The toughest details are those that have to match up with someone else's work, or those done — even done well — when energy was really cheap. These details are a collection of some common — and tough — dovetails of existing work with retrofits or additions. Bear in mind that green remodeling means creating a new operating regime that is better, not worse, than the one that may well have been working just fine before. Integration of energy efficiency, moisture management, and indoor air quality is much more important and challenging in remodeling than in new construction.
Mechanically fastened subfloor over 1" rigid insulation
Basement and slab-on-grade floors can be retrofit to improve thermal performance but not without managing moisture along the way. There are a host of ways to do this, but headroom and clearance at exterior doors often limit the options. This detail (and its neighbors) assumes that standing or bulk water are not part of the deal; if either is, refer to these details: 9-00030 through 9-00033.
To restrict the flow of both heat and moisture, tape all joints. If the assembly contains more than one layer of rigid insulation, stagger the joints to further restrict the movement of air and water.
If your basement floor is wet, you need one of these details:
9-00030 - interior water managed existing stone rubble wall
9-00031 - interior water managed existing brick wall
9-00032 - interior water managed existing CMUConcrete masonry unit. Precast concrete block used to build walls. CMUs have hollow cores that can be filled with concrete onsite for additional reinforcement. The use of stronger, more lightweight types of concrete such as autoclaved aerated concrete (AAC) is becoming increasingly popular in CMU manufacture. wall
9-00033 - interior water managed existing concrete wall
If your basement floor (or slab-on-grade) is not actually wet, you only need to manage two forms of moisture: water wicking up through the existing concrete slab; or vapor diffusing into (or maybe through) the retrofit floor assembly. If your existing slab has a capillaryForces that lift water or pull it through porous materials, such as concrete. The tendency of a material to wick water due to the surface tension of the water molecules. break/vapor retarder material between it and the soil, you are lucky. How do you know if you are lucky? You either assume you are not, and then place a nonporous, water- and vapor-impermeable layer over the existing slab before you build your retrofit floor, or you tape down a square of plastic, go away for two days, and then come back and see if water has condensed on the underside of the plastic.
If the latter is true, then you need that layer, but you now have another consideration: Where could that condensation go? It could go up wherever you penetrate the capillary break/vapor retarder material, or it could work its way out to existing mud sills or bottom plates, causing rot or mold. Dealing with fasteners is relatively easy; use coated concrete screws and seal the heads before putting down the finish floor material. Dealing with water condensing and moving to outside walls (mainly a problem for slab-on-grade floors, not basements) is more difficult and may involve installing some sort of drain network in the slab.
Can you continue to let this moisture simply make its way up through the new floor assembly, the same as it has before? You could, so long as you don't have any soil gas problems like radonColorless, odorless, short-lived radioactive gas that can seep into homes and result in lung cancer risk. Radon and its decay products emit cancer-causing alpha, beta, and gamma particles. to contend with and you put down a floor assembly that is just as water- and vapor-permeable as the existing slab.
There are three types of foam board—expanded polystyrene, extruded polystyrene and polyisocyanurate. Key differences are R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. per inch, water resistance, compressive strength, how permeable they are to water vapor, available facings and, of course, their cost.
Board insulation is manufactured with the help of a “blowing agent” that creates tiny bubbles in the foam which slow down the flow of heat. Manufacturers of expanded polystyrene (EPSExpanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest.) and polyiso board use hydrocarbon blowing agents that don’t damage the earth’s ozone layer. A switch away from the ozone-damaging hydrofluorochlorocarbons (HFCFs) used to make extruded polystyrene (XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation.)is not expected to take place until 2010, giving this type an environmental disadvantage for the time being.
Expanded polystyrene. The least expensive of the three, EPS can be manufactured in different densities to increase its compressive strength but it’s still not as strong as extruded board and it’s more susceptible to crumbling at the edges and to other job-site damage.
Extruded polystyrene. Because of it shigher strength and water resistance, XPS is often used below grade to in-sulate slabs and foundation walls.
- R-value: About 5 per in.
- Permeance: 1.1 per in. up to 2 in. then 0.55 per in.
Polyiso. With higher insulating values and no ozone-depleting blowing agents, polyiso board has some advantages over XPS for above-grade use (it’s not recommended for below-grade applications because it can absorb water). Polyiso often comes with a foil facing, which gives the material a very low vapor permeance.
- R-value: up to 6.5 per in.
- Permeance: 0.03
GBAGreenBuildingAdvisor.com Encyclopedia: Rigid Foam Insulation
Green Product Guide: Board Insulation.
Building Science Corp: Performance properties of different types of rigid insulation
Either extruded polystyrene (XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation.) or high-density (Type IX) expanded polystyrene (EPSExpanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest.) rigid insulation, rather than polyisocyanurate insulation, should be used in this application. Polyisocyanurate absorbs water, and therefore should not be used to under slabs or on the exterior of foundation walls.
For more product information on rigid insulation:
Product Guide-Board Insulation
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