Any attic that contains mechanical equipment and ducts should be included within the conditioned space of the house. That means insulation should go in the roof rafters instead of the floor.

As for venting, the purpose of it is to allow moisture to escape the attic so a 1" space can be left between the insulation and the bottom of the roof deck with eave and ridge vents or foam insulation can be sprayed against the bottom of the roof deck and the vents omitted (sealed attic).

In no case should you use a gable vent or a wind turbine to ventilate your attic.

A member named energyrater is sure to chime in and is very familiar with the smart techniques and best practices for your area. I will go ahead and agree with the usual recommendation of foaming the roof deck and NOT ventilating the attic. This is a no brainer in the parts of the country that routinely put ducts and HVAC equipment in the attic. I would suggest to find a place for the air handler out of the attic and minimize all ducts up there but most importantly have them use lots of mastic and let them know that their work must pass a minimum duct blaster test.

One key problem with this increasing trend in home building is that spray foam companies are spraying WAY below minimum R value requirements to be competitive with traditional insulation. You should be spraying an average of 11" to achieve an R38 in your climate unless you are going to use foam sheathing on top of your structural roof deck. Open Cell at 7" is R25, and it may be performing better than the usual alternative but its still a VERY lousy R value for roof insulation in your climate.

Two other points, your architect is misinformed as to the benefits of mushroom vents. They are worthless. Forget tankless water heaters, find yourself some space or a location for a heat pump water heater. And since comfort and energy use seems to be important to you, get a third party certification and shoot for a blower door test of 1.5 ACH50 or below.

Probably too late for big picture design, but stretching the mass of the house from East to West and minimizing windows on those elevations can make a huge comfort and energy use difference.

An unvented attic assembly is the best choice in a climate this is mostly hot/humid.

Thank you, everyone. A couple follow-up questions:

Does "roof deck" = attic floor? If so, it sounds like Renovator8 is recommending foam insulation on the bottom of the roof deck (if we decide not to use ridge/eave vents). We would definitely insulate the roof rafters. Would we need additional insulation in the 2nd floor ceiling, as well?

Brian K: thanks for the advice and spray foam info. Regarding the mechanical equipment, can you explain a little more about your concern about putting the air handler in the attic? We weren't planning on treating the attic as conditioned space, but I'll look into that... And are you not a fan of tankless water heaters in general, or just not in an attic?

Thanks again --

Roof deck or attic floor?

One or the other, not both. Roof deck for a conditioned attic; attic floor for unconditioned (vented) attic.

A vented attic makes building scientist Dr. Joe Lstiburek's list of Top Ten Dumb Things to do in the South.

Putting the air-handling equipment in the hot attic puts a greater load on the system than putting it in conditioned space. IOW, it costs a lot more to run. Instead of conditioning the whole attic, an enclosure can be built around the exposed HVAC. But that can be just as expensive as conditioning the entire attic.

You might want to consider closed cell rather than open cell foam for its higher R Value per inch.

As well, per Dr. Lstiburek,consider concrete or clay tiles for the roof rather than asphalt. Greater initial cost, but a longer lifespan.

This post was edited by worthy on Tue, Aug 6, 13 at 13:28

We did the seald attic, closed cell foam, in the upper part of SC. Very happy with doing that, on the hottest days, the attic is in the 90s.

When it comes to HVAC, might I also suggest using small air returns in each bedroom (not just one big one in the hall). Most of us close our doors at night, and the pressure buildup can really be felt as air gushes under the doors. Then put an electrostatic filter on the whole air return.

Don't forget the ERV if you get a tight house built, lke what's being suggested.

We also have Tankless WH. Good for endless hot water. Bad for having to run a faucet for 3 minutes to get the hot water. We did two smaller ones working together, wife thought I should just get one bigger one... until one broke and we still had hot water. We've had 2 motherboards replaced and 2 full unit replacements. Not happy with the Rheem brand.

