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nanj

energy_rater - SLEMCO's recommendations

nanj
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

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

  • 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.

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