[creamaster]

Just wanted to post a couple questions on my basement reno project ( i know this topic gets beat to death!) I havn't posted to this site in quite awhile, but we purchased a colonial this summer and the projects are flying by and now we are working on the basement this winter.

House was built in 1964, located in Rochester, NY...concrete block foundation, I want to insulate with 2" foamboard then build 2x3 wall then drywall. Part of the foundation already has some type of covering painted on, I don't know if it is oil/latex paint or waterproofer.

1) I am thinking of applying a "waterproofing" substance like Drylock to help reduce moisture entering the basement. Is this a fair idea and should I apply it over the "painted" areas, just wondering if it will adhere ?

2) When installing the foamboard, should I have it sit right on the slab or should it be an inch or 2 off the slab? There is a small french drain present around the perimeter of the foundation.

We have already added fill dirt around the outside to slope the drainage away from foundation and extended gutter drains 4-6 ft away from foundation. The basement has a sump pump, not sure if drainage tile is inside or outside the footers.

Thanks for the input.

 

[Millertyme]

No need to use the drylock if you are using foam. Drylock is a vapor barrier, but your foam will be serving as the vapor barrier so no need for 2.
I bring my foam all the way to floor.
Are you using fiberglass too. If so you might want to go with a 2x4 wall instead

 

[creamaster]

I was thinking of skipping the fiberglass and just going with foam.

My concern was if I didnt use Drylock or some type of waterproofer I may get condensation/mold on the interior of the drywall. We do use a dehumidifier and keep it around 45-50% humidity, so I'm not sure if I should be concerned.

Thanks.

 

[Millertyme]

2" foam only has an r8 value which might not make code which is why I would add fiberglass.

The rigid foam is the vapor barrier. It creates a thermal break where it hits the concrete. As the warm air from the living space travels through your drywall it will hit the foam. Because the foam is insulation and a vapor barrier the warm air will not make contact with the cooler foundation wall. Which will eliminate any moisture from forming. If it does, it will form between the foam and concrete keeping your drywall and insulation dry. Make sure to tape all seams in foam with proper tape too.

 

[Mingledtrash]

2" foam only has an r8 value which might not make code which is why I would add fiberglass.

The rigid foam is the vapor barrier. It creates a thermal break where it hits the concrete. As the warm air from the living space travels through your drywall it will hit the foam. Because the foam is insulation and a vapor barrier the warm air will not make contact with the cooler foundation wall. Which will eliminate any moisture from forming. If it does, it will form between the foam and concrete keeping your drywall and insulation dry. Make sure to tape all seams in foam with proper tape too.

I dont know what zone you guys are in but i was just looking at R10 2 in. foam.
http://www.homedepot.com/p/Owens-Co...uared-Edge-Insulation-Sheathing-45W/100320352

 

[creamaster]

Yeah I am using that 2" foam from Owens Corning, it states a R 10 rating.

As for the tape to seal the seams what tape is recommended? I was thinking of the Tyvek house wrap tape.

Thanks.

 

[craig11152]

sort of a sidebar question....how often does your sump pump kick on?

 

[carpdad]

First you need a complete plan. Plumbing first, electricals (including any communications) then other things. These things get in the way of insulation and you don't want surprises.
Start with rim boards and the joist bays. Each bay, cut the foam boards 1/4" small all around and fill the void with canned foam. Plan on using up many cans. Practice light touch on spraying the foam as not to waste too much.
Don't start thinking you can achieve some sort of 100% dry structure. If you foam the structure joints, and that means every joint you see, you are blocking most of the draft and the vapor carried with the draft.
Once the joist bays are insulated, you need fire blocking - before wall insulation and wall frame. 2x or 1" thickness ply layers separating the basement wall from the floor joists. The fire must not travel from the wall to the floor above.
Butt the insulation to the blocking. If using glue, vertical beads so any potential leak can flow down. Leave 1/4" space all around and fill with foam. I still don't like depending on tape.
Even with that much work, plan on using dehumidifier in the basement.
Outside, regrading with top soil may not work. It is a good idea to get to know your basement first before finishing it. 2015 was dry and you may not know what kind of trouble you may have.

 

[Millertyme]

My mistake 2" is r10. What I did on mine was j went with the 1" foam on walls then batt insulation after that. It gives me an r 18 value and I think ends up costing less than just 2" foam and a 2x3 wall.

 

[Gary in WA]

Appears you have a perimeter trench drain possibly leading to the sump (test it), if so- use faced insulation to stop any moisture from entering the foam board. be sure to leave the bottom UN-foamed at the wall/trench joint for wall drainage.
Use foil faced (or plastic) foam board on the rim joist after caulking the wood joints at rim/plate/subfloor/joist to stop infiltration of moisture/air from exterior/interior- post #8;http://www.diychatroom.com/f103/insulating-rim-joist-caulk-spray-foam-around-edges-168849/

Post #6 AND #10; http://www.diychatroom.com/f103/insulate-rim-joists-canned-spray-foam-roxul-307313/

Gary