I have been doing a lot of reading about exterior basement wall insulation and under-slab insulation and have a couple of questions and am looking for advice. First, I plan on building in a moderate but heating oriented region (4800 heating degree days) of Tennessee. I plan to construct a SIP envelope over a basement or crawl space with a slab and poured concrete walls. I have read that exterior slab insulation is a good idea. However, I have also read warnings regarding termites (we will also be building in a an area where termites are a concern. I have read that EPS insulation may provide harborage termites and carpenter ants and termites. Is this limited to EPS? What about rigid fiberglass? I plan on installing insulation to R-5 or R-6. Being in an area that averages 50"+ annual rainfall, a good water drainage plane and waterproofing is also needed. Any way to combine the drainage plane and insulation? I read a lot. I have also read that fiberglass looses most of it's insulating qualities when wet. If buried underground in a relatively wet climate won't it always be wet? Second question (or third or fourth...) is what type of insulation should be used under the basement slab? I plan on a 4"-6" gravel bed with a minimum Class B vapor barrier above the gravel and the insulation above the vapor barrier. As with the exterior basement insulation, I am only looking at a total of R-5 or R-6. Standard 4' x 8' x 1" EPS sheets? Did I say that I plan on installing a wet hydronic radiant heat system in the basement floor?

Mark,

Thanks for the response. I anticipate that the basement walls will extend into the grade no more than 5’. Actually, I hope to get enough depth to the soil to even have a basement. The bedrock is shallow and I am not about to blast to get the depth for a full basement. The land does slope, but the building location is only slightly sloped. The bedrock is exposed around the perimeter of the bluff and during the winter the water seeping from the soul above the bedrock freezes where it exits so I know that there is water movement in the soil. I had planned a spray-on waterproofing membrane and also a dimpled water plane over that as well as the footer drain and even a subsurface system to catch the roof drainage from the gutters. I have specified a 1:10 or steeper slope away from the house for final grading. I currently live in Florida and don’t have to worry about basement drainage problems. I do have friends and family in the area in which we plan to build (Tennessee) and they do have basement water problems. I will continue to research the issue.

A product like Insul-Tarp® works great.

Scott as stated not everyone agrees on the best methods to eliminate the termite problems in various areas and it changes depending on many differant climatic, vegatation, and soils.

We have carpenter ants in our area but no termites I would almost rather deal with the termites they at least stay below grade for the most part, the ants stay above grade and and have very easy access into the wood areas of most any home.

Yes it is true that termites will bore into foam products to nest it is not a food source so it is strictly for nesting. Buy the way if you built a house entirely out of wood they would still bore in and nest but now they also have a food source. In most of the areas where I have trained ICF construction and they have had termite problems, the little buggers have entered through a wood frame window or door openig and worked their way into the foam. Termites do not like day light and stay mostly hidden and find ways to travel where it is dark. There are sheilds available or that can be made to stop them from geting at the wood portions of a home such as wood bucked areas, or those areas can be built with V-Buck that is not a food source.

This only my opinion based on common sense but not insulating the concrete on the out side greatly reduces the effectiveness of insulation, specifficly if you are building the above grade portion with wood. You see if the concrete gets cold it projects the cold into the wood above and the wood only has an R value of 1 so nothing there to stop that cold from radiating up through the walls leaving cold surfaces.

I think Mark makes the most important point and that is a good seal coat on the exterior of the below grade foam surface, this can be done with a trowel on or spray on parging coat or cement coat that the little buggers can not get through in the first place, and depending on what you use you can either put the waterprooof on the outside or the inside of that check with the manufacturer of those products on the application.

Last fall there was an episode on the learning channel that dealt with this issue and termite traps that are sunk in your yard where used at regular intervals, if termites are prevalant in your area I would suggest you look into some back episodes on this issue they are very informative.

Don't give up on good energy practices just because of termites!

While basement ceilings can be insulated as a low cost option to save energy by keeping heat inside the house above, this does not impact the usefulness of the basement as additional living space.


Source Link :

www.waterproofingpa.com

EPS (aka "beadboard") can be had that comes preloaded with borates, which limits the degree to which termites & ants can use it for tunneling purposes. This was a serious drawback to early versions of SIP construction (an employee of mine lives in a late- '80s SIP house with carpenter ant issues.)

XPS (eXtruded-expanded PolyStyrene) has better compressive strength ~25% higher R value/inch lower moisture permeability, and also comes in borate-loaded versions, and is the preferred insulation below grade, exterior or interior (particularly under slabs.)

Insulation on the inside of the foundation wall needs to be at least semi-permeable to water vapor or you can end up with mold issues on any furring-strips or stud-wall insulations you put down there. If using multiple insulation types, place the least-permeable next to the concrete, more permeable toward the interior. eg: R5 (1") of XPS held to the wall with glue furring strips, with un-faced fiber batting on the inside. If the total permeablity goes much below 1 there can be issues of ground moisture wicking well above grade causing efflorescence & spalling on the exposed exterior.

The best solution (IMHO) is to use borate-loaded insulated concrete forms (ICF) for the foundation walls. (The insulation for ICF is semi-permeable EPS, which allows some drying in either direction.) In a 4800HDD climate the lowest-R value ICFs are just fine- you'll end up well over R10 everywhere (~R16-20 is pretty common, but it's possible go higher where the climate calls for it.) In some areas code may still require you to cut a "termite inspection" slot in the insulation the full width to be able to visually verify that termites haven't tunneled in. (See the ICF forum for more suggestions & details. Of course some peops are gonna try to convince you to go with ICFs instead of SIPS for the whole house though. :-) ) Be sure to use waterproofing over any exterior insulation that's below grade (ICF or XPS).

Sheet copper between the sill-gasket and sill can be effective at stopping termites from getting to your SIPs & first floor. (Copper doesn't do much for ants though.)

Dana, do you have any references to XPS pretreated with borates. I knew about PerformGuard, but that's EPS.

I guess it was my imagination gone wild! (Again? :-) )

I had recalled discussion of borate-loaded XPS under development from several years ago and (apparently wrongly) assumed it was available by now.  I'm now wondering if/what technical issues have kept it from production.

Dana,
I heard, some time ago, that the introduction of borates to EPS caused the foam to become less stable, more brittle, if you will. I have not heard anything else about this is some years, so I assume that problem was corrected. But it could be, a similar situation exists with XPS, and remains unsolved.

I would recommend researching the Polycore foundation system. It will provide the insulation you are looking for, it is mold and mildew resistant, will install quickly, does not use concrete and is quite affordable. If you are worried about termites and other insects you could finish the outside with an accrylic stucco. I can't find any reason why this won't work for you.

Let me know if you have any questions.