energy_rater - SLEMCO's recommendations

10 years ago

energy_rater, thank you for posting SLEMCO's energy efficient construction checklist! So much information in one easy-to-read document. Just curious, though, what parts are you not 100% in agreement with?

We will be building in the upper middle part of SC where it gets hot and humid like Louisiana, but not for as many months. Our home will have no tree cover until the trees we plant mature. From what I have read on the ORNL site and other scientific-based sites, I had just about decided that an attic radiant heat barrier would not have a reasonable payback period. (We do not plan to have HVAC ducts or equipment in the attic.) Does SLEMCO recommend it just for homes with attic HVAC? What are your thoughts on radiant heat barrier?

Thanks for your valuable input on the forum!

Here is a link that might be useful: Energy Efficient Checklist - Hot and Humid Climate

Featured Answer

8mpg

10 years ago

last modified: 9 years ago

Well, I didnt start my own thread but hoping you could advise me on my remodel.

Im doing a 1650sq ft + 400sq ft garage conversion. Doing 6" of open cell spray foam on the roof line, air tight drywall (ceiling and walls). Also going to go ahead and do spray foam walls (it is $1200 more than conventional insulation batts). Im going to go ahead and do the walls because the cost difference is so low and I cant do any foam outside the house since we have brick.

Windows will probably be Simonton vinyl Reflections 5050 with .30u and .22shgc. Im 99% sure these will be the windows are getting.

Im looking for advice on the HVAC side. We are going to keep using the 3 ton heat pump and existing air handler. Since we are adding square footage and keeping existing HVAC (which is probably oversized for the 1700sq foot it was cooling/heating), I believe it will suffice the additional 400sq ft. I have been following Matt Risinger's blog/youtube and he really recommends an ERV with tight houses. Im not sure how tight the house will be in the end but Im hoping pretty decent. Do you think I need an ERV and if so, where is the best place to install one in the ceiling? We may end up adding a dehumidifier later on if needed. We will be adding a 4" air filter on the return at the air handler. Cheap $125 Aprilaire unit and can do a 13merv filter once a year. Also will be reducting the house. It has 60' under the floor (pier and beam) supply side that will be converted to ceiling ducting. Would you suggest getting a manual D? I found an online place that had some pretty decent rates ($75 manual J and $75 manual D for 2000 sqft). Im thinking if I do the manual J/D I will do the actual ducting myself.

THanks
Tim

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Comments (10)

energy_rater_la
10 years ago
last modified: 9 years ago
what I wanted added to design one ...
1-raised house on piers 3" closed cell foam
2- use 1" foil faced foam sheathing on
exterior of walls tape seams, caulk foam board to sole plates & top plates & at each window/door opening.
not R-3 foam board but R-6.5.
3-http://www.nrel.gov/docs/fy05osti/37583.pdf
details of window flashing with foam sheathing
4-foam sheathing of walls, conventional insulation
air tight drywall to interior
http://www.buildingscience.com/documents/information-sheets/air-barriers-airtight-drywall-approach
5-windows .35 shgc & ufactor or less .30 is ideal
6-locate ductwork & mechanicals in conditioned space
7-if mechanicals & ductwork are in attic make unvented attic with open cell foam sprayed on roofline.depth of open cell 7" for 2x6 rafters. rafter bays filled
with no dips or gaps, faces of 2x's covered with open cell
depth at least 1-1/2"unvented semi conditoned attic
8-R-8 ductwork, masic sealed (not foil tape, or duct tape, but paint on mastic or mastic tape I perfer Hardcast brand 1402 mastic tape)
9-ceiling as air barrier to vented attic with conventional insulation on attic floor. seal all penetrations. supply boxes, return airs, oversized cuts at bath fans.
recessed lights all ICAT insulation contact air tight. use mastic tape to seal penetration of housing to sheetrock, trim will cover tape.
or avoid recessed lights completely...why cut more holes in the air barrier??
10-strap ducts (flex) with 3" strapping in straight tight runs with no sharp bends or constrictions, max 1" drop per 4 ft section of flex.
11-size hvac system with manual j load calc, not rule of thumb sizing. with heat pumps 15-17 SEER range,variable speed air handler.
12-mastic seal supply boxes, not caulk that shrinks as it dries and leaves voids or attaches to supply grills & not oversized cut in drywall.
13-R/A chase drywalled & sealed air tight, if ceiling R/A
caulk all 2x's to each other, at corners and to attic floor.
14-4" media filter buy return air with 4" filter depth, filter prices per case will make up extra cost in 2 years.
15-if unitis oversized...(see #11) whole house dehumidifier.
add fresh air intake with 12x12" filter back grill, 4" duct with barometric damper ducted to return air so that air is cleaned, measured and dehumidified before entering conditoined space.
16-be willing to pay for load calc, or use online free load calc systems. oversizing costs in upfront costs, short cycling of units shorten life of system and does not allow enough runtime to properly remove humidity.
17-blower door test of house to achieve .30 air changes per hour level of tightness, duct test to achieve minimum of 10% duct leakage.
18-if foam isn't in the budget, radiant barrier is small upgrade charge for benefit of summer radiant gain in attic.
little to no winter benefit but works well for may-oct.
19- and this is my biased personal issue....no cellulose in attic. I perfer batts, R-19 laid in joist bays, with unfaced R-19 laid across joists to provide continous R-values.
blown insulation varies in depth, settles over time and cellulose produces a fine 'dust' of borate treated newspaper
that finds its way into the house via unsealed openings.
while if I am paid by homeowner I can't let this bias influence my recommendations...but having spent the better part of my adult life in attics...cellulose is the worst insulation to work in if you ever have to change a bath fan,
or run a new electrical line. online....I can voice this bias,
as I am not bound by constraints. any additional work in attic can be done by simply moving batts out of the way
and properly putting them back when done.

