in a comprehensive and methodical manner. The article begins with the introduction of the classical analysis, which assumes surface convection with a constant heat transfer coefficient, h. Next, various modifications of the basic theory are discussed in detail. These modification allow for:

The variation of h with outside radius, ro (constant-property forced convection)

The variation of h with ro, with temperature-dependent fluid properties (variable-property forced convection)

Circumferential variation of h with forced convection The variation of with outside radius and the temperature difference between the outside surface and the surroundings (natural convection) Surface radiation

Combined radiation and natural convection Combined radiation, natural convection, and surface heat release due to change of phase of the surrounding fluid Effects of radiation, inclination, and insulation opacity

The last three sections of the article consider the optimum configurations for a circular pipe covered with insulations of equilateral polygonal, rectangular, and eccentric circular shapes. For polygonal and rectangular geometries, the two-dimensional conduction analysis reveals that the conduction for the critical configuration is the same whether the outside surface boundary condition is that of convection or constant temperature. This permits the use of conduction shape factors to determine the optimum configuration for polygonal and rectangular insulations. The analysis leads to the concept of critical perimeter, which is more general than the concept of critical radius. The optimum sizing of eccentric circular insulation, however, requires a complete two-dimensional analysis. A total of 12 examples have been included to illustrate the various theoretical models described in the article. The detail and the number of examples makes the article pedagogicatly as well as practically appealing.