Basement R-24 insulated wall construction method

blahname · 05-11-11, 02:38 PM

This past year, after an "energy audit" (we live in Ontario, Canada), we qualified for a $2500 government rebate if we insulated our basement walls to R-24, from their previous nothing/bare concrete (R-0).

I thought that I'd take a moment and share my chosen construction method, as this ended up costing us less than the government rebate and we may have actually made money doing this one.

Basically, the walls we built in front of the concrete had a moisture barrier on the concrete (tar paper), 1/2" of rigid roam sheeting, 5.5-6" of blown-in, compacted cellulose, 6mil vapor barrier, then drywall.

Our basement has 8' ceilings and our main floor is also poured concrete, so adjust this method to suit your purposes. We didn't have any wood to nail the top plate to as the ceiling was concrete. This is actually a big problem in the winter as there isn't much between the edge of the concrete floor and the cold outside!

Instructions:

Prep the walls:
- We coated the inside of our walls with asphalt foundation coating to seal any small gaps/cracks for water seepage (house built in 1981).
- Apply 15lb tar paper horizontally on the wall, starting at the bottom, working up. We stuck ours to the wall with "plastic cement" which is a thick, black asphalt roof repair sold in pails at the hardware store. Gobs every couple of feet worked. You set the paper into the gob, then remove & wait a minute, then reattach and it sticks.

Our poured basement floors aren't 100% level/straight, so we cut each stud and built the wall in place rather than build on the floor and erect, so this describes our method. We also have ducts and other junk in the way of sliding a pre-built wall up into place.

- Attach 2x6 top and base plates. We used a 2x6 top & base plate with a foam gasket under the base plate at the floor, fastened with concrete nails into pre-drilled holes. The top & base plates are attached to the ceiling and the floor with a 1/2" spacing from the concrete wall. (There goes 6" of space!)
- Attach 2x4 studs. To save on material costs, and to have a gap behind the studs for the cellulose insulation, we attach 2x4 studs 16" on center between the top & base plates, flush with the front/inside of the top & base plates, to create a gap behind the 2x4. (see pictures)
- As you go, slide in your 1/2" rigid foam behind the studs and seal the seams with red construction tape.
- Install electrical/whatever else.

Walls are built, time to insulate.

- Install 6-mil vapor barrier (per our local building code) starting at the bottom, working up. Leave the top 4" of wall open (see pictures) to blow in insulation.
- Caulk the bottom of the vapor barrier to the base plate with whatever caulking you have that's cheap & staple to hold until dry. This is key to stop air infiltration and/or convention currents up through the wall.
- Install the first course of horizontal drywall to hold in the cellulose, otherwise you have to push the insulation flush with the stud cavities before you drywall later (thanks to Corey for this tip; it served us well). This also ensured the vapor barrier didn't buckle or break through the staples when I was shoving the insulation into the wall.

Time to insulate!

For the roughly 180 lineal feet of wall we had to insulate, we used about 85 20kg bags of cellulose and a free blower rental from Home Depot to blow it in.

I stuck the hose down into the cavity from the top, and worked the hose up and down as the insulation blows in to compact it to the "desired" (which is to say manufacturer recommended) density in the walls. If you don't pack it enough, it will eventually settle and leave gaps at the top of the wall cavities, which you can always revisit and add to later. I pushed the insulation down with my flat hand or a block of wood to compact it in some spots, then blew in more insulation until full, & staples the vapor barrier back up and on to the next cavity.

Be careful to get insulation around horizontal electrical wires - get that hose down in there and work it up & down!

Insulation should spill behind the studs and into the next cavity, which is exactly what we're after.

The insulation is adequately compacted when you push down on it from the top of the wall cavity and it springs back slightly after you release pressure & stop pushing, in case you needed to know when enough insulation is enough.

Wow.. What a long post!

So with all that, we stapled & sealed the top of our vapor barrier, took back the blower and called it a night. Drywalling is a little fun, as you have to first push in the insulation between the stud cavities so the surface is flush with the studs for the drywall, otherwise the screws pop through as you try to attach the sheets because the sheets would otherwise have to push in the insulation.

Sadly, I don't have many cost estimates on any of this, aside from the rigid foam at $20 a sheet (I only did this because of the strict R-24 requirement and I feared doing all this work for nothing otherwise) and the cellulose bags were on sale for $8.39 a bag with a free blower rental when you buy more than 20 bags. I paid my step brother to coat, prep and build the walls for us and my wife & I did the insulating & drywall.

So that's it. If you have any questions or comments, fire away! Now for the pictures...

Daox · 05-11-11, 03:47 PM

First off, welcome to the site!

Second, nice job on the basement. How much did it end up costing you?

blahname · 05-11-11, 04:23 PM

Thank you!

I estimate is was about $380 for lumber, $50 for fasteners, screws, etc, an optional $350 for insulation sheets, $115 for vapor barrier & staples, $730 for the insulation itself, and likely another $200 in tar paper and such. I guess it came pretty close to the $1800 mark for 180 lineal feet of basement wall.