While Im not an expert, I live in the south and am doing a complete gut remodel on my 60's house. I have done a lot of research and Im going with:

6" open cell sprayfoam on the underside of the roof deck
unvented attic
airtight drywall (including ceilings)

Check out Matt Risinger on youtube. He is a builder in Austin with lots of great info on building in the South. There just isnt near as much info for southerners.

I would only even consider a tankless water heater if you have natural gas. Electric ones are a waste. There are some quite efficient tank water heaters out there.

Worthy explained the concerns well. A non-vented attic with insulation at roof deck is considered semi-conditioned space. Most feel its best to keep all HVAC (sans bath/kitchen vent hoods) in completely conditioned space IF you have the room for it. If not, dont worry about it but the shorter and straighter your duct runs the better. Consider open web floor trusses or dropped soffits between levels as a better alternative.

There is no where in the country that 6" of open cell should be getting past competent code inspection departments or educated designers, builders and homeowners. 6"xR3.6 per inch=R21.6. The lowest level allowed anywhere in the country for the 2009 IECC (zones1-3) is R30.

6" of closed cell is entirely different: 6" x R6 per inch(aged) = R36. Technically, R36 should only be allowed in Zone 1. Zones 2-3 are now calling for R38 in the 2012 IECC. I would call it close enough but this also would be the poorest performance allowed by international law. Closed cell is a much more effective air seal too.

Iam not a fan of tankless in general but they can certainly be a good fit in the right situation. A poplular University of MN study concluded that NG tankless are NOT cost-effective. The work involved retrofits and new construction is much more debatable.

Its mainly my personal philosophy for all-electric homes but now that heat pump water heaters are becoming available there is no comparison for their efficiency in hot and mixed climates but it can be tricky finding a proper location for one. I feel that if building a custom home, one can always find a place and its possible that your semi-conditioned attic is a good spot for it. Attached garages are also a great location in hot climates.

Point of use electric tankless can be useful for remote fixtures but they are still a bad choice for whole house use in my opinion. Natural Gas NG can be efficient but I think its wise to avoid as many combustion appliances as possible. Also, the monthly fee from the gas company and upfront costs of gas line installation are very undesireable when comparable or more efficient options exist. I would install a Rheem Marathon electric tank before NG tankless personally. I could go on.. and will if others want to get into it.

delete dupicate post

This post was edited by Brian_Knight on Wed, Aug 7, 13 at 12:26

Mushroom vents work well ONLY if you have adequate soffit vents so air can flow in the soffits and out the 'shroom. A single mushroom up there can't vent because there is only one opening.

Ridge vents might work better, but again, to flow, air has to havea place to flow into as well as out of.

I can't comment further ... AZ/NM are hot, but not terribly humid, so the problem is much simpler. I don't have to worry about condensation summer and winter.

duplicate ...

This post was edited by lazygardens on Wed, Aug 7, 13 at 14:02

Also, if the attic is vented, the ridge vents should have an open area that is less than that of the eave vents so air is not pulled from the conditioned spaces below. This is one reason why large gable vents and wind turbines are not a good solution.

I'm planning on venting my roof here in SC and insulating the ceiling (R49), in addition to careful air sealing. My HVAC will be mini-splits, so there is no equipment in the attic at all. Should I be re-thinking this while I still have the chance? My roof is tin, with a pretty good reflectance. The attic doesn't seem to get all that hot, even without being vented yet.

I have to disagree some with the airflow quoted for ridge vents. When I vented the roof in out FL house, the sawdust shot up in the air as I cut. It made a dramatic difference in the attic temperature, although not as much as insulating the roof deck.

This info is so helpful -- thank you! Dropped soffits for the ducts are definitely a possibility for us. I'll look up Matt Risinger on youtube.

And re: tankless water heater -- it would be natural gas... We might be able to place that in the garage instead of the attic. More to research....

flgargoyle, I think your approach is sound when people are ok with flat ceilings and simple gables with two major caveats:
1. Air-sealing the ceiling plane is critical.
2. Vented attics are more susceptible to damage from major wind events.

