help on installing xps on cinder block

phoenix2000

15 years ago

OK, the 3rd code official I spoke to (he's an assistant code official) has said we can put XPS on the foundation wall and frame and sheetrock over it. Initially, they said the drywall had to be in contact with the XPS.

We're going to mechanically fasten the XPS onto the wall, using probably 2'x8' tongue and groove 2" XPS board. No one seems to sell the 4'x8' which I prefer in order to have fewer seams to tape. I have the following questions:

1. If the goal is to just fasten to the wall, then will 2 screws (one at center top and center bottom) be enough? Or should we use 4 screws per sheet (at the corners)? Or is there a benefit to screwing one in the center of the board in addition to the 4?

2. I know we need to tape the seams, but what do we do about at the top and the bottom of the board? Do we tape there or use foam spray?

3. We've got an interior perimeter drain that channels liquid to the sump pumps. Should we not tape the bottom of the boards then to allow any condensation or water to drip to the drain?

4. I've got cinder block columns as shown in the picture at the link below - do we just score XPS pieces to cover as much of the columns as possible (ex: along the sides of the column)? We will be framing 1/2" along the wall and then around the columns to maximize space

5. We've got what looks like an old window (see picture at the link) that was covered with cement, but it isn't flushed with the rest of the wall - do we need to cut XPS pieces to fasten directly on the window or do we just ignore it b/c it's fine as long as this space lies underneath the 2'x8' board?

6. It seems tapcons and fender washers are used - what about standard masonry nails?

7. What should be done at the rim? Use unfaced fiberglass insulation? It seems like a lot of work to cut XPS and then cover it with drywall (mandatory with XPS) at the rim in between all the joists.

thanks in advance for your help.

Here is a link that might be useful: foundation wall pictures

Sort by:Oldest

Comments (5)

worthy
15 years ago
AS you say, the Wallmate would really be a lot faster. Check directly with Dow or at lumber yards, as opposed to the Big Boxes.

Use as many or as few fasteners as needed to keep the XPS tight to the wall, including the bottom. I've not tried concrete nails. If you can get them to hold the washers tight, why not? Please use goggles! (I once warned a neighbour about that. He brushed me off. The next day he was sporting a massive patch on his eye after a visit to the ER.)

Adhere the XPS directly to the blocked window. The idea is to keep the XPS directly on the wall; this prevents condensation and keeps the R Value as high as possible.

Use XPS on the columns (actually, they're pilasters) too.

If you use T&G, it's not really necessary to tape the joints as long as they're tight.

The rim area is actually the most important area to insulate tightly as it's above grade.

Pull out all that fg; it was just filtering the drafts anyway. And if you put plastic over it, you'll get mould and mildew.

Caulk any spaces between the blocks and wood. Then fill the spaces between the joists tightly with either XPS or EPS (extruded polystyrene. Fill any gaps with handheld spray. Tape too, if necessary. It won't look pretty! But it should be tight.

AS an alternative, at the rim, you could have professionals spray in cc foam. This is what I do on new homes when I'm not spraying the entire basement wall. (Some at this board say they've used the DIY sprays successfully. I have no experience with them.)

Glad you persisted and got through to a Code Official who understood what you were doing!
andrelaplume2
15 years ago
Worthy, Others:

Re: Adhere the XPS directly to the blocked window. The idea is to keep the XPS directly on the wall; this prevents condensation and keeps the R Value as high as possible

