Basement insulation question

S Ebels

Which of these is the correct method of insulating a poured concrete basement wall, 1/3 exposed, 2/3's below grade.

A. Wrap the exterior of the concrete in foam. My thinking is that this would allow the concrete exposed to the basement act as a heat sink. It would also keep the dewpoint outside of the wall. No isulation in interior stud walls.

B. Stud the interior [2x4] and blow it full of cellulose insulation. Less hassle as the walls have to be studded for wiring and plumbing purposes in either case.

Anxiuosly awaiting the sage advice of the "Wall" on this one.

Weezbo

sir i'd go with A.

with bitchuthane on the outside of the foam for starters. lots a people dont, just because to do nothing is easier..the use of insullation is a one time expense ,fuel oil and nat gas and propane is'nt. think about it.

Dale

Mold

One thing to consider is the possibility of mold. A damp basement can grow mold inside of the loose fill or fiberglass insulated stud wall. Current opinion is to put nothing in a damp basement that mold could grow in. So, if you do go with a stud wall spray in foam between the studs, If there's any chance of a basement water leak, and when is there not, I like to insulate the exposed portion of the wall, the upper 4 feet, and leave the deeper below grade uninsulated, the major heat loss and radiant loss from you is up higher on the wall. I shoot a 2X4 horizontal 4 feet down, put 1 1/2 inch styrofoam there and cover it with drywall, I run the electric in conduit below the 2X4. Even a little leaking wall crack or sewer backup won't hurt it. If you live in termite land I would not put foam on the outside.

Constantin

Check out Building Science Corporation

Buildings benefit a great deal from having the foundation insulated on the outside. However, as the water inside the concrete has nowhere to go during its curing process, you have to leave the inside open to an extent to allow the water to escape. Otherwise, you'll get mold, particularly if you use a vapor barrier.

Take a look at this basement insulation primer published by the Building Science Corporation. You may find it enlightening.

Mike T., Swampeast MO

Coming from land of termites and humidity, I personally don't care for any form of finished basement. I've torn out a number of finished basements and have always found termites, mold, "dry" rot--often all three.

Basement walls are rarely insulated around here even if the basement is completely finished. They do though sometimes insulate the floor above with fiberglass--bad--if over a crawlspace or partial basement--disaster. The fiberglass gets wringing wet in the summer and the "dry" (brown) rot occurs with amazing speed.

Were it me finishing a basement around here I'd fur out with metal studs, insulate with rigid insulation against the concrete (leaving a good air gap behind the finished walls) and ensure a CONTINUOUS ventilation path from top-to-bottom in the walls (yes, this requires a full width "slot" near top and bottom--I've only seen pictures [FHB?]--never done it). Ceiling would be removable for access/inspection/repair.

In less humid climates you probably don't have to be so paranoid I just don't like the idea of any form insulation with the ability to trap moisture in a basement.

If the home has forced air-conditioning with the ductwork in basement make certain it is VERY well sealed and VERY well insulated before "hiding" it behind a ceiling. Around here they often condense just enough water to support a thriving mold colony on the back of the ceiling...

Harold

The approach I am taking is to build a stud wall 1/2" or so from the concrete. I will then spray urethane into the cavaties and behind the studs.

The urethane should act to isolate internal concrete water and prevent condensation on the inside from ambient vapor. The concrete will have at leasst 3 months to bleed initial water into the basement air.

S Ebels

Addtional details

The home in question will belong to my son-in-law and daughter and is located in Northwest Lower Michigan. The building site itself is about a good as you can get. Nice sandy soil, not a trace of clay anywhere, well drained on a hill. This is not termite country. The basement will be a partial walkout facing south. The floor, of course will be radiant. I am trying to design the structure to attain a 10 btu / sq ft heat loss.

Weezbo

oki:)

there are new things made that look like gert leggo blocks,these are foam forms insulated to the Hilt! pour cement and rebar into them,sheet rock directly to the bad boys. use a heat knife to lay in electrical circuits. place 6" or what ever you need through the walls prior to pour,these things are remarkable in their strength and insulative qualities... there are a few breeds of them each has its own assorted gizmoes however if you seriously are looking for the non go back an hassel with concrete insulated basement roll "With."still insulate slabs on grade still insulate insulate insulate... water proofing block walls basically can only be done from the outside of a structure. its like sandwich Boat construction...

Scott Lind_3

ICFs

We used ICFs (insulated concrete forms) for our house and carriage house and now wouldn't do a foundation any other way. Toasty warm and dry here in Wisconsin. In fact if I were doing a new house I'd use them all the way to the roof.

I also put WR Grace 3000 on the outside, tile in and out, backfilled with pea gravel 4 feet out and bottom of footing to 12" below final grade. With 2" of foam below the floor and a little Wirsbo in the floor it's a very nice place to be in the winter - even though the rest of the house isn't done yet.