After doing the math of Roxul (rock wool) insulation, fiberglass and spray foam, cellulose was the clear price winner. I liked that it gets in behind the 2x4 studs easily, around the backs of corners, etc. Did I mention that it's cheap?

If I ever find that scrap of paper where I wrote down all my price comparison notes, I'll be sure to post them.

If I had to do it again, I would have omitted the optional 1/2" foam sheeting and opted for a few extra bags of cellulose instead. It was a waste of money for not too much gain anyway.

S-F · 05-12-11, 10:41 AM

Nice job!
I'm about to start finishing my basement also.

Some interesting reading:

http://www.buildingscience.com/docum...lation-systems

http://www.buildingscience.com/docum...g-your-basment

blahname · 05-12-11, 10:55 AM

Interesting reading indeed - great information for those starting out to make them aware of the issues with having water infiltration issues with a new wall system.

Sadly, I should have done a better job checking the concrete walls for cracks and such before hastily putting up my wall system. After we were almost finished mudding & taping the drywall, we came into the spring rainy season and suddenly, 2 spots of puddling on the floor. Especially disappointing after already fixing some "popcorning" in the concrete under a window.

So, we tore apart two wall sections to reveal a shoddy caulking job on one basement window, combined with an incorrect slope on the concrete sill (it slopes into the house rather than away!).

The second spot was a vertical crack that I missed. I got out the hammer drill, drilled a hole at the bottom of the crack, then put on a spade bit and chipped out the crack all the way up to the top, making about a 1/2 - 1" gap as deep as I could get it. I sprayed the crack out with semi-pressurized water from a pump-sprayer and sucked it up immediately with a wet vac to get it clean, then after drying it thoroughly, I hit it with a can of expanding foam and with rubber gloves on, mashed the foam into the concrete to make sure it stuck absolutely everywhere. Next, I readied a section of 1/2" foam board that was 4" larger than the repair on all sides, filled the crack/gap with foam and slammed the foam board over the whole thing and braced it against the concrete so the foam expands out through the crack instead of inside the house.

Yes, it certainly is a cheap basement wall fix, but it sure does work, and for a long time! I repaired wall cracks without doing as much cleaning and prep on a drive-in theater I used to work at years ago and the repairs still don't leak. Three cheers for expanding foam!

05-11-11, 02:38 PM	#1
blahname Lurking Renovator Join Date: Sep 2010 Posts: 10 Thanks: 0 Thanked 1 Time in 1 Post	Basement R-24 insulated wall construction method This past year, after an "energy audit" (we live in Ontario, Canada), we qualified for a $2500 government rebate if we insulated our basement walls to R-24, from their previous nothing/bare concrete (R-0). I thought that I'd take a moment and share my chosen construction method, as this ended up costing us less than the government rebate and we may have actually made money doing this one. Basically, the walls we built in front of the concrete had a moisture barrier on the concrete (tar paper), 1/2" of rigid roam sheeting, 5.5-6" of blown-in, compacted cellulose, 6mil vapor barrier, then drywall. Our basement has 8' ceilings and our main floor is also poured concrete, so adjust this method to suit your purposes. We didn't have any wood to nail the top plate to as the ceiling was concrete. This is actually a big problem in the winter as there isn't much between the edge of the concrete floor and the cold outside! Instructions: Prep the walls: - We coated the inside of our walls with asphalt foundation coating to seal any small gaps/cracks for water seepage (house built in 1981). - Apply 15lb tar paper horizontally on the wall, starting at the bottom, working up. We stuck ours to the wall with "plastic cement" which is a thick, black asphalt roof repair sold in pails at the hardware store. Gobs every couple of feet worked. You set the paper into the gob, then remove & wait a minute, then reattach and it sticks. Our poured basement floors aren't 100% level/straight, so we cut each stud and built the wall in place rather than build on the floor and erect, so this describes our method. We also have ducts and other junk in the way of sliding a pre-built wall up into place. - Attach 2x6 top and base plates. We used a 2x6 top & base plate with a foam gasket under the base plate at the floor, fastened with concrete nails into pre-drilled holes. The top & base plates are attached to the ceiling and the floor with a 1/2" spacing from the concrete wall. (There goes 6" of space!) - Attach 2x4 studs. To save on material costs, and to have a gap behind the studs for the cellulose insulation, we attach 2x4 studs 16" on center between the top & base plates, flush with the front/inside of the top & base plates, to create a gap behind the 2x4. (see pictures) - As you go, slide in your 1/2" rigid foam behind the studs and seal the seams with red construction tape. - Install electrical/whatever else. Walls are built, time to insulate. - Install 6-mil vapor barrier (per our local building code) starting at the bottom, working up. Leave the top 4" of wall open (see pictures) to blow in insulation. - Caulk the bottom of the vapor barrier to the base plate with whatever caulking you have that's cheap & staple to hold until dry. This is key to stop air infiltration and/or convention currents up through the wall. - Install the first course of horizontal drywall to hold in the cellulose, otherwise you have to push the insulation flush with the stud cavities before you drywall later (thanks to Corey for this tip; it served us well). This also ensured the vapor barrier didn't buckle or break through the staples when I was shoving the insulation into the wall. Time to insulate! For the roughly 180 lineal feet of wall we had to insulate, we used about 85 20kg bags of cellulose and a free blower rental from Home Depot to blow it in. I stuck the hose down into the cavity from the top, and worked the hose up and down as the insulation blows in to compact it to the "desired" (which is to say manufacturer recommended) density in the walls. If you don't pack it enough, it will eventually settle and leave gaps at the top of the wall cavities, which you can always revisit and add to later. I pushed the insulation down with my flat hand or a block of wood to compact it in some spots, then blew in more insulation until full, & staples the vapor barrier back up and on to the next cavity. Be careful to get insulation around horizontal electrical wires - get that hose down in there and work it up & down! Insulation should spill behind the studs and into the next cavity, which is exactly what we're after. The insulation is adequately compacted when you push down on it from the top of the wall cavity and it springs back slightly after you release pressure & stop pushing, in case you needed to know when enough insulation is enough. Wow.. What a long post! So with all that, we stapled & sealed the top of our vapor barrier, took back the blower and called it a night. Drywalling is a little fun, as you have to first push in the insulation between the stud cavities so the surface is flush with the studs for the drywall, otherwise the screws pop through as you try to attach the sheets because the sheets would otherwise have to push in the insulation. Sadly, I don't have many cost estimates on any of this, aside from the rigid foam at $20 a sheet (I only did this because of the strict R-24 requirement and I feared doing all this work for nothing otherwise) and the cellulose bags were on sale for $8.39 a bag with a free blower rental when you buy more than 20 bags. I paid my step brother to coat, prep and build the walls for us and my wife & I did the insulating & drywall. So that's it. If you have any questions or comments, fire away! Now for the pictures... Attached Thumbnails

