[BasementSkill]

Good afternoon all,

My wife and I are in the process of redoing our basement and have insulation questions.

Background: House built in 1925 and located in western long island. We have had the basement waterproofed with sump up and French drain. Also we have Drylocked the outside and inside of the future foundation.

My plan is to use the 2X8 XPS boards all along the wall with glue and seal any gaps. The potential issue is our house is quite old and isn't 100% flat in places. If I use cutting and leave minor gaps in places what is the moisture and fire risk?

The previous owner used roll up fiberglass and was wet during demo.

Thanks.

 

[WhatRnsdownhill]

can you explain second paragraph plz?.." If I use cutting and leave minor gaps in places what is the moisture and fire risk? "????

 

[Windows on Wash]

The air gap behind the insulation isn't ideal, but condensation at that surface should still be minimized via the lack of diffusion through the XPS (more or less depending on the facing of the board) as well as the air seal you get with the board.

The board needs to be air tight at minimum to the wall.

http://buildingscience.com/document...-foundation-8-xps-2x4-framing-with-fiberglass

 

[BasementSkill]

Thank you for the information and generally what I thought. So to summarize it should be OK from a moisture perspective as long as it's glued tight to the wall and I use a sealer between gaps.

On my wife's concern about increased fire risk, any truth to that and how do I minimize and how serious is it?

Thanks

 

[Windows on Wash]

No fire risk from the air gap between a foam sheet and a concrete wall. The foam does need to be covered though. You need to have a stud wall and sheet rock in front of it in most cases.

You can't leave it exposed in a conditioned space.