probably 70% of my retrofit work is for 'dust' & allergy issues 90% of the time the insulation is cellulose.
once leakage sites are sealed the problems lessen if not
stop completely...but it is a major pita to seal from attic side.

my thoughts on radiant barriers? I have a radiant barrier. single sided fsk (foil skrim kraft paper) installed as retrofit...10 years ago in 2 early morning work days. my attic has no ductwork or mechanicals.
this is the absolute cheapest RB material & it performs as well as foil bubble foil for a fraction of the cost. I used button cap nails...(xtra holding strength with gable vents & hurricanes...enough said ....)
two layer of batts & gable end vents on gable roof. air handler unit & return air are in closet centrally located in conditiond space whole house dehumidifier is also in this closet space. ducts are in fur downs to each room.
I have a 15 SEER heat pump and July's kwh usage was 694. this is the highest bill I've had...because I cranked tstat down after spending my days in attics...my bill was $65, $15 more than usual. (and worth every penny!)

on average my bill is $50. While I have a whole house dehumidifier, I seldom use it. right now at 11:30 pm it is 52% RH (afternoon/evening showers) & 74 degrees. the vs ahu keeps RH @ 50-52/53 without using dehumdifier.
now they have a whole house dehumdifier that has two parts, one inside and one outside that rejects heat out of conditioned space. IMO this is an ideal set up.

http://www.ultra-aire.com/products/dehumidifiers/ultra-aire-sd12

I put a lot of thought into my hvac choice. figured out how to fur down to each room...sacrificed half of my linen closet and have no regrets...except where to keep the extra sheets & towels.

I think that Slemco did an excellent job of simplifying what we have learned in the past 20 years, while trodding that fine line of not offeneding home builders or heat pump association. not being connected to either...I can take my recommendations a few steps further.

here is a link to florida solar energy center that has a faq that includes radiant barrier info. as this is an unbiased site, educational only it is an excellent source of info.

http://www.fsec.ucf.edu/en/consumer/buildings/homes/faq.htm

best of luck with your new build!
nanj
Original Author
10 years ago
last modified: 9 years ago
Wow! Between your post and the SLEMCO checklist, I think I have my insulation plan! A load calc has been on my list of things to invest in from early on. And I am back to seriously considering radiant heat barrier. Your suggestion to use single-sided fsk balances the benefits with material costs.

Your comments about cellulose give me something to think about. Our current home is 11 years old and about 5 years ago we had cellulose blown in our attic to beef up the pitiful insulation job the builder had done. The insulation contractor also used spray foam to cover the small amount of ductwork that was routed through the attic. When I climbed up the ladder to see the finished work, I gasped at how "beautiful" it looked! At the time, I did think to myself that I hope I never had to do anything in the attic to mess up his meticulous work.

