How to Insulate Knee Walls
- Use an R-value map to determine the amount of insulation you need. ...
- Cut unfaced batt insulation to fit between the floor joists in the space behind the knee wall.
- Lay each unfaced strip of insulation between the floor joists.
- Cover the floor joists with a second layer of unfaced insulation perpendicular to the first layer. ...
How do you insulate a knee wall in an attic?
Knee Wall Insulation When it comes to insulating knee walls, you will want to insulate this space using the same material and method as the rest of your attic. The best materials for the attic, and thus the knee wall, are spray foam, fiberglass, and cellulose.
What is the best material to insulate a knee wall?
The best materials for the attic, and thus the knee wall, are spray foam, fiberglass, and cellulose. If you plan to insulate the roof deck of your attic, then you would use spray foam or fiberglass batts. Cellulose is much better suited for the attic flat.
Do I need rigid foam on the back of a kneewall?
One final point: When it comes to rigid foam on the back of kneewalls or walls facing attics, it really isn't necessary to meet the minimum R-value requirements for exterior rigid foam, because these spaces aren't at outdoor temperature -- they are generally warmer. Condensation problems in this type of wall are almost unheard of.
Should knee wall insulation and air barrier be continuous?
A.Bruce Harley, technical director of Conservation Services Group in Westboro, Mass., and author of Insulate and Weatherize, responds: In this notoriously leaky and difficult-to-insulate area, both the insulation and the air barrier must be continuous to prevent outside air from moving freely through the knee wall and into the rest of the house.
Should a knee wall be insulated?
As a bonus, access doors into the conditioned space behind the knee wall won't need insulation or weather stripping. If you can't get at the underside of the rafters, or if creating a continuous air barrier would be impractical (for example, with truss roof framing), then you'll need to insulate the knee wall itself.
How do you insulate a basement knee wall?
0:552:16How to Insulate a Basement Foundation Wall - YouTubeYouTubeStart of suggested clipEnd of suggested clipAnd customers to install a polystyrene rigid foam board at least an inch thick onto that exteriorMoreAnd customers to install a polystyrene rigid foam board at least an inch thick onto that exterior wall first. Once.
Do knee wall attics need ventilation?
Ventilation. Like everything in life, you need an 'in' door and an 'out' door. While the house should be tight, the attic should breathe to allow excess heat and moisture out of the house.
What are knee walls for home insulation?
The knee wall is the short wall that reaches from the sloped ceiling to the floor, or connects the upper ceiling to the lower ceiling inside the attic. Not only are air leaks common in these areas, but they are frequently not insulated properly. Insulation itself does not stop air flow.
What is the cheapest way to insulate basement walls?
The smart and inexpensive way to insulate joist bays is to use extruded polystyrene (XPS) foam insulation panels cut to size to fit inside the bay and "glued" in with expanding foam. When the expanding foam hardens, trim away the excess and cover the foam with a piece 1/2" thick drywall to meet fire code.
Should basement walls be insulated to the floor?
Once these groundwater control strategies are employed, the basement should be insulated to minimize cold surfaces that can condense water and elevate local relative humidity. Basements should be insulated on their perimeters—they should not be insulated between floors.
Can you have too much insulation in your attic?
It's possible to over-insulate an attic as too much will cause moisture buildup and eventually result in mold. Eventually, adding more insulation leads to diminishing returns in trapping heat as well.
Is it better to insulate ceiling or roof?
If you are deciding between insulating the roof deck or the ceiling, Insulating your ceiling should be the priority. Not only is it easier but ceiling insulation is beneficial in a number of ways: Keeps the temperature in the building regulated. Saves on energy costs.
Should attic walls be insulated?
A finished attic should be insulated much like the rest of the house, with insulation in the walls and ceiling. If your attic is already finished, it probably is at least partially insulated. However, most older attics are under-insulated so it's a good idea to raise the R-value where possible.
