Lintel above window


22 Apr 2006
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West Midlands
United Kingdom
I've built a 2 story extension and installed a catnic lintel above the upstairs window.

I had to instal a standard duty lintel because the height of a heavy duty lintel would have clashed with the pre-formed roof trusses. I was assured that this would be adequate.

Above the lintel is 100mm high thermalite block and the wall plate sits directly onto the blocks. There is nothing on the outer skin of the catnic, as the soffit runs directly on to this.

I have now noticed a crack in the block work and the catnic under the block work has dipped slightly. I have put a straight edge across the trusses and 2 out of the 4 trusses (which are above the window opening) are out of line - making me think that the roof has dropped.

The roof has been complete for about 6 months, should I be concerned or not?

Would it be possible to jack up the 2 dropped trusses and remove the thermalite blocks above the window area and put in a 100 x 100 mm square steel beam on top of the catnic (on the inner skin)?
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For Catnic standard lintels the inner:eek:uter leaf loading ratio is given as between 1:1 and 3:1.
If your lintel has no load on the outer leaf then it shouldn't have been used, although depending on the overall loadings Catnic may be able to advise otherwise.

It may be possible to insert a steel section to resupport the trusses. However, the size will depend on the loading and the span.
What suprises me is that you didn't check your structural engineers calcs to verify the type of lintel required.
Who assured you that a standard lintel was adequate?
Why did you use a catnic lintel - surely a length of I beam could have been better.
I should think you should be concerned. So should your building inspector?

A length of steel might be the answer, though you should ask your structural engineer. but the concern is really that you appear to be "winging it".
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This situation is not at all unusual.

Instances where the roof eaves finish at the head of the window and where no masonry is showing above the window, i.e. soffit board straight onto the window top, then we use a catnic box lintel dealing with the inner masonry only.

You only then need to fix cradling above the window in order to secure the soffit.

If the window span is rather wide then this box lintel may need to be prohibitively deep such that it interferes with the wall plate detail.

In this case we have used a piece of 152mm x 89mm steel.

As the guys have said, speak to the bloke who designed it.

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