Basement insulation concerns?

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Posted by: from Stouffville
2/27/2015 at 3:38:32 PM

Want to put 1" 1/2 R-7.5 styrofoam on concrete walls, then tape up joints, then stud walls, then put R-20 batt insulation. Wondering if I'm overdoing it?

I have builders insulation on half the walls. Is it ok to put insulation on bottom half then frame?

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Petros from Q-Cor Designs in Brampton
Date/Time2/27/2015 at 4:56:58 PM

Hi Fab,

Some municipalities actually have a max value for insulation allowed to be installed in the basement. If you plan to make it a legal basement I would advise you to talk to a plans examiner in your City, they expert advise is always free. If the basement won't be legal then I don't see an issue with your suggestions.


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Date/Time2/27/2015 at 5:29:52 PM

Hi Fab,

Don't worry about a maximum insulation. What matters is installing it correctly.

First remove the builders insulation from the walls and plastic vapour barrier. Don't remove the insulation that has been installed between your floor joists at the ceiling. Keep the vapour barrier their as well. Then glue the foam board to the concrete walls. Leave a quarter inch between the bottom of the foam board and the concrete walls. If you ever have a crack in the foundation or leakage at the footing you need some where for the water to go.. I normally use Foam Core Blue, 2" with a R factor of 10. Then use tuck tape to seal all the seams properly.

Then using the tuck tape, seal between the foam board and the vapour barrier left above.

You now have a proper vapor barrier.

Then install the bottom plates for your walls with Blue wood over foam. When you go to ramset the boards in I put a glob of Pl sealant at the spot for each ram set nail.

Then build away.

If I can suggest, I always install a subfloor with 2'x2' panels. I like the product with the patterned blue plastic base. This allows for water to move if you ever have a leak. As well as air flow to dry any water that gets in or comes from an interior leak such as a cut or burst pipe.

So to answer your question......I and most of my clients don't believe in overkill.

Warmer and more comfortable is better. And always over build.

Enjoy your basement.


James Fram

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Fab in Stouffville
Date/Time2/27/2015 at 6:52:27 PM

Hey James,

Thanks for the advice. I am putting sub floor. I'm using the amdry sub floor. o I still need a gap between sub floor and foam board? Or can I set it right on top? Also, do I leave extra vapor barrier to tape foam board to?

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Date/Time2/27/2015 at 11:31:19 PM

Hi Fab,

You may want to consider spraying your walls with closed cell foam instead of using sheets of Styrofoam. You can achieve a much better seal in less time and its not a great difference in price when u take in cost of styrofoam, tape, poly etc. You may also want to consider spraying headers in the basement at same time as that is where its known to leak the worst.

Thank you,

Elvis fagundes

Sure-seal insulation

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Date/Time3/3/2015 at 12:07:03 AM

Hi Fab,

I leave a gap at the bottom of the foam core all around the exterior walls. Then I also leave an eight of an inch gap between the dry core floor and the bottom of the foam core.

And yes, you leave extra plastic up top so you can tuck tape it to the top of the blue foam core. are looking for a great vapour barrier.

One more thing, when you frame and drywall. you will have the four inside sections to finish around each basement window. I do not use drywall, blue board or even cement board.

I always finish these panels will oak and then paint them out to match the trims, baseboards and doors.



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