Insulating concrete walls

[hansen1]

Today they finally poured the walls for my detached shop. The walls are 8" thick and vary from around 4' tall in the front to 9' in the rear. On top of the walls will be standard 2x6 framing to bring the interior wall height to 14'. I will have a 6" floor with radiant heating. Based on what I have read on GJ, I plan on putting 2" foam under the floor along with a vapor barrier.

The will be waterproofing the exterior walls next week before the backfill begins. Would it help if I put some of the 2" 4x8 sheets of insulation on the outside walls? I was thinking this may help to keep some of the radiant floor heat from being absorbed by the ground. All the walls will be at least 4' underground.

Looking forward to your recommendations and experiences.

 

[hansen1]

Would like anyone's thoughts about insulating the outside walls of my shop. If I will get a big return on doing this, I will need to install it in a couple days before they do the backfill.

I estimate it will cost around $1100 in materials.

thanks,

 

[Steve in Mi]

The will be waterproofing the exterior walls next week before the backfill begins. Would it help if I put some of the 2" 4x8 sheets of insulation on the outside walls? I was thinking this may help to keep some of the radiant floor heat from being absorbed by the ground. All the walls will be at least 4' underground.

I'm sure it will help you maintain a more uniform floor temperature around the perimeter. Payback time will depend on your location but it will come with increasing energy costs. I put an inch inside my footings and an inch outside the footings 42" down. Plus an inch under the floor. The outside inch continues on up to the roof peak and 6" fiberglass in my stud spaces. Very comfortable and very reasonable to heat full time (~ 6 month Winter) with nat. gas forced air.

Caution; be sure that whatever waterproofing is used is compatible with your rigid foam insulation or provide poly to keep it from melting the foam.

 

[kuhner]

I built a garage into a hillside and I insulated down to my frost line with 2" pink foam. Problem I had was the transition from the foam above ground to my wall covering. I used the Hardy type concrete siding 12" wide and made a band around the three side. Then applied my Dryvit with 4" foam to the top of the foam-hardy siding.

greg

 

[5wndwcpe]

I used 1" foam from the bottom of the siding (vinyl) down to the footers. I stepped the 2x6 plates off of the block so that the sheathing would be even with the foam. I then used Tuff II, an exterior acrylic (which is similar to Dryvit) over the foam to replicate stucco on the exposed portions.

 

[Ezzie]

When I poured my walls, they put 2" x 2' foam sheets suspended inside the top of the form (with special plastic spacers to center it in the form). This eliminated the need for any special coverings to protect the foam on the outside.

You obviously can't do that now since the walls are already poured. Is there a reason you can't lay a 2" foam against the inside of the wall even with the height of the floor you are going to pour - or have you already poured the floor as well??

 

[hansen1]

The floor has not been poured. I dont' know that I want 2" foam exposed along the walls. I would think this would deteriote over time. As I type this, it dawns on me that I will be putting a 2x4 wall inside the concreate walls all the way around. This wall could cover the 2" foam between the floor and the wall. I could also seal the bottom of the wall so water doesn't get back into the foam. That should be easy enough to do.

The 2x4 interior wall that I will build will also have insulation so I will not just have concrete exposed. I will be installing the electrical and air in these walls before I insulate them.

As for the outside, my frost line is around 36" and every wall I have is 36" or higher. I don't have anything on the footings for insulation. It should be easy enough to dig out a couple inches on the footings to put down the insulation. This would be only 8-10" of height.

The outside will be stucco. I was planning on leaving any foam that I may install outside to be below grade so I didn't have to worry about the transition. I know this does expose 8-10" of concrete.

I am not sure if doing foam on the outside AND either blown in or batt on the inside is worth the cost.

Thanks for the suggestions. Keeps me thinking.