I feel both things can be planned for and executed successfully. There are some big advantages to the vented attic with insulation at ceiling plane. As you stated, R49 is a much better performance number than what you would see with typical spray foam jobs. You can use much cheaper and environmentally friendly insulation and its cheap and easy to pile it thick and add more in the future.

Another advantage people point to is that roof leaks are much more detectable and easy to find and fix. A tricky detail that ties into this aspect is the access. Its best to have the access from outside on a gable which doesnt really lend itself to easy access and inspection. Traditional hatches can be done appropriately but it takes attention to detail. I think a good compromise is a small interior access hole without the fold down stairs.

Sealing the ceiling plane presents challenges but smart design can make it much easier. Avoiding recessed cans is wise because they need boxes built around them and air sealed. One smart strategy is to hang and tapt the drywall ceiling before interior walls are built. This will of course increase your drywallers costs but it eliminates trying to seal at the top plates which is tough.

Another great strategy that we will probably be trying next opportunity is to use closed cell foam to flash the ceiling plane and then adding the cheaper fluffy stuff (cellulose or fiberglass) on top of that.

lushkaloo, One of the tankless major advantages is that they are small and can be put anywhere. The heat pump water heater is what presents challenges for placement because they require minimum volumes of air to extract heat from. Garages in hot climates are a good fit.

In my opinion, I would always choose a heat pump water heater before tankless even if it required redesign.

Brian- Thanks for the input! I am using some recessed lighting, but bought air tight, insulation contact cans. Good idea about flashing the ceiling prior to cellulose.

The Building Dept. won't allow drywall first- I asked. It would have been easier for me, since there are no interior structural walls- it's just one big room.

Code requires attic access, but just a hatch, not a stairway. It is tricky to seal and insulate even a hatch, though. I can get into the main attic through the garage attic, but don't have room for a code-legal opening. I can wriggle through there and spread insulation over the hatch once everything is finished and inspected. As for wind resistance, I built my roof to FL code, using higher rated trusses, closer nailing schedule, and the strongest truss clips they make. I had to get them in FL, as they are not available in SC. Save a rare small tornado, we are not in a windy area.

Everything about my DIY house far exceeds code both structurally and energy-wise.

With the air tight IC recessed light cans you should still build air sealed enclosures around them because they leak a lot apparently. LEDs are a great choice for these locations especially without enclosures as they have a weaker "mini chimney" effect.

Did the building dept give a reason for not allowing a ceiling before interior partition walls?

I wish I had a better suggestion for the attic hatch, if anybody knows a good product, please let us know.

I also wish more people would strive and be proud of exceeding minimum building codes. Its a cheap and smart thing to do.

Here is the hatch I built for my attic. Iam sure code requires a bigger hole now. I just wish I had looked up here 4 years earlier and realized I had dirt and squirrel nests for insulation.. I knew looking up there would result in work but I couldnt resist the thought of buried treasure, which in a way I found!

This was a VERY cost effective weatherization upgrade to say the least. I think Ive already paid it back in comfort and reduced oil and electric costs in 2 years. Air sealing ceilings and blown cellulose is cheap.

The efficiency of the hatch to my labor may not be so cost effective but I like it and it wasnt that bad. I used two layers of 2" XPS (cut to size of inside hole) and then one more layer cut bigger than the hole which gives more surface area for that high performance flashing tape to get a good seal. Plus the tape seals the layers.

Awfully proud of the bonus energy detail, using another layer of the 2" foam to create a thermal break between the insulation dam framing and the ceiling joists. Eat that this old house.

