Papercreters: [papercreters] Supporting window openings. -was- Re: Lintels

Sunday, July 27, 2008

[papercreters] Supporting window openings. -was- Re: Lintels

Whether or not you need a lintel is determined by the type of support
structure used for the entire house.

There ALWAYS should be some method of supporting the upper wall and
roof. Windows are not strong enough to support those loads.

A lintel is usually used with masonry construction. The lintel can be
a series of arched bricks over the window opening.
http://www.inspectorsjournal.com/forum/uploads/Scottpat/200832861829_IMG
_8200.JPG
same link again
http://tinyurl.com/69zwy8

It also can be a strong beam spanning across the opening.
http://www.sakrete.com/images/projects/TraditionalBlockAndBrick09.jpg
same link again
http://tinyurl.com/6czm97

In either case, the goal is to cause all the loads from the wall and
roof above the window to be supported by the wall surrounding the
window.

It is important to note that an arch needs to be supported properly.
Some arch designs can produce lateral forces that cause the bottom of
the arch to want to spread apart as loads are applied from above.
Proper support of the arch is as important as the construction of the
arch itself.

While papercrete construction differs dramatically from standard stick
framing, a lot can be learned by looking at the tried and true stick
framing methods.

A typical stick framed house has a modern equivalent to a lintel. It's
called a "header". In reality a header a hidden non-decorative lintel.

Typical headers are built by gluing and screwing the flat sides of 2x8
or larger lumber together with a layer of plywood sandwiched in the
middle. This produces a beam that is just as thick as a standard
studwall.

This header is supported by "jack studs". It's important to note the
header is wide enough that it extends beyond the width of the window
opening. This extra length allows the jack studs to be positioned
directly underneath the header. The jack studs carry the weight of the
header, wall above the header, and any roof loads above that all the
way down to the floor.

Some people call jack studs, "trimmers".

This means the window supports none of those loads. The window
essentially hangs inside the wall. It doesn't support anything but
itself.

Here is a graphic that describes the framing of a standard stud wall:
http://www.instructables.com/files/deriv/FS4/XGWR/F9N2E0F5/FS4XGWRF9N2E0
F5.MEDIUM.jpg
Yahoo will probably chop up that link.
Here's the same link as a tiny clickable url:
http://tinyurl.com/6k8vkl

Post and beam framed structures do things a little differently.
Roof loads are not carried through the wall itself, they are carried by
the big structural members.
http://www.sycamoreshouse.org/Rawson_House_files/droppedImage.jpg
http://tinyurl.com/64vj86

Note how the windows and doors are suspended by a series of studs.

One other alternative is the use of "window bucks".
These are used extensively in strawbale construction.
http://www.dancingrabbit.org/img/sb_south.jpg

The bucks need to be very strong. Significantly stronger than the
surrounding material. The bucks also need to be cross braced so that
they will not rack and get out of square. If the buck can easily flex,
windows and doors will quickly break, or at least sick and become
difficult if not impossible to operate.

The top brace of a buck can be thought of as a lintel. It certainly
needs to be as strong. It should be strong enough that it will not bow
as wall and roof loads push down on it. No window will ever be strong
enough to support those loads. The lintel and bucks will redirect
those loads around the windows (and doors).

The most important consideration is to always have some kind of support
over any window or doorway. It needs to be strong enough to support
everything above the opening and protect the window or door from those
loads.

I hope this helps.

--- In papercreters@yahoogroups.com, JUDITH WILLIAMS
<williams_judith@...> wrote:
>
>
> I need some clarification on lintels. If you build a solid papercrete
wall, either slip formed or block and then you go back and cut out the
openings for doors and windows, do you have to put a lintel over the
opening? Sincerely, Judith Visit my papercrete website at www.judith-l-
williams.com.'Never be afraid to try something new. Remember, amateurs
built the Ark. Professionals, on the other hand, built the Titanic.'
Author unknown.
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