I have NEVER seen any mositure on my walls. If I have never seen any, why do I need the XPS. Does the fact that I construct an insulated wall and inch away from the concrete increase the possibility of there being condensation? I am just at a loss as to why I need the XPS.
Related Discussions
using cinder blocks???
Q
Comments (5)
Hi JB, Welcome to RMGÂandÂthe only stupid question around here is the one you donÂt ask, so donÂt be afraid to ask whatever comes up! ThereÂs always somebody whoÂs ready, willing, and able to help! Where are you located? Since youÂre posting on RMG, I assume youÂre high and dry out here somewhere! If thatÂs true, the only possible problem I see with what you want to do is that theyÂll probably need to be watered pretty often once the weather warms since each individual "pot" wonÂt have a whole lot of soil, and, if theyÂre right next to a bunch of pea gravel, the area and the cinderblocks will probably heat up quite a bit. So planting snaps, or just about any other annuals (or herbs) should work as long as you keep an eye on them to be sure they get watered whenever they need itÂthe same as youÂd need to watch a pot. When it comes to planting them out already, since theyÂre apparently already hardened off, I donÂt think there should be any problem at all. Snaps can take really cold weather. If youÂre in the Denver areaÂor any of the other spots that are currently included in the most recent snow, IÂd say wait a couple days till it warms up againÂand then go for it! If you want snaps in the same place next year, just let this yearÂs plants produce seed when they finish blooming and enough seed will drop to reseed themÂand if you want to be even more sure that theyÂve reseeded, just hand scatter some of the seed from the seedpods after itÂs ripened. Snaps reseed very easily, and theyÂll come up all by themselves next yearÂmaking it even easier than this year. Also, some of them will probably germinate in late summer or fall this year and survive next winter to give you a really early start next springÂjust be sure the soil stays moist over winter if some get started by fall. Glad you found us here! Bring on your questions! Skybird
...See More
Foundation Help: Wood Pilings vs Cinder Block
Q
Comments (3)
carterinms, I must thank you again. I remember now seeing something on the FEMA website right afte Ike and we were doing all of our mitigation research. So many websites I have visted for sure. Many of the homes destroyed during Ike were older and in High Velocity zones and from what I hear it didn't matter what type foundation they had, becuase the surge was just so high and the debris field was so broad, that they didn't stand a chance. The ones that were left standing, whether wood or concrete, were the new construction that were at 18'-20' elevation above grade. We aren't high velocity, although after Ike, I don't think I can ever be too sure what may happen. We are a 1/4 mile from the bay and never dreamed we'd get that much water up here! Have you all gotten to move in yet? I hope so, it certainly was a long time coming. We haven't broke ground yet, but we are closer. Many of our neghbors are back in their homes, so the neighborhood appears to be coming back, which is a blessing. Anyway, I do thank you again. Would you mind posting the link to the journal on your build? I thought I had it in my favorites, but I don't and I can't find my other post. Best Wishes!
...See More
Cinder block sitting wall
Q
Comments (3)
I don't know where you live, but a footing shoud be down to the frost line. It's 30" where I live. Any block wall that's mortared in place needs a poured foundation to keep it stable. The stucco would crack & fail in no time. The mortarless block systems being sold can be installed on gravel foundations. They can shift around a bit with no problems.
...See More
New to Florida and Cinder Block Walls
Q
Comments (14)
Laurel- I was hoping that was the case. That means that any standard drywall hanger can be used for pictures and mirrors and such because you should have enough depth for the typical screw or nail that holds the fastener to go in without hitting the block. You should drill a tiny hole through the sheetrock and insert a nail to determine just what that depth is. As far as bookshelves, it depends on what kind and how much weight. If you are doing adjustable shelving with brackets and standards, like these: then the screws need to go into the wooden furring strips behind the sheetrock to be secure. If you are using wire shelving in closets, like this: the sheetrock should be able to support it as long as you don't load the shelves heavily (although it would be best if these could be secured to the furring strips, too). If you are planning to mount floating shelves or load the shelving with a lot of heavy stuff, like books, then this would be trickier. What kind of shelving do you have in mind? And, by the way, there is no need to hire a professional for this unless you have zero DIY skills.
...See More
worthy
15 years ago
Water vapour is moving in and out of your basement all the time. You just can't see it. But impede its flow with water sensitive materials and the trouble will begin.
phoenix2000
Original Author
15 years ago
Worthy, thanks so much for your advice.

Regarding the rim, if I put XPS on it, won't I need a fire-resistant covering, such as drywall? This would be a lot of work - is there another fire-resistant covering I could use that would be easier to install over XPS after caulking?

I read somewhere that if a high enough R-value (like R-19) for unfaced batts at the rim is used, I could prevent condensation from taking place there and still allow warm vapor to breathe in and be dehumidified in the room (through dehumidifiers). I understand that if there are air gaps, that the batts would deteriorate with time. Any thoughts?

Also, do I have to insulate the rim joists before putting up the walls? It's probably easier before, but could it be done after the walls are framed?

thanks.
worthy
15 years ago
The rim is the most important part because that's where there's the most exposure to the outside air.

Lstiburek in Understanding Foundations says:

"Of particular concern are rim joist areas
which are cold not only during the summer but
also during the winter (Goldberg & Huelman,
2000).

Basement walls should be insulated with non-
water sensitive insulation that prevents interior
air from contacting cold basement surfaces
the concrete structural elements and the rim
joist framing. The best insulations to use are
foam based and should allow the foundation
wall assembly to dry inwards."

The simplest way to provide the required thermal barrier for the rim joist area when it is insulated with any type of foam is to drywall the ceiling. After all, you're drywalling the rest of the area. Why leave off the ceiling?

When one client insisted on just that, I used a gypsum-based sprayed plaster that's used for fireproofing industrial buildings. There is also now a paint-like product that can be applied. Sprayable Portland cement is another possibility.

Here is a link that might be useful: Understanding Foundations

help on installing xps on cinder block

Comments (5)

worthy

andrelaplume2

Related Discussions

worthy

phoenix2000
Original Author

worthy

COMPANY

BUSINESS SERVICES

GET HELP

CONNECT WITH US

help on installing xps on cinder block

Comments (5)

worthy

andrelaplume2

Related Discussions

worthy

phoenix2000Original Author

worthy

COMPANY

BUSINESS SERVICES

GET HELP

CONNECT WITH US

phoenix2000
Original Author