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jjcobra99 01-14-2013 09:31 PM

Help with odd basement (LONG)
Hello all. New guy here in a real pickle. Would like to have some advice on framing/finishing a messed up basement. Long story short (this is really messed up), our contractor built our basement a foot too wide. Nobody caught it until weeks later when half of our modular was sitting on it. The set up crew split the difference (in width), and now the front and back of my house are sitting on the foundation walls by only the outer rim joist. The modular company are having us frame up 2x6 walls inside to help support the house, and we're unsure what we are going to do with the 5" ledge on the outside. I know. It's insane. We are trying to push forward though...

Any advice is appreciated on this whole situation, but the reason I am posting right now is to figure out how to--under the circumstances--properly frame and finish the basement. We are in Mineral Co. WV, I believe climate zone 5. The walls are 8" poured concrete with dimple board on the outside. Back side is 3/4+ below grade, front is above grade, sides slope down accordingly. I have searched and read for hours about this and would like to do the XPS against the walls and then also fill the cavities with something else. The problem is, I don't want to move my framing out more than a half inch or my header won't be under the inner rim joist.

Right now I have about 24' of framing complete, and don't want to go any further until I figure this out. We were holding out 1/2" from the wall, and using PT bottom plate. Also I sealed the interior walls with Foundation Armor S2000, and now (after all of my reading) I'm not sure that was the right thing to do. No way to change that now though.

Could I use 1/2" XPS and make up the difference in the cavities?

Thanks for any help/advice.

Gary in WA 01-14-2013 10:21 PM

You realize the slab should be thickened per SE for the added loads...I hope this will be Inspected by the local AHJ. Use a poly sill sealer under the pt plate for a thermal/air/capillary break.
For your location, 1/2" XPS (R-2.5) with R-19 cavity, will put the inside face of foamboard at 32* above grade and to the frost line, with 24% RH at 70*F room temp. 1"- R-5 and f.g = 36* foam temp., and 28% RH for condensation there. You will need to control the RH during the winter, if going that route. Did the SE say you could offset the top (doubled) plate for more room from the concrete? Why isn't the contractor fixing this or are you saving money (may think) .... be sure to notify your HO Insurance carrier if ever a claim and at selling. This could snowball without written fix from SE/AHJ.


jjcobra99 01-15-2013 04:26 PM

1 Attachment(s)
Thanks for the reply Gary. The slab is thicker where these walls are being framed (5"). Directly underneath we are still on top of the footer as well. There was 6" of footer inside the walls (footers are 20" wide).

I did not use sill seal under what we've already done but will do so for the rest.

The only engineer involved to this point has been the engineer from the modular company. I will try to attach what he sent...

I'm not sure how difficult it would be to keep humidity that low inside of basement. That is very low.

The contractor (that built basement) said he would help with costs of modifications that had to be made. If he was fixing this, I'm sure he would do as little as possible as it's coming out of his pocket. I am doing this myself to try to ensure that it's done correctly, and then I will fight him on costs. We had every intention of finishing our basement in the future, but was absolutely not in our budget at this point in time.

I do NOT want this to snowball. Forgive me, but I'm not sure what AHJ is.

I am completely open to suggestions on this. Thanks.


Gary in WA 01-15-2013 05:13 PM

Show that to the building inspector and see what he thinks on how you can get more insulation to control the humidity on the concrete wall. Did they use any exterior insulation before back-filling? Authority Having Jurisdiction. Ask the modular Engineer to draw a revision on off-setting the top plate from the other one below to gain insulation space moving the wall studs/bottom plate inward. Never-mind, already framed...

Moving you to get more/better responses from "Insulation".


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