There are a ton of brands and systems out there. I used two of them and was very impressed with AMVIC.

Good luck!

Weezbo

Scott Lind....

Let me ask did you remember to put some abs or pvc in the forms for the hose bib?,Any dryer vents kitchen vents hrv vents boiler vents? ok now i gonna share an idea ,..your heating bills must be like ziltch compared to those around you,i have R 71 in the ceiling of my modest home and ) my fuel oil bills for This neck of the woods is OBSCENE in the minds of the fueloil companies:)))

Uni R

Basement Insulation - Outside!!!

A. all the way if you can! Protect it from the elements. Doing this you can use minimal stud walls inside without insulation for hanging walls if you decide to finish it.

S Ebels

Constantin

Lot's of good info at that site. I enjoy knowing why one should do things a certain way. Thanks for the heads up.

Constantin

What I like about BSC

is that they don't just research a lot, they actually publish their results for the world to see. That's unusual for consulting companies... furthermore, I consider their arguments fairly well-laid out and comprehensive.

Hopefully, their web-site will increase the level of knowledge all-around so that fewer basements are constructed incorrectly, leading to mold city. Mold is going to become an increasingly interesting problem as houses get tighter and there is less air movement to keep things dry.

Anyway, due to historical district regulations, we have to have brick on the outside above ground. Ideally, that would have entailed the use of 1 3/4" insulation + a 1/4" brick veneer. However, that idea is a no go due to structural as well as historical considerations. Instead, I'm insulating with XPS on the outside below ground (2") and Icenyne on the inside. It's too bad I cannot use the interior wall as a thermal mass the way the floor will be.

I also recommend you have a look at Rub-R-Wall. It seems to be a great product, if hard to find. It's a spray-on waterproofing goo that stretches over concrete cracks up to 18x its thickness (!!!) and you can use it to glue the XPS to the exterior wall.

We're done with our footings... now the exterior wall forms are starting to get assembled. The rebar still has to go in, as well as the bucks for windows, doors, and the house lifting beams.... one of the funniest stories I ever heard from the house lifters was a builder who had them lift a house to replace the foundation, then left no holes for the houselifter's I-beams in the foundation! So how was the house supposed to come back down? Hee Hee!

Tony_8

In NYS

Foundation/basement wall insulation is now code for new builds. Blueboard on the outside, below grade. I like the thermal mass potential of the insulated cementious walls.

Constantin

All well and good...

until you realize that for typical basements (i.e. where 1/3 is above, the rest below grade) most of the heat loss and gain is via the above ground walls. What we really need is a means of insulating exterior walls above and below ground that is durable and pleasing to the eye. As I stated above, I couldn't do it for structural as well as aesthetic reasons.

Above the basement level, SIPS seem to offer a great alternative to traditional stick building, as long as you don't mind dealing with some of the rethinks they require (like routing infrastructure). Once sheathed though, the only thing you'll notice is the much lower infiltration and thermal transfer rates...

In many respects, ICF's represent a fantastic means of achieving both energy efficiency and strength. Yet there appears to be a steep learning curve associated with these panels and I've read enough nightmare reports to elect to go with a regular cast concrete foundation instead. As with high-end appliances, the end-quality is usually limited only by the quality and experience of the installer.

Tony_8

typical

Most basements I've seen (thousands) around here are at most 3 blocks above grade, the majority are less than 2, usually only a foot from grade to sill plate. A couple of the builders here pour in vermiculite as well. I really like the pre-cast concrete system.

steve_49

a good source of information

For the latest word on on basement insulation systems see http://www.buildingscience.com/resources/foundations/default.htm

Mike T., Swampeast MO

That IS a good article!

Interesting to me that the damage/mold in the pictures there are just what I see around here with NO insulation either inside or outside the walls! Of course I don't believe basements are as common in other places where the outside dewpoint regular exceeds the temp of a basement during the summer.

Constantin

BSC does some great work

... and they do not shy away from putting excellent resources in the hands of homeowners and contractors alike. I bought their cold weather construction/insulation guide as a primer on how I want to do things... I highly recommend it.

Scott Lind_3

ENT Prep in wall forms

Weezbo,

I'd like to say I did but I didn't. I thought about it but we were under a weather crunch and getting walls poured was a higher priority than planning outlet locations (and I'm a EE!). So we chopped out foam later to run surface conduit and I'm foaming back in before drywall goes up. Certainly not the best method...

No good data on heating bills yet since structure above is a plywood box with only 2" of spray applied poly inside - we are still roughing MEP in. I like your R71 roof. I went with 7" of spray applied within the rafter bays and then 1-1/2" rigid atached to the rafters and am doing an unvented roof assembly ala BSC papers. My situation is a little unique since this is a rebuild of an 1890 home.

Scott