# Insulating basement walls, couple quick questions.



## Windows on Wash (Aug 30, 2011)

1. Mechanical fasteners with a compatible adhesive. Most construction adhesives will melt the foam and won't hold it to the wall. Be sure to check. 

2. If the wall is plumb and true, tight to the wall if fine. I think you will find there are enough inconsistencies in the walls that you will just wind up leaving a minimum gaps in many place. You can stick some shims between the framed wall and the foam to help clamp the foam slightly. Don't over shim it though. Just a little pressure is all. 

3. That is correct. 

Be sure to address the ribbon/band board areas and get that all sealed and insulated prior to closing up the walls. Also be sure to use the right thicknesses of foam here. More is more.


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## ponch37300 (Nov 27, 2007)

Thanks for clearing these things up.

What is the best fastener for attaching the foam to the CMU blocks?

What is the ribbon/band board area?


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## mikegp (Jul 17, 2011)

He's talking about area right behind/under the "C" in this pic:










Also known as the rim joist. I highly recommend Roxul or any other rock wool insulation for a basement.


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## Gary in WA (Mar 11, 2009)

Plastic housewrap tape or Tuck tape is not as good as furnace-- fiberglass tape/mastic because the foamboard does shrink/expand breaking the important air seal you want from repeated wet/dry cycling; http://buildingscience.com/file/3718/download?token=N09-JWGV

Any gap behind the board will condense moisture there, if carrying water vapor. Glue the boards in 2' square grid patterns to limit any air gaps from the interior; http://joneakes.com/jons-fixit-database/743

Page 9/22 covers rim joist foamboard; http://buildingscience.com/sites/default/files/migrate/pdf/BA-0202_Basement_Insulation.pdf
Air seal the rim to other wood with caulk to limit infiltration behind the foamboard.

Gary


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## Gary in WA (Mar 11, 2009)

Further thoughts; Shim the walls everywhere you can and use enough fasteners that the foam doesn't move when you push on it anywhere. Clean the wall first, with a mild TSP solution to be sure the adhesive sticks. Knock off any grout protrusions so the board lays flat, imperative to get it sealed at the perimeter with canned foam; http://www.carb-swa.com/Collateral/Documents/CARB-SWA/Research/Challenges_of_Basement_Insulation.pdf

Two thin layers of foam board are better than one stiffer layer, stagger the joints for less air pathways. Hard to build the wall on the floor, then install the foam, then shim the foam at the studs because most adhesives set in 15 minutes or less... at least in my experiences insulating basements. Takes that long to stand the wood wall and set/shim it plumb, nail the top to caulk line mark, and fasten the bottom plate down (be sure to use some foil-faced for the vapor barrier (required per code) strips for an air/thermal/capillary break under the foam board) with a bead of caulking under/over it to stop draw; http://www.greenbuildingadvisor.com...ressure-treated-sill-plates-and-building-code

Use a knife for the foam, or table saw for repeating cuts/rips accurately. Local code may require fire-stopping with a stud tight to the concrete wall every 10' lineally (with foam between studs, check local AHJ); "1. In concealed spaces of stud walls and partitions, including furred spaces and parallel rows of studs or staggered studs; as follows: 1.1. Vertically at the ceiling and floor levels. 1.2. Horizontally at intervals not exceeding 10 feet (3048 mm)." from;http://publicecodes.cyberregs.com/icod/irc/2006f2/icod_irc_2006f2_6_sec002_par017.htm
ADA the drywall to further prevent air from interior reaching cold concrete wall; http://www.buildingscience.com/documents/information-sheets/air-barriers-airtight-drywall-approach/
Gary


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## KarenStein (May 30, 2016)

I've had to clean up after a few flooded basements, so my opinions about basement conversions are a bit different from "conventional wisdom."

First, place your face to the floor level and look. That floor isn't nearly flat enough. Have someone use a topping cement (like gyprock) to level it. Those little dips will otherwise hold moisture and make that musty smell.

Your home's HVAC was never designed for the extra space of a basement. You'll really want to add heat- and wildly increase your ventilation. 

Now... insulation ... even in Northern Wisconsin, most of the basement is 'insulated' from the worst simply by being below the frost line. The problem is that your walls will always be "wet."