I'm kinda late to the discussion...having spent all week in a foam insulated attic.
most valid op's questions have been answered I believe.

one thing...put the tankless gas water heater on exterior
wall..not in foam sealed unvented attic. let the heat gain be to the exterior..it doesn't get cold enough in south la for freezing to be an issue.
if you put a combustion appliance in a foam sealed attic
you need to have a dedicated fresh air sorce for it.
so just take it out of the attic.
or if going the unvented foam sealed semi conditioned attic route...heat pump water heater.

open cell is the install I recommend.
here is a link to some pics and videos I uploaded recently of foam installs etc.
http://s1313.photobucket.com/user/EnergyRaterLa/library/?sort=3&page=1#/user/EnergyRaterLa/library/?sort=3&page=1&_suid=13761061489950010639468707426047

keep in mind that when you put ducts & ahu in the attic
that the tradeoff for spending more for the foam sealed attic is to reduce the size of the hvac system.
while you haven't mentioned a load calc or sizing of hvac system...these 95 degree days & RH in the 80 percent range make oversizing an expensive cost of install...and operation. we need long run times to lower humidity inside the house, that you simply won't get with 500 sq ft per ton sizing that is the norm ..sadly.
if your hvac company is using a rule of thumb sizing..you need to invest in a load calc. seriously.
and a properly sized unit with a variable speed air handler is your best investment for handling high Rh.

if you design your house with ducts inside the house..inside of fur downs & create a space..closet would be sufficient for the ahu then instead of foam sealing the roofline, you could just foam the attic floor.

where abouts in La are you building?

about foam companies...beware of companies that talk about 'average' fill for R-values. you have to meet code.
foam should be installed with no voids, no exposed framing members & inspected to verify the install.

and Brian..I'm still looking for that coffee can of $100 bills I'm sure is in some attic nearby..LOL!
and your diy sealing of your attic hatch is top knotch!

best of luck.

The building department inspects the framing, rough electric, and rough plumbing all at once (!) The interior framing has to be in place for inspection, and of course for the various electrical and plumbing devices mounted to it. You can't cover any work before inspection, including the ceiling structure. And no, they are not willing to climb into the attic to inspect.

It is true that the 'air-tight' cans are pretty leaky. I've experimented with the Cree LED's that I'm going to use throughout the house, and they give off almost no heat at all, so I feel comfortable further sealing the cans as I go. The cans rely on a perfect seal between the light bezel and the ceiling. Since the LEDS should outlast me, I'm thinking of caulking them to the ceiling.

Code requires a 22X30 access hatch for the attic unless the attic is very small.

As for added costs- my higher wind rated trusses, with a 12" energy heel came up to the same cost as regular old trusses. The truss builder seemed to think I was nuts, but I got what I wanted.

Here is the hatch I built for my attic.

Close to what I've been doing. But I also put a strip of closed cell foam around the bottom of the hatch and pull the cover tight to the lip at the bottom of the opening with hook and eye fasteners.
*********
There is no where in the country that 6" of open cell should be getting past competent code inspection departments or educated designers, builders and homeowners. 6"xR3.6 per inch=R21.6.

But you're dealing with Codes!

Making a YouTube video qualifies as expertise above and beyond.

Flgargogle, some amount of visible light will be reflected from any shiny surface but infrared light reflectance depends on the material. Tin will absorb 95 percent of infrared light but I'm sure your roof isn't actually tin coated and probably not zinc-tin either. If it is polished aluminum it will reflect most of the infrared energy. You might need an IR barrier in the attic to achieve the energy savings you desire.

on my jobs the oc foam is 8" at least 7" but the
foam installer I've educated always over fills.
what works for us here in La. where codes are
very minimal is that R-25 is code for cathedralized
ceilings. which in essence is what is foam sealed
attics.

code inspectors..on my jobs always comment on
the quality of the install as opposed to others
they inspect.as I've seen these other companies work...
I totally agree,

which is why I have certain companies that
I work with. with the other companies ...even after years of them knowing the quality of install I require...I still have
to blower door test the air seal of the attic and spray paint each leakage site,,each low spot and every missed
rafter face. just not worth the hassle IMO..
and the cost of this extra inspection & testing is always
on the homeowner...even though foam companies say
seal is air tight. ha ha ha

some homeowners are price driven., which I do understand..and hire these
larger companies against my recommendations.
but that is their option..free will & all that jazz!

flgargogle...I'm confusing your posts with OP's.
so it isn't that I'm not wanting to comment...just
difficult to seperate the two projects on the one
thread.

best of luck & have a great weekend everyone!