How do you insulate a knee wall in an attic door?
Attic kneewall doors should be tightly weather-stripped, have a secure closure and have increased insulation R-value on the door (this can be achieved by gluing several inches of insulating foam board to the attic side of the door with construction adhesive and fastening with screws and washers - see below).
How do you insulate a one and a half story house?
2:287:25How to Insulate a One and a Half Story House - YouTubeYouTubeStart of suggested clipEnd of suggested clipSo the best way to address this type of home is we do it from the outside or we do it from theMoreSo the best way to address this type of home is we do it from the outside or we do it from the inside and we use our spray foam application.
How do you frame a knee wall in an attic?
InstructionsThe knee wall will be built on the floor of the attic, and then tipped into place against the rafters. ... Cut six lengths of 2x4, each 2 1/2 feet long.Use a template to determine the angle on each of those six pieces of 2x4; draw a line across that angle.Use a miter saw to cut each 2x4 on that angle.More items...•
How do you spray foam a knee wall?
0:543:08What is the Best Way to Insulate a Knee Wall? | Foam UniversityYouTubeStart of suggested clipEnd of suggested clipSystem is set up. So the first way you can do it so you have your vertical knee wall. You canMoreSystem is set up. So the first way you can do it so you have your vertical knee wall. You can insulate the knee wall itself.
How do you insulate a one and a half story house?
2:287:25How to Insulate a One and a Half Story House - YouTubeYouTubeStart of suggested clipEnd of suggested clipSo the best way to address this type of home is we do it from the outside or we do it from theMoreSo the best way to address this type of home is we do it from the outside or we do it from the inside and we use our spray foam application.
How do you insulate a frog room?
0:363:02What to do When the Room Over Garage is Hot in the Summer and ...YouTubeStart of suggested clipEnd of suggested clipYou also need to address the floor we'll get more into that in a minute but keep in mind whateverMoreYou also need to address the floor we'll get more into that in a minute but keep in mind whatever insulation material you use should have an air seal built in like foam.
How do you insulate a cape?
2:524:31Insulating Exterior Walls and Dormers of a Cape with Injection FoamYouTubeStart of suggested clipEnd of suggested clipWe're actually going to remove roof shingles drill our two-and-a-half inch holes in each Bay. AndMoreWe're actually going to remove roof shingles drill our two-and-a-half inch holes in each Bay. And inject those slopes with injection foam from the roof.
What is the best material for insulating a knee wall?
The best materials for the attic, and thus the knee wall, are spray foam, fiberglass, and cellulose. If you plan to insulate the roof deck of your attic, then you would use spray foam or fiberglass batts.
What material is used to insulate knees?
In rare instances, they may change materials to insulate the knee wall itself with either wet cellulose or fiberglass batt.
Which insulation material creates an air barrier and prevents air movement?
Of the three materials, spray foam insulation is the only one that creates an air barrier and prevents air movement.
Can you put fiberglass on the floor of an attic?
If the attic flat is done, the fiberglass is installed on the flat and up the knee wall. A good contractor would also put fiberglass on the floor of the cubby. One thing to keep in mind with fiberglass and cellulose – is that these materials don’t create an air barrier, so air movement is still possible.
Can you blow in cellulose insulation?
Cellulose insulation is only an option when insulating the attic flat. In this process, most insulation contractors will blow-in cellulose on the attic floor. When it comes to the knee wall, in most cases, the contractor will install the cellulose on the floor of the cubby on the other side of the wall. This is the only instance when the knee wall ...
Can you insulate a roof deck?
But that is only in the case of insulating the roof deck. If you are insulating your attic flat, then you would insulate the knee wall, cutting off that cubby space from the rest of the conditioned space. If you are insulating the attic flat, just remember you will also need baffles to ensure airflow from the soffit up to the ridge vent, ...
Is cellulose better for attic flats?