Water in basements comes either in with the air (and condenses on cool walls) or through the walls. Folks who make "normal" walls only succeed in trapping moisture in the wall and creating a fungus farm.

I suggest: Use "hat channel" to attach the wall materials directly to the block walls. put a dimpled membrane on the wall itself (to allow drainage), and attach the insulation over that. "Shooting" anchors is probably the easiest way. 
Cover the walls with paperless (mold resistant) drywall, or even tileboard - then use "hot mud" on the joints. Don't feed the mold. Stop all wall coverings at least an inch above the floor - let plastic molding (or rubber cove base) conceal the gap.

Finally, commercial carpet tiles will make a soft, warm floor - one that can readily be pulled up and set in the sun to dry, should they become wet.


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## lenaitch (Feb 10, 2014)

If the house was built to fairly-recent code, the HVAC should be sized to accommodate the basement space since it is still a 'heated space', but a good point is raised that basement hot and return air needs to be adequate to ensure proper air movement. Also, if done to recent code, the foundation should already be waterproofed.
As I know it, dimpled waterproofing membrane is intended for the outside of the foundation wall. On the inside, any moisture trapped behind it will run down the wall and pool on the floor.


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## KarenStein (May 30, 2016)

Exactly, Lenaitch.

Remember, water can originate from within, as well as without. Moisture that condenses on the walls also needs a place to go .... and my plan gives it one. 

Likewise, basements flood. It's inevitable- whether from rainwater or a broken pipe, it doesn't matter.. Then it becomes a matter of getting the water out, and reducing the damage.

Water drainage is why I advised to start with a level floor. Ever notice how pump pits always seem to be at the high point of the floor? Plus, those little dips in the floor will hold water, unseen, under the carpet - making ideal mold conditions.

Even an inch of water can cause $10,000 worth of damage. That inch will quickly wick 4" up drywall and 12" up fiberglass insulation. Wood framing, especially at floor level, quickly rots. Ever try carrying a soaked carpet out of a basement? Within 36 hours, you will get that familiar 'moldy' smell.

Folks should also be aware that basements are NOT insured for 'flood damage,' The insurance industry has the attitude that "basements are NOT living spaces."


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## mikegp (Jul 17, 2011)

KarenStein said:


> Folks should also be aware that basements are NOT insured for 'flood damage,' The insurance industry has the attitude that "basements are NOT living spaces."



My sis in law had a slop sink back up in her basement and her insurance co paid for everything.


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## mikegp (Jul 17, 2011)

lenaitch said:


> If the house was built to fairly-recent code, the HVAC should be sized to accommodate the basement space since it is still a 'heated space'


Most basements I've seen including my own when I had the house built are not part of the conditioned space. They insulate the ceiling to separate the basement from the living space.


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## KarenStein (May 30, 2016)

All I can say is .... look carefully at the exact wording of your insurance policy. You'll find all manner of exclusions ... typically, water damage be covered only if it is from something like a broken pipe IN the basement. Talk to your agent for a more complete discussion of basement coverage.

Modern HVAC equipment usually has enough capacity to add the basement. However, the ducting is not designed to serve the basement, and basement venting (fresh air supply) is to code minimum. This makes for a less comfortable, musty basement. While you're likely to have the right furnace, you need to address these other issues.

A generous supply of (conditioned) fresh air is needed to control humidity and prevent that musty smell.


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## lenaitch (Feb 10, 2014)

mikegp said:


> Most basements I've seen including my own when I had the house built are not part of the conditioned space. They insulate the ceiling to separate the basement from the living space.


Different standards for different regions. Up here, basement ceilings (main level floor) are not normally insulated and HVAC ducts feed the basement (admittedly minimally). Basement finishing construction does carry lumber right to the floor although most good contractors will use 'blue wood'. Proper exterior waterproofing is critical.

Basements are included in water damage insurance coverage but only for in-house sources. Overland flooding is not covered and I am told not available at any price.


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## Gary in WA (Mar 11, 2009)

Poly or a dimpled membrane of low permanence should never be installed on a basement interior concrete wall to encourage pooling on the floor, unless there is an interior drainage system in place.

Gary


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