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I should finally start my 2nd floor addition this summer. I’m leaning towards using an I-Joist flooring deck and SIPs for the walls. The first floor walls consist of 2 x 4 studs, with retrofitted cellulose blown-in insulation (I always had my doubts as to whether all the cavities where filled), 1 x 6 sheathing boards, felt wrap, and vinyl siding. I plan to finish the entire house in stucco. My goal is to try to balance, or match as much as possible, the 1st floor’s energy efficiency with that of the second floor (SIP). How do you suggest I go about it? At the least, I plan to install house wrap. I guess I should also add foam boards. What about the 1 x 6 exterior wall boards. They seem to be in decent shape (maybe a few might need replacing). They are not the tongue and groove type, and there is spacing between most of them. Plus, the insulation guys never plugged the holes they made in the sheathing. Does it make sense to replace the boards with 4 x 8 sheeting? I undertand that insulation needs a barrier in order to be effective. Will the house wrap be enough? Any suggestion. Thnx. |
Edited 5/2/2009 7:29 pm ET by djthx
Edited 5/2/2009 7:30 pm ET by djthx
Replies
if you install you house wrap properly and therefore and effective air barrier/ drainage plain then I think you dont need to replace any thing thats not rotting. I would go with ply sheeting for the second story.
-Benjamin Franklin-
your location and climate type dictate what type and location of different barriers(air,vapor) you must employ..Where are you building?
All I ever wanted in life was an unfair advantage...
Hello Captain,
My home is located in Fresh Meadows, NY (Queens County, NYC). We get about 40"s of rain annually. 90 degrees + in the summer, 20 degrees (-) in the winter. And I'm adding/building a second floor. I plan to add 6" SIPs with a rating of R-25.
Edited 5/3/2009 10:05 am ET by djthx
OK, so you got r-25 in your new walls and r-17.5 for your older walls(r-11 for 2x4 max, assuming it's older than a decade or so and no more than r-6.5 or so for your foam sheathing) So your thermal boundry is already improved.Vapor barrier that sucker and make sure your attic is done proper(air seal, airseal ,airseal, every penetration, and don't be shy with insulation up there..)Contrary to popular belief, windows and doors mean a lot less than attics and crawlspaces..I'd spend money on your thermal boundry and envelope before sinking any money into new windows and doors.Not saying that R&R of said old units won't help, but probably not as much as you think.All I ever wanted in life was an unfair advantage...
I plan to stucco the exterior walls. Does the foam board go directly over the wall board? Does it need furring stips? Does house wrap go over the wall board of over the foam sheathing?
why are you putting foam board over an r-25 sip wall? So let's say you don't go with sip walls here would be your layers...studs with bays full of insulation,plywood/osb,house wrap, foam, furring, what ever material your stucco will adhere to(hardi backer???? sorry not a stucco guy),than your stucco. hope that helps..All I ever wanted in life was an unfair advantage...
The new construction, i.e, the 2nd floor will have SIPs. The existing first floor exterior will be update to increase its thermal efficiency (wrap, foam sheething, etc.).
What R values do you expect to achieve with the SIPS panels?
If you're trying to balance the thermal efficiency of the downstairs to match SIPS, you'll need a lot more than a layer of foam sheathing, won't you? Even Thermax gets...what...6.5 r's per inch?
You plan to switch out all the existing windows and doors for high efficiency units?
The 6" SIPs I plan to use have a rating of R-25. The 1st floor exterior walls consist of 2 x 4 studs, retro-fitted cellulose insulation, and 1 x 6" wall board sheeting.
And yes, I plan to install high efficiency window/door units in the entire house.
Edited 5/3/2009 10:18 am ET by djthx
House wrap should really do you well in your situation. No need to go overboard w/ 4x8 sheathing in addition to what you have.
If the cellulose was done right (dense-packed) neither the board sheathing nor the holes should be an issue. It's pretty self-sealing at high densities.
I'm confused about the old in relation to the new. Are you going to be able to alter the present location of face-of-sheathing when you do the second floor?
Are you talking about foam boards on the outside or the inside? Matters in terms of how thick it would have to be not to be a condensible surface.
Steve
Hello Steve,
How can I determine whether the cellulose was done right (dense-packed).
I'm adding/building a second floor. I plan to add 6" SIPs (Structural Industrial Panels) with a rating of R-25. And my goal is to match/increase the 1st floor's exterior wall's energy efficiency.
Thnx.
>>How can I determine whether the cellulose was done right (dense-packed). <<How big and how far apart are the holes in the sheathing where they blew? Can you put your finger in feel how fluffy the cellulose is? If it was done right the holes will be 3-4 inches and probably no more than 6-8 feet apart (but depends highly on circumstance), and the cellulose that you can feel through the holes will be firm. It should take effort to stick your finger into it.If the holes are 1" holes, then unless there is a hole every 2 feet, it would not be possible to get a good dense-pack, and even then, it's pretty tough to do with a small hole.As far as foam board on the outside, I would not be comfortable with anything less than 2" in your climate to make sure that the inside surface of the foam stayed above dew-point and was in no danger of become a condensing or frosting surface. There is a way to calculate exactly what thickness you can get away with, and someone who is better at searching can find that information here. Steve
if your worried about condensing on the back side of your foam. Either go thicker, or use an un faced open cell foam ie. EPS. The rule of thumb here in AK is 1/4 insulation inside your V.B. and 3/4 out. this ensures the dew point at least wont occur on the warm side of your V.B.
As for dealing with the eventual amount of consensation incorperate an ait space behind your siding that can breathe bottom to top and vice versa. this will create a convective loop serving to pull moisture out of your wall."A small leak can sink a great ship."
-Benjamin Franklin-
You may want to rethink SIPS for your walls. Though they have their uses, I don't like them much. They're expensive and aren't nearly the labor saver as advertised. Then more $ for window jamb extensions. Electricians I know don't like them and charge more. And your deck better be very flat, level and right to the number (on an addition). Why not a standard 2x6 wall,foam sheeting,wrap and blown in insulation for the same or better R value. Talk to people who have built with them, as I have, and don't have an agenda, like the SIPS salesman.