Knee Walls

by Andy Sheldon

in Designing

Every once and a while I get asked about knee walls. What are  they, how high should they be etc. In a classic small cabin design with the second floor under the main route, knee walls become an important way to finish the space.

What are Knee Walls?
Basically the term comes from walls that are about as tall as your knee. Most commonly they are the short walls that define a room under a sloping roof and are shorter than normal headroom height.

How tall should need walls be?
The knee wall height is really determined by the function of the space. For example:  In a closet, the knee wall can be very short providing storage almost to the eave.  If you want to put a desk of the knee wall, you will need to be able to stand up in front of the desk, so the desk depth becomes important. I you have a bed against a knee wall  you can determine its height by a combination of headroom and head board height.

For my use, I have settled on a knee wall height of 4′-0″ as a default. I can always change it during the design, but I found that this height serves many purposes. Our classic cabins normally have a roof pitch of 12:12 (45 degrees). I’m about 6′-2″ with a 3 foot reach which means that I can touch a 4′-0″ tall knee wall standing upright ( about 7′-0″ headroom ).

A 24 inch desk or counter can also stand in front of a 4′-0″ knee wall. And a bed with a 4 foot headboard and an 18 inch deep side table is perfectly workable. And building a closet in front of a 4 foot and knee wall allows for a rod at about 54 inches off the floor which is fine for single rod hanging.

As always, your comments are very valuable not only to me but to the others who drop by.

Best,

Andy

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{ 8 comments… read them below or add one }

ldfdog July 21, 2013 at 2:28 am

I want to put a roof on a small portion of my patio. Approx 6×6. In order to do this, I need to have a kneewall coming off of the roof. What is the best way to do this. How do I use flashing and tar to prevent leaks? THANKS

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Andy Sheldon September 3, 2013 at 7:08 am

I would contact a local builder (buy them lunch). It is very difficult to give meaningful advice with ought knowing the details of your local conditions.

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Vicki June 27, 2012 at 12:11 pm

Thank you Andy,
Alas, I do not know any engineers. Dang.
In my research on building a little house on a trailer I have seen others use a knee wall to gain height. The knee wall does not make sense to me as I, too, see it as a weak point, a hinge, no matter how you strap it. I would prefer to use the full height studs rather than have the extra construction and weight of a knee wall since weight is an issue with a little house on a trailer. I would rather use the added weight of any knee wall material to fortify the wall structure instead. My trailer is custom built with cross members to match the studs at 16 o.c.. The framing will be lag bolted through the trailer framing. What do you think?…….

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Andy Sheldon July 2, 2012 at 8:50 pm

If the cross members tie the walls together and you do not have a knee wall, you should be ok. Tiny houses like this are really pretty strong. When you mention “lag” bolting, do you really mean through bolting with a washer and nut? If so, that is great. Lag bolts usually mean bolts that have a screw thread that goes into wood. Not as strong as a bolt with nut and washer, since the threads are in wood and not the steel of the nut.

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Vicki St John June 25, 2012 at 2:01 pm

Hello Andy,
I am building a 24′ x 8.5′ “tiny House on wheels” . I would like to add a knee wall to the loft area as I am 6′ tall and would like to have the extra space. Is there a structural reason to build the knee wall separately and strap and stack it on the lower wall or can I just use 8′ studs? Thank you,
Vicki

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Andy Sheldon June 26, 2012 at 11:14 pm

You might be better to use the full height studs. A separate knee wall will create a hinge joint and increase the chances of the knee walls spreading. Knee walls can be tricky, especially if you are not using a structural ridge. You might play it safe and take an engineer to lunch.

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John Snape February 18, 2012 at 5:28 pm

sir: i still do not know what a knee wall is. you state a 4′ knee wall is 7’0″. i am confused.What neeed to knoe is what type foundation is needed? how about peirs, how many and how high?

I would also prefer 1 story designs.

Reply

Andy Sheldon February 18, 2012 at 8:04 pm

Hi John,
Sorry if I was unclear. Have you ever have been in the 2nd. floor of a Cape Cod style house and noticed that the sloped ceiling ended at a low wall (much shorter than normal)? That short wall is the knee wall. My 7′-0″ comment referred to the headroom at 3ft away from the 4′-0″ knee wall. Since the roof is rising at 12″ per ft. It will be 3ft higher 3ft away. 3ft + 4ft = 7ft.

As far as your question on the foundation type and pier spacing… that depends on the specific design of the cabin and the roof/snow loads that will be on the beams that the piers support. There is no one common answer to what type of foundation is best, or what pier spacing should be used. All this is best solved with a local professional who knows the required loads and soil bearing conditions.

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