Cellulose is much better suited for the attic flat. The thing to keep in mind is the space behind the knee wall is an extension of the roof deck. That’s why up above I said you really aren’t insulating the knee wall at all – it’s really the space behind it. But that is only in the case of insulating the roof deck.
What is knee wall?
The knee wall is the short wall that reaches from the sloped ceiling to the floor, or connects the upper ceiling to the lower ceiling inside the attic. Not only are air leaks common in these areas, but they are frequently not insulated properly. Insulation itself does not stop air flow. For wall insulation to do its job, ...
How many sides of an air barrier should be sealed?
For the air barrier itself to be effective, it must create a continuous layer around the insulation. This means the insulation must be air sealed on all 6 sides in order to be effective. All holes and cracks should be fully sealed, and the air barriers must be in full contact with the insulation.
Does insulation stop air flow?
Insulation itself does not stop air flow. For wall insulation to do its job, it must have an air barrier on all sides, so that it is enclosed in the wall cavity. An air barrier is any material that restricts air flow.
Can you insulate the floor behind the knee wall?
You can insulate the floor behind the knee wall and the attic above it the same way you would a regular attic.
How much R value for knee walls?
As far as making the knee walls conditioned space, as long as you get ventilation and adequate R-value of at least R-49, I say go for it. We did it in one house, but the customer was not as satisfied as I would like (of course she was a little tougher than most customers.)
What is the white stuff in a knee wall?
The white stuff is vinyl-faced fiberglass to fill most of the hole with Fireblock foam insulation around it. Added bonus, the floor of this knee wall leaked too, so there is a line of foam just above the floor joist. We reduced the air leakage nearly 50% on this house in Shaker Heights, without insulating the walls.
What is R-13 insulation?
a. Knee walls have R-13 fiberglass rolls (also called batts) in them, covered with stapled on reflective insulation. I call this “tin foil on steroids”, because that’s what it is. The main purpose of this material is to seal the fiberglass batts. If the batts are even 1/4″ away from the wall, they have an effective R-value of 0 because air flows behind them. Fiberglass also performs poorly when the ‘fluffy’ side is showing, losing up to 1/2 its R-value to convection. Check out this study from Oak Ridge National Laboratory. The radiant barrier also adds a little R-value and reflects 97% of the radiant energy that hits it. Most of the heat in the attic in the summer is radiant energy, so reflective insulations are a nice fit for this application, in my humble opinion.
What is the R value of solar guard insulation?
This gives a total R-value of R-17 (R-13 fiberglass plus R-4 for the Solar Guard.)
Can you use plastic on fiberglass knee walls?
Bonus Section: If you try this yourself, DO NOT use plastic or you will cause water problems. Foam board, if not sealed very well can also cause problems. A house wrap like Tyvek or a perforated (with pinprick holes) radiant barrier are good covers for fiberglass in knee walls. Don’t use the usual radiant barriers sold at Home Depot and Lowe’s, they are not perforated. The key is whatever material you use must allow water vapor through it. (I’ll deal with double vapor barriers more fully in another post.)
Can you insulate a knee wall?
Now, a note on materials for insulating the actual knee wall. There are as many ways to do it as there are people who do it. One of the best methods is rigid foam board with sealed joints over insulation in the knee wall. This is not very easy in most of the older houses we work on because the hatches and attics are too small to get rigid foam board through.
Can you vent a knee wall attic?
Ventilating knee wall attics is challenging. In an ideal world, we install soffit vents as intakes, make sure the slopes can breathe with ventilation baffles, and exhaust through a ridge vent. Old school roof vents (which look like rectangles on the roof) work pretty well too.
What is the best material for kneewall insulation?
If you are using air-permeable insulation (fiberglass, cellulose cellulose, or mineral wool), it’s essential to include an air barrier on the back side of the kneewall. The best material for this purpose is rigid foam; acceptable alternatives include OSB, ThermoPly, or drywall.
What is the best way to protect air permeable insulation?
