how do you build a knee wall in an attic

How do you build knee walls in an attic?

1. The knee wall will be built on the floor of the attic, and then tipped into place against the rafters.
2. Cut six lengths of 2×4, each 2 1/2 feet long.
3. Use a template to determine the angle on each of those six pieces of 2×4; draw a line across that angle.
4. Use a miter saw to cut each 2×4 on that angle.

Full Answer

How high should knee walls be in attic?

approximately 2 to 3 feet highAttic knee walls are typically short, vertical walls approximately 2 to 3 feet high in an attic that separates attic space from conditioned space.

Do you need a knee wall in attic?

Knee walls aren't technically needed for a structurally sound home, but they do help to alleviate some of the pressure on the rafters. If you live in an older home and are worried about the stability of the roof, installing them may be a smart idea.

What is a knee wall in an attic?

An attic knee wall is a vertical separation between attic space on one side and conditioned space on the other side.

Are attic knee walls load-bearing?

They're typically framed with 2x4s and built 4-feet-high so they can easily be covered with full sheets of drywall. In most cases a knee wall is not a load-bearing partition. If you're not sure if a knee wall is load-bearing, you should consult a licensed contractor or structural engineer.

How do you insulate an attic knee wall?

Knee Wall Insulation 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.

What is the difference between a pony wall and a knee wall?

Also known as half walls, pony walls only come up—you guessed it—halfway or partway to partially divide a space. Pony walls differ from knee walls, which are generally intended to support something such as a countertop, handrail, or rafter.

Do knee walls need a top plate?

The number one way that knee walls are installed incorrectly is to build them without a floor to top plate. People do this, not understanding the purpose of those plates. They incorrectly think that all they need to do is scab 2”x 4” from the ceiling joists to the rafters and cover them with sheetrock to make a wall.

Should I insulate knee wall?

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.

What is the difference between a knee wall and a purlin?

what is the difference between a knee wall and a purlin? knee walls and purlins both provide mid point support for rafters. knee walls provide their support by transferring the loads down the ceiling joints and walls or beams below. purlins act as beams running along the underside of rafters.

Should attic walls be insulated?

Insulating your attic (including knee walls) is one of the easiest ways to make your home more energy-efficient. As you probably know, hot air rises, making attics one of the biggest sources of heat loss in your home — but you don't have anything to worry about if your attic is properly insulated!

How can I make my knee wall stronger?

0:573:52Building A Strong Half Wall - Avoiding the WOBBLE! - YouTubeYouTubeStart of suggested clipEnd of suggested clipSo you can work above. So the question is how many wall studs would you attach from that half wall.MoreSo you can work above. So the question is how many wall studs would you attach from that half wall. Well.

How do you make knee wall storage?

0:031:27How to Install Knee wall Storage Space in Finished Attic VideoYouTubeStart of suggested clipEnd of suggested clipBack end of it and slide the whole unit in and then secure it on to the 2x4 wall structure. And thenMoreBack end of it and slide the whole unit in and then secure it on to the 2x4 wall structure. And then just trim it out and then you're able to slide your drawers in like you see here.

Can I remove a knee wall?

If there is, that wall is probably a load-bearing wall, making the knee wall load bearing. It should not be removed, unless it is done so to replace it. In that case, temporary support of the rafters should be installed, before removing the knee wall.

What is the difference between a knee wall and a purlin?

what is the difference between a knee wall and a purlin? knee walls and purlins both provide mid point support for rafters. knee walls provide their support by transferring the loads down the ceiling joints and walls or beams below. purlins act as beams running along the underside of rafters.

How short can a knee wall be?

3-feet-tallThe knee wall definition is a short wall, usually just shy of 3-feet-tall, that supports the rafters in your attic. They are usually found in older homes where the ceiling on the top floor is an attic.

Why is it called a knee wall?

The term is derived from the association with a human knee, partly bent. Knee walls are common in houses in which the ceiling on the top floor is an attic, i.e. the ceiling is the underside of the roof and slopes down on one or more sides.

What is knee wall?

A knee wall is a short vertical wall, roughly two or three feet high, thats used to support rafters in the roof. It also blocks off the space that's too small (due to the sloping roof) to use for anything in an attic.

What is the shape of an attic?

