Thermal Expansion of Window Lintels in 1960's house

[henllys]

Hi

I have a house built in 1960. The house has large windows of between 2 and 3 metre widths.

We have cracks at the top left and right of the windows on the first floor at the rear (south facing). The cracks are in the plaster work and start at the corner of the window and rise to the ceiling at an angle away from the window.

The cracks only appear when the sun is on the windows and disappear once the sun has gone.

I have been told it is thermal expansion of the lintels by an engineer.

I am thinking of fitting some cladding with thermal qualities to try to insulate against the problem.

Does anyone else have any experience of this and any advice.

Thanks.

 

[tony1851]

Steel expands by approximately 0.015mm per meter length for every 1 deg C temp. rise.
If your lintel is 3m long, a daytime rise in temp of, say 20 deg C (which would be a lot!) would cause it to expand by just under 1mm. You would probably hardly see this, and this would be an extreme example.
I wonder if something else is causing the cracking.

 

[henllys]

Thanks for your reply. 1mm expansion for 20 degrees does seem to be very little.

The lintels, from my understanding will be concrete with metal rods reinforcing them running through.

If it isnt the lintels then I am unsure of what it could be.

I have seen another posting on this forum about the same issue.

 

[^woody^]

I can't understand how expansion can cause shrinkage cracks?

Surely if the plaster cracks are repaired when its hot, then they won't open again on the next thermal cycle