Thank you so much for your generosity in sharing your knowledge. Insulation and air sealing literally leaves money in your pockets every single month of every single year. What is not to love about that?

NanJ
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Comments (14)
the only way to get ducts out of the attic is in the design stage. hard to add it later. IF you can design the house with fur downs for ducts it can be built that way. to add it in later hardly ever works. so the option is to foam the roofline. this moves the air and thermal barrier to the roofline instead of the attic floor. http://slemco.com/pdf_folder/SLEMCO_Design_One_checklist-2010.pdf this is a checklist from my local utility co-op. something I'd request you take a look at. we have built many houses with this wall construction that are as tight and efficient as houses with foam in walls. and at a lesser cost. what I'd tell you do is this. save foam in walls for exterior foam foil sheathing boards R-7 foil faced. spend that foam in walls $ for the roofline. install foam sheathing with foil facing out, as described in slemco hand out. tape all seams, seal all holes. put conventional insulation in walls. in a 2x4 wall R-13 plus the R-7 is R-21. sole plate caulked to slab, air tight drywall. foam board on exterior of walls stops thermal conductivity, insulation value of wall is raised and wall performs. see buildingscience.com perfect wall system. in the attic..6-7" of open cell on the roofline. you have to meet code. 2" of open cell foam on attic floor & RB doesn't meet code. even adding lose blown insulation on attic floor to meet code requirements still leaves ductwork in hot humid attic. instead create an unvented attic, rafter bays filled with open cell foam and faces of rafters covered with 1" of foam, to lessen thermal conductivity. ductwork is mastic sealed and in conditioned attic. mechanicals are also placed in attic. putting RB on roof and insulation on attic floor will still allow the ductwork to condensate. when R-8 ducts are in an unvented attic, with 130 degree air surrounding the ducts dewpoint is met and ducts condensate. add in a vs unit that gets air colder and ducts stay wet from condensation in the attics in august & september ..even earlier this year if today's temps are any indication! get some bids ask for regular install of foam for roofline & then bid that includes full rafter fill and covering face of 2x's. don't buy into the double the price for double the product. companies I work with give the average bid of 3" open cell (R4x3"=R12...not code) and then 6-7" open cell. R4x6 1/2"=R26 code for cathedral ceilings. the better bid is not twice the cost because set up and installation is covered in initial set up. once they are there it doesn't cost but product & labor to bring foam level to meet code. and remember this is minimum code. the bonus is the air sealing, but it doesn't figure into R-value but in air tightness. once walls and attic are air tight and you've chosen windows with .30 or less solar heat gain coefficients & Ufactors, then sizing of the hvac system is the next step. with improved building envelope more sq ft per ton. load calcs based on building improvements, and a tight (not leaky or average) house, tons of units required are lessened. these suggestions are based on my 13 years of energy rating in hot humid La. RH here is a killer. we oversize...all the time. vs units please both hvac contractors & homeowners. but air is colder...putting those ducts in a vented attic, even well sealed ducts condensate. no way that R-8 duct insulation keeps ducts from condensating in our attics when they are unvented attics. best of luck.
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ahh..so you are in my part of the world!! techshield roof decking is a radiant barrier decking to reflect heat out of the attic. your insulation levels are nothing special..the only over code is high density batts R-15 over R-13. I'd put 1" foam sheathing over plywood/osb walls.. another added cost but one that is very worthwhile for thermal break of studs and added R-value to walls. air sealing of the house is where you'll invest to save with simple products like sill seal under sole plates of walls and caulking prior to drwyall install. 