05-11-11, 03:47 PM	#2
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	First off, welcome to the site! Second, nice job on the basement. How much did it end up costing you? __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

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05-11-11, 04:23 PM	#3
blahname Lurking Renovator Join Date: Sep 2010 Posts: 10 Thanks: 0 Thanked 1 Time in 1 Post	Thank you! I estimate is was about $380 for lumber, $50 for fasteners, screws, etc, an optional $350 for insulation sheets, $115 for vapor barrier & staples, $730 for the insulation itself, and likely another $200 in tar paper and such. I guess it came pretty close to the $1800 mark for 180 lineal feet of basement wall. After doing the math of Roxul (rock wool) insulation, fiberglass and spray foam, cellulose was the clear price winner. I liked that it gets in behind the 2x4 studs easily, around the backs of corners, etc. Did I mention that it's cheap? If I ever find that scrap of paper where I wrote down all my price comparison notes, I'll be sure to post them. If I had to do it again, I would have omitted the optional 1/2" foam sheeting and opted for a few extra bags of cellulose instead. It was a waste of money for not too much gain anyway.

05-12-11, 10:41 AM	#4
S-F You Ain't Me Join Date: Nov 2009 Location: Northampton MA Posts: 662 Thanks: 6 Thanked 71 Times in 58 Posts	Nice job! I'm about to start finishing my basement also. Some interesting reading: http://www.buildingscience.com/docum...lation-systems http://www.buildingscience.com/docum...g-your-basment

05-12-11, 10:55 AM	#5
blahname Lurking Renovator Join Date: Sep 2010 Posts: 10 Thanks: 0 Thanked 1 Time in 1 Post	Interesting reading indeed - great information for those starting out to make them aware of the issues with having water infiltration issues with a new wall system. Sadly, I should have done a better job checking the concrete walls for cracks and such before hastily putting up my wall system. After we were almost finished mudding & taping the drywall, we came into the spring rainy season and suddenly, 2 spots of puddling on the floor. Especially disappointing after already fixing some "popcorning" in the concrete under a window. So, we tore apart two wall sections to reveal a shoddy caulking job on one basement window, combined with an incorrect slope on the concrete sill (it slopes into the house rather than away!). The second spot was a vertical crack that I missed. I got out the hammer drill, drilled a hole at the bottom of the crack, then put on a spade bit and chipped out the crack all the way up to the top, making about a 1/2 - 1" gap as deep as I could get it. I sprayed the crack out with semi-pressurized water from a pump-sprayer and sucked it up immediately with a wet vac to get it clean, then after drying it thoroughly, I hit it with a can of expanding foam and with rubber gloves on, mashed the foam into the concrete to make sure it stuck absolutely everywhere. Next, I readied a section of 1/2" foam board that was 4" larger than the repair on all sides, filled the crack/gap with foam and slammed the foam board over the whole thing and braced it against the concrete so the foam expands out through the crack instead of inside the house. Yes, it certainly is a cheap basement wall fix, but it sure does work, and for a long time! I repaired wall cracks without doing as much cleaning and prep on a drive-in theater I used to work at years ago and the repairs still don't leak. Three cheers for expanding foam!