Insulation under sleeper system
TACSTUDIOS
| Posted in Green Building Techniques on
WHAT SHOULD THE INSULATION UNDER THIS FLOOR SYSTEM :
ZONE 3A
SLEEPER SYSTEM OF 2X12 ON A CONCRETE SLAB.
CONCRETE SLAB IS ON 2″RIGID INSULATION, WITH FOUNDATION VAPOR BARRIER SEALED & TAPED SEAMS.
FOUNDATION WALL ARE INSULATED AS WELL.
WE HAVE SUGGESTED R-5 UNDER THE FINISHED FLOOR SYSTEM.
WOULD A HIGHER R-VALUE HARBOR CONDENSATION WITH IN THE SLEEPER SYSTEM CAVITY?
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Replies
Cara,
We need a better description.
I understand what a slab is. You also mention a "foundation wall." What is that? Is that a frost wall? Does this building have perimeter frost walls that support the exterior (above-grade) walls, with compacted gravel and a slab inside the frost walls?
Why are you installing 2x12s? Are these joists being installed on a garage slab to raise the level of the garage, as part of a garage conversion project?
You wrote, "We have suggested R-5 under the finished floor system." For purposes of reference, you should know that the 2012 IRC requires floor assemblies in Climate Zone 3 to have a minimum R-value of R-19.
THE 2X12 FUNCTION AS A SLEEPER SYSTEM ABOVE THE CONCRETE SLAB, SO WE CAN RUN THE HVAC UNDER THE FLOOR .
YES THIS FLOOR SYSTEM HAS FOUNDATION WALL AROUND THE PERIMETER, THE ROOF SYSTEM IS SUPPORTED ALONG THE FOUNDATION WALLS.
THE DUCTWORK WILL BE INSULATED AT WELL.
Start by turning caps lock off- it makes it a bit hard to read.
If the foundation walls/slab edge are insulated all the way down to the level of the 2" sub-slab foam there is no further code requirement for insulation between the slab and the finished floor. Any insulation you add between the 2x12s would make the edges of those timbers cooler, and more susceptible to moisture accumulation than if they were not insulated.
By "sleeper system", do you mean to say that the 2x12s are resting on the slab?
Or are you talking about fully structural joist spans supporting the floor, with a very low crawl space below to accommodate the HVAC?
Cara,
You might want to check with your local code authority. In many jurisdictions, there is a minimum height for crawl spaces (see illustration below).
.
thank you for your responses.
perhaps this will help
Here is a drawing
.
As-drawn the stem walls are not insulated above grade at all and there is no slab edge insulation, which renders the sub-slab insulation useless from a thermal performance point of view.
If there's enough room under the bottom edges of the 2x12s to run ducts, they're not exactly sleepers.
With the slab resting on top of the ledge in of the stem wall it's all but guaranteed to crack.
It would be a thermally better use of the foam to drop back to 1" under the slab but have 2" of foam continuously to the top of the stem wall, floating the slab rather than resting it on the stem walls, at which point there is no need to insulate between the slab and finish floor.
Using an insulated concrete form(ICF) for the stem wall and floating the slab looks something like this, and would be an effective approach:
https://www.greenbuildingadvisor.com/sites/default/files/images/Double-Stud_wall-Slab-On-Grade-with-Stem-Wall.jpg
This happens to be high-R variation on that theme- you obviously don't need 8" sub-slab foam, but with 2" of foam on both sides of the stem wall that it continuous with the sub-slab foam you can put anything you like above the slab without further insulation.
You could also do it this way, with the sub-slab foam extending over the ledge-step:
https://s-media-cache-ak0.pinimg.com/564x/3c/07/b7/3c07b776cc8b8cc21c0ec0a345cd6437.jpg
Cara,
I really don't think that it's legal to run ducts in a crawl space unless (a) the crawl space is high enough to allow human access, and (b) there is an access door for maintenance.
duct work is allowed to run in the floor system, the mechanical equipment is not allowed.
Cara,
If your local code inspector allows it, you can go ahead if you want to. Remember, though, that if a duct seam ever opens up, you won't have any way to inspect or seal the duct.
If you go forward with your plan, you need to address the insulation problems noted by Dana Dorsett in Comment #8: "The stem walls are not insulated above grade at all and there is no slab edge insulation, which renders the sub-slab insulation useless from a thermal performance point of view."
we are looking into a detail to insulate the outside of the foundation wall. How that will be finished is an issue. The structural details for the stem wall have been detailed to curtail failure, they are not addressed in our drawings, but in the structural. The ducts will be inspected prior to cover-up, however in your view what is the difference between the mechanical in a typical floor system which is sealed- as well. We have never need to have access to ductwork in a floor system. I had Carl Seville reviewing the detail in our studio yesterday, so I am confident we will have a great detail.
Cara,
Sounds good. Good luck.