If your attic space is framed with rafters and is unfinished, it has a triangular shape. At the bottom points of the triangles, the rafters meet the top plates of the exterior walls. The exact height of the knee wall is your choice.

What to use to fill cracks in fiberglass batt?

Caulk all other holes or cracks or stuff with fiberglass batt insulation or spray foam.

Does a knee wall provide insulation?

The knee wall, by itself, can provide some degree of insulation against air infiltration from the outside. However, the knee wall is usually not enough to provide all the insulation you need. To reduce air infiltration, the U.S. Department of Energy recommends that you complete several steps: Insulate the rafters.

Where does attic air go in a knee wall?

The bottom plate of the knee wall rests on top of the floor joists, leaving a large pathway for attic air to come up into the air cavity of the knee wall. Secondly, without an air barrier on the back of the knee wall, and with the potential to sag as indicated above, attic air goes around the insulation into the cavity on the vertical space as well.

What does it mean to seal a knee wall?

It also means sealing off all penetrations to the knee wall from drywall penetrations. And it might mean building a back to the wall. This can be any material accepted as fire-rated for attics. Drywall that is taped and mudded is one possibility. This wall can help with insulation as well as controlling air pathways.

What are the problems with a wall?

There are a number of potential energy problems with this type of wall: 1 It has no mandatory back to the wall, so insulation placed in the wall often sags or falls out, leaving an uninsulated wall. Sometimes the insulation is omitted altogether. And in times of air conditioning, that uninsulated space, even if it small, will conduct a great deal of heat from a hot attic. [show diagram of normal exterior wall and an attic knee wall to illustrate issue] 2 Insulation levels are inadequate. The level of insulation should be equivalent to the ceiling insulation. However, with ceiling insulation requirements far exceeding the amount of insulation that can fit in a 2×4, it is difficult to attach and can lead to insulation falling out. 3 No air barrier: Although drywall may work as a sufficient air barrier if not penetrated, knee walls can suffer from insufficient air barriers. The bottom plate of the knee wall rests on top of the floor joists, leaving a large pathway for attic air to come up into the air cavity of the knee wall. Secondly, without an air barrier on the back of the knee wall, and with the potential to sag as indicated above, attic air goes around the insulation into the cavity on the vertical space as well.

How thick is R38 insulation?

If you are putting in R38 insulation in the kneewall, that may be 12” of batt insulation material. That is a huge thick wall for an attic. First, make sure that your ductwork and electrical runs are to be located outside of this area and construct the kneewall with appropriate studs to the desired depth.

Can air leak from above knee?

There is also potential for air leakage from above the knee wall. Finally, like all barriers between conditioned space and the attic, any penetrations in the drywall for lights, outlets, ductwork or other features leaves potential pathways unless sealed.

Can you retrofit a knee wall?

Retrofit solution: Follow the steps above as much as possible. You may find that you don’t have room to construct new knee walls, but you may be able to use foam air barriers to block airflow below and above the knee wall. If there is existing insulation, check to see if it has any sags or gaps. You may need a new piece of insulation or simply be able to reattach the piece that is there.

Is there insulation in an uninsulated wall?

There are a number of potential energy problems with this type of wall: It has no mandatory back to the wall, so insulation placed in the wall often sags or falls out, leaving an uninsulated wall. Sometimes the insulation is omitted altogether. And in times of air conditioning, that uninsulated space, even if it small, ...

Why use knee walls in attic?

Provides Greater Stability. One of the benefits to using knee walls in the attic is the increases stability they provide. Once installed, they’ll support some of the weight from the rafters. It’s not uncommon for builders to place them up against the rafters while working on the roof.

What Are Knee Walls?

Knee walls are short, usually wooden, walls installed around the sides of an attic where the rafters meet the floor. You can see the image below for an example of a knee wall. In most instances, they are no taller than 3 feet, but some builders may custom fit them according to the roof’s shape and size.

Do you need knee walls on a house?

Knee walls aren’t technically required for a structurally sound home or building, but they do take some of the load off the rafters. If you live in an older home and are concerned about the roof’s stability, it might be a good idea to install them.

Do knee walls provide insulation?

Knee walls also provide “pockets” for additional insulation in the attic. If you go back and view the illustration above, you’ll notice there’s an enclosed area behind the knee wall. Rather than leaving this space empty, homeowners can fill it with insulation for additional thermal protection.