14 seer isn't much better than code. what type fuel will you have for heating? gas...electric? if electric, you should get heat pump bids. it will be a huge winter savings over electric strip heating. I like 15-17 SEER for heat pumps. variable speed air handler units to remove humidity...and correctly sized...aka load calcs not rule of thumb sizing for hvac system. ductwork in vented attic with tech shield should be R-8...not R-6 small upgrade cost...but they may have to special order as La. still allows R-6 (stupid home builder association driven delay of better codes) putting ducts & equipment in vented attic...will add another 15-30% per month of operating cost to the utility bill. foam insulating the attic to create a unvented semi conditioned attic is a much better option. but again...an added cost.upside is smaller hvac system, lower utility costs and comfort. windows should have solar heat gain coefficients & ufactors of less than .35 all recessed lights should be ICAT, not IC. Insulation Contact Air Tight. these openings into the hot attic have a direct effect on comfort of the house. IC allows attic air to be drawn into living space, ICAT minimizes openings into attic. things that will allow you to cut costs & upgrade later are not insulation, windows, air sealing of house, hvac equipment & ducts and mastic seal of ducts. these things you get right now..or pay the added cost for life of the item. things that can be upgraded or added later... ceiling moldings. have sheetrock installers tape & float wall to ceiling & add moldings later. cabinets & counter tops can be upgraded later. do a stained concrete...and add wood floors later. would a gravel or limestone driveway be an option for you? I see few problems with osb...usually when house isn't blacked in but left open to elements for extended times. and I too, favor 30 lb felt for roofing. you have a huge amount to cut off the total cost. maybe less sq ft would bring you closer without compromising the efficiency & comfort of the house. with our utility costs at .13 cents per kwh for large utility providers..saving energy is a smart move as costs increase and don't decrease. I've seen people build homes where they couldn't afford the utility bills..had zero comfort...but had a pretty place to show. where in the south La. are you building? here is a design one pdf from my utility co-op slemco (.08 cents per kwh!) good info for new construction. http://www.slemco.com/uploads/SLEMCO_Design_One_checklist2010.pdf even if not on slemco service the info can be applied where ever you build. best of luck.
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invest in a load calculation to size the unit to the house. avoiding rule of thumb sizing will allow smaller units, and dehumidification. 500 sq ft per ton is approx what is speced for your home. this will result in oversized units that will short cycling, resulting in higher operating costs & shortened life of equipment. tightness of house, and reducing the duct leakage are also good investments. the average duct system has 25-30% duct leakage. upgrade the insulation package to include foam seal of attic if ducts are placed in attic. there are several guides you can access through LSU Ag Center for building in a hot humid climate. Slemco has a design one brochure you can access online. building science has a builder's guide to hot humid climates also acessable online. use your time wisely to educate yourself as to what makes an efficient house in our climate. where are you building? best of luck.
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don't you think it is because this rb paint is not hvac approved? HERs Raters rarely recommend radiant barriers as ducts and mechanicals condensate in our attics. If the ductwork is in a conditioned space...that is a different story. As we go to two stage units and R-8 ductwork in unconditioned attics, the condensation due to colder air being produced in these units that operate in mostly low speed produce so much condensation that they literally cause 'rain' in the attic. while it took me a long time to get on the open cell foam roofline install..it solves the problems. of course that total encapsulation of attic is a joke. there is always areas missed when foam is installed. few test with blower door to verify leakage. fewer actually go back and seal areas of leakage. if you do a rb install there is still air movement between attic and living space. a better investment is air sealing. 25% reduction seems to be an inflated % to me. I would think half of that would be more accurate. there is a reason that Energy Star removed rb from their recommendations. my rb works well because my air barrier between attic and living space is well sealed, and no ductwork or mechanicals in attic. foam companies also want to use foam to 'seal' ductwork (which you don't mention that your company does) foam does not seal duct leakage, nor is it approved by hvac industry. Mastics seal. not foam, duct tape or bubble gum. approved products work.
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8mpg
10 years ago
last modified: 9 years ago
I also wanted to say thank you for all the great advice. I have been following your posts here on garden web for a while about energy efficiency. Im going to work hard to do airtight drywall and doing an unvented attic with open cell spray foam on the roof line. My plan was cellulose before in the walls (damp blown) though may switch to netted fiberglass (I have allergy issues).