Air-permeable insulation should be protected by a durable air barrier on both sides of the insulation. The top-side air barrier is usually some type of panel forming the bottom of the ventilation chute, while the bottom-side air barrier can be drywall, OSB, ThermoPly, or rigid foam. To ensure a tight air barrier, the seams of these panels should be sealed. It’s also important to caulk the joint between these panels and the kneewall top plate.
How to insulate a triangular attic?
There are two ways to insulate triangular attics behind kneewalls. The traditional approach is to insulate the kneewall and the attic floor behind the kneewall. This method can be made to work, but the necessary air-sealing details are demanding and fussy. A better approach is to insulate the roof slope above the attic.
What is a kneewall?
Kneewalls—short walls under sloped ceilings—are common in story-and-a-half homes and in bonus rooms above garages. Although kneewalls can help turn attics into living space, they often present insulation challenges. Most builders install fiberglass batts between the studs and some type of blown insulation between the floor joists.
What is the minimum insulation required for a 2012 insulated house?
Make sure that you install enough insulation to meet or exceed minimum code requirements. The 2012 IRC requires at least R-30 in climate zone 1, R-38 in zones 2 and 3, and R-49 in zones 4 and higher.
Can a leaky kneewall heat up a roof?
A leaky kneewall also can provide a pathway for escaping warm air to heat up roof sheathing, which can contribute to ice dams.
Can you insulate a sloped ceiling?
Better: insulate the sloped ceiling. It’s usually easier and more effective to insulate the sloped ceiling rather than the kneewall. In a traditional story-and-a-half Cape, the insulation should extend from the rafter bird’s mouths to somewhere above the flat ceiling above the second floor.
What is the purpose of installing insulation?
Do: Install insulation to fill the cavity between conditioned and unconditioned space without gaps, voids, misalignments or compression. Do: Install insulation to fill the cavity between conditioned and unconditioned space without gaps, voids, misalignments or compression.
What is the best way to seal windows and doors?
Do: Air seal around windows and doors using backer rod, caulk or low expansion foam. Do not use fibrous insulation or air-permeable foam.
When using kraft-faced batts, what do you do?
When using kraft-faced batts: Fasten kraft face tabs of insulation to framing members. Note: no kraft paper overlapping required.
Do walls have to be insulated?
Do: For walls that will not have an interior finish and are separating conditioned and unconditioned spaces, wall cavities are insulated and an interior rigid air barrier is installed.
What is knee wall?
A Knee Wall is created when a finished room is built within a sloped roof. A short wall called a Knee Wall forms a triangular space that can be accessed with a short door or access panel in the attic. The floor of the knee wall space forms the ceiling of the room below it. A lot of homeowners tend to use this space for storage.
Can knee walls be insulated?
Knee Wall: Poorly Insulated. While they can be an ideal storage spot, Knee Walls can’t do much without being properly insulated. Fiberglass is layered down on the floor of the Knee Wall but since fiberglass doesn’t stop airflow, it doesn’t do anything to insulate the area.
What is the easiest foam to tape?
My favorite material in these circumstances is foil-faced polyiso, because it's the easiest type of rigid foam to tape.
What material is used for taped seams?
My favorite material in these circumstances is foil-faced polyiso, because it's the easiest type of rigid foam to tape.
Do you need an air barrier on both sides of a wall?
Bob,#N#As you correctly guessed, you need to have a durable air barrier on both sides of any wall insulated with fiberglass batts. A wide variety of materials can be used, including rigid foam with taped seams, drywall with taped seams, OSB with taped seams, or carefully installed housewrap.
Does rigid foam trap moisture?
The bottom line: Properly installed, exterior rigid foam does not create a "moisture trap." For more information on this issue, see Worries About Trapping Moisture.
Can you put poly under drywall?
Unless you are in a very cold climate zone, poly under drywall is not recommended. If your inspector requires it, try a product like Membrain which varies its vapor retardance based in the conditions.