We're at the early stages of design/planning, so we do plan to have a thorough load calc done, and discuss all the options with our HVAC company, including the idea of putting tankless water heater on the exterior (or in the garage). The answers and ideas on this thread have been hugely helpful -- I don't feel like a total HVAC newbie now :o)

The house is new construction in New Orleans, so we do have concerns about high winds and water, of course. Brian -- love your attic hatch! I've started looking for an insulated hatch and would flash/caulk/seal the heck out of it.

Thanks! I had forgotten about it till now. An airtight insulated hatch is only necessary when insulation is at the attic floor/ceiling plane (vented attic). Sounds like youre going with roof deck insulation (typically unvented attic).

Curious why you are choosing NG tankless instead of a heat pump water heater?

Renovator8- My roof isn't real tin, of course (were they ever?) It is Galvalume, in the natural metal color. I'm surprised how much heat this material reflects. I was going to install water heating tubing under the metal for solar hot water, but experiments yielded very little heat gain under the metal. On a hot day, the metal gets warm, but not blazingly hot like some metal roofs.

My contractor is an advocate of foil bubble film stapled to the trusses to reflect IR, but I'm not sure if it would help in my case. I guess I could do some more experimenting. My roof structure is still open to the inside, so I have all of the options available to me.

I apologize if we've hijacked the original thread somewhat, but this is a valuable discussion that too few people have when designing and building a home. Here in SC, we are still under 2006 codes, and the new houses I see going up aren't much different than the last 50 years. But hey, that granite sure is pretty.....

"With the air tight IC recessed light cans you should still build air sealed enclosures around them because they leak a lot apparently. LEDs are a great choice for these locations especially without enclosures as they have a weaker "mini chimney" effect."

in all my projects new and existing I've found many ways
to seal IC cans. retrofit with inserts. then seal housing to sheetrock ceiling...from inside the house before putting
trim kits in place. even 'air tight' trims don't stop the oversized cuts in sheetrock from leaking. I use a mastic tape made by Hardcast #1402 for all my holes in ceiling.
more on this later.
this seal described above is the best with no measurable air leakage.
building boxes..maintaining the 4" air space on all sides & top of can light..also works, cheaper cost..harder install. problem is the 'legs' of the can lights that are attached to ceiling joists & properly sealing around them. this is where the air leakage occurs. I never use foam..because it shrinks over time, you have little control over where it goes & unless it is fire rated..shouldn't be next to heat producing areas. and yeah..I'm overly cautious about this.
this method can be well done..and still leaky.

foam installs I've seen online in videos put fg batts around recessed lights and foam them. I don't like this at all, and it is never done on my jobs.

best of all is to use ICAT only, and use the hardcast tape to seal the cut between housing & sheetrock.

Hardcast brand mastic tape #1402 is a 3" wide strong mastic tape. I perfer it over any other brand on the market. cut it into 1 1/2" wide strips and use it in full width depending on size of opening to be sealed.
sticks to just about any clean dry surface...to the point of pulling paper off sheetrock if you try to remove it. so use it carefully.

opeings at bath fans, supply boxes, stove vents, recessed lights..I use hardcast. use it once..and you'll understand why. not the cheapest on the market @ $22-
$35 per 100' roll. but absolutely great stuff.

while it is hard to describe the sealing of supply boxes with hardcast from inside the house..a picture shows it well. I'll attach one to this post.

flgargoyle ..
foil bubble foil is an overpriced product that performs no better than the cheaper radiant barriers. in my house with a tin roof..I have a single sided foil scrim fraft paper like what is used for ductwrap. I used button cap nails to attach it to the undersides of my rafters. with gable end vents..and 3 hurricanes later I've had to do a little repair on it..but it was worth the few bucks it cost me & the 2 mornings it took to install.
good benefit in summer little to none in winter.
my attic has fg batts on attic floor, one layer in joist bays
the other unfaced layer laid across joists.
no ducts, no equipment no recessed lights and a damn near perfect air barrier from living to attic space.