I will also look more into the whole house dehumidifier. Fortunately on my remodel, there is a relatively new heat pump that was installed so adding a dehumidifier wont be cost preventative for us.
8mpg
10 years ago
last modified: 9 years ago
I also wanted to say thank you for all the great advice. I have been following your posts here on garden web for a while about energy efficiency. Im going to work hard to do airtight drywall and doing an unvented attic with open cell spray foam on the roof line. My plan was cellulose before in the walls (damp blown) though may switch to netted fiberglass (I have allergy issues).

I will also look more into the whole house dehumidifier. Fortunately on my remodel, there is a relatively new heat pump that was installed so adding a dehumidifier wont be cost preventative for us.
energy_rater_la
10 years ago
last modified: 9 years ago
you are very welcome.

a variable speed air handler with a
properly sized hvac system will remove
a lot of humidity.

best of luck.
energy_rater_la
10 years ago
last modified: 9 years ago
It is really better to start your own thread.

homes need mechanical ventilation when they are tight.
tested to verify tightnss...not just assuming that it is tight.
even new construction builders had to learn where to seal to make homes tight...it doesn't just happen.

so, you are adding 400 sq ft in garage conversion...the garage itself will be living space...or adding room on top of garage? it isn't clear in your posting.

rather than erv, which only exchanges air for a hefty price, I'd look into a whole house dehumdifiier set up with fresh air intake. a bit pricier...but at least it has a function that is more than just air balancing.

what is your location?

converting from crawlspace duct location to ceiling...ducting...ducts in attic?? fur downs in conditioned space?
if from crawlspace to attic...it is a lateral move.
while hopefully critters cant get to ducts in attic...there is a lot of heat gain for ducts only insulated to R-8.
what type of ducting?
are both house & garage on piers?

3 tons for 1700 sq ft is oversized for most houses, but it depends on tightness of house & amount of duct leakage. most older houses have considerable amounts of both. tighten the house, mastic seal the ducts & you should have enough capacity for garage living area.
but without the air/duct sealing...its a wag.

there is more to installing ducts than most realize.
flex duct requires mastic seals of (flex) inner liner,
outer liner & some use lock or pundit ties. supporting ducts..strapping off insulated attic floor...or under floor joists is also required in some climates.

more info please.

best of luck.
8mpg
10 years ago
last modified: 9 years ago
Thanks so much for the answers... now for the more info.

The garage will be converted to the living space. We will not be adding a room above (4:12 pitch roof). Im in the hot humid south (Dallas, TX). I was looking at the Panasonic ERV which is only $350 but more than willing to go dehumidifier if I can get one at a reasonable price ($1500?). The roof line will be unvented and spray foamed which should make it better than the current unconditioned crawl space. Also, the garage is on slab while the rest of the house is on pier and beam.

My plan for the ducting will probably be based off a manual D. Solid tubing for the big runs and just the last couple feet to the vent will be flex. All the ducting will be sealed with mastic. If I could move them into the house with fur downs, I would but we only have 8' ceilings.

As for other air sealing, all the base plates and headers, as well as the areas where studs double/triple will be caulked. Foam around the new windows. Im going to do the best I can to keep a nice tight house.
energy_rater_la
10 years ago
last modified: 9 years ago
I have 8' ceilings & fur downs, the trick is to keep them
to interior walls.

anyway,,,garage is attached to house?
your plan is to install a trunk line with flex take offs.
and main house & garage will be foamed @ roofline..
correct?

I'm not a big fan of erv's. why use something that
consumes electricity & will eventually need repair/replacement?
instead I usually put a 12"x12" filter back grill in soffit, patio or porch ceilings with a filter to change every month. barometric damper set to cfm's required,
ducted to return side of hvac system.
material costs $175 labor to install about the same.
no mechanical parts to break down, no electrical costs to operate. passive fresh air, cleaned, measured & dehumidified before entering the house.

while foam crew is on site...what would they charge to put 2-3" of closed cell under floors? as they are already set up, the only added cost should be product. I'd ask & invest in air sealing/insulation of floors @ same time.

do you have the info together for duct sizing & design?
basic layout of house, size of rooms,orientation, size of overhangs, window specs, exterior shading & insulation values of walls? where is heating system currently located? will return inside the house location change or stay the same?

will you blower door test the house to determine tightness or just assume % of leakage?
8mpg
10 years ago
last modified: 9 years ago
The garage is attached and will become living space. We have an attached carport that will be converted to the future garage. Luckily it is already sectioned off from the attic space.

Foamed at the roofline above all living spaces. I will take your advice on the barometric damper and filter. We have a porch somewhat close that will be easy to grab the air from.

I will check on the foam price of the floors. They will have to come out a 2nd time to do the walls so I can do the floors at that time.

I believe I have all the info for the manual J/D. We were just waiting on window u-value/shgc. I have drawn up the house on a home cad software.

energy_rater - SLEMCO's recommendations

8mpg

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