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Foam board + backed fiberglass insulation -- bad?

Foam board + backed fiberglass insulation -- bad?

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#1

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03-24-19, 06:27 PM

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jsm11482

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Foam board + backed fiberglass insulation -- bad?

I've installed foam board along the exterior walls of our basement where I'm building a guest room. I've framed the 2x4 walls along the foam board. Soon I need to insulate those walls.

I bought insulation already but it has a backing. Now I'm thinking I should have got non-backed so I don't create a "vapor trap" between the foam board and sheetrock.

Should I use what I have?

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03-24-19, 07:14 PM

XSleeper

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Yes, that would have been better. You can return it... tear off the kraft facing... or cut a lot of slits in the paper after its up.

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04-01-19, 09:14 PM

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JB324

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How thick was the foam board insulation? Xps foam?

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#4

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04-02-19, 05:25 AM

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jsm11482

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3/4" foam board. Exterior walls are 3" brick + 8" cinder block. Foam board is being used as a thermal break as well as vapor barrier against the cinder block. I built out 2x4 walls after that, and filled with R-15 insulation (removed the facing). Yes, it is XPS foam.

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Insulation, Radiant and Vapor Barriers
1 1/2 story gut, insulation methods

J

JB324 on Apr 01, 2019

Hi all, new user here although I’ve used info found on this site many times for diy projects I’ve done and thank everyone for the bounds of information available here, finally signed up as a user and need advise on my insulation work. ive read a million articles and posts about this topic and just want to ask if the method I’m hoping to use will work! Im gutting my second story (1/2 story) with knee walls and vaulted slant side ceilings. It currently has no ventilation, and about R13 of fiberglass stuffed behind everything, needless to say the roof melts snow instantly and ice dams are EVERYWHERE, so I’m just gutting the drywall out as it was a poor job anyway to fix this problem. my original plan was a hot roof with closed cell spray foam encapsulating the under side of the roof and end walls, problem with that is, budget :( So my New hope is a vented and insulated area. For venting I will have open soffit vents on both sides, a ridge vent across the roof peak and as a bonus there is a fable vent at the peak already. So this creates circulating airflow as long as I don’t fully block the slant ceiling (vaulted area). my plan to save money was to do as follows, please advise me if my plan is a bad idea, my only true concern is if vapor/moisture could be a problem with my plan. fully vented as stated knee wall area FLOORS already have fiberglass in cavities, going to add 2” XPS rigid foam to entire floor and seal with can foam around perimeter. knee walls- 1” XPS rigid foam across BACKS of studs, sealed with can foam inside cavity, fill cavity (2x4) with R15 fiberglass batts (faced or unfaced??) Slant ceilings (vaulted)- 5” deep cavities, use 1” rigid foam, cut and cobbled into the cavity 4” back from inside stud edge. Seal them in with can foam. This creates a 1” opening behind the foam board as an air baffle so air can pass from lower attics on sides to upper vented attic space. Then stuff remaining cavity again with R15 fiberglass batts. Top ceiling- 1” rigid foam on back side of studs, air sealed with can foam and again stuff cavity with R15 batts. Finally use another layer of 1” rigid XPS foam board to line the entire interior (between studs and drywall) This method will give me far more R value than I have, create a fairly air sealed space with the cut and cobble method of sealing the rigid foam with can foam, give me ventilation throughout the unfinished space, and the interior sheet of rigid foam will help stop thermal bridging across the studs/rafters. My #1 concern and question is, will the double layer of rigid foam with fiberglass sandwiched in between them have any moisture problems? Am I creating a vapor barrier on both cold and hot side and going to sand which moisture into the fiberglass? Or because it’s only 1” foam on each side and the cold side is ventilated, will moisture not be a problem for me? Thank you greatly for any input, comments, suggestions that you may have! Read More
Insulation, Radiant and Vapor Barriers
Replace Basement Joist Fiberglass Insulation with Foam Boards

M

Masoric on Apr 04, 2019

Good Afternoon all, I have hopefully three quick questions. [B][U]First a little on what I am looking to do:[/U][/B] I am currently beginning a project to finish my basement. One of the items I want to take care of while I am doing this is to replace the fiberglass insulation in the Joists. There were quite a few pests in the past and its in bad shape. What I was curious about was is it possible to replace the fiberglass with the foam insulation boards as they are more pest resistant.I know that the foam boards require a ignition barrier.... So questions are as follows. 1) Would placing a 5/8 inch sheet of sheet rock over the foam board in between the joists be sufficient as an ignition barrier? 2) Is there any issue you all can see that would make that a bad plan? 3) Is there a better material I can install myself other then the foam boards or fiber glass that would insulate and be pest resistant? Regards, MasoricRead More

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