ducts are in fur downs inside living space, vs air handler in side living space also. a bit over sized @ 2 tons with an whole house april air dehumidifier..also in conditined space. 4" media filter at return. 15SEER unit

the addition I re-roofed last summer, batts in rafter bays 1" R-7 foil foam sheating lathes & gavalnized tin.
as rafter/ceiling joists are 2x4 (yeah...go figure) the batts are R-13 with the R-7 gives me R-21 for this large bedroom. prior to this install the room was used for storage as it was too hot in summer & too cold in winter and too expensive & uncomfortable to use.

with radiant barriers there always has to be a mininum of a 3/4" air space. thus the lathes on top of foil foam board under tin in addition & opposite install in big attic with rb under rafters with foil facing into attic space.

gotta run...but wanted to share my take on things.
oh here is the pic of the supply sealed from inside the house with hardcast tape.

best of luck

Great stuff EnergyRater, thanks. Been using the 3m flashing tape at some of those locations but will have to try the hardcast, it looks a little cheaper too.

I think you did the thread a service flgargoyle by highlighting that the traditional ways can be more cost-effective with the right situations and designs.

And many of us agree, those shiny granite cttps, that trim color, or even floorplan dont contribute a lick to making a home more comfortable or saving money. The decisions surrounding this thread could impact generations of inhabitants while most of the issues discussed in this forum will come and go in the blink of an eye compared to the longevity of the building envelope.

Good thread and bunch of good information.

Should be required reading for new homebuilders.

Few homeowners truly understand the importance of proper attic ventilation. After all, who cares what goes on in a part of your home you rarely use? You should!
In hot months, attic ventilation is important for two reasons: 1) it keeps your attic cool by eliminating heat buildup and 2) it prolongs the life of your roof by preventing early failure of roof materials.

Although attics are required to have passive ventilation like soffit, gable, dormer and whirlybird vents -these vents do not effectively circulate and extract hot air. In hot months, attic temperatures can shoot up to 140˚ F (60˚ C). Ultimately increasing temperatures in your living space below.

Example of a passive ventilation unit.
To reduce discomfort, homeowners often respond by turning on fans and single-room or centralized air conditioning systems. While this may lower interior temperatures, it also raises energy consumption and utility bills.

Excessive heat buildup is also detrimental to your roof. With the sun beating down on it, roof sheathing can heat up to 170˚ F (76˚ C). Over time, roofing materials can warp and eventually crumble, exposing your home to the elements and resulting in roof leaks. If not properly protected, the outcome could include an expensive roof replacement or perhaps repairs in the interior of your home due to water damage.

Solar Star Attic Fan

Solar-powered attic fans are a cost-effective and energy-efficient solution to attic ventilation issues. Using the power of the sun, they cost nothing to operate while pulling hot air out of the attic allowing cooler air to enter through the intake vents. The outcome is a continuous cycle of air flow so heat never has a chance to build up. With a solar attic fan, you can quickly and easily convert your home’s current passive vents into a powerful, active ventilation system.

Solar Star thermal switch

To get the most out of your investment, you may want to consider a solar fan with a thermal switch option. This device maximizes performance through temperature-controlled operation. On warm days, it activates the fan once temperatures reach 85° F (29° C. On cool days when attic temperatures drop and extra venting power isn’t needed, the switch automatically turns the fan off at 65° F (18° C By running only in pre-determined temperature ranges, the thermal switch minimizes wear and tear on the motor and prolongs the life of the fan.

Tip for spammers: Dont use your product in your user name.

Adding mechanical ventilation to vented attics, even solar powered, has never been proven to save energy. Most experts feel it will make the problem worse by sucking more conditioned air out of the home. This relates to why air-sealing the ceiling is usually considered the most important performance variable for vented attics.